SNP-based identification of QTL for resistance to black point caused by Bipolaris sorokiniana in bread wheat

Black point disease caused by Bipolaris sorokiniana is a problem in wheat production worldwide.We aimed to identify major quantitative trait loci(QTL)for resistance to black point and develop molecular markers for marker-assisted selection(MAS).A recombinant inbred line(RIL)population derived from a cross between Wanyuanbai 1(susceptible)and SN4143(resistant)was evaluated for black point response at three locations during two years under artificial inoculation with B.sorokiniana,providing data for six environments.Thirty resistant and 30 susceptible RILs were selected to form resistant and susceptible bulks,respectively,that were genotyped by the wheat 660 K SNP array;685 singlenucleotide polymorphisms(SNPs)were identified,among which 385(56.2%)and 115(16.8%)were located on chromosomes 4 A and 2 B,respectively.Bulked segregant RNA-Seq analysis identified candidate regions on chromosomes 4 A(4.60–40.28 Mb)and 5 A(1.22–48.47 Mb).Genetic linkage maps were constructed for chromosomes 2 B,4 A,and 5 A using 59 polymorphic d CAPS and SSR markers.Finally,two QTL,designated QBB.hau-4 A and QBB.hau-5 A,were detected on chromosomes 4 A and 5 A,respectively.The resistance allele of QBB.hau-4 A was derived from SN4143,and that of QBB.hau-5 A came from Wanyuanbai 1.QBB.hau-4 A with a large and consistent effect(15.1%)is likely to be a new locus for black point resistance.The markers linked to QBB.hau-4 A and QBB.hau-5 A have potential application in MASbased breeding.

High-temperature wheat leaf rust resistance gene Lr13 exhibits pleiotropic effects on hybrid necrosis

Dear Editor,Wheat is one of the most important staple food crops.Leaf rust caused by Puccinia triticina Eriks.(Pt)is a destructive foliar disease that threatens world wheat production.Complementary wheat genes Necrosis 1(Ne1)and Necrosis 2(Ne2)on chromosome arms 5BL and 2BS,respectively,cause hybrid necrosis(Caldwell and Compton,1943;Chu et al.,2006).Ne2 shows extremely tight genetic linkage with leaf rust resistance gene Lr13(Zhang et al.,2016).We previously identified a temperature-sensitive leaf rust resistance gene LrZH22 in Chinese wheat cultivar Zhoumai 22(ZM,Figure 1A)that was effective against most Chinese Pt pathotypes(Wang et al.,2016)and shared an overlapping genetic interval with Lr13.In a separate study,a recessive early leaf senescence 1(els1)gene(Figure 1B)shared an overlapping interval with LrZH22/Lr13/Ne2(Chu et al.,2006;Wang et al.,2016;Zhang et al.,2016;Li et al.,2018).However,the function and relationship of LrZH22/Lr13/Ne2/els1 remained unknown for decades.Here,we report the map-based cloning of LrZH22 and els1 and characterize their relationship with Lr13 and Ne2 in conjunction with a companion paper(Hewitt et al.t 2021)studying the same gene.