Comparative response of selected grapevine rootstocks and cultivars to inoculation with different mycorrhizal fungi

The need to replant vineyards due to the impact of phylloxera and other roo t disease problems has led to practices of soil fumigation that generally e liminate beneficial microbes like vesicular-arbuscular mycorrhizal (VAM) fu ngi. Replanting is done with cultivars grafted on nematode- and phylloxera- resistant rootstocks or with own-rooted cultivars. The question of the rela tive responsiveness of a selection of these rootstocks or cultivars to seve ral VAM fungal species prompted this study, The tests, conducted under low phosphate (14 mg kg(-1) available) conditions, revealed that all rootstocks and cultivars exhibited significantly increased growth in response to inoc ulation with VAM fungi. The degree of responsiveness varied, depending on t he plant genotype and fungal species used. Noninoculated plants were clearl y stunted and showed foliar symptoms of undetermined nutrient deficiencies, thus confirming the high dependence of grapevines on VAM. Based on these r esults, it would be expected that vines planted in soils lacking VAM fungi, due to fumigation or terracing that exposes poor soils, would be highly re sponsive to VAM colonization.