Seven four-way bread wheat mixtures were compared to their components (individual cultivars and two-way mixtures) for septoria tritici blotch severity, grain protein content, and grain yield. Four-way mixtures and two-way mixtures performed better than the average of individual pure line components. Disease severity and protein content were most influenced by mixtures, with mixture efficiencies being greater in the four-way than in the two-way mixtures. Performances of four-way mixtures in terms of diseased leaf area reduction, grain yield, 1000-grain weight, and grain protein content were better predicted by performances of two-way mixtures than by those of pure lines. Our results suggest that two-way mixtures should be screened to remove unfavourable cultivar pairs and those binary mixtures that show complementarity should be selected in order to construct four-way mixtures.

No abstract

The study of multiple pathosystems has played a central role in the development of botanical epidemiology, leading to a number of approaches and concepts. Multiple pathosystems are facts, which are experienced by many non-cultivated, or cultivated, plant communities. The shapes and composition of multiple pathosystems vary in space and time because of their inherent structure of relationships, and also in response to management. Examples of variation in multiple pathosystems are given, of groundnut in Coˆte d'Ivoire, of wheat in Brittany, and of upland rice in northern Laos. Variation in the yield-reducing effects of multiple pathosystems is discussed, including interactions among disease elements, relationships with attainable performances, and linkages with production situations. Progress has been achieved in understanding the links between injury profiles, production situations, and attainable performances. Questions about the functioning and consequences of multiple pathosystems are central to defining the scientific bases for, the design of, and the implementing of IPM. The complexity of multiple pathosystems, however, remains a deterrent, not a challenge, to many plant pathologists. Progress achieved in designing production systems for hardy wheat in France, however, is very promising, because of the multidisciplinary science it involves, and because of the promise to deliver it carries. The concepts of epidemiological guilds and of guilds of harmful agents are offered as perspectives to address and manage syndromes of production and syndromes of disease. Relevance of multiple pathosystems in botanical epidemiology Multiple pathosystems as a research themeThe study of multiple pathosystems has played a central role in the development of botanical epidemiology. As a subject, it is the equivalent in botanical epidemiology of community ecology in general ecology. Research in the field has led to the development of a body of approaches, often statistical and multivariate, as the objective often has been mostly descriptive, rather than explanatory.Studies on multiple pathosystems (i) led to attempts to understand and manage them (e.g., Jo¨rg et al., 1987;Daamen et al., 1989;Bastiaans and Daamen, 1994), (ii) resulted in analyses of case-studies, and efforts dealing with specific cases and contexts (e.g., Hamelink et al., 1988;Avelino, 1999), and (iii) often were perceived as practical endeavours only. Studies of multiple pathosystems, dealing with a complex subject, inviting complex analyses, and leading to complex interpretations, have arguably led to results that were difficult to share. Arguably, this type of research often addresses open-ended questions, not specific

No abstract

— Disease progress of Pseudocercosporella herpotrichoides in mixed stands of winter wheat cultivars. Epidemic development of Pseudocercosporella herpotrichoides in pure stands of a susceptible variety and a variety with the Pch1 resistance gene, and in their (1:1) mixture was examined in six situations differing for location, fungicide protection or contamination. At growth stade 32, no significant difference was found between the disease level in mixtures and the mean of the disease levels of the mixture components in pure stand. At booting and milky ripe stages, plants sampled in the mixtures were separated according to the variety. No significant difference was found between the disease level in pure stand and in mixed stand either for the susceptible variety nor for the Pch1 one. Triticum aestivum / Pseudocercosporella herpotrichoides / cultivars / variety mixture Résumé — Le développement du piétin-verse sur une variété sensible, une variété possédant le gène de résistance Pch1 et leur association à parts égales est étudié dans six situations qui diffèrent par le lieu, la protection fongicide ou le mode de contamination. Aucune différence de niveau de maladie n'est observée entre l'association et la moyenne des deux composants au stade deux nœuds. Aux stades gonflement et grain laiteux, les variétés sont identifiées dans l'association et notées séparément. Le niveau de maladie en culture pure n'est pas significativement différent de celui de l'association ni pour la variété sensible, ni pour la variété Pch1. Triticum aestivum / Pseudocercosporella herpotrichoides / variété résistante / association variétale