Items from Mexico.

ITEMS FROM MEXICO

 

International Maize and Wheat Improvement Center - CIMMYT

Lisboa 27, Colonia Juárez, Apdo. Postal 6-641, 06600, México, D.F., México.

 

CIMMYT Advanced Wheat Improvement Research Training For Developing Countries. [p. 64-65]

R.L. Villareal, O.T. Bañuelos, and S. Rajaram.

The CIMMYT Advanced Wheat Improvement Course is an integral part of the Center's Global Project 8, on 'Building Human Capital'. The course has two main objectives: 1) to impart to senior NARS scientists knowledge on the efficient management of a germ plasm improvement program and 2) to give NARS scientists the opportunity to select new wheat germ plasm from the CIMMYT wheat-breeding program. The major focus of the course is on senior scientists who have at least 5 years of wheat-research experience. The course exposes them to the most up-to-date wheat technologies and materials available at CIMMYT, gives their work a considerable boost, and provides valuable stimulus to national programs. Participants have a unique opportunity to exchange ideas among themselves and with CIMMYT staff, discuss research results, and generally strengthen the interpersonal and professional bonds that hold the international network together. The advanced course is scheduled to take place once a year or every other year in Mexico, depending on financial availability. By offering this training, CIMMYT also benefits by continually strengthening its international networks of research scientists, whose collaboration is essential to advancing the cause of global food security.

Course description. The CIMMYT Advanced Wheat Improvement Course is designed for more experienced national-program scientists with significant research leadership responsibilities and emphasizes crop-improvement research and program design; a special training category of CIMMYTs wheat visiting-scientist program. The course was established in 2000 as an attempt to further define and more efficiently manage the 'active' visiting scientists who work directly with CIMMYT senior scientists in on-going research programs. Participants get a unique opportunity to exchange ideas among themselves and with our staff, discuss research results, and generally strengthen the interpersonal and professional bonds that hold the international network together. Information is exchanged through personal contacts, group discussions, and seminars. Throughout the course, the participants constantly work and interact with fellow participants and CIMMYT staff of all disciplines in the classroom, laboratory, and field as they conduct research activities. The program also provides opportunities for in-depth studies in wheat improvement and specialized topics of interest to the scientist, the scientist's host institution, and CIMMYT. The experience gained fosters camaraderie between staff and the participants and increases confidence, knowledge, and competence in, and appreciation of, field activities. Participants also develop appreciation for the multidisciplinary approach in wheat improvement.

Another important aspect of this course is the exchange of germ plasm. Visiting scientists send germ plasm to CIMMYT, and while they are at the Center, they can observe the performance of their materials. These participants also get a free hand to select wheat, triticale, and barley germ plasm and, after the seed has been appropriately treated with fungicides and other chemicals, to take it to their home countries for use in their own cultivar-development programs. The concept of international coöperation, the exchange of information and breeding materials, is a significant component of this course.

Program outlook. CIMMYT works closely with more than 50 developing countries that have programs focused on wheat research. The national agricultural research system (NARS) in these countries express a strong and continuing demand for human resource development in order to maintain and strengthen the research capacity of their staff. Trained professional manpower is essential precondition for the development of improved agricultural technologies to benefit farmers. New skills are constantly required as the practice of agriculture becomes increasingly complex (e.g., the application of biotechnology and information technology to plant breeding; the integration of improved varieties with sustainable crop management practices; and the need to carefully balance food, forage, and nonfood uses of agricultural products). Staff turnover in the NARSs also implies that newly trained professionals are in continual demand, hence the training job is never done. As the work of CIMMYT has evolved, so have the training needs of NARS. National agricultural research centers now request more specialized training at a higher level to enable them to keep abreast of the changes in agricultural science such as those mentioned above.

 

Backcross-derived, synthetic bread wheats under drought stress. [p. 65-66]

R.L. Villareal, O.T. Bañuelos, S. Rajaram, and A. Mujeeb-Kazi.

Thirty-seven percent of the developing world's wheat area is semiarid where moisture is the principal production constraint. Two field experiments were conducted at the CIMMYT experimental station near Cd. Obregon, Sonora, to test the agronomic potential of 260 BC2F1-derived F6 lines with an Ae. tauschii base. The three backcross populations were 'Altar 84/Ae. tauschii 219//3*Seri 82', 'Croc1/Ae. tauschii 224//3*Opata 85', and 'Duerd/Ae. tauschii 214//3*Bcn 88'. Trials were arranged in an alpha-lattice design with three replications. The experimental plots, each consisting of eight rows, 20-cm apart, and 4-m long, were machine-drilled into dry soil at a seeding rate of 100 kg/ha. Results of the 2 years research involving 260 BC2F1-derived F6 lines from three backcrosses on selected six agronomic traits under one irrigation are presented (Table 1). Data on harvest index, grains/m^2^, grains/spike, flowering date, grain-filling duration, and spike length are not shown to simplify the table presentation. The mean of the crosses showed some lines superior to the recurrent bread wheat parents for 1,000-kernel weight (38 %), spike length (10 %), test weight (8 %), spikes/m2 (3 %), above-ground biomass at maturity (2 %), and grain yield (2%). A higher frequency of the lines possessing heavier kernels than the recurrent parent was observed from the cross 'Duerd/Ae. tauschii 214//3*Bcn 88' (51 %), followed by 'Croc1/Ae. tauschii 224//3*Opata 85' (43 %), and 'Altar 84/Ae. tauschii 219//3*Seri 82' (23 %). The yield of the advanced derivatives ranged from 1,952 kg/ha (Altar 84/Ae. tauschii 219//3*Seri 82) to 5,042 kg/ha (Duerd/Ae. tauschii 214//3*Bcn 88). Twenty-one percent of the derivatives were taller and headed (12 %) and matured later (3 %) than their recurrent parents. Using the mean of nine yield-related traits, 19 % of the lines are superior to the recurrent parents. These results show that SHs developed from artificial hybridization of durum wheat with Ae. tauschii can enhance yield or yield components under drought stress.

Table 1. Percent of lines in three BC2F1 synthetic-derived F6 populations significantly greater than (>) or less than (<), or not significantly different than (=) their recurrent parents for six traits averaged over 2 years under one irrigation at Cd. Obregon, Sonora. Number in parenthesis are the number of F6 lines from each population.
 Recurrent parent    Seri 82 (100)    Opata 85 (76)    Bacanora 88 (84)
 Trait  >  =  <  >  =  <  >  =  <
 Grain yield  2  95  3  3  72  1  0  63  21
 Biomass  5  95  0  1  75  0  0  81  3
 1,000-kernel weight  23  72  5  33  43  0  43  39  2
 Test weight  9  64  27  5  64  7  7  56  21
 Physiological maturity  0  83  17  6  70  0  1  83  0
 Plant height  21  79  0  26  49  1  8  73  3

 

 

Elite, synthetic bread wheats (Triticum turgidum/Aegilops tauschii) under one irrigation. [p. 66]

