Assessing plant health in a network of experiments on hardy winter wheat varieties in France: multivariate and risk factor analyses

Abstract

A large network of field experiments has been conducted over several years across France to identify combinations of winter wheat cultivars and management practices in which partial resistances under limited chemical protection would achieve adequate disease management, while leading to satisfactory yield performance, and so achieve the double objective of ecological sustainability and economic viability. Little information is available to document the variation in multiple disease levels, a necessary step towards a chemical extensification process, in wheat networked experiments. This article provides a description of disease intensities in a set of 101 experiments totalling 3525 individual wheat plots over eight successive years (2003–2010). The diseases considered are brown rust (BR, Puccinia triticina), yellow rust (YR, Puccinia striiformis), fusarium head blight (FHB, Fusarium graminearum, F. culmorum, and F. avenaceum), powdery mildew (PM, Blumeria graminis), and septoria tritici blotch (STB, Zymoseptoria tritici). Hierarchical cluster analysis led to the identification of three variety groups associated with (1) moderate-low disease levels in general, except for YR (moderate levels) – 16 varieties; (2) moderate-low BR, YR, and FHB levels, and moderate PM and STB levels – 12 varieties; (3) comparatively higher BR, YR, FHB, and STB levels, and moderate PM levels – 17 varieties. The association of disease levels represented as binary categories (i.e., epidemics vs. non-epidemics) with climatic years corresponded to chi-square values (χ2 = 87.0–1402) that were one to two orders of magnitude larger than the values corresponding to the associations of diseases with variety groups (χ2 = 6.41–321) or with levels of crop management (χ2 = 21.2–82.1). Multivariate non parametric analyses indicated the existence of three disease syndromes, two of which being dominated by BR or STB, and a third associated with diverse diseases and frequent FHB. This suggests that STB and BR might each be considered as key-stone species dominating specific wheat disease syndromes. Multiple correspondence analysis highlighted the linkages between multiple epidemic occurrence and the three characterized variety groups. Risk factors analyses conducted through logistic regressions provided quantitative estimates of the contribution of climatic years, variety groups, and crop management, to the likelihood of epidemic occurrence for each of the five diseases considered. The results indicate that climatic years, wheat varieties, and crop management, in this decreasing order, define disease epidemic risk in the multiple wheat-diseases pathosystem.