Occurrence and geographic distribution of Squash leaf curl virus in the Baja California Peninsula, Mexico

Abstract

Squash leaf curl (SLC) disease causes serious damage in a great diversity of horticultural crops worldwide and is due to infection by different ssDNA bipartite begomoviruses (Family Geminiviridae). Symptoms of leaf yellowing, stunting and curling have been observed in squash crops in the southern region of the Baja California (BC) Peninsula in the northwestern region of Mexico for at least a decade. The damage estimated for all localities showed disease incidence of 73.3% to 97.7% and severity of 49%. Infected plants were collected in three localities in addition to adult whiteflies for species determination. Squash leaf curl virus (SLCuV) was detected in both infected plants and whiteflies by PCR using specific primers that amplified a 601 bp fragment. The full-length DNA-A sequence was 99.1% identical to sequences in GenBank. Phylogenetic studies using the core CP region showed that the BC isolate grouped within a well-defined clade together with SLCuV from the Mediterranean Middle East and USA. The molecular analysis in individual adult whiteflies determined that all populations belonged to Bemisia tabaci (MEAM1) (biotype B) species. No evidence of the Mediterranean (MED) species (biotype Q) was found. The SLC disease has prevailed in squash in the region in several growing cycles and in geographically separated localities. To the best of our knowledge, this is the first report of SLCuV associated with squash plants in BCS, Mexico.