R.L. Villareal, O.T. Bañuelos, S. Rajaram, and A. Mujeeb-Kazi

The principal objective of the study was to evaluate the agronomic performance of 28 elite, primary synthetics derived from 'T. turgidum/Ae. tauschii' crosses developed from CIMMYT's Wheat Wide Crosses Program under one irrigation conditions in Cd. Obregon, Sonora, Mexico. The field trials were arranged in randomized complete block design with three replications. The experimental plots, each consisting of 8 rows, 20-cm apart and 4-m long were machine drilled at a seeding rate of 100 kg/ha. Baviacora 92 (Bav92) and Dharwar Dry (DD) were used as the high yielding drought tolerant bread wheat check cultivars. Grain yield, biomass at maturity, yield components, and other agronomic traits were determined. Data on the eight best SHW and the drought-tolerant bread wheat cultivars Bav92 and DD is presented (Table 2). Results of the yield tests identified three primary synthetics with similar yield to the highest yielding check (Bav92, 4,338 kg/ha). Grain yield of the synthetics ranged from 1.069 kg/ha (D67.2/P66.270//Ae. tauschii 223) to 3,439 kg/ha (Ceta/Ae. tauschii 1024) with an overall mean yield of 2,223 kg/ha. The majority of the synthetics have a comparable 1,000-kernel weight (86 %), biomass yield (79 %), and spike length (61 %) to that of Bav92. The three SH wheat lines with heavier kernels than Bav92 (45.2 g) were 'Doy1/Ae. tauschii 1026' (53.2 g), 'Doy1/Ae. tauschii 188' (53.1 g), and 'Croc1/Ae. tauschii 444' (52.1 g). Forty-three percent of the lines have test weight comparable to Bav92 (77 kg/hl). Aboveground biomass yield at maturity ranged from 3.8 t/ha (Gan/Ae. tauschii 897) to11.8 t/ha (Ceta/Ae. tauschii 1024) with an overall mean biomass yield of 8.8 t/ha. All the synthetic materials flowered and matured later than Bav92. However, grain-filling period of 93 % of the SH wheats are comparable to Bav92 (39 d). Plant height of the SH were similar to those of the two bread wheat checks. Two SH wheat lines possessed more spikes/m2 than Bav92. Results indicate the potential use of the best primary synthetics as progenitors in drought tolerance breeding in T. aestivum at CIMMYT.

Table 2. Agronomic traits of eight synthetic hexaploids (Triticum turgidum/Aegilops tauschii) and bread wheat check cultivars, Baviacora 92 and Dharwar Dry combined over 2 years under one irrigation at Cd. Obregon, Sonora.
 Entry no.  Cross  Yield (kg/ha)  Biomass (t/ha)  1,000-kernel weight (g)  Test weight (kg/hl)  Physiological maturity (d)  Plant height (cm)
 2  Ceta/Ae. tauschii 1024  3,439  11.8  45.3  74.6  135  106
 8  Ceta/Ae. tauschii 327  3,260  10.2  41.8  76.1  132  94
 21  68.111/RGB-U//Ward/3/FGO/4/Rabi/5/Ae. tauschii 629  2,806  11.4  48.8  73.5  133  104
 23  Ceta/Ae. tauschii 1031  2,738  10.1  48.2  72.5  133 98 
 17  Ceta/Ae. tauschii 1026  2,721  11.8  47.2  70.7  131  91
 3  Croc1/Ae. tauschii 444  2,597  10.0  52.1  72.8  135  85
 18  Doy1/Ae. tauschii 1026  2,587  9.3  53.2  74.4  133  98
 22  Doy1/Ae. tauschii 1029  2,465  9.7  49.2  73.7  135  97
 29  Baviacora 92  4,338  10.0  45.2  77.5  125  86
 30  Dharwar Dry  3,233  8.4  36.8  79.7  122  94
   LSD (0.05)  1,560  4.0  6.6  4.2  5  21

 

 

Human-resource development for wheat-improvement research at CIMMYT. [p. 67]

R.L. Villareal, O.T. Bañuelos, and S. Rajaram.

The objective of CIMMYT wheat-improvement research training course is to help upgrade the skills of scientists from the national agricultural research systems of the developing world, so they can more effectively utilize new genetic materials from CIMMYT and, thereby, make available a continuous flow of new technologies to their client farmers. Since CIMMYTs inception in 1966, more than 2,600 wheat-improvement researchers from 90 developing countries have attended the course (Tables 3 and 4), which is characterized by a strong emphasis on field activities (50-60 % of course hours) and on linking theory with the application of breeding and agronomic principles. A unique opportunity also is offered for participants to come into contact with many colleagues worldwide. Recent surveys have shown that many wheat research leaders in NARS are former CIMMYT trainees. Because many alumni move into administrative positions or have retired, there is a continuing need to train promising researchers for their replacement, thus, maintaining a critical mass of knowledgeable and field­oriented wheat scientists. By offering this training, CIMMYT also benefits because it constantly strengthens its international networks of research scientists, whose collaboration is essential to advancing the cause of global food security.

Table 3. CIMMYT wheat-improvement trainees in Mexico from 1967 to 2002 (Source: CIMMYT Training database).
 Year  Asia  Africa  Latin America  Other countries  Total
 1967  10  0  2  0  12
 1968-72  41  27  23  4  95
 1973-77  35  27  26  6  94
 1978-82  56  21  34  3  114
 1983-87  57  31  39  6  133
 1988-92  53  26  28  2  109
 1993-97  23  20  13  10  66
 1998-02  51  23  2  12  88
 Total  326  175  167  43  711


Table 4. Origin based on regional aggregates of CIMMYTs Wheat Program visiting scientists in Mexico from 1966 to 2002 (Source: CIMMYT Training database).
 Origin  No. of visiting scientists
 Sub-Saharan Africa  145
 West and north Africa  193
 East, south, and southeast Asia  507
 Latin America  509
 East Europe, central Asia, and Caucasus  70
 High-income countries  548

 

The impact of synthetic wheat on breeding for stress tolerance at CIMMYT. [p. 67-69]

R.M. Trethowan, Jose Borja, and A. Mujeeb-Kazi

Synthetic hexaploid wheats are developed by crossing tetraploid wheat with Ae. tauschii, the probable donor of the D genome. The bread wheat, stress-breeding program at CIMMYT has steadily increased the contribution of synthetic wheat parentage in the breeding program over the past 5 years (Figure 1). Currently, more than 40 % of all breeding materials in the breeding program have a synthetic wheat somewhere in their parentage. These synthetics have provided significant new variability for a range of characteristics important to wheat adaptation in marginal environments, including new variability for tolerance to drought, heat, micronutrient imbalances, and resistance to diseases that affect the roots and crowns.

Drought screening at CIMMYT is conducted near Cuidad Obregon in northwestern Mexico. This site is arid, and wheat is grown using irrigation. Drought is generated using a combination of gravity and drip irrigation methods to generate controlled moisture-stress scenarios. The 'genotype x year' interaction under moisture stress is low (Trethowan, unpublished data) and the relevance of germ plasm selected at this site, under limited and optimal irrigation, to global wheat-growing environments has been demonstrated (Trethowan et al. 2001, 2003). When germ plasm selected at this site using one or two gravity irrigations is tested globally, significant rates of improvement in productivity have been observed (Trethowan et al. 2002). The soils at this location have been carefully characterized for biotic stresses (nematodes, root rots) and other abiotic stresses (micronutrient imbalances) thereby ensuring that the observed differentiation of genotypes is due to water and not other confounding factors.

