Factors affecting carpogenic germination of Sclerotinia sclerotiorum (Libert) de bary, a potential mycoherbicide

Abstract

Sclerotinia sclerotiorum (Libert) de Bary is a highly pathogenic fungus currently being investigated as a potential mycoherbicide on New Zealand pastures. However, many important agricultural and horticultural plants are susceptible to this pathogen and undesirable infection can occur by spread of ascospores produced from apothecia. Potential risks of using the pathogen as a mycoherbicide suggest that studies on the environmental factors trigger carpogenic germination would be useful.

Induction of apothecia formation in the fungus S. sclerotiorum was investigated on both naturally-occurring sclerotia obtained from Californian thistle (Cirsium arvense) and laboratory-cultured sclerotia grown from a strain obtained from the same host.

The influence of sclerotial size, substrate, production and incubation temperatures on apothecial formation were assessed. The size of laboratory-produced sclerotia mostly did not significantly influenced carpogenic germination, but when incubated on 1% water agar under a 14L:10D photoperiod had a significant effect on carpogenic germination, with the larger sclerotia producing more sclerotia. Incubation temperature had a significant effect on carpogenic germination with a highest germination taking place at 10ºC, in both silica sand (pH 5.6) and quartz sand (pH 6.5) substrate. Sclerotia formed apothecial initials in 16 weeks, when it was produced and incubated at temperatures of 10ºC and 15°C. Incubation at temperature of 20°C completely inhibited carpogenic germination for both field and laboratory-produced sclerotia.

From this study, it can be concluded that the factors influencing the formation of ascospores from apothecia in natured are largely related to the time the sclerotia are deposited in the soil, and the temperature of that soil. A cold conditioning together with incubation at low to moderate (5°C to 15°C) substrate temperatures is conducive to carpogenic germination.