The potential importance of diversity in Eutypa lata and co-colonising fungi in explaining variation in development of grapevine dieback

The diversity of Eutypa lata was studied in 56 isolates collected from Lang uedoc-Roussillon, France. The pathogenicity of isolates varied within a ver y broad range and was not influenced by the cultivar from which they origin ated. Using 27 RAPD markers, each isolate was identified as an unique genot ype. Gene diversity averaged 0.292 for the regional population. Lack of gam etic disequilibrium between RAPD loci supported the hypothesis of random ma ting. The RAPD analysis did not allow subdivision of the population accordi ng to geographic location, Vine cv. or pathogenicity of E. lain. The compos ition of the community of fungi was studied in 116 vines showing eutypa die back symptoms collected at several localities in the region. E. lata was re covered from 80% of the samples, from the sectorial brown lesion characteri stic of the disease. This lesion was associated in half of the vines with a central zone of discoloured hard wood and/or a light-coloured lesion of so ft consistency. E. lata was isolated alone from 124% of the vines and was a ssociated in 67% of the vines with one, two or three of the following fungi : Sphaeropsis malorum, Phomopsis viticola, Gliocladium roseum, Phaeoacremon ium chlamydosporum, P. aleophilum and Phellinus igniarius. The Variation in symptoms observed in the vineyard may be partly explained by the wide gene tic diversity in E. lain and differences in the composition and functioning of the fungal community.