Currently, CIMMYTs benchmark standard for drought tolerance is a Bavuacira derivative called Weebill 1. Combining variation for drought tolerance from traditional sources, such as advanced-line performance in dry environments globally, with that of synthetic wheat has led to the development of synthetic derivatives with greatly enhanced drought tolerance. Figure 2 demonstrates the superiority of a few of these new synthetic derivatives over Weebill 1 and Pastor, a line adapted to dry environments globally, under drought stress in northwestern Mexico.

The superior performance of these synthetic derivatives is linked to a number of characteristics including deep root systems, root systems that can efficiently extract more water per unit volume of soil (Copeland et al. 2002), improved emergence and establishment, and the ability to maintain seed size under stress.

One of the primary mechanisms or expressions of stress tolerance is the maintenance of kernel weight under stress. Wheat plants grown under moisture or heat stress often produce shriveled seed, reducing the yield and market value of the wheat crop. Significant new variability for maintaining kernel weight has been found in the primary synthetics (Figure 3). Each of the primary synthetics in Figure 3 have larger seed size (measured as the 1,000-kernel weight) than Baviacora (which is recognized as having large seed) under stress-free conditions. However, all the synthetics in Figure 3 have higher seed weight than the check under all test conditions. Synthetic # 1 is able to maintain its seed weight best under both drought and heat stress with very little observable difference among treatments. This important new variability is being introgressed into germ plasm targeted to marginal environments.

Apart from seed size, poor industrial quality and low protein levels have been disincentives to plant breeders wanting to improve stress adaptation using synthetic sources of variability. Historically, breeding for both high yield and high protein content, as these characteristics are negatively associated, has been very difficult. However, the synthetic wheats offer significant new variability for protein subunit composition (Peña et al. 1995). When these synthetics are crossed to high yielding, drought-tolerant, elite bread wheat parents, it is possible to find lines with both high yield and high protein (Figure 4). The two synthetic derivatives in Figure 4 have yields equivalent to the elite, drought-tolerant check cultivar Weebill 1, however, they produce up to 20 % more grain protein.

Reference.

  • Copland S, Reynolds MP, Trethowan R, Davies WP, and Gooding MJ. 2002. Moisture stress resistance of wheat lines derived from synthetic hexaploids. In: Proc Conf 'Genotype to phenotype: narrowing the gap', 16-18 December, 2002, Association of Applied Biologists, Royal Agricultural College, Cirencester, U.K.
  • Peña RJ, Zarco-Hernandez J, and Mujeeb-Kazi A. 1995. Glutenin subunit compositions and bread-making quality characteristics of synthetic hexaploid wheats derived from Triticum turgidum x Triticum tauschii (Coss.) Schmal Crosses. J Cereal Sci 21:15-23.
  • Trethowan RM, Crossa J, van Ginkel M, and Rajaram S. 2001. Relationships among bread wheat international yield testing locations in dry areas. Crop Sci 41(5):1461-1469.
  • Trethowan RM, van Ginkel M, and Rajaram S. 2002. Progress in breeding for yield and adaptation in global drought affected environments. Crop Sci 42(5):1441-1446.
  • Trethowan RM, van Ginkel M, Ammar D, Crossa J, Cukadar B, Rajaram S, and Hernandez E. 2003. Associations among twenty years of bread wheat yield evaluation environments. Crop Sci (in press).


Triticum aestivum/Aegilops geniculata and Triticum durum/Aegilops geniculata hybrids, BCs, and amphiploid production. [p. 69-71]

M. Zaharieva, A. Cortés, V. Rosas, S. Cano, R. Delgado, and A. Mujeeb-Kazi.

Aegilops geniculata is an annual, self-fertile, allotetraploid (2n = 4x = 28, MU genome) species (Van Slageren 1994). For wheat breeding, the species is a source of biotic and abiotic stress resistance (Zaharieva et al. 2001b). Promising Ae. geniculata accessions resistant to BYDV, CCN, and rusts were identified and hybridized with susceptible high-yielding bread and durum wheat cultivars (Zaharieva et al. 2001a). The results of Triticum/Ae. geniculata hybridization efforts are presented here.

Genetic material and hybridization strategy. Two bread (Prinia and Baviacora) and durum (Kucuk and Sooty9/Rascon37) wheat cultivars were crossed as female parents with 10 Ae. geniculata accessions using conventional protocols (Mujeeb-Kazi et al. 1987). Within each cross, some F1 hybrids were treated with colchicine to produce amphiploids. The remaining F1 hybrids were backcrossed to their wheat parents to produce BC1 derivatives. The BC1 plants having complete parental chromosome sets were crossed with bread or durum wheat parents (BC2) or selfed to produce BC1F2 plants. Crosses between Chinese Spring (phph) and Ae. geniculata accessions also were made to promote homoeologous wheat/alien chromosome pairing. Mitotic, meiotic, and Giemsa C-banding cytological analyses were made on the F1 and the backcrossed and amphiploids plants according to protocols in Mujeeb-Kazi et al. (1994).

Triticum/Ae. geniculata hybrid and amphiploid production. A total of 323 hybrid plants were obtained for 30 (out of 40 potential) cross combinations. Crossability rate was higher for T. durum/Ae. geniculata (15 %) than for T. aestivum/Ae. geniculata crosses (9 %) and varied according to the bread and durum wheat parent (Table 4). The hybrids obtained expressed codominant phenotypes. Mean meiotic associations where univalency predominated suggested that wheat/alien recombinations did not occur.

Table 4. Genotypic variation in bread and durum wheats for crossability with Aegilops geniculata accessions.
 Triticum/Ae. geniculata cross combinations  Florets pollinated  Seed set  Embryos excised  Plants obtained  Crossability (%)
 Prinia/Ae. geniculata  766  99  98  76  12.9
 Baviacora/Ae. geniculata  624  34  34  26  5.4
 Kucuk/Ae. geniculata  570  103  101  75  18.1
 Sooty9/Rascon37//Ae. geniculata  570  68  66  46  11.9

After colchicine treatment, seeds were obtained from 19 out of the 30 F1 cross combinations. Seed (C0) frequency was significantly higher for durum wheat/Ae. geniculata (94 %) than for bread wheat/Ae. geniculata combinations (29 %). Seed number also was higher for durum wheat based amphiploids than for bread wheat and depended on the cultivar used (Table 5). A total of 46 seeds were obtained from four T. aestivum/Ae. geniculata cross combinations (out of 14 F1s) and 851 seeds from 15 T. durum/Ae. geniculata cross combinations (out of 16 F1s). Chromosome numbers were between 67-70 in T. aestivum/Ae. geniculata amphiploids and 51-56 in T. durum/Ae. geniculata amphiploids. Complete chromosome sets (2n = 10x = 70) for bread wheat and (2n = 8x = 56) for durum wheat combinations were observed in 25 % and 57 % of the tested plants, respectively. These amphiploids were seed increased and are under further evaluation.

