Sclerotinia stem rot (Sclerotinia sclerotiorum) is a serious disease in oilseed Brassica crops world-wide. Temperature adaptation in isolates of S. sclerotiorum collected from differing climatic zones is reported for the first time on any crop. S. sclerotiorum isolates from oilseed rape (B. napus) crops in warmer northern (WW3, UWA 7S3) differed in their reaction to temperature from those from cooler southern (MBRS-1, UWA 10S2) agricultural regions of
Accepted ArticleThis article is protected by copyright. All rights reserved.Western Australia in virulence on B. carinata, growth on agar, and oxalic acid production.Increasing temperature from 22/18ºC to 28/24ºC increased lesion diameter on cotyledons of B. carinata BC05411344 more than ten-fold for warmer region isolates, but did not affect lesion size for cooler region isolates. Mean lesion length averaged across two B. carinata genotypes (resistant and susceptible) fell from 4.6 mm to 2.4 mm for MBRS-1 when temperature increased from 25/21ºC to 28/24ºC but rose for WW3 (2.35 mm and 3.21 mm, respectively). WW3, usually designated as low in virulence, caused as much disease on stems at 28/24ºC as MBRS-1, historically designated as highly virulent. Isolates collected from cooler areas grew better at low temperatures on agar. While all grew on potato dextrose agar between 5-30ºC, with maximum growth at 20-25ºC, growth was severely restricted above 32ºC, and only UWA 7S3 grew at 35ºC. Oxalate production increased as temperature increased from 10 to 25⁰C for isolates MBRS-1, WW3 and UWA 7S3, but declined from a maximum level of 101 mg/g mycelium at 20⁰C to 24 mg/g mycelium at 25⁰C for UWA 10S2.