Screening faba bean for chocolate spot resistance: evaluation methods and effects of age of host tissue and temperature

Abstract

Chocolate spot is an important disease of faba bean (Vicia faba) caused by the necrotrophic fungus Botrytis fabae. The aims of this work were: i) to compare different methods of screening for resistance; ii) to assess the influence of the age of host tissue and temperature on this pathosystem. To this effect, a collection of 42 faba bean accessions was evaluated in mature plant stage in the field in Cordoba (Southern Spain) and in detached leaflet and whole plant tests under controlled conditions. Field results correlated better with those of the whole plant test than with those of the detached leaflet assay. Integration of results from the field and whole plant experiments resulted in the selection of six accessions of interest as sources of resistance. Influence of leaf age on disease development was found to be genotype dependent. Older leaves were more susceptible than younger ones in 23 accessions, while no difference between leaf ages was detected in the remaining accessions. The effects of plant age and temperature were assessed by a whole plant test on seven accessions at two plant ages (4 and 7 weeks) and three temperatures (13, 20, and 25°C). Results showed that the differential genotypic responses to B. fabae were not significantly influenced by either plant age or temperature, although there was a tendency towards lower susceptibility to chocolate spot in faba bean plants as they become older. Further, a partial high-temperature, young-plant resistance was detected.