Evaluation of methods for long term storage of the boysenberry downy mildew pathogen Peronospora sparsa

Abstract

Downy mildew of boysenberry is caused by the biotrophic pathogen Peronospora sparsa. To ensure supplies of viable spore inoculum for infection experiments, six storage methods were assessed: the leaf discs cut from sporulating areas of the leaf stored dry or in 20% glycerol, and spores were suspended in 20% glycerol, all three of which were stored at either -20°C or -80°C. After 1, 2, 4 or 6 months storage, spore viability and the capability to infect leaf discs were evaluated. Storage methods had no signiicant effects on spore germination or infection. Storage time and temperature signiicantly (P<0.001) affected spore viability and infection, being greatest after 1 month and at -80°C. Overall, viability of spores stored as suspensions at -80°C (the most effective treatment) was greater than all other methods tested, and spore germination decreased from over 60% after 1 month of storage to less than 5% after 4 months. © 2013 New Zealand Plant Protection Society.