Near-isogenic Line Development And Fine Mapping Of Qfhi.nau-4B For Resistance To Fusarium Infection In Bread Wheat

Qfhi.nau-4B identified in the Fusarium head blight-resistant germplasm Wangshuibai is a major quantitative trait locus (QTL) against Fusarium graminearum infection. In our study, with the help of molecular marker assisted selection, using Mianyang99-323, PH691 and Mianyang2000-1 as recurrent parents, near-isogenic lines (NILs) of Qfhi.nau-4B derived from "Wangshuibai" were developed. The resistance and agronomic traits of these NILs and recurrent parents were investigated. The results showed that Qfhi.nau-4B could be stably expressed in different genetic backgrounds and environments. All NILs showed much better resistance to initial infection than their recurrent parents in all trials.Morphological and agronomic traits of these NILs were similar to the recurrent parents except that NILs were taller and had a longer spike. A F2 population developed by crossing Qfhi.nau-4B NIL with its recurrent parent Mianyang99-323 was evaluated to analyse the inheritance of Qfhi.nau-4B. The ratio of resistance segregation in this population fitted 3:1,suggesting that Qfhi.nau-4B was inherited like a single dominant gene. It was thus designated as Fhb4.To fine map Fhb4, a recombinant inbred line (RIL) population of 530 lines derived from Nanda2419 × Wangshuibai was used to construct a high-density genetic map of the Fhb4 region. The map spanned 22.4 cM and included 56 polymorphic markers. 22 of these markers were developed based on deletion bin-mapped wheat ESTs, RFLPs, the collinearity of wheat 4BL with rice chromosome 3S and Brachypodium chromosome 1L and the genomic sequence information of the positive Wangshuibai BAC clones identified with the markers in the Fhb4 interval.Plants with recombination occurring within Fhb4 interval were identified in Nanda2419-Wangshuibai RIL population using the flanking markers BARC20 and WMC349, in a BC4F2:3 population with the PH691 background using the flanking markers GWM368 and CFD39, and in a F2:3 population derived from Fhb4 NIL crossed with its recurrent parent Mianyang99-323 using the flanking markers HBG226 and GWM149. 44 recombinants without Fhb5 were identified from RIL population, 20 from PH691 BC4F2:3 population and 459 from Fhb4 NIL-Mianyang99-323 F2:3 population. These recombinants together with 50 Mianyang99-323 NIL recombinants identified in a previous study were evaluated in multiple field trials and their resistance performance showed significant differences according to phenotypes between the resistant group and susceptible group.According to the genotypes and phenotypes of these recombinants in different genetic backgrounds, Fhb4 was placed into the interval of Xmag6888-Xmag7237, Xhbg226-Xgwm149 or Xhbg226-Xmag7237, respectively. According to the overlapping relationship between these three intervals, Fhb4 was finally delimited to 1.06 cM interval flanked by HBG226 and MAG7237.The sequence information of mapped ESTs and positive BAC clones were used to determine the collinearity of Fhb4 region with rice and Brachypodium genome. The marker order is conserved between rice and Brachypodium, although there are some re-arrangements and deletions in the wheat genome. Comparative genome analysis showed that the Fhb4 region corresponded to a ?140 kb region in chromosome 3 of rice and a110 kb region in chromosome 1 of Brachypodium.