A Database for Triticeae and Avena
International Maize and Wheat Improvement Center - CIMMYT
Lisboa 27, Colonia Juárez, Apdo. Postal 6-641, 06600,
México, D.F., México.
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
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.
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.
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.
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).
Table 4. Origin based on regional aggregates
of CIMMYTs Wheat Program visiting scientists in Mexico from 1966
to 2002 (Source: CIMMYT Training database).
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
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.
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
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.
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
Table 6. Crossability data for Chinese Spring
ph and Chinese spring Ph wheat crosses with Aegilops geniculata.
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.
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
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
Table 7. Crossability data for Mexicali 75/Aegilops
umbellulata hybrid and BC seed production.
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
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.
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
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
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. 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.
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.
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
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.
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.
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.
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.