Abstract
Squash leaf curl virus (SLCV) and Squash mild leaf curl virus (SMLCV) are bipartite begomoviruses that naturally infect cucurbits and common bean. Isolates of these viruses occur in a tight geographical zone within the Sonoran Desert and close relatives/strains are known in Central America and the Caribbean Basin. Comparison of the experimental host range for SLCV and SMLCV indicated that SLCV infects species in the Cucurbitaceae, Fabaceae and Solanaceae, whereas hosts of SMLCV are limited to the Cucurbitaceae and Fabaceae. Analysis of the SMLCV and SLCV DNA-A and DNA-B components revealed that they share 84% and 72% nt identity, respectively, indicating that they are distinct species. Nucleotide sequence comparisons for SMLCV and SLCV and other SLCV clade viruses revealed that the Cucurbit leaf curl virus and Bean calico mosaic virus are the closest relatives, at 82 and 79% (DNA-A), and 66 and 62% (DNA-B) nt identities, respectively. Reassortment experiments for all DNA-A and DNA-B combinations revealed that DNA-B components were more likely to form viable reassortants with a heterologous DNA-A, than were DNA-A components with a heterologous DNA-B.