Effects of bean line pattern mosaic virus on the monocyclic components of rust and angular leaf spot of Phaseolus bean at different temperatures

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Abstract
Monocyclic components (development rate during the incubation period or latent period, lesion density, lesion size and disease severity) of rust (Uromyces appendiculatus) and of angular leaf spot (Phaeoisariopsis griseola) in two bean (Phaseolus vulgaris) cultivars (Rosinha G‐2 and Carioca), pre‐infected or not with bean line pattern mosaic virus (BLPMV), were determined. Trials were conducted at temperatures in the range from 9 to 27°C for rust and from 12 to 30°C for angular leaf spot. Regardless of viral pre‐infection, the effect of temperature on the four monocyclic components followed an optimum curve and could be described by a generalized beta function. Generally, angular leaf spot was favoured by higher temperatures with an optimum for disease severity between 24.2 and 28.3°C compared with 15.9–18.5°C for rust. Pre‐infection with BLPMV did not change the shape of the optimum curves for all components, but significantly reduced lesion density and disease severity on both cultivars. The development rates during incubation and latent periods for both fungal diseases were not affected by BLPMV. Pre‐infection with virus did not alter the ranking of cultivars with respect to resistance to both fungal diseases.