Survival of sclerotia of Sclerotinia and Sclerotium spp in New Zealand horticultural soil

The survival capabilities of four sclerotial plant pathogens (Sclerotinia minor Jagger, S. sclerotiorum (Libert) de Bary, Sclerotium cepivorum Berkeley and S. rolfsii Saccardo) under New Zealand horticultural soil conditions was determined. Percentage recovery of sclerotia for each pathogen in soilbox and field survival trials was significantly reduced after 11 months. Sclerotial numbers of Sclerotinia minor and Sclerotium cepivorum rapidly declined in the soilbox trial over the first 3 months. Low recoveries (9–11%) were observed in the field after 6 months. For the remaining period of the trials, only a small proportion (2–15%) of the original population was recovered. Numbers of sclerotia of Sclerotinia sclerotiorum and Sclerotium rolfsii were significantly reduced in both trials from 6 months onwards. At each sampling, a greater proportion of sclerotia declined in the field compared with the soilbox trial. In the field, there was little difference in sclerotial survival for all pathogens at depths of 50 and 150mm. Recovered sclerotia of S. rolfsii exhibited a high viability (90–100%) over the period of both trials whereas a reduction in sclerotial viability was observed for the other three pathogens. In an additional soilbox trial, the numbers of naturally-produced sclerotia of S. rolfsii declined more rapidly compared with cultured sclerotia over 6 months.