Transmission dynamics of mungbean yellow mosaic virus (MYMV) in blackgram: Vector and seed perspectives

Mungbean yellow mosaic virus (MYMV), a devastating begomovirus transmitted by the whitefly (Bemisia tabaci), is a major constraint in blackgram (Vigna mungo) production across India. The present study aimed to assess the spatial distribution of MYMV disease incidence, confirm the viral identity through molecular diagnostics, investigate vector transmission efficiency and evaluate the seed-transmissible nature of MYMV in blackgram cultivar CO 5. Field surveys in Tamil Nadu during 2023 revealed disease incidence ranging from a minimum of 45 % at Sukkampatti, Madurai, to a maximum of        78 % at Narasipuram, Coimbatore. PCR analysis with CP, MP and REP genes confirmed the presence of MYMV in all field-collected samples, with sequences submitted to NCBI (PQ384577, PV500803 and PV500802). Transmission of MYMV with whitefly Asia I genotype recorded a maximum transmission efficiency of 87.5 % and 93.75 % at 24 hr acquisition access periods (AAP) and inoculation access periods (IAP) respectively, with consistent symptom expression and was further confirmed with PCR. In a grow-out test conducted with field-collected seeds from infected plants, the plants were symptomless, but 51 % of the tested plants were positive in PCR. The dissected seed parts from these PCR positive first-generation grow-out test plants indicated the presence of MYMV in 100 % of seed coats, 80 % of cotyledons and embryonic axes. A second grow-out test conducted with 25 seeds from first-generation PCR-positive plants was again asymptomatic and 40 % of plants were PCR positive. These results provide strong evidence of asymptomatic, latent MYMV infections that act as cryptic inoculum for whitefly-mediated spread. These findings emphasize the need for integrated disease management strategies, including seed certification, molecular diagnostics and early whitefly control to limit MYMV spread and ensure virus free seed production in blackgram.