Genetic diversity and environmental associations of wild wheat, Triticum dicoccoides, in Israel

Allozyme variation in the tetraploid wild progenitor of wheat, Triticum dicoccoides, was studied for the proteins encoded by about 50 gene loci in 457 individuals representing 12 populations from Israel. Six spikelet morphological traits were measured in the same populations. The results indicate that: (a) 16 loci (= 32%) were monomorphic in all 12 populations, 15 loci (= 30%) were locally polymorphic, and 19 loci (= 38%) were regionally polymorphic. All polymorphic loci (but one) displayed high levels of polymorphism (≧ 10%). In Israel, the proportion of polymorphic loci per population, P, in wild wheat averaged 0.25 (range, 0.16-0.38), and the genetic diversity index, He averaged 0.07, (range, 0.03 - 0.12). (b) Altogether there were 110 alleles at the 50 putative loci tested (c) Genetic differentiation of populations included regional and local patterns: (i) The coefficients of genetic distance between populations were high (mean D = 0.10 range, 0.02 - 0.25), and indicated sharp genetic differentiation over short distances, (ii) Common (≧ 10%) but sporadic and localized alleles were frequent (76%), and (iii) Rare alleles were few (only 5 alleles). (d) The patterns of allozyme and spikelet variation in the wild gene pool were significantly correlated with, and partly predictable by, water factors, including those of precipitation, evaporation, and relative humidity as well as of soil type, (e) All six spikelet characters showed statistically significant variation among localities and (f) Allozymic variation was correlated with spikelet variation.These results suggest in T. dicoccoides: (i) the operation of natural selection in population genetic structure, (ii) local adaptive genetic differentiation caused by diversifying selection through climate and soil, and (iii) the guidelines for sampling these resources for use in wheat breeding programs.