P.51. A severe leaf crinkle disease of cowpea, caused by Mungbean yellow mosaic India virus and a satellite DNA
Abstract
In the kharif crop season of 2004, severe leaf distortion symptoms were seen in cowpea plants (Vigna unguiculata) in agricultural fields and in kitchen garden in northern India. The affected plants showed downward leaf curling, puckering, vein enations, and bright green mottling along with yellow mosaic. In Southern analysis, total nucleic acid extracted from symptomatic plants showed hybridization with radiolabelled probe to DNAA and DNA B of Mungbean yellow mosaic India virus MYMIV-[Cp]). As veinal enation is characteristic symptom associated with the presence of satellite DNA β, PCR was performed with universal DNA β primers β01/β02 (Briddon et al., 2003). An amplicon (∼ 1.4 kb) obtained was cloned and sequenced (GenBank accession no. AT728263). Nucleotide sequence analysis of DNA β showed that the product had typical features of satellite DNA β like satellite conserved region, ‘A’ rich region and the positionally conserved open reding from βC1. Nucleotide sequence comparison revealed only 58% sequence identity with DNA β associated with Cotton leaf curl Rajasthan virus (GenBank accession No. AY083590).
Agroinoculation of cloned satellite DNA β along with MYMIV-[Cp]) DNA A and DNA B components gave rise to severe leaf curl symptoms in cowpea as seen in natural conditions, thereby confirming its role in symptom induction.
This is the first report of a satellite DNA β associated with a bipartite begomovirus infecting leguminous host. While MYMIV-[Cp] alone causes yellow mosaic symptoms, in the presence of DNA β different symptom phenotypes of vein enation, puckering and leaf curl are seen. This finding is significant as it gives direct evidence for acquiring of novel genetic material by a helper begomovirus, which could increases the pathogenicity of the helper virus as seen here. The results also strongly suggest that satellite DNA β is widespreading in northern India.
