L.I. Gilchrist and A. Mujeeb-Kazi.
F1 hybrids from T. turgidum/T. tauschii crosses were sources of synthetic hexaploids. Several hundred such SHs have been produced forming a bridging germplasm base for bread wheat improvement. Screening for S. tritici in Toluca, Mexico, led to identification of resistant SH combinations that were crossed onto susceptible bread wheat cultivars. Advanced, resistant derivatives were evaluated over three cycles using a mixture of five isolates. Disease severity was recorded in each cycle using a modified double digit 1.1 to 9.9 resistant:susceptible scale during the watery, milky, and doughy grain-filling stages. The diversity observed in the SH/bread wheat advanced lines was influenced significantly by 1,000-kernel weight. These resistant lines can be readily utilized in breeding programs (Tables 16, p. 162 and 17, p. 163), and are superior than the resistant conventional bread wheat germplasm.
Table 16. Pedigrees of ten Septoria leaf blotch-resistant spring bread wheat cultivars/T. tauschii derivatives.
|Germplasm||Cross and selection number 3|
|Seri1//Croc1/T. tauschii (224)2||CIGM90.358-1Y-1M-2Y-0B-0Y-1M-2M-0Y|
|Altar84/T. tauschii (224)//2*Cupe1||CIGM91.191-5B-3Y-0B-0Y-1M-2M-0Y|
|Yaco//Croc1/T. tauschii (205)/3/Yaco1||CIGM91.153-1B-2Y-0B-0Y-2M-0Y|
|Pgo//Croc1/T. tauschii (224)/3/2*Weaver||CIGM91.248-2Y-0B-1Y-2M-7M-0Y|
|Altar 84/T. tauschii (191)//Yaco3/3*Bau1||CIGM92.337-0B-0Y-1M-2M-0Y|
|Altar 84/T. tauschii (191)//Opata1||CIGM90.483-4Y-1B-2Y-0B-1M-3M-0Y|
|Croc1/T.t auschii (205)//Kauz1||CIGM90.248-1Y-2B-11Y-0B-1M-1M-0Y|
|Croc1/T.t auschii (205)//Weaver1||CIGM90.250-4Y-3B-4Y-0B-1M-4M-0Y|
|Croc1/T.t auschii (205)//Weaver||CIGM90.250-4Y-3B-4Y-0B-1M-3M-0Y|
|Croc1/T. tauschii (213)/Pgo1||CIGM90.412-5Y-3B-6Y-0B-2M-1M-0Y|
1 bread wheat cultivars
2 synthetic hexaploid with Ae. tauschii CIMMYT accession number in parenthesis
3 B = Batan, M = Toluca, Y = Yaqui Valley
Conclusions. S. tritici-resistant
SH wheats upon crossing with elite but susceptible bread wheats
have yielded advanced derivatives resistant to the disease. Ten
lines with desirable agronomic characteristics studied over 3
years, have maintained their resistances with scores between 1.1
to 2.1. Resistant bread wheats score 3.1 to 4.1, susceptible
bread wheats 8.7 to 8.9, and all durum cultivars score between
8.7 to 9.9. Direct crosses between T. tauschii accessions
contributing resistance to S. tritici and susceptible bread
wheat cultivars are in progress. Monosomic analyses only are
concentrated on the D genome, because T. tauschii is the
donor source. DH protocols will be merged with the conventional
Amphiploids of Triticum turgidum with some A, B, and D genome
Triticeae accessions resistant to Septoria tritici leaf blotch.
R. Delgado, L.I. Gilchrist, and A. Mujeeb-Kazi.
A-, B-, and D-genome Triticeae species in the primary and secondary gene pools offer a potent avenue that facilitates pyramiding of diverse stress resistances for wheat improvement. We have produced a wide array of genetic stocks using the above
genomic accessions. These amphiploids are hexaploids of AA AABB,
AABB BB, and AABB DD genomic compositions. They were derived
from crosses of several A-, B-, or D-genome diploid accessions
with durum wheat cultivars. Screening these germplasms in Toluca,
Mexico, for S. tritici for 3 years has led to the identification
of several resistant entries. The diagnostic parameter was disease
damage during three grain-filling stages. Amphiploid germplasm
provides a unique diversity for improving both bread and durum
wheat cultivars through bridge crosses as one utilization option.
