Molecular investigations reveal bitter gourd crop is more susceptible to tomato leaf curl New Delhi virus infection in diverse crop cultivation practices

Small- and medium-scale farmer's typically follow polyculture or diverse crop cultivation. However, cultivation of diverse crops in small area can cause cross infection leading to disease spreading across crops. A microplot-based field study was conducted to understand the disease susceptibility and disease mobility across various crops, including tomato, chilli, mungbean, and bitter gourd. The mungbean yellow mosaic virus (MYMV) incidence was noted first in the mungbean crop followed by tomato leaf curl New Delhi virus (ToLCNDV) in tomato and chilli leaf curl virus (ChLCV) in chilli crop. Interestingly, bitter gourd crop was infected lastly with symptoms including yellow and green mottling, severe leaf curling, and stunted growth. However, in bitter gourd crop symptoms, like typical leaf curl virus, could not be conclusively related to a certain type of begomovirus. Molecular diagnosis using begomovirus specific deng primers and coat protein (CP) gene primers specific to begomovirus species revealed the presence of ToLCNDV in bitter gourd samples. The phylogenetic analysis of CP gene sequences revealed 98 per cent nucleotide identity with ToLCNDV. Further cross infectivity assays confirmed the transmission of ToLCNDV from tomato to bitter gourd and vice versa. The cryptic species of whiteflies isolated from the bitter gourd fields were sequence confirmed to belong to Asia-I genetic group that were reported to transmit ToLCNDV previously. Overall, our study suggests the vulnerability of bitter gourd crop for ToLCNDV infection when cultivated by the side of tomato plots.