Molecular evidence for association ofTomato leaf curl New Delhi virus with leaf curl disease of papaya (Carica papaya L.) in India

Abstract

Association of Tomato leaf curl New Delhi virus with leaf curl disease of papaya (Carica papaya L.) was detected by polymerase chain reaction using begomovirus-specific primers and confirmed by highest sequence similarities and close phylogenetic relationships. Papaya (Carica papaya L.) is cultivated commercially throughout the world's tropical and subtropical regions for its edible fruits. Papain, an enzyme prepared from dried latex of immature fruits, is used for meat tenderising, food processing and in the leather industry (Singh 2006). The vasculature latex of papaya has medicinal value and is used to treat ulcers, dissolve membranes in diphtheria, and reduce swelling, fever and adhesions after surgery (Singh et al. 1983). The limiting factor of papaya cultivation is its susceptibility to ring spot, leaf curl, mosaic and distortion diseases. Among them leaf curl disease caused by Begomovirus species is one of the most serious threats to papaya cultivation in most of the papaya growing countries (Singh 2006). Various RNA viruses have been reported on papaya worldwide, viz. Papaya ring spot virus (Potyvirus), Papaya mosaic virus (Potexvirus), Tomato spotted wilt virus (Tospovirus), Papaya apical necrosis virus (Rhabdovirus), Tobacco ring spot virus (Nepovirus), Tobacco streak virus (Ilarvirus), Tobacco rattle virus (Tobravirus) and Cucumber mosaic virus (Cucumovirus) (Singh 2006). However, a limited number of DNA viruses are known to be associated with the leaf curl disease of papaya: Papaya leaf curl virus (Nadeem et al. 1997; Singh 2006), Papaya leaf curl China virus and Papaya leaf curl Guangdong virus (Wang et al. 2004), and Papaya leaf curl Taiwan virus (Chang et al. 2003). These viruses are members of (a) (b) (c) Fig. 1. Naturally infected Carica papaya plants exhibiting (a, b) severe downward leaf curl, swelling of veins, twisting and reduction of petioles, and distorted fruits, compared with (c) healthy plants.