Perspective on FHB Resistance Breeding and Research on DNA Marker Assisted Selection

摘要

Epidemics of Fusarium head blight (FHB) during the last decade have had a devastating impact on the higher rainfall wheat growing areas of the U.S. Resistance to FHB in wheat is quantitatively inherited and results of field-based screening for resistance to this disease are often confounded by environmental factors, so repetitive screening over environments is necessary. Because of the difficulties in breeding wheat for resistance to FHB using conventional methods, the identification of DNA markers associated with resistance has been a high priority for wheat breeders and geneticists. We have been investigating a major QTL, designated as Qfhs.ndsu 3BS, derived from the Chinese cultivar 'Sumai 3', the most important resistance source worldwide. The best simple sequence repeat (SSR) markers near this QTL are highly polymorphic among different wheat genotypes and are therefore amenable for use in marker-assisted selection. We developed and tested more than 30 pairs of near-isogenic lines for this QTL in diverse genetic backgrounds and found a consistent effect of about 20% reduction in FHB severity. On the basis of cytologically based physical mapping, Qfhs.ndsu-3BS is most likely located in the deletion bin 3BS 0.78-0.87. To increase the DNA marker density of this QTL region, sequence-tagged site (STS) markers were developed from wheat ESTs that are homologous to rice genes on the sub-distal region of rice chromosome 1S. Twenty-seven STS markers were localized in the deletion bin 3BS 0.78-0.87. We constructed a high-resolution map of this major QTL region by screening a population of 3155 F_2 plants derived from a cross between a pair of near isogenic lines for the Qfhs.ndsu-3BS region with two SSR markers (Xgwm533 and Xgwm493) that flank this QTL. A total of 382 recombinants were identified and the high-resolution map currently contains 11 markers covering a distance of 6.2 cM between Xgwm533 and Xgwm493. The high-resolution map revealed a complex microsynteny among wheat, rice and barley at this QTL region. Homozygous recombinants are being used to place the QTL within the high-resolution map.