Biology, growth parameters and enzymatic activity of Pochonia chlamydosporia isolated from potato cyst and root-knot nematodes

Abstract

Pochonia chlamydosporia, a widespread fungal parasite of potato cyst nematodes (PCN), Globodera spp., and root-knot nematodes (RKN), Meloidogyne spp., has been studied as a biological control agent. Three Portuguese isolates (Pc1, Pc2, Pc3) obtained from PCN eggs and two non-native isolates (Vc10, Pc280) were characterised using ERIC-PCR and screened by in vitro assays for their ability to produce chlamydospores, parasitise eggs of Globodera rostochiensis and Meloidogyne chitwoodi and colonise the rhizosphere of barley. The effects of temperature on growth, sporulation, parasitism and enzymatic activity were also evaluated. Isolates Pc1 and Pc3, despite their different geographical origins, had identical molecular profiles. Pc2 produced the higher numbers of chlamydospores in solid medium (1.15 × 107 chlamydospores g−1), whereas Pc3 produced the least (3 × 105 chlamydospores g−1). These isolates extensively colonised the rhizosphere of barley (>90% root fragments) and the proportion of parasitised eggs, detected on agar plates, was low (<60% for RKN and <55% for PCN), Pc1 being the best parasite against both nematode species. The influence of temperature was similar for all isolates: no growth was observed at 10, 33 and 35°C. Spores/hyphal fragments remained viable for nearly 1 month at 10 and 33°C and isolates resumed growth after incubation at 25°C, although chlamydospores and conidia production, viability and nematode egg parasitism were affected. Exposure to 35°C was lethal for isolates Pc1, Pc2 and Pc280. When grown in liquid media all isolates produced esterases, but protease activity was only observed in Pc2 and Vc10. The highest enzymatic activity was detected in isolate Pc2 in low nutrient media. Enzymatic activity decreased in the presence of nematode eggs for both Pc2 and Vc10. Molecular, biochemical and biological analyses, including biotic and abiotic factors, are important in the screening of potential biological control agents, particularly in the case of P. chlamydosporia, due to the high variability among isolates.