Some descriptors and disease scores of the above germplasms are
presented (Table 18, p. 164). These amphiploids will enable breeders
to exploit the diversity for durum and bread wheat improvement
by amphiploid bridging crosses, direct diploid single-genome crosses,
or tetraploid combinations involving accessions of two resistant
genomes exemplified by resistant AADD tetraploids.
Table 17. Agronomic characteristics and disease reaction of Mycosphaerella graminis resistant spring bread wheat germplasm grown in Atizapan, Toluca, Mexico state, over three crop cycles.
|13.||Seri 82 CM33027|
Table 18. Cross combination details of some AA AABB, AABB BB, AABB DD, AADD amphiplids resistant to Septoria tritici with a few descriptors.
Durum cultivar/Diploid species
|Descriptors1||S. tritici score2|
|Sca/T. boeoticum (23)3||90.674||88||130||134||1-1||1-1||1-1|
|Scoop/T. boeoticum (50)||90.700||100||135||127||1-1||1-1||1-1|
|Scoop/T. boeoticum (87)||90.707||100||130||127||1-1||1-1||1-1|
|Aos/T. monococcum (98)||90.791||110||105||150||1-1||1-1||1-1|
|Aos/T. monococcum (118)||90.794||115||110||144||1-1||1-1||1-1|
|CPI/-----44/T. boeoticum (93)||93.129||100||135||138||1-1||1-1||1-1|
|Stn/T. monococcum (111)||93.134||105||115||127||1-1||1-1||1-1|
|Stn/T. monococcum (112)||93.136||100||110||134||1-1||1-1||1-1|
|CPI/-----44/Ae. speltiodes (129)||94.37S||115||100||140||1-1||1-1||1-1|
|Ceta/Ae. speltoides (135)||94.45S||120||115||145||1-1||1-1||1-1|
|Ceta/Ae. speltoides (140)||94.254S||120||115||145||1-1||1-1||1-1|
|Arlin/Ae. speltoides (141)||94.255S||120||105||150||1-1||1-1||1-1|
|Altar/Ae. squarrosa (224)||86.942||110||100||135||1-1||1-1||1-1|
|Yar/Ae. squarrosa (518)||90.846||105||100||140||1-1||1-1||1-1|
|Yar/Ae. squarrosa (493)||89.463||105||100||135||1-1||1-1||1-1|
|Altar/Ae. squarrosa (502)||93.395||100||105||130||1-1||1-1||1-1|
|Sca/Ae. squarrosa (409)||93.237||105||100||140||1-1||1-1||1-1|
|Croc/Ae. squarrosa (879)||89.479||100||110||135||1-1||1-1||1-1|
|Ae. squarrosa (1027)/T. boeoticum (42)||94.32S||110||135||150||1-1||1-1||1-1|
|BW Susceptible Seri 82||CM33027||83||90||140||2-1||8-4||8-9|
|BW Resistant Bobwhite||CM33203||83||90||138||1-1||1-1||4-1|
Management of an abiotic stress in wheat - salinity - through
alien Triticeae germplasm, cytogenetic manipulations, and screening
J.L. Diaz-de-Leon and A. Mujeeb-Kazi.
Abiotic stresses are static mechanisms that tend
to be more durable, because of the absence of pathogen influence.
Of these abiotic stresses, salinity tolerance in wheat poses
an almost unsurmountable challenge. Conventional diversity is
limited and significant practical outputs are few. We present
here our research strategy that encompasses screening under two
controlled conditions, and a field screening protocol using sea
water dilution as the irrigation source. The dilutions equate
variable electrical conductivity levels. Complementing this screening
procedure is novel germplasm development by exploitation of the
annual and perennial Triticeae species of the primary and tertiary
Some salinity screening methodologies. In
general the methodologies are separated into field evaluations
and in vitro testing. Both procedures provide information on
genetic diversity among the germplasms. We present here procedures
that are being used in our experimentation.
Field Screening using sea water dilutions.
Germplasm screening for salinity response is conducted under
field conditions in La Paz, Baja California Sur, Mexico. Normal
well-water for irrigation with an electrical conductivity
(EC) level of 4.5 ds/m serves as the control concentration. Sea
water, in close proximity to our field screening site, is kept
in 1,200 liter containers. Mixing sea water with the normal well-water
provides the necessary EC levels selected for the field evaluation.
