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Acharya N G Ranga Agricultural University
The present investigation on “Characterization of mungbean genotypes with variable reactions to mungbean yellow mosaic virus infection” was carried out at the Regional Agricultural Research Station (RARS), Lam, Guntur, Andhra Pradesh during rabi 2021-22. Mungbean [Vigna radiata (L.) Wilczek] is an important short duration grain legume because of its low water requirement, and as a crop suitable for rotation and nutritional security being a rich dietary source of protein. Biotic stress produced by viruses especially mungbean yellow mosaic virus (MYMV) is the major constraint in its cultivation causing substantial yield losses. Total twenty five mungbean genotypes along with LGG 450 as susceptible check were screened against Mungbean yellow mosaic virus disease under field conditions. Symptoms of MYMV first appeared on young leaves in the form of yellow, diffused, round spots scattered on the leaf lamina. The infected leaves later turned necrotic. The diseased plants matured later and had relatively few flowers with shriveled pods. Disease symptoms first appeared in genotypes LGG 673, LGG 677, LGG 460 and LGG 450 by 20 DAS while in genotypes, LGG 610, LGG 604, LGG 606, LGG 625, LGG 645, IPM 2-14 and Pusa 9072 disease occurred at 60DAS. The data on incidence and severity of yellow mosaic virus was recorded at different intervals i.e., 20, 40 and 60 DAS. The per cent disease incidence of MYMV among 26 mungbean genotypes was varied from 4.25 to 51.76% and disease severity (PDI) ranged from 1.58 to 76.49 % during 60 DAS. Further, tested genotypes were grouped into different categories based on 0-9 disease scale given by AICRP and MULLaRP. Among the 26 genotypes of mungbean, seven were found resistant, 15 genotypes xv were moderately resistant, two were moderately susceptible, three genotypes were susceptible and the check LGG 450 showed highly susceptible reaction to yellow mosaic virus of mungbean. Morphological characters viz., trichome density, leaf thickness, stomatal frequency, leaf epicuticular wax content and leaf colour intensity were evaluated in all 26 mungbean genotypes during 40 and 60 DAS. It was observed that trichome density, leaf epicuticular wax content and leaf colour intensity in MYMV resistant mungbean genotypes were comparatively high to that of susceptible genotypes. Similarly, leaves of MYMV resistant mungbean genotypes were thicker when compared to susceptible genotypes and highly susceptible check. However, stomatal frequency was found maximum in susceptible genotypes than the resistant genotypes. The biochemical parameters viz., total sugars, reducing sugars, total phenols, total protein and total chlorophyll content were studied both at 40 and 60 DAS in all mungbean genotypes. Decreased total sugar content was observed in susceptible entries compared to resistant ones during both periods of observations i.e., 40 and 60 DAS.It was found that total reducing sugar content was maximum in MYMV resistant genotypes followed by moderately resistant genotypes and then susceptible genotypes. The similar trend was followed in total phenols, total proteins and total chlorophyll content in all tested mungbean genotypes. The molecular characterization of yellow mosaic virus (YMV) in infected mungbean genotypes was done by using the coat protein (CP) and movement protein (MP) gene specific primers from isolates collected at RARS, Lam farm to confirm their strain as MYMV or MYMIV.PCR based characterization of strains (MYMV/MYMIV) were carried out using their gene specific primers respectively.Distinct viral gene specific PCR products corresponding to CP ~648 bp, ~704 bp and ~920 bp were obtained for MYMV and MYMIV respectively. The movement protein gene sequence was also successfully amplified with a fragment size of 900 bp using MYMIV- MP gene specific primer.The samples were further confirmed by CP and MP gene sequencing.The obtained sequences were compared with the other selected begomovirus sequences from the NCBI blast database. The full length coat protein and movement protein gene sequences of MYMV and MYMIV isolates along with available corresponding DNA-A and DNA-B sequences of yellow mosaic virus (YMV‟s) infecting mungbean genotypes when subjected to phylogenetic analysis formed two major clusters. Results were found to show more sequence homology with MYMIV isolates from South India confirming that the begomovirus causing yellow mosaic disease in mungbean is explored to be as strain of MYMIV and not as MYMV.