Faba bean (Vicia faba L.) is gaining importance as a crop in northern Europe. In this region, the most important disease of faba bean is chocolate spot disease, attributed to the pathogen Botrytis fabae. However, other Botrytis species have been found to contribute to the disease. Hence, it was decided to isolate fungi from faba bean plants showing symptoms of chocolate spot disease in Latvia, identify the Botrytis species using the DNA sequences of three definitive genes, evaluate the morphological diversity of the isolates in vitro and, finally, to determine the pathogenicity of the isolates in a detached-leaf test. In addition to B. fabae, B. cinerea, B. pseudocinerea and B. fabiopsis were all identified. Phylogenetic analysis of the DNA sequences put all the obtained 44 isolates unequivocally into clusters with known examples of each species. Every species showed wide diversity in its in vitro colour, texture and growing pattern of mycelium, production of sclerotia and pigmentation of the growing medium with much overlap between species showing that this method is not adequate for species discrimination. B. fabae produced the largest lesions on infected leaves, followed closely by B. pseudocinerea and B. cinerea, while B. fabiopsis produced much smaller lesions. The results show that chocolate spot disease of faba bean is attributable to Botrytis four species in northern Europe. This knowledge needs to be considered when controlling the disease by genetic or agronomic means.
Grain legumes are important crops for the diversification of European farming system. In Latvia, the areas of faba beans (Vicia faba) and field peas (Pisum sativum) are increasing and legumes that have not been previously cultivated are sown. Globally, the important causal agent of legume diseases belongs to the genus Botrytis. Botrytis spp. cause significant losses in faba beans and infect a wide range of legume crops. Currently, the composition, pathogenicity and biological characteristics of Botrytis species in legumes in Latvia are not known. The aim of this study was to summarize the information about Botrytis spp. on legumes, using monographic method. The researches carried out all over the world show a high genetical diversity of Botrytis cinerea. Non-host specific B. cinerea has been found on 586 plant genera, including many legume crops. B. cinerea causes gray mold on leaves and pods of field peas, gray mold on pods of faba beans, and chocolate spot of faba bean leaves. B. fabae can infect plants from Fabaceae family. B. fabiopsis is known as a pathogen of faba beans. B. fabiopsis has been observed in Latvia, but no information is available on its presence in Europe. B. pseudocinerea has been found on beans, peas, and clover (Trifolium). Some other Botrytis spp. have been detected on legumes; however, their occurrence and importance are not clear. Summary of existing knowledge about Botrytis spp. on legumes is necessary to continue investigations about the diversity and economic importance of Botrytis spp. in legumes.
Fungi of genus Botrytis are important pathogens of legumes, causing gray mold and chocolate spot diseases. The use of molecular methods to identify pathogens has resulted in the discovery of several new Botrytis species and new associations of pathogens with diseases. Thus, chocolate spot of faba bean is now associated with at least four species: B. fabae, B. cinerea, B. pseudocinerea and B. fabiopsis. Species of Botrytis differ in host plant, pathogenicity, fungicide resistance and other relevant properties that affect disease control. The aim of this study was to identify the species of Botrytis isolated from different legume crops and to evaluate their in vitro pathogenicity. Between 2014 and 2019, 278 isolates of Botrytis were obtained from infected legumes in Latvia. A phylogenetic analysis was carried out by sequencing three nuclear genes, RPB2, HSP60, and G3PDH, considered to be diagnostic for species in this genus. A set of 21 representative isolates was selected for pathogenicity tests on detached leaves of faba bean, field pea, lupin and soybean using 5-mm mycelium-agar plugs. The diameter of the formed lesions under the inoculated plug was measured crosswise each day. The datasets were subjected to analysis of variance with the split-plot design of the experiment and repeated-measures model. Six species were identified: B. cinerea, B. fabae, B. pseudocinerea, B. fabiopsis, B. euroamericana and B. medusae. In addition to the expected combinations of host and pathogen, naturally occurring infections of B. fabiopsis were found on chickpea, B. euroamericana on faba bean and B. medusae in lupin seeds. Species and isolate had significant effects on pathogenicity on all crops tested. Several isolates were pathogenic on two or more host species: two of B. pseudocinerea, two of B. cinerea, two of B. fabiopsis and the one of B. medusae. One isolate of B. pseudocinerea and two of B. fabiopsis caused primary lesions on all five host species. The results show that these Botrytis species have a broad host range that should be borne in mind when planning crop sequences and rotations.
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