Effect of nutrition on infectivity of the nematophagous the fungus pochonia chlamydosporia on nematode eggs

Abstract

Effective establishment of microbes applied to soil often requires addition of an exogenous nutrient source to overcome competition from the resident microflora. However, readily-available nutrients may compromise the parasitic ability of facultative microbial parasites added as biological control agents. A study to investigate the role of nutrition in regulating the switching from the saprotrophic to the parasitic phase of nematophagous fungus Pochonia chlamydosporia, was undertaken. Improvements were made to a bioassay to assess the parasitism of P chlamydosporia on eggs of Meloidogyne javanica and Globodera pallida under varying concentrations of exogenous nutrient source (Yeast extract medium). Meloidogyne janica eggs obtained infected tomato plants were adjusted to 1000 eggs ml' and inoculated with sterilised yeast extract medium (YEM) and 2.75 x 104 ml' P chlamydosporia conidiospores in sterilised distilled water to a volume of 10m!. The experiment constituted of 2 controls being 0.0125% YEM (no fungus) and Water (no fungus) plus the 3 media (0.00625% YEM, 0.0125% YEM and Water) by 6 fungal isolates. Significant differences (P<O.OOI) were observed on the influence of the media on egg parasitism of M. javanica and G. pallida eggs, respectively with, egg parasitism being lowest at 24 hours and highest at 48 hours in all media. The YEM media at both concentrations stimulated higher infection rates on both Meloidogyne and Globodera eggs compared to the water medium. Compared to M. javanica eggs, higher infection proportions on G. pallida eggs were observed across all the media demonstrate host preferences among the isolates. Molecular techniques used to assess variation in P chlamydosporia isolates, including analysis of the VCPl gene egg infection showed this gene to be highly conserved. Further, expression of the VCPl gene was up-regulated in media containing 2% glucose and suppressed in nitrogenous media.