Distribution of the necrosis and chlorosis genes in two wild tetraploid wheats, Triticum dicoccoides and T. araraticum

Distributions of the Ne1 and Ne2 alleles for type 1 hybrid necrosis, and Ch1 allele for type 1 hybrid chlorosis in two wild tetraploid wheats, Triticum dicoccoides (wild emmer wheat) and T. araraticum (wild timopheevi wheat), have been investigated by crossing the collections of these species from their entire distribution areas with their appropriate testers. The frequencies of the Ne1 and Ch1 alleles were 53% and 13%, respectively, in T. dicoccoides; whereas they were 69% and 0% in T. araraticum. The Ne2 allele was not found in both species. The Ne1 allele of T. dicoccoides was mainly Ne1m, while that of T. araraticum was mainly Ne1w. The frequency of the Ch1 allele differed significantly between the two species. These facts indicate that the emmer and timopheevi groups of tetraploid wheat had been differentiated genetically before their domestication. On the frequencies of the Ne1 and Ch1 alleles, Israeli T. dicoccoides revealed high genetic homogeneity within local populations. While there was extreme variability among these populations, they showed no geographical inclination of their frequencies. These alleles are assumed to be neutral for selection and have been randomly fixed in most populations. A limited numbers of Sitopsis accessions of the genus Aegilops were tested for the two alleles, Ne1 and Ne2. None of them carried these alleles. Thus, the origin of the Ne1 alleles found in tetraploid wheats could not be traced back to any Sitopsis species.