NORTH DAKOTA
USDA-ARS CEREAL CROPS RESEARCH UNIT
Northern Crop Science Laboratory, North Dakota State University, Fargo, ND 58078, USA.
Justin Faris, James Miller, Daryl Klindworth, Leonard Joppa,
Phil Meyer, Mary Johnshoy, David Birdsall, Karri Haen, Kristin
Simons, and Erik Doehler.
Karri M. Haen and Justin D. Faris.
Sensitivity to the tan spot necrosis toxin (Ptr ToxA) is conferred
by a single dominant gene (Tsn1) located on the long arm
of wheat chromosome 5B. Because chromosome walking is laborious
and time-consuming, especially in large and genetically complex
genomes like that of wheat, chromosome landing via high-density
and high-resolution mapping may be a more feasible approach to
map-based cloning. We have combined the techniques of AFLP and
cDNA-AFLP with bulked-segregant analysis to target markers to
the Tsn1 region. Bulked DNAs derived from 'CS/CS-DIC 5B'
and 'LDN/LDN-DIC 5B' RSLs were analyzed to identify polymorphic
fragments within the Tsn1 region. Positive fragments were
converted into RFLP markers and mapped in segregating RSL populations.
Over 400 primer combinations have been screened resulting in
the identification of 33 positive fragments. So far, 21 of the
33 fragments have been cloned and mapped resulting in three markers
tightly linked to Tsn1. A population of ~2,000 F2s has
been constructed for high-resolution mapping. Other research suggests
the bp/cM ratio within this region is approximately 200 kb/cM.
Therefore, our goal is to identify markers within 0.5 cM of Tsn1
before screening BAC libraries to identify clones spanning the
locus.
Justin D. Faris, John P. Fellers, Steve Brooks, and Bikram S. Gill.
The Q gene is largely responsible for the domestication
of bread wheat because it confers the free-threshing character
of the spike. The Q gene has also been shown to influence
many other agronomic characters depending on the genetic background.
Thus, Q is likely a major regulatory gene. High-density
and high-resolution mapping are the first steps toward positional
cloning. The Q gene has been physically mapped on the
long arm of chromosome 5A between the chromosomal breakpoints
of deletion lines 5AL-7 and 5AL-23. To target markers to this
genomic region, we compared the two deletion lines using RFLP,
AFLP, and mRNA differential-display analysis. The use of these
techniques resulted in the identification of 18 markers within
the deletion interval. A population of 465 F2 plants was used
for high-resolution mapping. The resulting genetic linkage map
of the region was 20 cM, indicating that the Q locus lies
within a recombination hot spot. Markers within 0.8 cM of the
Q gene were identified and used to screen a T. monococcum
BAC library. A chromosome walk has been initiated and a partial
BAC contig constructed. To date, we have sequenced about 250
kb spanning 0.6 cM and currently have markers within 0.1 cM of
the Q gene.
Justin D. Faris, Karri M. Haen, and Bikram S. Gill.
Distorted segregation ratios of genetic markers are often observed in progeny of inter- and intraspecific hybrids and may result from competition among gametes or abortion of the gamete or zygote. Homoeologous group-5 chromosomes of the Triticeae are known to possess segregation distortion factors, and detailed analysis of Ae. tauschii chromosome 5D indicated that it possessed at least three different segregation-distortion loci that conferred gametophytic competition among pollen when an F1 plant was used as a male parent. In this study, we developed genetic linkage maps of chromosome 5B in male and female populations derived from Langdon (LDN) durum and Langdon/T. turgidum subsp. dicoccoides 5B disomic chromosome substitution (LDN-DIC 5B). Genetic markers in the female population had expected segregation ratios, and the recombination frequencies were similar to those found along chromosome 5B in other wheat and durum populations. However, segregation ratios of markers in the male population were highly skewed in favor of LDN alleles, and recombination frequencies were severely suppressed. At least two distorter loci appear to be present along chromosome 5B of durum, and they are likely homoeoalleles of those identified in Ae. tauschii. This research agrees with previous research in that segregation distortion is likely the result of gametophytic competition for preferential fertilization in a heterogeneous pollen population, and suggests that this phenomenon may lead to reduced recombination frequencies.
Erik Doehler, Justin Faris, James Miller, and Leonard Joppa.
