Seed Transmission of Cowpea Mild Mottle Virus in Common Beans in Brazil

Cowpea mild mottle virus (CPMMV) is a carlavirus that is transmitted by whiteflies and can also be spread through seeds in cowpea, soybean, and common bean. Seed transmission of CPMMV has been described in various countries; however, it was only recently reported in Brazil as a seed-transmitted virus in soybean. CPMMV has spread widely in bean-growing areas in recent years. Most Brazilian farmers use harvested grains as seed for reseeding, increasing the risk of seedborne infection. In this study, we examine seed transmission of CPMMV in two bean cultivars using RT-PCR in combination with nucleic acid hybridization. The plants evaluated were obtained from seeds harvested in commercial and experimental fields and from seeds collected in transmission experiments using either mechanical or whitefly inoculation. The observed seed transmission was estimated between 10 to 45% for 'BRS FC 401 RMD' and 13 to 22% for 'Pérola'. In addition, evidence of secondary transmission (23.3%) by Bemisia tabaci MEAM1 was observed. These results suggest that CPMMV could be spread in bean fields by sowing infected seeds and that germinated plants could serve as an inoculum for whitefly transmission. This is the first report of seed transmission of CPMMV in common bean in Brazil.