Interaction between arbuscular mycorrhizal fungi and rootstock cultivar on the susceptibility to infection by Ilyonectria species

Abstract

Arbuscular mycorrhizal fungi (AMF) have been shown to increase tolerance of grapevine rootstocks to black foot disease caused by Ilyonectria spp. The effect of pre-colonisation of different rootstocks with two AMF species on the susceptibility to Ilyonectria spp. was determined. Three rootstocks (3309C, 5C and Schwarzmann) commonly used in New Zealand colonised with either Acaulospora laevis, Funneliformis mosseae or untreated were grown in soil and inoculated with a mixture of Ilyonectria spp. isolates representing the species diversity recovered from New Zealand grapevines. After 9 months growth, root and shoot dry weight and trunk base infection by Ilyonectria spp., and the catabolic function of the rhizosphere microbial community using MicroResp™ was assessed. Both A. laevis and F. mosseae increased root dry weight, with no effect on shoot dry weight. Grapevine rootstocks varied in susceptibility with SC being most susceptible. AMF species altered rootstock susceptibility, with A. laevis inoculation of 5C decreasing disease severity and F. mosseae having no effect on disease severity of this rootstock. However, Funneliformis mosseae inoculation of Schwarzmann decreased disease compared with A. laevis. In the absence of the pathogen, the catabolic function of the microbial community in the rhizosphere of 3309C and Schwarzmann differed significantly from that of 5C, but this difference was not apparent following Ilyonectria spp. inoculation. AMF inoculation had no effect on the carbon utilisation profile of the rhizosphere microbial community. The results suggested a direct effect of AMF inoculation on rootstock susceptibility rather than changes in the function of the rhizosphere microbial community.