Development peculiarities of bean common mosaic virus (Potyvirus, Potyviridae) in Moscow region and initial material for resistance breeding

Recent years have seen a significant expansion in the distribution area of bean common ( Phaseolus vulgaris L.) mosaic virus (BCMV) that has become an economically significant disease agent for the non-chernozem part of Russia. As early as 2014, the epiphytotics were observed in the Moscow region, but no BCMV resistance screening in both Russia and foreign bean accessions has been performed yet in these agroclimatic conditions. Thus, the presented study is the first one that has described the features of BCMV development in the Moscow region and defines climatic factors affecting the disease progression. An assortment of bean accessions has been estimated on a level of resistance to BCMV using different techniques including molecular markers. The goal of the study was to find an initial breeding material as a source for development of new competitive BCMV-resistant local yardlong bean cultivars. The research was carried out in the Moscow Province in 2014-2019. The research methods included visual and serological diagnosis and phytopathological monitoring of disease progression of artificial and natural infection. Field testing of disease resistance in accessions of various genetic and geographical origins over time was performed using a four-point scale; the accessions were ranked into resistance groups based on the degree of the disease with regard to the stability of expression of the characteristic in various years. DNA analysis of the main resistance genes, i.e. dominant gene I and recessive genes bc-12 and bc-3 , was performed using the respective markers SW13, SBD5, and ROC11, following the developed procedures. The result of the study was the identification of the biological features of the BCMV isolate from the Moscow region affecting Phaseolus vulgaris L. and Pisum sativum L. from the Fabaceae family in biotest. The expression of symptoms and intensity of the disease in indicator plants in a greenhouse and bean accessions in field trials significantly depended on temperature, and the spread of the virus - on the accumulated precipitation. In general, reduced precipitation in combination with elevated temperatures served as a deterrent preventing the pathogen from further spreading in the climatic conditions of the Moscow region. At the same time, this combination facilitated viral infection manifestations on the plant leaf apparatus, especially during the vegetation period. Out of 207 accessions studied, only 6 % demonstrated a persistently high BCMV resistance in the context of epiphytotics. Screening of 30 accessions with different resistance levels showed that recessive genes bc-12 and bc-3 were present in the majority of the accessions and dominant gene I only in half of all accessions. Most accessions had genotypes I / bc-12 / bc-3 (33 %) and bc-12 / bc-3 (47 %), among which only 1/3 demonstrated a persistently high virus resistance. The plants lacking the genes I and bc-12 were severely damaged by the virus. The chi-square test (χ2) revealed a more significant effect of gene bc-12 on the field resistance of common bean accessions to BCMV. Based on the results obtained, as an initial breeding material for developing yardlong bean cultivars with high BCMV resistance we recommend 17 most promising accessions of different origin, including 5 cultivars (Khavskaya Universalnaya, Rant, Zolushka, Marlinka, Svetlyachok) and two perspective hybrids (SP-232, KP-84) selected at Federal Research Center for Vegetable Growing that are distinguished by several agronomic characters.