Abstract
Rice blast, caused by Magnaporthe oryzae, causes yield losses associated with injuries on leaves and necks, the latter being in general far more important than the former. Many questions remain on the relationships between leaf and neck blast, including questions related to the population biology of the pathogen. Our objective was to test the hypothesis of adaptation of M. oryzae isolates to the type of organ they infect. To that aim, the components of aggressiveness of isolates originating from leaves and necks were measured. Infection efficiency, latent period, sporulation intensity, and lesion size were measured on both leaves and necks. Univariate and multivariate analyses indicated that isolates originating from leaves were less aggressive than isolates originating from necks, when aggressiveness components were measured on leaves as well as on necks, indicating that there is no specialization within the pathogen population with respect to the type of organ infected. This result suggests that the more aggressive isolates involved in epidemics on leaves during the vegetative stage of the crop cycle have a higher probability to infect necks, and that a population shift may occur during disease transmission from leaves to necks. Implications for disease management are discussed.
Highlights
A few important pathosystems involve infections and injuries on different organ types
The analysis of the relationships between epidemics occurring on two organ types, or dual epidemics [1], is important to better understand the mechanisms underlying the quantitative and dynamic interplay between infections occurring on both organ types, and to provide a sound basis for disease management
The different analyses conducted indicate that isolates originating from necks were more aggressive than isolates originating from leaves, when aggressiveness components were measured both on leaves and necks
Summary
A few important pathosystems involve infections and injuries on different organ types This is the case for example in diseases affecting leaves and fruits (e.g., powdery mildew and downy mildew on grapes, powdery mildew on strawberry, and apple scab), or diseases affecting leaves and storage organs (e.g., rice blast, wheat Septoria nodorum blotch, southern corn leaf blight). This may have important implications, because the types of organ injured correspond to different damage mechanisms, leading to different crop losses, both from the quantitative and qualitative standpoints. Yield losses associated to neck blast are much higher than yield losses associated to leaf blast in the tropical rice lowlands of Asia [5,6]
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