Plant Virus Laboratory, National Botanical Research Institute, Lucknow - 226 001, India
Papaya has considerable economic importance to agriculture in India. Papaya leaf curl disease was first reported in 1939 by Thomas and Krishnaswamy (3). This disease is of moderate incidence and widely distributed in India. Recent observations of papaya fields in India indicated that there has been a continued increase in the incidence of papaya leaf curl disease (as shown by symptoms), resulting in severe economic losses. The disease is characterized by downward curling and cupping of leaves followed by vein clearing and thickening. Enations develop in the form of frills on green veins. The affected leaves become leathery and brittle and the petioles become twisted in a zig-zag manner. Diseased plants may bear a few small fruits, which are distorted in shape and tend to fall prematurely. The disease could be transmitted by the whitefly Bemisia tabaci Genn. Therefore, possible involvement of a geminivirus was suspected. Three different cloned geminiviral DNAs, Indian tomato leaf curl virus (ITLCV) (2), tomato yellow leaf curl virus from Sardinia (TYLCV Sar), and tomato golden mosaic virus (TGMV), were used as probes (with radioactive labeling) to detect the presence of geminiviral DNA from infected papaya tissue in both slot-blot and Southern blot hybridization studies with high stringency washes. These DNA probes gave strong signals with DNA isolated from infected papaya tissue whereas they did not give any signals with DNA from healthy tissue. Further, successful polymerase chain reaction (PCR)-based amplification of fragments from both DNA-A and DNA-B components with geminivirus degenerate primers (1) was accomplished only from the DNA of infected papaya plants. The PCR-amplified DNA fragments gave positive signals in Southern blot hybridization with the three geminiviral DNA probes. These results suggest that the causal agent of papaya leaf curl disease is a bipartite geminivirus that may be provisionally called papaya leaf curl virus (PLCV).
References: (1) M. R. Rojas et al. Plant Dis. 77:340, 1993. (2) K. M. Srivastava et al. J. Virol. Methods 51:297, 1995. (3) K. M. Thomas and C. S. Krishnaswamy. Curr. Sci. 8:316, 1939.