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

Abstract

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.