The Effect of the Rht1 Haplotype on Fusarium Head Blight Resistance in Relation to Type and Level of Background Resistance and in Combination With Fhb1 and Qfhs.ifa-5A

Abstract The semi-dwarfing reduced height alleles Rht-D1b and Rht-B1b have been deployed in modern wheat cultivars throughout the world, but they increase susceptibility to Fusarium head blight (FHB). Here, we investigated the impact of the Rht1 genes on anther retention (AR) in relation to FHB resistance using four different sets of near isogenic lines (NILs) with contrasting levels and types of background FHB resistance. NILs were evaluated for FHB severity, plant height, and anther retention in three greenhouse and three field trials using artificial spray inoculation. Rht-B1b and Rht-D1b alleles increased AR and FHB susceptibility in all genetic backgrounds. The magnitude of the effects differed between NIL groups. Increased FHB susceptibility largely followed increased anther retention. Differences in FHB susceptibility between tall and dwarf haplotypes were largest in the NIL group with the highest changes in AR. In the most resistant NIL group, dwarfed lines had only slightly higher AR than tall lines and maintained good resistance, while both tall and dwarf lines had high levels of retained anthers in the most susceptible NIL group. We further investigated the effect of the Rht1 genes in combination with the major Fusarium resistance QTL Fhb1 and Qfhs.ifa-5A. Qfhs.ifa-5A enhanced anther extrusion in tall as well as semi-dwarf haplotypes whereas Fhb1 did not affect AR. Qfhs.ifa-5A supported FHB resistance more efficiently than Fhb1 in lines that were more responsive to AR, while both Fhb1 and Qfhs.ifa-5A were equally efficient in NILs that had high background resistance and low response to AR.