Table 5. Genotypic variation for amphiploid production involving bread and durum wheat/Aegilops geniculata accessions. The Ae. geniculata accession number used in the CIMMYT Wide Crosses working collection is in parentheses.
 Triticum/Ae. geniculata cross combinations  Florets pollinated  Seed set  Embryos excised  Plants obtained  Doubled seed set
 Prinia/Ae. geniculata (MZ 77)  64  16  15  9  8
 Baviacora/Ae. geniculata (MZ 77)  56  6  6  6  5
 Kucuk/Ae. geniculata (MZ 149)  56  11  11  11  185
 Sooty9/Rascon37//Ae. geniculata (MZ 149)  48  7  7  5  26

BC seed production. BC1 seeds were obtained from F1 hybrids after backcrossing to the durum or bread wheat parent. Crossability rate was higher than for the F1 hybrids. Seeds were more frequent in 'T. durum/Ae. geniculata//T. durum' crosses than in 'T. aestivum/Ae. geniculata//T. aestivum' (21 and 15 % crossability rates, respectively). Chromosome number was in the range 41-60 for the T. aestivum combinations and 32-45 for T. durum combinations. C-banding on plants having complete chromosome sets confirmed 21 II + 14MU and 14 II + 14 MU associations for the T. aestivum and T. durum combinations, respectively. These BC1 plants were backcrossed to their bread or durum wheat parent (BC2) or selfed (BC1F2). Their seeds will be used to advance desired combinations for applied wheat production purposes.

ph gene strategy. Transfer of traits of interest from alien donor species into wheat can be facilitated using the ph genetic stock of Chinese Spring (Mujeeb-Kazi 2001). Chinese Spring ph and Chinese Spring Ph (as a reference) were crossed with the 10 Ae. geniculata accessions producing 100 and 80 seeds, respectively, from all cross combinations (Table 6). Chromosome numbers ranged between 34-35 for the Chinese Spring ph/Ae. geniculata and 35 for Chinese Spring Ph/Ae. geniculata hybrids. The crossability rate was high (20.2 and 21.4 %) compared to the two bread wheat cultivars previously described. However, when F1 Chinese Spring ph hybrids were crossed to different bread wheat cultivars, no or very few seeds were produced. Only two plants with incomplete chromosome number were obtained after crossing with Prinia. When Chinese Spring Ph hybrids were crossed with Prinia and Bacanora, seven plants were obtained from four cross combinations with chromosome numbers from 54-60.

Table 6. Crossability data for Chinese Spring ph and Chinese spring Ph wheat crosses with Aegilops geniculata.
 Triticum/Ae. geniculata cross combinations  Florets pollinated  Seed set  Embryos excised  Plants obtained  Crossability (%)
 Chinese Spring ph/Ae. geniculata  494  100  100  68  20.2
Chinese Spring Ph/Ae. geniculata  374  80  80  58  21.4

Amphiploids also were obtained after colchicine treatment. Fifty-two seeds (C0) were produced from four Chinese Spring ph combinations (40 % frequency) and 60 seeds from five Chinese Spring Ph combinations (50 % frequency). Chromosome numbers ranged between 64-72 in Chinese Spring ph-based amphiploids and from 62-70 in Chinese Spring Ph-based amphiploids. Complete chromosome counts of 2n = 10x = 70 were observed in 24 % and 35 % of the tested plants, respectively. The ph-based amphiploids are anticipated to be a very potent source of enhanced translocation events (homologous and homoeologous) after several rounds of selfing.

In general, crosses between Chinese Spring ph-based hybrids and bread wheat cultivars are difficult. We decided to use Chinese Spring ph as backcross parent for the Ph locus BC2 progenies and amphiploids in order to produce Phph-heterozygote progeny from which ph derivatives are being identified and exploited (Mujeeb-Kazi 2001).

Conclusions. Elite bread and durum wheat cultivars were hybridized with different stress resistant Ae. geniculata accessions and a great number of amphiploids and BCI derivatives were produced. The durum wheat cultivar Kucuk and the bread wheat cultivar Prinia had good crossing ability and might have priority for use in wheat-Ae. geniculata hybridization programs and for other combinations. After evaluation for resistance to the concerned diseases and pests, some desired combinations are to be advanced via production of Ae. geniculata addition lines and ph-based cytogenetic manipulation for achieving alien introgressions in targeted wheat cultivars.

References.

  • Mujeeb-Kazi A. 2001. Intergeneric Hybrids in Wheat: Current Status. In: Triticeae IV (Hernandez P, Moreno MT, Cubero JI, and Martin JA eds). Viceconsejeria, Servicio de Publicaciones y Divulgacion, Spain. Pp. 261-264.
  • Mujeeb-Kazi A, Jahan Q, and Vahidy A. 1994. Application of a somatic and meiotic cytological technique to diverse plant genera and species in the Triticeae. Pak J Bot 26:353-366.
  • Mujeeb-Kazi A, Roldan S, Suh DY, Sitch LA, and Farooq S. 1987. Production and cytogenetic analysis of hybrids between Triticum aestivum and some caespitose Agropyron species. Genome 29:537-553.
  • Van Slageren MW. 1994. Wild wheats: a monograph of Aegilops L. and Amblyopyrum (Jaub and Spach) Eig (Poaceae). Agricultural University, Wageningen, the Netherlands. 512 pp.
  • Zaharieva M, Cortéz A, Rosas V, Cano S, Sanchez J, Juarez L, Delgado R, and Mujeeb-Kazi A. 2001a. Potential of Aegilops geniculata genetic resources for wheat improvement. Ann Wheat Newslet 47:102-103.
  • Zaharieva M, Monneveux P, Henry M, Rivoal R, Valkoun J, and Nachit MM. 2001b. Evaluation of a collection of wild wheat relative Aegilops geniculata Roth and identification of potential sources for useful traits. Euphytica 119:33-38.

 

Triticum durum/Aegilops umbellulata hybridization. [p. 71-73]

M. Zaharieva, A. Cortás, V. Rosas, S. Cano, R. Delgado, and A. Mujeeb-Kazi.

Aegilops umbellulata is an annual, self-fertile, diploid (2n = 2x = 18, U genome) species distributed in the eastern Mediterranean and western Asian regions (Van Slageren 1994). Ae. umbellulata is a source for resistance to powdery mildew, CCN, Hessian fly, and greenbug (Gill et al. 1985; Bekal et al. 1998). Leaf rust resistance gene Lr9 from Ae. umbellulata was transferred to bread wheat by Sears (1956). However, information on durum wheat/Ae. umbellulata hybridization is scarce and mainly concerns hybrid production (Ozgen 1983a, b). Furthermore, no germ plasm is globally available for incorporating this genetic diversity for wheat improvement compelling us to initiate the effort herein reported.

An Ae. umbellulata accession MZ 163, originating from Iran and resistant to Mexican and Bulgarian isolates of leaf and stripe rust at seedling and adult stages (Zaharieva, unpublished data), was crossed as the male parent with the CIMMYT durum wheat cultivar Mexicali 75. The hybrid and backcross derivative production is reported.

