Quantitative evaluation of genetic diversity in wheat germplasm using molecular markers

Characterization of germplasm by means of DNA fingerprinting techniques pro vides a too] for precise germplasm identification and a quantitative estima te of genetic diversity. This estimate is important because a decrease in g enetic variability might result in a reduction of the plasticity of the cro ps to respond to changes in climate, pathogen populations, or agricultural practices. In this study, 105 Argentine bread wheat (Triticum aestivum L.) cultivars released between 1932 and 1995 were characterized by simple seque nce repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. A selected subset of 10 highly informative SSR was used to construct an Id entification Matrix that allowed the discrimination of the 105 cultivars. D ata obtained from SSR markers were complemented by information derived from AFLPs. Molecular data were used to quantify genetic diversity across Argen tine wheat breeding programs and to determine if modern wheat cultivars hav e a lower genetic diversity than earlier cultivars (genetic erosion). No si gnificant differences in genetic diversity were found among the large priva te and public breeding programs, suggesting that each of them contains a re presentative sample of the complete diversity of the Argentine germplasm. S ignificant differences were found for both SSR and AFLP only between breedi ng programs with large differences in number of released cultivars. No sign ificant differences in genetic diversity were found between the group of cu ltivars released before 1960 and those released in each of the following th ree decades. Average diversity values based on SSR markers were almost iden tical for the four analyzed periods. Genetic diversity estimates based on A FLP data confirmed the absence of a reduction of genetic diversity with tim e, but significant differences (P = 0.01) were found between bread wheat cu ltivars released in the 1970s (PIC = 0.28) and those released in the 1980s (PIC = 0.34). These results show that the Argentine bread wheat germplasm h as maintained a relatively constant level of genetic diversity during the l ast half century.