These levels have been kept at 8.0, 12.0, 16.0, and 20.0 ds/m
and can be extended further. Plots are separated from each other
on all sides by black plastic line dividers. The plots are individually
flood-irrigated with 200 liters twice a week according to the
treatment category. Electrical conductivity of the irrigation
water is measured, and soil samples randomly taken from each plot
after 24 hours. Determination of the soil EC follows the established
extraction procedure with steps of soil sampling/lot at random
points. After 1 week of plant growth, all plots are fertilized
with 15 g of urea per week up to 8 weeks. The urea applications
are made weekly with each irrigation and are discontinued after
In vitro screening. These
protocols utilize the hydroponics system (Gorham 1990) where NaCl
levels from 50 mol/m3 up to 200 mol/m3 have
been used as discrimination levels. Growth parameter assessments
are made, and the procedure is strengthened by K:Na discrimination
In addition, we have used two other strategies where
growth analyses are made by 15 days from the start of the experimentation,
allowing a first selective cut of the germplasm, and using these
initial selections for the field sea water dilution study. These
strategies utilize (i) a saline agar media based upon the standard
Murashige-Skoog culture medium with variable EC levels that
simulate the field sea water dilution ranges and (ii) the same
sea water dilutions for doing a petri dish germination/growth
study, complemented by Hoagland's
nutrition solution as a variable if necessary.
Genetic diversity of the salinity status in the Triticeae.
The conventional germplasm.
Triticum aestivum cultivar Kharchia 65, a salt-tolerant
cultivar, has been exploited by growers in Rajasthan, India, for
several decades. Controlled testing in saline media unequivocally
attests to the cultivar's
salt tolerance potential (Mujeeb-Kazi et al. 1993). Attempts
to incorporate the cultivar's
salinity tolerance genetic diversity for wheat improvement have
been made, and the singular success is accredited to the KRL 1-4
wheat cultivar release. Another salt-tolerant T. aestivum
cultivar selected from Lu 26 is Lu 26S. Additional inputs
to this conventional gene pool of Kharchia 65, KRL 1-4, and
Lu 26S are some collections of promising cultivars and land races
acquired from various programs and countries. These are Chinese
Spring, SNH-9, WH-157, Sakha 8, Shorawaki, Candeal,
and Pasban-90. Susceptible cultivars in the above tester
group of diverse germplasms were a durum wheat, PBW34, and the
bread wheat cultivar Oasis. More susceptible wheats are needed.
We have developed this tester set in order to establish germplasm
evaluation uniformity among researchers. Undoubtedly, additional
entries will be added to the current set, and a revised list of
Our current status and projections for incorporating salinity tolerance through alien genetic diversity.
Interspecific hybridization or short-term product
output strategy is focused on use of Ae. tauschii using
the bridge cross route that exploits the various synthetic hexaploids.
We have produced several hundred synthetics.
Through intergeneric hybridization, we are attempting
to exploit the salt tolerance potential of two diploids (Th.
bessarabicum and Th. elongatum). Thinopyrum bessarabicum
focuses on direct exploitation through its 56-chromosome amphiploid
for bread wheat improvement. The amphiploid form of both these
diploids (Wang 1986) is also being used for durum and bread wheat
and involves the Ph manipulation strategy. This manipulation
avenue is an integral part both for bread wheat and durum wheat
improvement and F1 hybrids have been produced. These
hybrids were cytologically validated, and the ph role was
elucidated for the alien amphiploid combination with Chinese Spring
ph. The meiotic associations in the durum/diploid alien
amphiploid also document the hybrid status and elucidate the genomic
associations. Use of the Cappelli durum ph is a route
that also has been used for alien introgressions. In bread wheat,
the significance is exemplified in F1 hybrids with
Ph showing less pairing as compared to the ph based
The novel route of PhI incorporation
introduced recently in this program holds substantial merit (Chen
et al. 1994), and will be an option to pursue. In addition, the
use of the molecular probes diagnostic for the Ph locus
(Gill and Gill 1996) is seen as an efficient means to exploit
the several Ph-based perennial F1 hybrids by
creating Phph BC1 derivatives and exploiting
only the ph-derived haploids, as described by Mujeeb-Kazi
et al. (1993).
