Abstract
Sclerotinia stem rot (SSR), caused by the necrotroph Sclerotinia sclerotiorum Lib. (de Bary), is a major disease of canola in Australia, greatly reducing yields in high infection years. This study investigated genotype by environment by management interactions at 25 sites across the south-west Australian grainbelt from 2017 to 2020. Up to 10 canola varieties were grown each year with +/− fungicide application at 30% flowering. Disease incidence was low, with less than 20% infection recorded across most sites. Most variation in yield occurred between sites, rather than by management or variety, due to the environmental differences between the sites. Petal assays were found to be a poor indicator of later disease severity, suggesting the winter growing season in south-west Australia does not have reliable conducive conditions for disease development following petal drop in canola. The Additive Main Effects and Multiplicative Interaction model (AMMI) indicated that the open-pollinated varieties were broadly adapted and stable when fungicide was applied but became unstable with no fungicide, indicating SSR has a significant impact on yield when disease incidence is higher. This study highlights that further research is necessary to determine disease thresholds that lead to significant yield loss.
Highlights
Canola (Brassica napus L., oilseed rape) is the second most important oilseed crop in the world, with Europe, Canada, China, India and Australia the largest producers, respectively [1]
Since the 1990s the average growth rate of canola yields has steadily declined in Australia and Europe, which has been attributed to less effective control of biotic stresses [1]
Weather conditions during the study period (Table 2) highlight the dry environment experienced for the large majority of sites, with 22 of the 25 locations receiving less than the long-term growing season rainfall (4–39%) and 10 sites receiving at least 80 mm less rain
Summary
Canola (Brassica napus L., oilseed rape) is the second most important oilseed crop in the world, with Europe, Canada, China, India and Australia the largest producers, respectively [1]. Due to a lack of host resistance, management of SSR typically occurs by prophylactic application of fungicides and crop rotation. Accurate prediction of disease incidence is difficult as potential infection is related to environmental conditions including rainfall, humidity and temperature, as well as previous infection and crop rotation [5]. The use of crop rotation as a management tool is challenging due to the wide host range of S. sclerotiorum and long-term persistence of inoculum. Sclerotinia sclerotiorum has over 400 plant hosts [6] including canola and other pulses such as lupins (Lupinus angustifolius L.) and chickpeas (Cicer arietinum L.). Integrated pest management (IPM) tactics including burning chaff windrows have the potential to reduce the carry-over of sclerotia into future years [10], but they are not recommended except in severe infection events. Strategies to maximize the efficacy of expensive fungicide applications and curtail the use of prophylactic spraying in order to reduce the impact of the disease is vital
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