Investigating components of the oilseed rape light leaf spot epidemic responsible for increased yield loss to the UK Arable Industry
About this project
Extensive research over the past 40 years has investigated different aspects of the epidemiology of the winter oilseed rape disease light leaf spot caused by the fungus Pyrenopeziza brassicae. Growers follow a variety of best management practices on their farms. Despite these efforts, the incidence and severity of light leaf spot and subsequent yield loss have increased substantially in the UK in recent years. This project aimed to re-assess the importance of different components of the epidemic with respect to the additive steps that result in yield loss.
The main objective of the project was to develop a novel decision support tool with respect to light leaf spot epidemic onset in autumn by modelling the inter-crop development and maturation of the fungus using pre-defined parameters readily available from the literature. The aim was to provide growers and advisors with a “heads up” warning that the start of the epidemic was imminent, much like the phoma leaf spot forecast. The model predictions were validated by PCR-based spore analysis of pre-existing multi-site air samples from England and Scotland and with air samples collected during the course of the project from project partner field sites along with field data on disease development on varieties with different levels of host resistance against light leaf spot.
Results from three years of field experiments indicated that there were differences in disease development on varieties across different geographic locations and also between seasons. This suggested that there were differences between populations of the P. brassicae fungus across the UK and that this had implications for breeders with respect to the development of commercial resistant varieties. In addition, the most striking result from the project was that spore sampling work indicated that large quantities of spores were produced from May onwards and were continuously released throughout the summer, much earlier in the season than previously reported. This observation not only indicates that crops can become infected and epidemics begin at any time following emergence of the new crop, but also negates the possibility of developing a date driven forecast system for light leaf spot since there is no effective “starting date” from which to model apothecial development and ascospore release. These results raise some important questions with regard to our current understanding of the epidemic cycle, such as, why are symptoms not seen earlier in the season (on cotyledons and young leaves, for example), are there as yet unknown resistance factors protecting young plant material and does the industry need to revisit autumn fungicide timing work targeted at light leaf spot control?
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