Chen PD, Tsujimoto H, and Gill BS. 1994. Transfer
of PhI genes promoting homoeologous pairing
from Triticum speltoides to common wheat. Theor Appl Genet
Gill KS and Gill BS. 1996. A PCR-based screening
assay of Ph1, the chromosome pairing regulator gene of
wheat. Crop Sci 36:719-722.
Gorham J. 1990. Salt tolerance in the Triticeae:
ion discrimination in synthetic hexaploid wheats. J Exp Bot
Mujeeb-Kazi A, Gorham J, and Lopez-Cesati
J. 1993. Use of wild Triticeae relatives for stress tolerance.
In: Inter Crop Science I (Buxton DR, Shibles R, Forsberg
RA, Blad BL, Asay KH, Paulsen GM, and Wilson RF eds). Ames, IA.
Wang R-C. 1986. Amphiploids of the diploid
hybrid Thinopyrum bessarabicum x T. elongatum.
Agron Abstr p. 86.
Karnal bunt screening of some D-genome synthetic hexaploids and germplasm derived from their crosses to bread wheat.
G. Fuentes-Davila and A. Mujeeb-Kazi.
D-genome synthetic hexaploid wheats derived from T. turgidum/T. tauschii accession combinations were evaluated for Karnal bunt resistance under field and greenhouse conditions in Mexico over three test cycles. Of 266 SH wheats tested, several demonstrate immunity (0 %) to KB. Four SH wheats have been registered. For breeding applications, crosses between KB-immune SH wheats and KB-susceptible bread wheats gave elite agronomic plant type segregants. These lines were inoculated and are further sources of elite KB-resistant germplasm. Infection of susceptible bread wheat cultivars ranged from 20.5 to 100 percent. The standard susceptible bread wheat cultivar WL711 was the check. Several `SH/bread wheat' derivatives were immune.
The interspecific crossing program at CIMMYT has
produced 570 synthetic hexaploids (T. turgidum/T. tauschii
accessions) over a span of 5 years. Those SHs produced during
the first 3 years were seed increased and formed the KB-screening
germplasm reported here.
STUDY 1. Screening of T. turgidum/T. tauschii SH wheats.
Field Screening. From
the first SH wheats produced during 1989-91,
266 were tested for KB resistance. Several lines with 0 % infection
were identified. Susceptibility also was present in this material,
and infection levels up to 35 % were observed. The durum parents
were either immune or showed up to 2.8 % infection. The bread
wheat cultivar WL711 had a mean infection value of 65 %. We have
registered four SH types from this immune group. The pedigrees
and characteristics of these four SH wheats have been described
(Villareal et al. 1996).
The SH germplasms gave 0 % infection to KB in all
tests over three cycles of evaluation, compared with a 65 % mean
infection of WL711, the susceptible bread wheat check cultivar.
The durum wheats in the pedigrees of the four SH wheats had levels
of infection from 0.3-0.84
%. Several other SH wheats also had an immune KB response with
a large number exhibiting less than 3 % infection. The SH entries
have acceptable agronomic characteristics that can significantly
contribute to bread wheat improvement.
The KB-screening data of the SH and durum parental germplasm under
field and greenhouse regimes is in Table 19. From the field-resistant
SH entries, a selected few showing a similar response under greenhouse
controlled conditions are included. The durum parents in these
SH lines were immune under field tests, but a differential response
existed under the stringent greenhouse testing. Durum infections
ranged from 2.5 to 64.2 %. Their corresponding SH amphiploids
with immunity strongly endorse the contribution made by the T.
tauschii accessions to these genetic stocks (Table 19).
STUDY 2. Screening of susceptible bread wheat/resistant SH wheat advanced derivatives.
Extending the utility of KB-immune SH lines, susceptible
bread wheat cultivars were crossed by several SH wheats. Advanced
F6 derivatives from these crosses were field tested
for KB resistance. All F1 combinations had the base
bread wheat cultivar susceptibility and SH immunity established
earlier in Study 1 through field and greenhouse evaluations.
These 750 advanced `bread
derivatives tested were selected earlier for desirable plant type
and acceptable agronomic characteristics. Karnal bunt infections
of the 750 F6 entries ranged from 0-51.9
% over two inoculation dates. There were 71 derivatives with
immunity (0 %) on both inoculation dates, 80 had less than 1 %
infection, and 66 lines had infections between 1.1 and 2.0 %.
