Fate of mycelial and conidial propagules of <i>Ilyonectria</i> and <i>Dactylonectria</i> species in soil

Abstract

Black foot disease of grapevines causes significant economic loss to the viticulture industry worldwide. A novel method was developed to investigate the fate of propagules of three species associated with black foot disease in New Zealand, Dactylonectria macrodidyma, Ilyonectria europaea and I. liriodendri, in soil. Conidia or mycelium of one isolate each of the three species were buried in soil in nylon mesh bags, and conidia/chlamydospore numbers were determined microscopically after 2 and 3 weeks. Conidia and chlamydospores were produced by mycelial inocula of all isolates, with greater numbers of chlamydospores after 3 weeks. Conidial inocula of all isolates also produced chlamydospores. Chlamydospores were formed at either the terminus or side of a hypha, and single and multiple conidia formed chlamydospores by combining their cellular protoplasm. Chlamydospores were produced from conidia, and conidia from mycelium faster for the I. europaea isolate than the D. macrodidyma and I. liriodendri isolates. The rapid formation of chlamydospores as survival propagules will facilitate the ability of these pathogens to persist in soil in the absence of a host.

Pathogenicity of <i>Ilyonectria pseudodestructans </i>propagules to grapevine rootstocks

“…Conidial inoculum resulted in higher rates of infection than mycelium, which is similar to that reported for D. macrodidyma and I. liriodendri by Probst et al (2019a). In soil in the absence of a host, mycelium propagules have been shown to disintegrate or rapidly convert into conidia or chlamydospores, resulting in lower inoculum levels (Probst et al 2019b). The fate of the different inoculum propagules in potting mix and in the presence of a host is not known but these results indicate that conidial and chlamydospore inocula may germinate and infect the grapevine rootstocks directly.…”