Interaction between rootstock cultivar and AMF species influences susceptibility to Ilyonectria spp. infection

Abstract

Tolerance of grapevine rootstocks to black foot disease caused by llyonectria spp. has been shown to be increased by arbuscular mycorrhizal fungi (AMF) inoculation. The susceptibility of three rootstocks (3309 5C and Schwartzman), commonly grown in New Zealand, precolonised with two AMF species to llyonectria spp. infection was determined. The root stocks precolonised with Acaulospora laevis, Funneliformis mosseae or uncolonised were grown in soil inoculated with a mixture of llyonectria 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. was assessed. Rhizosphere soil was used to assess the catabolic function of the rhizosphere microbial community using the MicroResp™ system. Both A. laevis and F. mosseae increased root dry weight, but had no effect on shoot dry weight. Rootstock 5C was the most susceptible to infection. AMF species, however changed rootstock susceptibility, with. A. laevis inoculation of 5C decreasing disease severity, whilst F. mosseae had no effect on disease severity ln contrast for Schwartzman, F. mosseae decreased disease compared with A . laevis. The carbon utilisation profile of the microbial community in the rhizosphere of 5C differed significantly from Schwartzman and 3309 in the absence of the pathogen, but this difference disappeared with llyonectria spp. inoculation. The catabolic function of the rhizosphere microbial community was not affected by AMF inoculation. A direct effect of AMF inoculation on rootstock susceptibility rather than changes in the function of the rhizosphere microbial community is suggested.