Though derivatives of all three categories will be tested further,
only 12 derivatives are indicated in Table 20 (p. 169). These
selections have desirable phenology traits and combine not only
the resistance of the T. tauschii accessions, but also
possess the genetic diversity of the A and B genomes of the respective
durum wheat cultivars. Apart from Weaver, all bread wheats have
a field KB susceptibility range between 7.9 and 11.98 %. These
cultivars under greenhouse conditions range from 8.8 (Weaver)
to 72.4 %.
Villareal RL, Mujeeb-Kazi A, Fuentes-Davila
G, and Rajaram S. 1996. Registration of four synthetic hexaploid
wheat germplasm lines derived from Triticum turgidum x
T. tauschii crosses and resistant to Karnal bunt. Crop
Table 19. Karnal bunt screening of durum parents and their synthetic hexaploids under field and greenhouse conditions.
|Parent and cross combination||Percent Karnal bunt infection|
|52||Altar/T. tauschii (198) 2||0||0|
|55||Altar/T. tauschii (205)||0||0|
|62||Altar/T. tauschii (211)||0||0|
|77||Altar/T. tauschii (219)||0||0|
|111||Altar/T. tauschii (315)||0||0|
|119||Altar/T. tauschii (328)||0||0|
|162||Chen/ T. tauschii (662)||0||0|
|80||Duergand/Ae. tauschii (221)||0||0|
|98||Duergand/Ae. tauschii (247)||0||0|
|61||CPI/Gediz"S"/3/T. tauschii(Aus 18912)||0||0|
|162||CPI/Gediz"S"/3/T. tauschii(Aus 18912)||0||0|
|145||Yar "S"/T.tauschii (493)||0||0|
|174||Yar "S"/T.tauschii (809)||0||0|
|128||68112/Ward/T. tauschii (369)||0||0|
2Number in parenthesis is the accession number in wide crosses program working collection.
Table 20. Advanced F6 derivatives from 'Karnal bunt-susceptible bread wheat/resistant synthetic hexploid' crosses screened under Obregon, Sonora, field conditions by the boot inoculation of ten spikes per entry, except for WL711 (the susceptible check) where 30 spikes were inoculated.
|Bread wheat Infection|
|13||WL711||1,373||424||31.36||5.42 to 100.0|
1Greenhouse data from the greenhouse screening of bread wheat cultivars in Study 1. Table 21. Some synthetic hexaploids for Triticum turgidum x T.Tauschii, 2n=6x=42; evaluated for Cochliobolus sativus in Poza Rica, Mexico.
|T. turgidum cultivar/T. tauschii accession (SH) combination|
and its CIGM cross number
|Doy 1/T. tauschii (188) CIGM88.1175||93||94||2||3|
|Rabi//GS/CRA/2/T. tauschii (190)CIGM88.1178||93||94||2||3|
|Rok/Kmli//T. taschii (214)CIGM88.1335||93||94||2||3|
|Yuk/T. tauschii (217) CIGM90.561||93||94||2||2|
|Arlin_1//T. tauschii (225) CIGM88.1228||98||99||4||8|
|Gan/T. tauschii (236)CIGM88.1228||93||94||2||6|
|Mexi/Vic//Yav79/3/T. tauschii (434)CIGM88.1335||92||92||2||2|
|Doy 1/T. tauschii (447) CIGM88.1344||92||93||2||3|
|Doy 1/T. tauschii (510) CIGM88.1360||93||95||3||4|
|Doy 1/T. tauschii (511) CIGM88.1363||93||94||3||4|
|Doy 1/T. tauschii (515) CIGM90.566||93||94||3||4|
|Yar/T. tauschii (524)CIGM89.474||94||95||3||6|
|68.111//RGB-U/Ward/3/FGO/4/Rabi/5/T. tauschii (629)CIGM90.590||92||93||2||3|
|Ceta/T. tauschii (850) CIGM89.552||93||94||2||4|
|Ceta/T. tauschii (872)CIGM89.555||93||94||3||4|
|68.111//RGB-U/Ward/3/FGO/4/Rabi/5/T. tauschii (878)CIGM89.559||92||93||2||3|
|Rabi//GS/CRA/3/T. tauschii (895)CIGM90.603||93||94||3||3|
|Rabi//GS/CRA/3/T. tauschii (895)CIGM90.605||92||93||2||3|
|Croc 1/T. tauschii (518)CIGM86.944||93||94||3||4|
|PBW114/T. tauschii (Introduction from India)||93||94||3||2|
|Ceta/T. tauschii (895) CIGM89.56||79||29||2||2|
|Arlin_1//T. tauschii (308)CIGM90.811||97||98||4||8|
|LCK59.61/T. tauschii (344)CIGM90.832||97||99||4||4|
|Rabi//GS/CRA/3/T. tauschii (457)CIGM90.832||92||94||2||2|
|Ciano 79 (Susceptible Bread Wheat)||97||99||5||9|
|BH 1146 (Resistant Bread Wheat)||95||97||3||6|
Helminthosporium sativum evalutions of D-genome dexaploids and germplasm derived from their crosses to bread wheat.
