Genetic diversity in Botrytis cinerea populations on vegetable crops in greenhouses in south-eastern Spain

Seventy-nine random amplified polymorphic DNA (RAPD) markers, of which 46 were polymorphic and 33 monomorphic, were used to determine the level of genetic diversity and to study the structure of populations of Botrytis cinerea in Almeria, Spain. Sixty-five isolates were collected in the first survey (December 1992, at the beginning of the epidemic) from 23 commercial greenhouses of common winter crops in two regions, Levante and Poniente. In the second survey, conducted three months later at the end of the epidemic, 75 isolates were collected from 16 greenhouses in Poniente. The analysis of population structure revealed that genetic diversity within subpopulations sampled in the two surveys accounted for 98% of the total genetic diversity, while genetic diversity between subpopulations represented only 2% of the total diversity. The relative magnitude of gene differentiation between subpopulations, G(ST), averaged 0.017. In the first survey, partition of genetic diversity into hierarchical components by greenhouses within regions showed that the within-greenhouse component of diversity was 93%, the between-greenhouses, within-region component was 6%, and the between-regions component was 1%. Similar results were obtained when comparisons were made between greenhouses in the second survey or between populations of different countries: genetic diversity within subpopulations accounted for 95 and 96%, respectively, of the total genetic diversity. In all comparisons, values of G(ST) were higher than 0.01, ranging from 0.011 to 0.055. Analysis of likelihood ratio chi-square (G(2)) statistics under the null hypothesis that frequencies of markers are similar between subpopulations showed that different markers contributed to the differentiation between subpopulations in each comparison. The relative importance of several evolutionary forces in populations of B. cinerea is discussed, together with implications for the management of grey mould.