Development of an Integrated Linkage Map of A Genome of Diploid Wheat and introgression and Mapping of Stripe Rust, Cereal Cyst Nematode and Karnal Bunt Resistance

摘要

Genetic analysis and gene discovery in hexaploid wheat has been arduous because of its polyploid nature, large genome size, abundance of repetitive DNA sequences and limited polymorphism. Diploid A genome species, T. monococcum ssp. monococcum (Am), a diploid A genome species is domesticated and T. monococcum ssp. aegilopoides (syn. T. boeoticum) (Am) is a wild form of T. monococcum ssp. monococcum. are very closely related to T. urartu (Au) the A genome donor of hexaploid wheat, T. aestivum. T. monococcum being diploid with smaller genome size compared to bread wheat, existence of a very high level of polymorphism for DNA based markers, sequence conservation at orthologous loci and availability of a large BAC library is an attractive diploid model for gene discovery and allele mining in wheat It harbours immense variability for stress resistance and productivity traits. Transfer of useful variability from diploid to hexaploid wheat is difficult but could be facilitated by marker assisted selection. Linkage maps developed in diploid progenitor species will complement the genome analysis and gene cloning in wheat. An integrated molecular linkage map using a RIL population derived from inter sub-specific cross of T. boeoticum/T. monococcum has been developed. The linkage map consists of 181 markers including two morphological markers and has a size of 1 248 cM with four gaps in linkage group 2, 4 and 7. With a few exceptions, the position and order of the markers was similar to the ones in other maps of the wheat A genome. The RIL population segregated for resistance against stripe rust, leaf rust, cereal cyst nematode (CCN), Karnal bunt (KB) and powdery mildew and for several domestication and productivity traits. Classical genetic analysis revealed that resistance in these parental accessions was non-allelic. QTL analysis was performed for mapping these genes because both the parents were resistant to most of the diseases but the population showed segregation. Based on QTL analysis, the adult plant stripe rust resistance genes in T. monococcum and T. boeoticum were mapped on chromosomes 2Am and 5Am, respectively with Xpsr331 and Xbarcl51 as the linked markers. The CCN resistance genes were mapped on chromosomes 1Am and 2Am with BE444890 and BE498358 as the linked markers, respectively. Similarly Karnal bunt resistance gene in T. boeoticum was mapped on chromosomes lAm with Xwmc470 as the linked marker. In addition to mapping, all these genes have been transferred to hexaploid wheat using tetraploid wheat as bridging species. The B genome of T. durum suppressed both stripe rust and leaf rust resistance in F, triploid plants (T. durum/T. monococcum) and the F1 pentaploid plants (T. durum/T. monococcum//T. aestivum). Resistant plants, however, were recovered after first backcross with hexaploid wheat. Hexaploid derivatives with stable chromosome number and desirable agronomic pbenotype have been recovered. Evaluation of the introgression progenies at seedling and at adult plant stages revealed transfer of one seedling and one adult plant leaf rust resistance gene and one adult plant stripe rust resistance gene from T. monococcum. These near isogenic introgression lines (NIILs) are being used for fine mapping of stripe rust and leaf rust resistance genes transferred from T. monococcum. The introgression of CCN and KB resistance in tetraploid wheat background has been validated with the markers found to be linked to CCN and KB resistance in the RIL population. All the introgression lines will be evaluated for yield and yield components in replicated trials in the year 2007-08.