Evaluation and precise mapping of QFhb.nau-2B conferring resistance against Fusarium infection and spread within spikes in wheat (Triticum aestivum L.)

QFhb.nau-2B previously identified in wheat cultivar Nanda 2419 conferred resistance against Fusarium graminearum infection (type I resistance) and fungal spread within spikes (type II resistance). In this study, this quantitative trait locus (QTL) was transferred into susceptible cultivars Chuanmai 42 and PH691 through molecular marker assisted backcross and was shown to be effective in different genetic backgrounds in repeated trials. To precisely map QFhb.nau-2B, the QTL interval was mapped with 43 markers, including 20 newly developed based on SNPs and Chinese Spring 2B reference sequences using 138 recombinants, identified from 530 recombinant inbred lines derived from Nanda 2419 × Wangshuibai, which yielded an average marker density of two markers per centimorgan. Of these recombinants, a collection of 19 and 20 lines without other known Fusarium head blight (FHB) resistance QTL alleles, representing 13 genotypes in each collection, was evaluated for type I and type II resistances, respectively. In field trials, the FHB symptom difference after inoculation on these lines was clear-cut and co-segregated with a few markers within the interval. The type II resistance QTL interval was thus delimited to the 4.1-cM interval flanked by Xwgrb1503 and Xwgrb1373, which contained the 0.9-cM type I resistance QTL interval flanked by Xwgrb1561 and Xwgrb1410. The precise mapping of QFhb.nau-2B with more closely linked markers could facilitate its use in breeding programs.