A distinct seed-transmissible strain of tomato leaf curl New Delhi virus infecting Chayote in India

Chayote (Sechium edule (Jacq. Sw.) is a single seeded cucurbitaceous vegetable crop mainly grown for its fruit. During 2015-2016, mosaic and leaf distortion type of symptoms were observed in chayote plants in hilly regions of Tamil Nadu. The disease incidence was 50. 3-100% and yield loss was about 69.9% in Dindigul district. The infected chayote plants showed yellow spots, yellow mosaic, leaf curling, puckering, and enations. The fruits of infected plants were malformed and were not marketable. The begomovirus causing the disease was identified as a variant of tomato leaf curl New Delhi virus. The chayote isolates of ToLCNDV share only 91 to 92% identity with other ToLCNDV isolates, deserving to be designated as distinct strain. The phylogenetic analysis on the basis of DNA A component nucleotides clearly indicated common origin of chayote, ridge gourd, ash gourd isolates of India along with Spanish isolates of ToLCNDV. This was contrasting to diverse origin of ToLCNDV isolates from other countries. The virus was sap transmissible to selected cucurbitaceous hosts. The whitefly population (Asia-I) reared in the glass house transmitted the virus to bottle gourd with 4 h of acquisition access period (AAP) and 24 h of inoculation feeding period (IFP). Heavy infestation of greenhouse whiteflies, Trialeurodes vaporariorum on infected chayote plant in Kodaikanal paved way to investigations on its role in vector transmission of ToLCNDV. The field population of T. vaporariorum was found to be viruliferous in PCR using virus specific primers. The greenhouse whitefly efficiently transmitted the virus with 4 h of AAP and 24 h IFP. Seed-borne nature of ToLCNDV was confirmed in PCR by using Roja's and ToLCNDV specific primers in different parts of the fruit viz., pericarp, mesocarp, seed coat, endosperm and embryo. This is the first report of seed transmissible nature of ToLCNDV, its implication in transboundary movement of the virus across several countries is discussed.