Biology and interactions of two distinct monopartite begomoviruses and betasatellites associated with radish leaf curl disease in India

Abstract

BackgroundEmerging whitefly transmitted begomoviruses are major pathogens of vegetable and fibre crops throughout the world, particularly in tropical and sub-tropical regions. Mutation, pseudorecombination and recombination are driving forces for the emergence and evolution of new crop-infecting begomoviruses. Leaf curl disease of field grown radish plants was noticed in Varanasi and Pataudi region of northern India. We have identified and characterized two distinct monopartite begomoviruses and associated beta satellite DNA causing leaf curl disease of radish (Raphanus sativus) in India.ResultsWe demonstrate that RaLCD is caused by a complex of two Old World begomoviruses and their associated betasatellites. Radish leaf curl virus-Varanasi is identified as a new recombinant species, Radish leaf curl virus (RaLCV) sharing maximum nucleotide identity of 87.7% with Tomato leaf curl Bangladesh virus-[Bangladesh:2] (Accession number AF188481) while the virus causing radish leaf curl disease-Pataudi is an isolate of Croton yellow vein mosaic virus-[India] (CYVMV-IN) (Accession number AJ507777) sharing 95.8% nucleotide identity. Further, RDP analysis revealed that the RaLCV has a hybrid genome, a putative recombinant between Euphorbia leaf curl virus and Papaya leaf curl virus. Cloned DNA of either RaLCV or CYVMV induced mild leaf curl symptoms in radish plants. However, when these clones (RaLCV or CYVMV) were individually co-inoculated with their associated cloned DNA betasatellite, symptom severity and viral DNA levels were increased in radish plants and induced typical RaLCD symptoms. To further extend these studies, we carried out an investigation of the interaction of these radish-infecting begomoviruses and their associated satellite, with two tomato infecting begomoviruses (Tomato leaf curl Gujarat virus and Tomato leaf curl New Delhi virus). Both of the tomato-infecting begomoviruses showed a contrasting and differential interaction with DNA satellites, not only in the capacity to interact with these molecules but also in the modulation of symptom phenotypes by the satellites.ConclusionThis is the first report and experimental demonstration of Koch's postulate for begomoviruses associated with radish leaf curl disease. Further observations also provide direct evidence of lateral movement of weed infecting begomovirus in the cultivated crops and the present study also suggests that the exchange of betasatellites with other begomoviruses would create a new disease complex posing a serious threat to crop production.

Complexity of begomovirus and betasatellite populations associated with chilli leaf curl disease in India

“…Recombination has been reported to be the major factor in the emergence of begomoviruses infecting crops and weeds in India Kumari et al, 2010;Singh et al, 2012). Begomoviruses associated with chilli and tomato contributed to 32 out of the 44 recombination events detected in ChiLCD-associated begomoviruses, and the remaining recombination events (12/44) were associated with yet undescribed or non-solanaceous-cropinfecting begomoviruses.…”

Potential linkage between compound microsatellites and recombination in geminiviruses: Evidence from comparative analysis

“…Based on genome organization, they are further classified as either monopartite (DNA A -like component) or bipartite (DNA A and DNA B components) encoding 5-7 proteins necessary for viral replication, movement and pathogenesis (Fauquet and Stanley, 2003;Fauquet et al, 2008). In addition, monopartite begomoviruses infecting both crops as well as weeds are often associated with satellite and satellite-like molecules named as betasatellites and alphasatellites, respectively (Briddon et al, 2003;Saunders et al, 2008;Chattopadhyay et al, 2008;Kumar et al, 2012;Singh et al, 2012). Recently, association of satellite molecules has also been reported with bipartite begomoviruses (Romay et al, 2010;Sivalingam and Varma, 2012).…”

Occurrence of begomoviruses in cotton-vegetable agro ecosystem in India

“…Kumar et al (2012) observed the upward curling, crinkling, puckering, reduction of leaf area along with stunting of whole plant in the plants of chilli infected with leaf curl disease. Leaf curl type of symptoms in radish associated with radish leaf curl disease in Northern parts of India has been reported by Singh et al (2012).…”