Fine mapping and distribution analysis of hybrid necrosis genes Ne1 and Ne2 in wheat in China

Hybrid necrosis of wheat is caused by two dominant complementary genes Ne1 and Ne2 present in normal phenotype parents and is regarded as a barrier to gene flow between crop species. However, the necrosis alleles still occur at high frequency in modern wheat varieties. In this study, we constructed two high-density genetic maps of Ne1 and Ne2 in winter wheat. In these cultivars, Ne1 was found to be located in a span interval of 0.50 centimorgan (cM) on chromosome 5BL delimited by markers Nwu_5B_4137 and Nwu_5B_5114, while Ne2 co-segregated with markers Lseq102 and TC67744 on 2BS. Statistical analysis confirmed that the dosage effect of Ne alleles also existed in moderate and severe hybrid necrosis systems, and the symptoms of necrosis can also be affected by the genetic background. Furthermore, we clarified the discrete distribution and proportion of the Ne1 and Ne2 in China’s major wheat regions, and concluded that introduced modern cultivars directly affect the frequencies of necrosis genes in modern Chinese cultivars (lines), especially that of Ne2. Taking investigations in spring wheat together, we proposed that hybrid necrosis alleles could positively affect breeding owing to their linked excellent genes. Additionally, based on the pedigree, we speculated that the Ne1 and Ne2 in winter wheat may directly originate from wild emmer and introduced cultivars or hexaploid triticale, respectively.