ANALYSIS OF CROP LOSS IN THE MULTIPLE PATHOSYSTEM GROUNDNUT-RUST-LATE LEAF-SPOT .3. CORRESPONDENCE ANALYSES

A series of experiments conducted during six growing seasons was used as a database to study the effects of rust and late leaf spot on groundnut in various production situations, using correspondence analysis. A first analysis demonstrates the existence of a threshold beyond which damage caused by the multiple pathosystem is likely to increase with improvement in production situation with more favourable environmental conditions and/or input of factors to the crop. A second analysis indicates differences between rust and late leaf spot in their harmful effects to the crop, which are discussed; the resulting injuries are less than additive. The results are in agreement with previous results on the same data set using multiple regression analysis, and results from independent factorial experiments. Correspondence analysis, a technique new to crop loss study, enables corresponding categorizations of yield levels, damage, and injury patterns to be established. The methodological relevance and the potential of applying correspondence analysis to disease management issues are discussed.