Sexual state of grape powdery mildew (<i>Erysiphe necator</i>) newly recorded for New Zealand

Abstract

Grape powdery mildew first reported in New Zealand in 1901 is widespread in New Zealand grape growing regions causing significant losses in some seasons In the summer of 2014 the sexual stage of this fungus was observed for the first time in New Zealand Subsequent surveys showed the sexual state as widespread in Gisborne Hawkes Bay and Marlborough Internationally two E necator populations are recognised Group A being asexual while Group B undergoes sexual recombination DNA was obtained from a sexual isolate from Hawkes Bay and from an asexual isolate from Canterbury and they matched Group B and Group A respectively Asexual populations overwinter in dormant buds and develop new infections at budbreak whereas sexual populations overwinter as cleistothecia (sexual fruiting bodies) with primary infections following ascospore release In Europe where both sexual and asexual populations are widespread overwintering through cleistothecia is considered most important for between season transmission The impact of this newly introduced powdery mildew population is as yet unknown but with the additional source of new season inoculum coupled with greater genetic diversity increasing the risk of fungicide resistance future control of the disease may become more difficult