Crossing, embryo rescue, and plant regeneration techniques applied were as described by Mujeeb-Kazi et al. (1987). From 56 pollinated florets (two spikes), 10 seeds were produced (17.9 % crossability rate). Ten embryos were rescued and nine plants obtained (90 % plant regeneration). Somatic chromosome numbers of all hybrid plants were 2n = 3x = 21, ABU. Morphologically, the F1 hybrids were intermediate between their parents and all of them were self-sterile.

BC1 seeds were obtained from F1 hybrids after backcrossing to the wheat parent (Table 7). The crossability rate (32.5 %) was higher than for the F1 hybrids. Thirteen seeds were produced from 40 pollinated florets and 10 plants were obtained (76.9 % regeneration). Chromosome number ranged between 34-36; most plants (60 %) had a complete chromosome set of 35 chromosomes (2n = 5x = 35, AABBU). The two plants with 34 chromosomes were self-sterile. Self-pollination of the remaining eight plants (having 35 or 36 chromosomes) produced 76 BC1F2 seed. On average, seed set was two seed/spike.

Table 7. Crossability data for Mexicali 75/Aegilops umbellulata hybrid and BC seed production.
 Combination  Florets pollinated  Seed set  Crissability (%)  Plants obtained  Regeneration (%)
 (F1) Mexicali 75/Ae. umbellulata  56  10  17.9  9  90.0
 (BC1) F1/Mexicali 75  40  13  32.5  10  76.9
 (BC2) BC1/Mexicali 75  120  54  45.0  ---  ---

After backcrossing eight plants with Mexicali 75, 54 BC2 seeds were produced from 120 pollinated florets (45 % crossability rate). Fourteen of these were germinated and 12 plants obtained (87.5 % regeneration rate). The chromosome number ranged from 28-32. Most of the plants (58.3 %) had 29 chromosomes with 14 bivalents plus 1 univalent at meiosis, suggesting that one Ae. umbellulata chromosome was added. Only two plants (16.7 %) had no alien chromosome added. Ten plants with 29 or more chromosomes were selfed and 120 BC2F2 seeds were produced from eight plants; two were sterile.

A preliminary test for leaf rust resistance at the adult stage was made on four BC2 plants with 29 chromosomes using a Mexican isolate virulent on durum wheat. The four plants were found to be completely resistant. Durum wheat cultivar Mexicali 75 was highly susceptible to this isolate.

These results suggest that leaf rust resistance of Ae. umbellulata was expressed in a durum wheat background via the added alien chromosome. This alien-resistance source is being identified and cytogenetically manipulated for introgression into an end product that will be euploid with 2n = 4x = 28 and carry the introgression; a lengthy complex process. At the same time, we are attempting to complete the full set of seven chromosome Ae. umbellulata chromosome-addition lines.

Conclusions. The durum wheat cultivar Mexicali 75 was hybridized with leaf- and stripe-rust resistant Ae. umbellulata accession and backcross progenies carrying one or more alien chromosomes were obtained. Production of durum wheat/Ae. umbellulata addition lines is in progress. A crossing program also is underway to hybridize BC2 progenies with Capelli (ph1c) and promote homoeologous pairing for introgressing Ae. umbellulata-resistance genes into durum wheat background.

References.

  • Bekal S, Jahier J, and Rivoal R. 1998. Host responses of Triticeae to species of the cereal cyst nematode complex in relation to breeding resistant durum wheat. Fund Appl Nematol 21:359-370.
  • Gill BS, Sharma HC, Raupp WJ, Browder LE, Hatchett JH, Harvey TL, Moseman JG, and Waines JG. 1985. Evaluation of Aegilops species for resistance to wheat powdery mildew, wheat leaf rust, Hessian fly and greenbug. Plant Dis 69:314-316.
  • Mujeeb-Kazi A, Roldan S, Suh DY, Sitch LA, and Farooq S. 1987. Production and cytogenetic analysis of hybrids between Triticum aestivum and some caespitose Agropyron species. Genome 29:537-553.
  • Ozgen M. 1983a. Hybrid seed set in wheat x Aegilops crosses. Wheat Inf Serv 56:9-11.
  • Ozgen M. 1983b. Morphological characters and meiotic associations in a T. durum Desf. var. hordeiforme Korn. x Ae. umbellulata Zhuk. hybrid. Wheat Inf Serv 57:1-3.
  • Van Slageren MW. 1994. Wild wheats: a monograph of Aegilops L. and Amblyopyrum (Jaub and Spach) Eig (Poaceae). Agricultural University, Wageningen, the Netherlands. 512 pp.

 

Genetic diversity of synthetic hexaploids with enhanced levels of resistance to Fusarium head scab. [p. 73-75]

M. Zaharieva, K. Suenaga (Japan International Research Center for Agricultural Sciences, 1-1, Ohwashi, Tsukuba, Ibaraki 305-8686.), H.M. William, and A. Mujeeb-Kazi.

The D-genome donor Ae. tauschii (2n = 2x = 14; DD) represents a valuable source for bread wheat improvement because of the close homology of its genome with that of the D genome of bread wheat and the availability of a wide range of accessions from diverse geographic regions. Among a great number of synthetic hexaploids (2n = 6x = 42, AABBDD), produced by crossing durum wheat cultivars and Ae. tauschii accessions, a subset was found to be highly resistant to scab (Mujeeb-Kazi et al. 2000b). Because all durum varieties are highly susceptible to head scab, the resistance observed in SHs should logically be due to the Ae. tauschii genome.

Pyramiding strategy. As a result of multiyear testing, a set of 15 highly resistant, synthetic hexaploids was selected and used to introgress head scab resistance traits into high-yielding bread wheat cultivars (Mujeeb-Kazi and Delgado 2002). By intercrossing these SHs made with different accessions of Ae. tauschii, we initiated a procedure to pyramid scab resistance. Progenies of these crosses are a precious genetic basis for improving scab resistance in bread wheat, because diverse genes are incorporated simultaneously, thereby enhancing breeding efficiency (Mujeeb-Kazi et al. 2000a). The efficient choice of parents to be used in intercrossing, however, needs a better knowledge of genetic relationships among SHs.

Germ plasm and microsatellite analysis. In addition to the 15 SHs mentioned above, 10 durum wheat cultivars, that were used to make the SHs, a synthetic derivative that has excellent resistance to head scab (Mayoor//TK SN 1081/Ae. tauschii (222)), two wheat cultivars, the head scab-susceptible wheat cultivar Flycathcher, and Chinese Spring were included in the analysis (Table 8).

