Neonectria ditissima spore release and availability in New Zealand apple orchards

Abstract

Conidia and ascospore release of Neonectria ditissima, the causal agent of European canker, was investigated using rainwater traps and Vaseline®-coated glass slides in the Tasman region, New Zealand. Trapping of spores was carried out from May 2013 to June 2015 in three separate apple orchard blocks planted with ‘Scifresh’/Jazzâ„¢, ‘Royal Gala’ and ‘Braeburn’, respectively. Conidia and ascospores were both produced at any time of the year when rainfall occurred. The numbers of both conidia and ascospores trapped peaked in April—May, but were produced throughout the year. There was a trend for lower spore numbers with increasing number of non-rainy days prior to rainy event 2mm, while more spores were trapped under frequent rainfall conditions. There was a significant correlation between mean conidia trapped and total monthly rainfall in all three orchards, but ascospore numbers were significantly correlated with rainfall on glass slides only in the ‘Braeburn’ orchard.