[Show abstract][Hide abstract] ABSTRACT: Wild relatives of wheat as new sources of genetic diversity are a potent resource for addressing biotic and abiotic stress constraints that limit wheat productivity. These are distributed in the three gene pools of the Triticeae and over the last two decades are being extensively utilized in breeding programmes globally. In this study, 200 accessions of Triticum turgidum (2n=4x=28; AABB), 40 accessions of Aegilops tauschii (2n=2x=14;DD), and 6 accessions of Ae. triuncialis (2n=4x=28;CCUU) were screened against stripe rust of wheat (Puccinia striiformis tritici) at seedling stage. Bulk inoculum collected from environmentally diverse wheat growing areas of Pakistan was used for the seedling screening. The innoculum had virulence for genes Yr1, Yr3, Yr4, Yr5, Yr6, Yr7, Yr8, Yr9, Yr18, YrSp, YrSD, and YrCV. Infection types (ITs) ranging from low to high were recorded within each germplasm category where 35 durum lines (T. turgidum,) and 13 of Ae.tauschii had good seedling resistance (0-2). Another 20 durum and 12 Ae. tauschii lines were found moderately resistant. Frequency distributions of the ITs was higher for Ae. tauschii lines (34%) as compared to the durum wheats (20%). Advanced germplasm testing involving synthetic hexaploid wheats have made available several lines that are resistant to stripe rust. The source of resistance in this germplasm is attributed to alleles on the A and B genomes of durum parents, or on the Ae. tauschii's D genome, or is a combination of genes that are pyramided as a consequence of A, B and D genome hybridizations. Ample diversity has been identified that warrants exploitation in wheat breeding.
Pakistan Journal of Botany 04/2007; 39(2). · 0.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Amongst alien germplasms that provide much needed genetic diversity for resistance to leaf-blotch (caused by Cochliobolus sativus) and karnal bunt (caused by Tilletia indica) is the tertiary gene pool tetraploid Aegilops variabilis (2n=4x=28; UUSS) resource. In order to exploit this species potential, it is crucial that intergeneric hybrids are first produced from which stable genetic stocks are developed for subsequent agricultural utilization. The hybridization of several durum and bread wheat cultivars with Ae. variabilis is reported herein which have yielded cytologically characterized normal F 1 hybrids (2n=4x=28, ABUS or 2n=5x=35, ABDUS). These upon colchicine treatment have generated fertile octoploid and decaploid amphiploids. The amphiploids in all cases possessed aneuploidy that was more pronounced with bread wheat cultivars (2n=10x=70, AABBDDUUSS). Durum amphiploid combinations had more normal 56 chromosome plant types with perfect bivalent meiosis (2n=8x=56, AABBUUSS and 28 bivalents across variable ring and rod associations). Reported here is the cytogenetics of these intergeneric hybrid cross combinations that have enabled the production of a novel genetic resource in the form of fertile amphiploids that hold the potential to address future work on improving wheat cultivars for resistance to C. sativus and T. indica.
Pakistan Journal of Botany 01/2007; · 0.82 Impact Factor