Table 8. Synthetic hexaploids, Triticum turgidum subsp. durum, and T. aestivum subsp. aestivum genotypes used in the analysis. The Aegilops tauschii accession numbers in CIMMYT Wheat Wide Crosses working collection are in parentheses.
 Genotype (pedigree)  Abbreviation
 68.111/RGB-U//WARD/3/FGO/4/RABI/5/Ae. tauschii (629)  SH/629
 YAR/Ae. tauschii (783)  SH/783
 68.111/RGB-U//Ward/3/FGO/4/Rabi/5/Ae. tauschii (878)  SH/878
 GAN/Ae. tauschii (180)  SH/180
 LCK59.61/Ae. tauschii (313)  SH/313
 Scoop 1/Ae. tauschii (358)  SH/358
 Botno/Ae. tauschii (625)  SH/625
 CPI/Gediz/3/GOO//JO69/CRA/4/Ae. tauschii (409)  SH/409
 Dverd 2/Ae. tauschii (1027)  SH/1027
 CETA/Ae. tauschii (172)  SH/172
 CETA/Ae. tauschii (306)  SH/306
 CETA/Ae. tauschii (445)  SH/445
 CPI/Gediz/3/GOO//JO/CRA/4/Ae. tauschii (1018)  SH/1018
 CETA/Ae. tauschii (1031)  SH/1031
 Ae. tauschii (1026)/DOY1  SH/1026
 68.111/RGB-U//WARD/3/FGO/4/RABI  TD 1
 YARMUK  TD 2
 GAN  TD 3
 LCK59.61  TD 4
 SCOOP_1  TD 5
 BOTNO  TD 6
 CPI/GEDIZ/3/GOO//JO/CRA  TD 7
 DVERD_2  TD 8
 CERCETA  TD 9
 DECOY 1  TD 10
 Chinese Spring  ---
 Flycatcher (susceptible check)  ---
 Mayoor/TK SN1081 (222)  M/TK (222)

DNA polymorphism within the selected head scab-resistant SHs was analyzed using SSR markers. Fifteen D-genome microsatellites derived from hexaploid wheat or Ae. tauschii were used (Table 9). DNA extraction, PCR amplification, and gel electrophoresis were according to standard established protocols of the CIMMYT Molecular Genetics Laboratory (Hoisington et al. 1994). The approximate size of the fragments was scored using a molecular-weight standard and Chinese Spring patterns as reference. Only D-genome-specific bands (absent in durum wheat parent varieties) were taken into account for the analysis. The presence or absence of each fragment was coded by 1 or 0, respectively, and scored in a binary data matrix. Jaccard's genetic distances were calculated for each pair of SHs and cluster analysis was performed based on the unweighted pair-group method with arithmetic average (UPGMA).

DNA polymorphism. All 15 primer pairs used revealed polymorphism between the tested synthetic hexaploids. A total of 91 alleles ranging from 105 bp to 250 bp were found (Table 9). The number of alleles/locus varied from 4 to 9, with an average of 6.1 alleles. From one to eight unique genotypes (with alleles occurring only once in a microsatellite locus) were found for 14 out of the 15 primers used. Two SHs, 'YAR/Ae. tauschii (783)' and 'Botno/Ae. tauschii (625)', revealed two alleles/locus for 8 and 2 microsatellite primers, respectively. This could be explained by the variability existing within Ae. tauschii accessions (Pestsova et al. 2000b) used as male parent for the production of SHs.

Table 9. Microsatellite markers used in the study, their chromosome location according Röder et al. (1998) and Pestsova et al. (2000a), number of alleles generated in the synthetic hexaploid and their size range, and number of unique genotypes per marker. The chromosomal location of microsatellites marked with an asterisk was determined using nullisomic-tetrasomic lines of Chinese Spring.
 Marker   Location  No. of alleles/locus  Size (bp)  No. of unique genotypes
 GWM 337  1D  6  160-190  2
 GWM 848*  1D  5  180-200  2
 GWM 934*  1D  4  140-146  2
 GWM 157  2D  6  100-142  4
 GWM 455  2D  9  135-190  5
 GDM 6  2D  9  120-250  8
 GDM 35  2D  7  160-250  3
 GDM 128  3D  5  110-125  3
 GDM 161  3D  4  150-165  1
 GDM 125  4D  8  120-160  4
 GDM 68  5D  4  125-140  1
 GDM 99  5D  9  155-250  5
 GDM 98  6D  7  170-190  3
 GWM 428  7D  4  120-130  1
 GWM 150  7D  4  105-115  0
 Total    91    44
 Average    6.1    2.9

The dendrogram produced on genetic dissimilarity values among accessions showed that 13 out of the 15 SHs could be distinguished with 15 microsatellite primers and clustered into four groups (Figure 5). Only two of the 15 SHs, 'GAN/Ae. tauschii (180)' and 'LCK59.61/Ae. tauschii (313)' could not be differentiated using the 15 SSRs. The smallest genetic distance (0.06) was between 'Ae. tauschii (1026)/DOY1' and 'CETA/Ae. tauschii (445)', which differ only at one locus. These results suggest that these four SHs are genetically closely related. The largest genetic distance (1.0) was observed between 'Ceta/Ae. tauschii (172)' and the synthetics including Ae. tauschii accessions 306, 409, and 1027 and between 'Ceta/Ae. tauschii (1031)' and SH/306, 409, 445, 629, 878, and 1026. Synthetic hexaploids 'Ceta/Ae. tauschii (172)' and 'Ceta/Ae. tauschii (1031)' were the most distant from the rest of accessions showing unique alleles for six or seven SSR primers, respectively. They were included in inter-synthetic crosses for pyramiding scab resistance genetic diversity.

When analyzed together with the SH-derivative line 'Mayoor//TK SN 1081/Ae. tauschii (222)' and the bread wheat cultivar Flycatcher, a total of 93 alleles were found; two being specific for Flycatcher. The SHs most distant from the susceptible bread wheat cultivar Flycatcher included Ae. tauschii accessions 172, 445, 609, 1018, and 1026 (sharing only two common alleles). These lines could be used to produce mapping populations for identifying QTL. Flycatcher and the synthetic derivative line 'Mayoor//TK SN 1081/Ae. tauschii (222)', already used for production of a DH-segregating population, were polymorphic for 8 out of the 15 tested SSR primer pairs.

Conclusions. The results suggest that a relatively small number of microsatellites can be used to estimate genetic diversity in the germ plasm of T. durum/Ae. tauschii SHs and also indicates the presence of a significant level of heterogeneity among the Ae. tauschii accessions. High intrasynthetic polymorphism was observed, and most SHs were distinguished with only 15 microsatellite primers. We postulate that most genes related to head scab resistance of the tested SHs may be different, revealing the important diversity of head scab-resistance sources. Based on our results, genetically distant SHs were intercrossed in order to create lines with pyramided Ae. tauschii-derived genes for scab resistance. The involvement of various Ae. tauschii accessions in the pedigrees of advanced material will contribute to wide range of genetic diversity that should be beneficial for imparting durability of scab resistance to bread wheat germ plasm.

References.

