Microclimatic stress and adaptive DNA differentiation in wild emmer wheat, Triticum dicoccoides

Genetic diversity was examined by RAPD-PCR analysis in 118 registered individuals of wild emmer wheat, Triticum dicoccoides, from a microsite at Yehudiyya, northeast of the Sea of Galilee, Israel. The test involved two climatic microniches in the open oak-park forest of Quercus ithaburensis: (1) sunny between trees and (2) shady under the trees' canopies. Comparisons were based on 97 loci amplified by 20 oligonucleotide primers. Significant genetic differentiations were found at single-, two- and multilocus structures between the neighbouring shady and sunny niches. These DNA polymorphisms appear to be associated with microclimatic stresses. The pronounced niche-effect on the significance of linkage disequilibrium and niche-specific linkage disequilibrium may suggest that natural selection directed the two-locus associations. The structure of the multilocus associations also mainly results from natural selection, and not by chance from population subdivision, or founder effects. These findings are largely parallel to the previous allozymic results at single-locus and multilocus levels. Both the DNA and the allozymic results suggest that microclimatic selection appears to play an important role in DNA differentiation as well as in protein polymophism.