The effect of medium and cold preconditioning on <i>in vitro</i> carpogenic germination of sclerotia of different <i>Sclerotinia sclerotiorum</i> isolates in New Zealand

ABSTRACT Sclerotia of Sclerotinia sclerotiorum germinate carpogenically developing apothecia and release ascospores which act as an inoculum in the field. Identifying the factors influencing the carpogenic germination of sclerotia is important in management of the pathogen. This study assessed the effect of medium and cold preconditioning on in vitro carpogenic germination of sclerotia and development of apothecia. Carpogenic germination was tested in sand, water agar and potting mixture and the effect of preconditioning of sclerotia at 4°C was assessed for isolates originating from different locations in New Zealand. Sclerotia germination and number of apothecia per plate were greater in water agar compared with potting mix. Development of stipes into apothecia was greater in compost compared with water agar. The isolates from sub‐tropical Auckland region showed greater carpogenic germination than most of the isolates from temperate Canterbury region under the experimental conditions used in the study. A few isolates showed a positive or negative response to cold preconditioning hence, no conclusions as to possible ecological adaptation of S. sclerotiorum to the field conditions in which the isolates originated could be made. The prominent isolate effect on all aspects of carpogenic germination assessed highlights the need to include several isolates in future studies.