R. Delgado and A. Mujeeb-Kazi.
Spot or leaf blotch caused by C. sativus (syn.
H. sativum) limits wheat production in many nontraditional
hot, humid, wheat-producing areas. Breeding for resistance is
a high priority that is hampered by scarcity of adequate resistance.
Intergeneric hybrid derivatives involving Th. curvifolium
currently are the most promising and widely utilized. Additional
superior resistant sources reside in T. tauschii accessions.
This inference is based upon screening data of their SHs. The
advanced progenies of T. aestivum/resistant SH wheats (T.
turgidum/T. tauschii) have enabled selections with high resistant
levels to C. sativus. These lines are agronomically acceptable
and have satisfactory quality. The quality diversity of the selected
resistant lines is equal to, or better than, the wheat parents
involved in the respective crosses.
Study 1. Intergeneric sources of resistance.
Five lines from our intergeneric hybridization
program were identified and characterized as resistant to C.
sativus and possessed satisfactory agronomic attributes.
The pedigree of the intergeneric cross was `Chinese
These five lines have been registered and described in Mujeeb-Kazi
et al. (1996). Two of the lines are called Chirya and Mayoor,
and all germplasms have been widely distributed. These lines
are being utilized for wheat improvement in the breeding programs
of CIMMYT, by several national programs, and other collaborators.
Study 2. Interspecific source of resistance.
The diversity of resistance in the various SH wheats was observed
from screening of several synthetic wheats. Some results highlighting
a few SH wheats are provided in Table 21. The durum cultivars
involved in these SH combinations were generally susceptible for
the leaf infection and seed blemish parameters. These scores
for leaf blotch, 8-9
for spike damage, and 4-5
for seed appearance. (see Table 21, p. 170, for scoring scales).
A SH wheat is interpreted to be resistant based on the reaction
of the respective T. tauschii accession parent.
Elite SH types have been identified for wheat improvement
based upon agronomic evaluations (Villareal et al. 1995) and C.
sativus disease-screening data (Table 21, p. 170). Synthetic
hexaploid wheats with leaf scores of 9-5
or less and seed damage of 3 or less are the preferred resistant
donors for wheat improvement.
Study 3. Bread wheat/synthetic hexaploid advanced
derivatives. The SH bridge in breeding
is advantageous for wheat improvement, because it allows not only
the T. tauschii resistances to be exploited, but also incorporates
the genetic diversity of the A and B genomes of the respective
durum wheat cultivars present in the SH wheats. Using this approach,
we have developed `bread
germplasms from which 30 highly-resistant C. sativus lines
were identified. The resistance of this germplasm is similar
to that observed for the interspecific material described in Study
Mujeeb-Kazi A, Villareal RL, Gilchrist LI, and
Rajaram S. 1996. Registration of five Helminthosporium leaf
blight resistant wheat germ plasm lines. Crop Sci 36:216-217.
Some applications of wheat/maize-induced polyhaploidy.
A. Mujeeb-Kazi and M. Inagaki.
Crosses between wheat and maize are an effective
means of producing wheat polyhaploids. The haploid generation
is independent of the maize pollen source and of recipient wheat
cultivars, though some pollen source preference does exist. Applications
of the haploid procedure are in breeding programs, developing
mapping populations, producing cytogenetic stocks, and as an offshoot
assisting wide crossing programs. Techniques that complement
satisfactory hybridization product frequencies strongly favor
the use of detached spikes, sucrose as a nutrient source, and
sulfurous acid for overcoming contamination. A post-pollination
2,4-dichlorophenoxy acetic acid treatment remains crucial.
