Two weather‐based models for predicting the onset of seasonal release of ascospores of Leptosphaeria maculans or L. biglobosa

Abstract

Weather‐based models (Improved Blackleg Sporacle and SporacleEzy) to predict the date of onset of seasonal release from oilseed rape debris of ascospores of Leptosphaeria maculans or L. biglobosa, causes of phoma stem canker, were developed and tested with data from diverse environments in Australia, Canada, France, Poland and the UK. Parameters were estimated, using the same datasets from experiments in the UK and Poland, with an accuracy of root mean squared deviation (RMSD) of 7·4 (with a bias of −4·54, L. maculans) and 8·5 (with a bias of 0·30, L. biglobosa) days for Improved Blackleg Sporacle, and of 2·9 (with a bias of −0·06, L. maculans) and 7·3 (with a bias of −1·18, L. biglobosa) days for SporacleEzy. When tested with data independent of those used for parameter estimation, overall predictions agreed well with observed data in five countries, both for Improved Blackleg Sporacle (R2 = 0·96, slope = 1·00, standard error = 0·03, P > 0·05, n = 46) and SporacleEzy (R2 = 0·96, slope = 0·98, standard error = 0·03, P > 0·05, n = 46). However, SporacleEzy performed better in Australia, Canada, Poland and the UK (RMSD = 10·6, 9·7, 5·4 and 3·4 days, respectively) than Improved Blackleg Sporacle (RMSD = 11·7, 11·0, 5·6 and 6·5 days, respectively). In contrast, the prediction from Improved Blackleg Sporacle (RMSD = 8·0 days) was better in France than that from SporacleEzy (RMSD = 15·9 days). Sensitivity analysis showed that better parameter estimation could improve the quality of prediction of SporacleEzy (RMSD = 7·6 days) under French conditions. These models are capable of estimating the first seasonal release of ascospores of organisms causing phoma stem canker on oilseed rape under many climates and thus could contribute to development of strategies for control of the disease.