Comparative Gene Analysis of Common Wheat and its Ancestral Species, I. Necrosis

1) It has been known that complementary necrosis in common wheat is mainly controlled by three genes, Ne1 located in chromosome 5B (V), Ne2 in 2A (XIII)and Ne3 in 3D (XVI). However, the B1 and F2 data from the cross T. macha subletshchumicum ×T. aestivum Chinese Spring indicated that a recessive gene in addition to the above-mentioned genes must be considered regarding the expression of necrosis.2) Relationships among various varieties of common wheat concerning necrosis are represented in the diagram of Fig. 2.3) Distribution of the three major genes in common wheat and its ancestors, Emmer wheat and Ae. squarrosa, was investigated using T. aestivum Prelude (Ne1ne2Ne3), T. aestivum Kharkov (ne1Ne2Ne3) and T. macha subletshchumicum (Ne1Ne2ne3) as test varieties.In Emmer wheat a majority of varieties were found to have the genotype Ne1ne2, while minor fractions were either ne1ne2 or Ne1Ne2.All strains of Ae. squarrosa so far tested had Ne3.In common wheat, most varieties were either ne1ne2Ne3 or ne1Ne2Ne3, while a small fraction were Ne1ne2Ne3. One variety only was found to be Ne1ne2ne3 and another only one to be Ne1Ne2ne3, both belonging to T. macha.4) From these results, the genotypes of Emmer wheat, that supplied the AB genomes to common wheat, are assumed to be Ne1ne2 or ne1ne2. T. dicoccoides spontaneo-nigrum, some forms of T. dicoccum, T. turgidum, T. persicum and T. orientale, and many varieties of T. durum have these genotypes.The donor of the D genome to common wheat must have possessed Ne3. All strains of Ae. squarrosa so far tested had this allele.5) The presumable hexaploid progenitor must have had either Ne1ne2Ne3 or ne1ne2Ne3. In common wheat, some forms of T. spelta, T. sphaerococcum, T. compactum and T. aestivum have these genotypes. T. macha, that is an exception in possessing the ne3 allele, is considered to be an isolated species among the hexaploids and seems not to have contributed to the origin of common wheat.6) It is suggested that Ne2 in common wheat originated at the hexaploid level rather than to have been derived from Emmer wheat. Possibility of selective advantage of Ne2 and disadvantage of Ne1 at the hexaploid level is suggested.