  • Gilchrist L, Rajaram S, Mujeeb-Kazi A, van Ginkel M, Vivar H, and Pfeiffer W. 1996. Fusarium Scab Screening Program at CIMMYT. In: Fusarium head scab: global status and future prospects (Dubin HJ, Gilchrist L, Reeves J, and McNab A eds). CIMMYT, Mexico. Pp. 7-12.
  • Hoisington D, Khairallah M, and Gonzalez-de-Leon D. 1994. Laboratory Protocols: CIMMYT Applied Molecular Genetics Laboratory, Second Ed. Mexico, D.F., CIMMYT.
  • Mujeeb-Kazi A, Delgado R, and Cano S. 2000a. Practical applications of a gene pyramiding strategy with D genome-based synthetic hexaploids for two major biotic stress resistances: wheat head scab and spot blotch. Ann Wheat Newslet 46:82-83.
  • Mujeeb-Kazi A, Gilchrist LI, and Delgado R. 2000b. New synthetic hexaploids and a set of bread wheat/synthetic hexaploid derivatives as sources for scab resistance. Ann Wheat Newslet 46:81-82.
  • Mujeeb-Kazi A and Delgado R. 2002. D-genome contribution to Fusarium type-II resistance in synthetic-hexaploid wheats (SH; 2n = 6x = 42, AABBDD). Ann Wheat Newslet 48:94-97.
  • Pestsova E, Ganal MW, and Röder MS. 2000a. Isolation and mapping of microsatellite markers specific for the D genome of bread wheat. Genome 43:689-697.
  • Pestsova E, Korzun V, Goncharov NP, Hammer K, Ganal MW, and Röder MS. 2000b. Microsatellite analysis of Aegilops tauschii germplasm. Theor Appl Genet 101:100-106.
  • Röder MS, Korzun V, Wendehake K, Plaschke J, Tixier MH, Leroy P, and Ganal MW. 1998. A microsatellite map of wheat. Genetics 149:2007-2023.

 

Microsatellite markers for detection of Aegilops geniculata M- and U-genome chromosomes in wheat background. [p. 75-78]

M. Zaharieva, K. Suenaga (Japan International Research Center for Agricultural Sciences, 1-1, Ohwashi, Tsukuba, Ibaraki 305-8686, Japan), H.M. William, and A. Mujeeb-Kazi.

Aegilops geniculata (2n = 4x = 28; MMUU) is a distant relative of cultivated durum and bread wheat. Some accessions of Ae. geniculata possess good levels of resistance to BYDV, CCN, and the rusts (Zaharieva et al. 2001b). We have made crosses between these accessions and susceptible high-yielding bread and durum wheat cultivars with the objective of transferring resistances originating in Ae. geniculata accessions to be utilized in CIMMYT durum and bread wheat improvement activities (Zaharieva et al. 2001a). Amphiploids and backcross derivatives have been produced. This material is under evaluation in order to select promising combinations for future advance via cytogenetic manipulation protocols (Mujeeb-Kazi 2001). To facilitate the detection of chromatin of Ae. geniculata in wheat backgrounds, we have evaluated the use of SSR markers and the ongoing initial efforts are reported here.

The Ae. geniculata genome. Ae. geniculata is presumed to be an amphiploid of two diploid species, Ae. comosa (2n = 2x = 14; MM) and Ae. umbellulata (2n = 2x = 14; UU) (Kimber et al. 1988). Friebe et al. (1999) confirmed the chromosome similarities between the U and M genomes of Ae. geniculata and its diploid progenitors. Based on the pairing affinities between Ae. geniculata (MU) and the wheat genomes (ABD), Fernandez-Calvin and Orellana (1992) revealed that the A- and D-genome chromosomes more frequently associated with the M- and U-genome chromosomes of Ae. geniculata than did the wheat A or D or Ae. geniculata M or U chromosomes with wheat B-genome chromosomes. By comparing the Ae. umbellulata and hexaploid wheat maps, Zhang et al. (1998) confirmed the homoeology between U- and D-genome chromosomes, but also observed that all seven Ae. umbellulata chromosomes display one or more structural rearrangements relative to wheat chromosomes.

Our objective was to explore some microsatellite markers that are reported to be located on D genome (Röder et al. 1998; Pestsova et al. 2000), in order to identify Ae. geniculata M- and U-genome chromosomes.

Genetic material and molecular markers. Twenty-four microsatellite primers showing polymorphism between Triticum and Ae. geniculata alleles were selected previously (Table 10) (Zaharieva et al., 2002). In the present study, these primers were tested on a set of Chinese Spring nullisomic-tetrasomic lines (Sears 1966) and on Chinese Spring/Ae. geniculata chromosome addition lines (Friebe et al. 1999) in order to identify the location of polymorphic fragments of these primers. A complete set of M-genome chromosome additions (1M to 7M) and an incomplete set of U-genome chromosome additions (1U, 2U, 4U, and 5U) were used. A complete set of addition lines for the U-genome chromosomes from Ae. peregrina (2n = 4x = 28, SSUU) developed by Friebe et al. (1996) also was tested in order to complete the missing Ae. geniculata U-genome chromosome additions.

Chinese Spring nullisomic-tetrasomic lines and Chinese Spring chromosome-addition lines (Chinese Spring/Ae. geniculata and Chinese Spring/Ae. peregrina) were kindly provided by Dr. A. Lukaszewski (University of California, Riverside) and Dr. B.R. Friebe (Wheat Genetics Resource Center, Kansas, U.S.A.), respectively. DNA extraction, PCR amplification, and gel electrophoresis were performed according to the protocols of the CIMMYT Molecular Genetics Laboratory (Hoisington et al. 1994).

Genome-specific markers. Nullisomic-tetrasomic analysis revealed that the location of most of the loci amplified by the 24 microsatellite primers was consistent with the information about their chromosome location reported by Röder et al. (1998) and Pestsova et al. (2000) (Table 10). Fourteen of these amplified fragment specific only to D-genome chromosomes. The remaining primers amplified fragments not only for D but also for the A and/or B genomes.

Table 10. Microsatellite primers used in the study, their respective chromosome location and the Aegilops geniculata and/or Ae. peregrina chromosome they can distinguish. Primers with --- have no chromosome-specific fragment.
 Primer  Chromosome location *  Group **  Addition line ***  Aegilops chromosome
 GWM 642  1D, 1A  1L  1U^g^, 1U^p^  1U
 GWM 848  1D    1U^g^, 1U^p^  1U
 4U^g^, 4U^p^  4U
 GWM 903  1D, 1B    1U^p^  1U
 
 GWM157  2D  2L  2M^g^  2M
 GWM455  2D, 2B  2S  2U^g^  2U
 GDM 35  2D  2S  2M^g^, 2U^g^, 2U^p^  2MU
 GDM 93  2D, 2A  2L  2M^g^  2M
 6U^p^  6U
 GDM 148  2D  2  2M^g^  2M
 
 GWM 114  3D  3S  3M^g^  3M
 GWM161  3D  3S  3M^g^  3M
 7U^p^  7U
 GDM 128  3D  3L  ---  ---
 
 GWM 165  4D, 4A, 4B  4S  4Mg, 4Up  4MU
 GWM 192  4D, 4A, 4B  4L  ---  ---
 GDM 34  4D  4  5U^g^, 5U^p^  5U
 GDM 61  4D  4  4M^g^  4M
 GDM 125  4D  4L  4M^g^  4M
 GDM 129  4D  4S  ---  ---
 
 GWM 159  5D, 5B  5S  5U^p^  5U
 GWM 205  5D, 5A, 5B  5S  5M^g^  5M
 5U^g^, 5U^p^  5U
 GDM 68  5D, 5A, 5B  5S  5M^g^, 5U^g^  5MU
 5U^p^  5U
 GDM 99  5D  5L  4U^g^, 4U^p^  4U
 5U^g^, 5U^p^  5U
 
 GDM 108  6D  6S  6U^p^  6U
 
 WMS 37  7D  7L  2U^g^, 2U^p^  2U
 WMS 974  7D, 7A, 7B    7Mg  7M
* Chromosomal location determined using nulli-tetrasomic lines of Chinese Spring.
** Data from the Catalogue of Gene Symbols for Wheat, 1998-2002 Supplements.
*** Chinese Spring-Ae. geniculata (M^g^ and U^g^) and Chinese Spring-Ae. peregrina (U^p^) addition lines where specific fragments were amplified.