Use of stored maize pollen gives positive results with a low
frequency. Improved frequencies result by using stored pearl
millet pollen. The technique gives a variable response with durum
wheats and X TriticoSecale.
Diverse species crosses with maize and Tripsacum
pollen. T. aestivum, T. turgidum, and synthetic
hexaploid / maize or tripsacum. We
obtained polyhaploid embryo recovery frequencies for 16 hexaploid
wheats, 5 tetraploid wheats, and 15 synthetic hexaploids, averaging
15.6, 16.9, and 19.8 %, respectively. Mean plant regeneration
frequencies for bread wheats was 68.5 %, durum wheats were 73.9
%, and the synthetic hexaploids were 74.5 %. When Tripsacum
was the pollen source, regeneration frequencies were 78.5, 66.7,
and 77.5 % for bread, durum, and synthetic wheats, respectively.
Successful chromosome doubling with colchicine averaged 64 %
for T. aestivum cultivars, 69.5 % for T. turgidum
cultivars, and 63.6 % for the synthetic hexaploids. The use of
Tripsacum allows for a prolonged crossing cycle under our
conditions in Mexico if both maize and Tripsacum are used
as pollen donors.
Production of alien chromosome disomic addition
lines. In wheat wide crosses, polyhaploidy
can be further exploited for the production of alien chromosome
addition lines from populations that have varying chromosome numbers.
Preferably, plants with 22 chromosomes (21 chromosomes of wheat
plus 1 alien chromosome) are recovered and colchicine treated.
The final products after colchicine treatment will be plants
with 44 chromosomes (42 wheat plus an alien pair). This process
simplifies the production of disomic addition lines, and resolves
the constraints of paternal transmission of alien chromosomes.
In addition, it reduces the analyses necessary for recovering
44-chromosome disomic derivatives following the selfing of
43-chromosome plants that have chromosomal associations of
21 bivalents plus 1 univalent.
If a wide cross program were built exclusively around
the wheat cultivar Chinese Spring, the H. bulbosum procedure
% polyhaploid recovery) first used by Islam et al. (1981) for
producing wheat/barley addition lines, would be satisfactory.
However, in our program where commercial wheat cultivars are
used, the H. bulbosum technique is ineffective and we have
logically favored the `wheat
methodology. We have initially applied the procedure to derivatives
elongatum x T. aestivum crosses.
From 180 backcross derivatives, we obtained seed set after colchicine
treatment of 62 plants with somatic chromosome numbers of 43,
44, and 45 that were crossed with maize. Several double haploids
with 44 chromosomes have been developed, which form the starting
phase for producing Th. elongatum disomic addition sets.
Embryo formation in wheat crosses with maize and
pearl millet. Embryo formation frequencies
(percent frequencies of the embryos obtained from wheat florets
pollinated) in crosses with maize and pearl millet are shown in
Table 22. In crosses using fresh pollen of maize and pearl millet,
embryos were obtained at frequencies of 18.9-20.4
% and 19.7-35.6
%, respectively, across three crossing methods. Embryo formation
frequencies indicated that crosses with stored maize pollen produced
embryos at lower frequencies (2.8-8.5
%) than other crosses (18.9-35.6
%) with no significant difference presented for fresh and stored
pearl millet pollen.
Use of pollen storage and detached-tiller culture
did not increase the wheat polyhaploid production frequency, but
these procedures do enhance production efficiency. Stored pearl
millet pollen can be successfully used when fresh pollen is unavailable.
Detached-tiller culture gives considerable savings in terms
of labor and space required for handling wheat plants. Hot-water
emasculation is a time saver and requires only 3 minutes for a
large number of wheat spikes, whereas hand emasculation takes
at least 3 minutes per spike. These techniques, used solely or
in combination, provide greater flexibility for polyhaploid production
in hexaploid wheat.
Table 22. Embryo formation frequencies (%)1 in crosses of hexaploid wheat with maize and pearl millet.
|Pollen donor||Pollen storage|
|Crossing method 1|
1 Numbers followed by the same letter are not significantly different at the 5 % probability level.
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