Root colonization and spore population by VA-mycorrhizal fungi in four grapevine rootstocks

Abstract

The occurrence of vesicular arbuscular (VA) mycorrhizae was investigated in an experimental vineyard at the Thessaloniki prefecture, in a soil which was poor in available P. The soil had not received any phosphorus fertilization for several years, nevertheless the leaves had an adequate P content (0.17 - 0.31 % of d.w.). The vineyard was planted with 4 introduced (Cinsaut, Syrah, Grenache, Carignan) and 4 local cultivars (Athiri, Roditis, Assyrtiko, Malagouzia), grafted to the rootstocks 110 R, 41 B, 140 Ru and 1103 P. Microscopic examination showed that all 4 rootstocks were colonized by VA-mycorrhizal fungi at frequencies ranging from 45 to 75 %. The number of vesicles varied between 16 and 47 and the number of arbuscules between 5 and 26 per cm of infected root. Spore number produced by the mycorrhizal fungi in the rhizosphere ranged from 196 to 280 per 100 g of soil. Spores of the genus Glomus were more commonly encountered, in particular those of G. mosseae and G. macrocarpum. The roots of 1103 P, followed by 41 B, 140 Ru and 110 R were most heavily colonized. The same pattern was observed with regard to the number of spores in the rhizosphere of these rootstocks. Grafted cultivars were found to have some influence on the degree of colonization of these rootstocks and on the population of spores, but had no effect on the formation of vesicles and arbuscules. The degree of colonization of roots by endomycorrhizal fungi was inversely related to the available P content of the soil. At the time of root sampling the P content of leaves was not directly related neither to the degree of root colonization nor to the P content of the soil. However, leaves were found to be adequately supplied with P in all cases. Therefore, the differences observed among the 8 cultivars can be attributed primarily to a variety-specific demand for P.