Impact of preconditioning temperature and duration period on carpogenic germination of diverse Sclerotinia sclerotorium (Lib.) de Bary populations in south-western Australia.

Abstract

The soil-borne pathogen Sclerotinia sclerotorium is the causal agent of sclerotinia stem rot, a severe disease of broad-leaf crops including canola/rapeseed Brassica napus that can result in significant yield losses. Sclerotia, the hard melanized resting structure of the pathogen, requires preconditioning before carpogenic germination can occur. We investigated the effect of pre-conditioning temperature (4°C, 20°C, 35°C, 50°C and field conditions) and duration (0, 30, 60, 120, 179, 240, 301 days) on germination of S. sclerotorium sclerotia collected from five canola fields in the south-western Australian grain-belt. The ecological diversity of each population was characterised using mycelial compatibility groups (MCGs) typing. No response was observed for isolates conditioned at 4°C at any time period indicating chilling is not a preconditioning requirement for these isolates. Sclerotia required preconditioning for a minimum of 60 days before any significant increase in germination occurred, with no further increases in germination recorded in response to longer conditioning after 60 days. The highest germination was observed in sclerotia conditioned at 50°C. The MCG results indicated significant within and between population diversity suggesting local adaptation to different environments as well as ensuring the ability to respond to seasonal variation between years.