Identification of Diagnostic Markers for Scab Resistance in US Wheat Cultivars.

Our research focuses on marker saturation of FHB resistance QTL in three mapping populations having resistance from ‘Ernie’, ‘Massey’ and VA00W-38.  One hundred and ninety-four SSR and AFLP markers were mapped in a Ernie/MO94-317 (EM) population consisting of 236 lines to identify diagnostic markers for type II resistance QTL on chromosomes 5A, 3BSc, 4B and 2B.  The 4B QTL and the B1 locus are also associated with field scab resistance (incidence, severity, DON and FDK).  Analysis of 589 DArT and 60 SSR markers on 152 lines of a Becker/Massey (BM) population identified two major QTL on chromosomes 4B and 4D.  The 4B QTL explained 6-30% of variation for field scab resistance while the 4D QTL explained 10-33%.  They are linked to Rht1 and Rht2 genes, respectively.  It was also confirmed that Rht2 gene associated with scab susceptibility.  On chromosome 2D, the Ppd1 and Rht8 are associated with field scab resistance.  Three minor QTL were mapped onto chromosomes 2B, 3BSc and 5A which have same alleles as Ernie.  Markers tightly linked to QTL for FHB resistance from both BM and EM populations are used to identify putative QTL in 180 lines of a VA00W-38/Pioneer26R46 breeding population.  The FHB resistance QTL will be comparatively studied to identify the most important chromosome regions conferring scab resistance in these US wheat cultivars.  These regions will be further evaluated for differences in mechanisms governing FHB resistance.  Diagnostic markers linked to several QTL are being used to select progenies having multiple FHB resistance alleles. The ultimate goal is to develop wheat varieties having multiple QTL from Ernie and Sumai 3 on chromosomes 3BS, 3BSc, 4B, 5A, and 6B using MAS.  Pyramiding different FHB resistance QTL from exotic and native sources is a primary goal in most Eastern and Southern US wheat breeding programs.