The results of evaluations with disomic addition lines of different U- and M-genome chromosomes also are indicated in Table 10. Out of the 24 primers showing polymorphism between Triticum and Ae. geniculata, three (GWM 192, GDM 128, and GDM 129) did not amplify specific fragments in any of the addition lines. Three other primers (GDM35, GDM 68, and GDM 165) amplified the same sized product in U- and M-genome chromosome addition lines and, therefore, cannot be used to distinguish the U and M genomes. The remaining 18 SSRs (75 %) showed additional amplification products and can be used to distinguish Ae. geniculata U- and M-genome chromosomes in wheat backgrounds.

Chromosome-specific markers. All three microsatellite primers located on 1D chromosome (Table 10) amplified specific additional bands in the disomic addition line with chromosome 1U of Ae. geniculata and Ae. peregrina, indicating that they could be used as markers for detecting Ae. geniculata 1U chromosome. GWM 848 also gave a specific product for 4U chromosome.

Out of the five SSRs located on 2D chromosomes, GWM 455 produced a fragment specific only to the 2U addition line, whereas GDM 35 amplified the same sized products in both 2U- and 2M-chromosome addition lines and, consequently, may be considered only as an Ae. geniculata chromosome-2 marker. The three remaining SSRs (GWM 157, GDM 93, and GDM 148) distinguished chromosome 2M. GDM 93 also generated a distinct PCR product in the addition line with chromosome 6U of Ae. peregrina.

Two SSRs specific to chromosome 3DS, GWM 114 and GWM 161, were identified as markers for Ae. geniculata chromosome 3M. GWM 161 also amplified a product specific to chromosome 7U of Ae. peregrina. Three out of the six 4D primers amplified products specific to 4M chromosome of Ae. geniculata. Only two of these (GDM 61 and GDM 125) can be used as M-genome markers, however, because GDM165 amplified the same size product in the 4U addition line. Two primers did not amplify any specific band for 4U or 4M disomic addition lines, and one primer (GDM 34) produced distinct fragment for the 5U chromosome addition lines of Ae. geniculata and Ae. peregrina, indicating homeology between 5U and 4DL chromosomes for this locus.

All four SSRs specific to group-5 chromosomes had distinct amplification products for the chromosome 5U disomic addition of Ae. geniculata and Ae. peregrina (Table 10). Two of these, GWM 205 and GDM 68, also could detect the chromosome 5M, disomic-addition line; the first one different from 5U in size and the second one of similar size. Moreover, GDM 99 detected chromosome 4U. Zhang et al. (1998) has noted the homoeology between 4U and 5DL and between 5U and 4DL chromosomes and confirmed the existence of a reciprocal T4UL·5UL translocation. GDM 108 located on the short arm of chromosome 6D distinguished 6U chromosome of Ae. peregrina. GWM 974, one of the two 7D microsatellites could be a marker for chromosome 7M of Ae. geniculata and GWM 37 for chromosome 2U of both Ae. geniculata and Ae. peregrina.

Conclusions. The results obtained in this study confirmed the homoeology between U- and/or M- and D-genome chromosomes and the presence of chromosomal rearrangements of U genome relative to wheat D genome. Eighteen microsatellites revealed specific alleles for chromosomes 2M, 3M, 4M, 5M, 7M, 1U, 2U, 4U, 5U, 6U, and 7U in Chinese Spring addition lines and could be used to identify wheat lines with chromosomes from Ae. geniculata. Other D-genome microsatellite primers are not yet explored for substantiating more data to confirm these results and for the identification of the remaining chromosomes 1M, 6M, and 3U.

References.

  • Fernandez-Kalvin B and Orellana J. 1992. Relationships between pairing frequencies and genome affinity estimations in Aegilops ovata X Triticum aestivum hybrid plants. Heredity 68:165-172.
  • Friebe BR, Tuleen NA, Budaeva ED, and Gill BS. 1996. Cytogenetic identification of Triticum peregrinum chromosomes added to wheat. Genome 39:272-276.
  • Friebe BR, Tuleen NA, and Gill BS. 1999. Development and identification of a complete set of Triticum aestivum-Aegilops geniculata chromosome additional lines. Genome 42:374-380.
  • Hoisington D, Khairallah M, and Gonzalez-de-Leon D. 1994. Laboratory protocols: CIMMYT Applied Molecular Biology Laboratory, 2nd Ed. CIMMYT, Mexico, D.F. Mexico.
  • Kimber G, Sallee PJ, and Feiner MM. 1988. The interspecific and evolutionary relationships of Triticum ovatum. Genome 30:218-221.
  • Mujeeb-Kazi A. 2001. Intergeneric hybrids in wheat: current status. In: Triticeae IV (Hernandez P, Moreno MT, Cubero JI, and Martin JA eds). Viceconsejeria, Servicio de Publicaciones y Divulgacion, Spain. Pp. 261-264.
  • Pestsova E, Ganal MW, and Röder MS. 2000. Isolation and mapping of microsatellite markers specific for the D genome of bread wheat. Genome 43:689-697.
  • Röder MS, Korzun V, Wendehake K, Plaschke J, Tixier MH, Leroy P, and Ganal MW. 1998. A microsatellite map of wheat. Genetics 149:2007-2023.
  • Sears ER. 1966. Nullitetrasomic-tetrasomic combinations in hexaploid wheat. In: Chromosome manipulation and plant genetics (Riley R and Lewis KR eds). Oliver and Boyd, Edinburgh, Scotland. Pp. 29-45.
  • Zaharieva M, Cortéz A, Rosas V, Cano S, Sanchez J, Juarez L, Delgado R, and Mujeeb-Kazi A. 2001a. Potential of Aegilops geniculata genetic resources for wheat improvement. Ann Wheat Newslet 47:102-103.
  • Zaharieva M, Monneveux P, Henry M, Rivoal R, Valkoun J, and Nachit MM. 2001b. Evaluation of a collection of wild wheat relative Aegilops geniculata Roth and identification of potential sources for useful traits. Euphytica 119:33-38.
  • Zaharieva M, Suenaga K, William M, Mujeeb-Kazi A. 2002. Identification of specific Ae. geniculata microsatellite markers potentially useful for detecting introgressions into cultivated wheat. Ann Wheat Newslet 48:108-110.
  • Zhang H, Jia J, Gale MD, Devos KM. 1998. Relationships between the chromosomes of Aegilops umbellulata and wheat. Theor Appl Genet 96:69-75.