Homozygous, durum/Ae. speltoides translocation lines were produced by homoeologous recombination and tested for reaction to the stem rust pathogen. The durum parent is a universal susceptible line, but the Ae. speltoides chromosome translocation conditions seedling resistance to at least nine races of stem rust. RFLP analysis indicates that the translocation chromosome involved is durum chromosome 2B, and it consists of the long arm and a portion of the short arm derived from Ae. speltoides. Experiments are underway to identify the Ae. speltoides chromosome involved in the translocation, to determine if the gene(s) on the translocated segment confer resistance to all races of stem rust, and to determine if this gene(s) is the same or different from Sr32 and Sr39 which were also derived from Ae. speltoides by translocations to hexaploid wheat chromosome 2B.
James D. Miller, Leonard R. Joppa, and Robert W. Stack.
Substitution of individual chromosomes from each of two FHB resistant accessions of T. turgidum subsp. dicoccoides into Langdon durum have been completed for 10 of the 14 chromosomes. The disomic substitutions were grown in replicated greenhouse tests, inoculated using the single spikelet method, and scored for type-II resistance to identify the chromosomes having genes for FHB resistance from T. turgidum subsp. dicoccoides. Of the disomic substitution lines showing average severities of 33 percent or less, we have found that genes in chromosomes 3A, 7A, 5B, and 7B appear to be contributing resistance to FHB.
Nine F2 families from a cross between the FHB resistant, T. turgidum subsp. dicoccoides disomic 7A chromosome substitution line and a susceptible cultivar Ben were inoculated with the scab fungus. A total of 1,046 plants were scored for type-II resistance (severities of 20 % or less) with 24 % appearing to contribute resistance to FHB. Attempts will be made to determine the inheritance of resistance and gluten strength in the F3 derived lines.
We also evaluated five BC1F2 families from a cross between a FHB-resistant accession of T. turgidum subsp. dicoccoides and the susceptible durum cultivar Ben, which were grown and inoculated in a FHB hill plot nursery. We selected and harvested 403 heads having scab severities of only 7 %, and the derived F3 lines are being evaluated in the greenhouse.
F4-derived F5 lines from two crosses between Ben and a FHB-resistant, T. turgidum subsp. dicoccoides accession continue to be evaluated and selected. In greenhouse tests, the selected F5 lines showed average severities of 10-15 % infection.
Daryl L. Klindworth and James D. Miller.
The most widely used set of durum aneuploids used in North America is the Langdon D-genome disomic substitutions. Studies of stem rust resistance in durum wheat are complicated because Langdon has at least three stem rust-resistance genes. As a result, aneuploid analyses can only be conducted when the stem rust race used is virulent on Langdon and avirulent on the genotype carrying the gene of interest. Studies of stem rust resistance in durum wheat would be facilitated by use of aneuploids based on a universal susceptible durum. Marruecos 9623 was identified many years ago as having only a single gene that confers resistance to only a few weakly virulent races of stem rust, most notably race 111. However, Marruecos 9623 has a poor ideotype and poor fertility. Therefore, we have crossed Marruecos 9623 to Langdon aneuploids and selected euploid progeny in an attempt to improve plant ideotype and fertility, and to select for susceptibility to race 111. We have identified a line, which is presently designated 47-1R1 which has these attributes. We presently are backcrossing 47-1R1 to the Langdon D-genome disomic substitutions to produce a stem rust-susceptible set of durum aneuploids.
Daryl L. Klindworth, Noman D. Williams, and S. S. Maan.
In 1978, Sasakuma et al. (Crop Sci 18:850-853) reported on the inheritance of several male-sterile mutants of wheat. The mutants FS2, FS3, FS20, and FS24 were conditioned by a recessive gene, with three of the mutants being allelic to each other. We wanted to determine the allelic relationship of these genes to ms1, which is the only mapped recessive male-sterile mutation in wheat. We crossed the mutants to Cornerstone (ms1c) to determine allelic relationships. We found that mutants FS2, FS3 and FS24 were allelic to ms1, and, therefore, the mutations in these lines must be located in chromosome arm 4BS. A monosomic study of the FS20 mutant was conducted and the mutated gene was located to chromosome 3A. From a telosomic analysis of the FS20 gene, we found the the mutated gene in FS20 was located in chromosome arm 3AL. A linkage chi-square test indicated that the FS20 gene was not linked to the centromere of chromosome 3A. The gene symbol ms5 was assigned to the mutated gene in FS20, and gene symbols ms1d, ms1e, and ms1f were assigned to the mutations in FS2, FS3, and FS24, respectively. The ms5 gene may be useful for mapped based cloning of a male-sterility gene from wheat