Location: Cereal Disease Lab
Project Number: 5062-21220-022-02-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 18, 2013
End Date: Aug 30, 2017
Initial association analysis based on lines derived from crossing of four Tunisian tetraploid sources of resistance with durum cultivars "Ben", "Maier", "Lebsock" and "Mountrail" has proven powerful. The Tun18 and Tun7 expressed similar resistance level to FHB as compared with the best hexaploid wheat sources (i.e. Sumai3 and Wangshuibai). A new significant QTL for FHB resistance was identified on the long arm of chromosome 5B (Qfhs.ndsu-5BL) with association analysis. This result was further confirmed by the traditional QTL analysis of a large population. A total of 10 different association mapping models were analyzed with the linear mixed model considering the structure (Q or P) and the kinship matrix estimated by REML (KT) identified as the best for association studies in a mixture of wheat populations from a breeding program. The results also demonstrated a region on the short arm of chromosome 3B as potentially linked to FHB resistance. This region is in proximity of major FHB resistance gene "fhb1" reported in hexaploid wheat. This finding was surprising considering the genetic distance and lack of relationship between Tunisian tetraploid sources studied here and Chinese sources used to identify fhb1. A possibility of having susceptibility or suppressor of resistance gene(s) on durum wheat chromosome 2A was further confirmed in this material explaining the problem in developing resistant genotypes without counter selection against this region. The outcomes of this project were diagnostic markers and germplasm that can be easily incorporated into the breeding programs to derive more resistant cultivars. This work is being continued by generating more advanced backcross derived lines using current durum cultivars as the recipient parent. In this period we plan to 1) finish the association analysis of two additional Tunisian- derived advanced backcross populations [Tun 108 × Lebsock/Lebsock and Tun 108 × Ben/Ben], 2) use gamma radiation to generate populations for analysis of deletion of the possible suppressor locus on chromosome 2A, and 3) initiate development of durum lines carrying resistance loci located on 5BL and 3BS.
Objective 1) The Tun108 lines will be screened for FHB resistance in both greenhouse and field. Our current data clearly indicates a segregation for and a number of highly resistant lines based on greenhouse and field screening. Although there are obvious discrepancies between the two set of data because of environmental effect, on the average, 53 out of 173 (30.64%) and 57 out of 170 (33.53%) lines showed less than 20% infection in the two Tun108 populations. Both populations were genotyped using DArT clones and resulted in 553 polymorphic loci that mapped on the A and B genomes. Additional SSR markers are being added to these populations to anchor the DArT map and saturate the regions of critical importance. Objective 2) The major limitation will be the type of marker identified to be associated with important FHB resistance loci. The system we plan to use for SSR and SNP marker detection is relatively easy to apply and can be directly incorporated into the durum wheat breeding program. The DArT markers would require conversion into an easily scored marker system to become part of the routine selection protocol. The majority of DArT markers have been or are being sequenced. Therefore, we can take that information and identify flanking regions to use in developing either a sequence tagged site (STS) or cleaved amplified product (CAP) marker for the locus of interest. Objective 3) We plan to initiate a project that involves the use of gamma radiation and chemical mutagens and search for resistance in cultivated durum lines. The use of gamma ray irradiation has not only been effective in high-resolution physical mapping and BAC contig alignment to the genome but also in high resolution map based cloning in wheat. We will utilize this approach to derive about 1-5 Mb deletions lacking different parts of chromosome 2A in durum wheat to map the exact location of the suppressor gene(s). Seeds of a susceptible durum wheat cultivar carrying many of the major QTL regions for FHB resistance will be irradiated to produce M1 plants. Objective 4) To pyramid FHB resistance regions on chromosomes 5BL and 3BS, identified in Tunisian derived lines into, durum cultivars we plan to initiate a traditional crossing strategy utilizing closely associated markers for selection. We have identified a number of lines in the current study that show excellent levels of resistance and carry the major QTL regions identified by association mapping. These lines will be intercrossed to develop lines that pyramid all of the important regions. Backcrossing this source to advance durum breeding lines and selection with molecular markers will allow us to identify lines that potentially carry the major QTLs.