Characterisation of begomoviruses causing yellow mosaic disease in zucchini (Cucurbita pepo L.) in South India
Zucchini (Cucurbita pepo L.) is a valuable cucurbitaceous crop cultivated widely in subtropical and temperate regions. However, its productivity is increasingly threatened by begomoviruses, especially in South India. The present study investigates the incidence, molecular characterisation, vector transmission and host range of squash leaf curl China virus (SLCCNV) and tomato leaf curl Karnataka virus (ToLCKV) infecting zucchini in Bengaluru and Mysuru districts of Karnataka. Field surveys conducted during 2020–21 revealed a high incidence of yellow mosaic and leaf curl symptoms in affected fields. Molecular analysis confirmed the presence of bipartite SLCCNV and monopartite ToLCKV in symptomatic plants. Whitefly (Bemisia tabaci) transmission assays determined that a minimum of 10 min acquisition period and 30 min inoculation periods were necessary for efficient virus transmission. Host range studies demonstrated that squash leaf curl China virus–Zucchini [Bengaluru-1] (SLCCNV-ZUB1) could infect pumpkin, ridge gourd and bottle gourd, while other cucurbits and solanaceous crops remained uninfected. Complete genome sequencing revealed > 91 % nucleotide identity with known SLCCNV isolates and 97.9 % identity of tomato leaf curl Karnataka virus–Zucchini [Bengaluru-5] (ToLCKV-ZUB5) with ToLCKV infecting tomato. Recombination analyses identified significant breakpoint events suggesting viral evolution from related begomoviruses. This is the first report of ToLCKV infecting zucchini in South India, highlighting the emergence of new begomoviral variants and their epidemiological significance in cucurbit production.