Geographic distribution and molecular variation of isolates of three whitefly-borne closteroviruses of cucurbits: Lettuce infectious yellows virus, cucurbit yellow stunting disorder virus, and beet pseudo-yellows virus

The geographic incidence and molecular variation of three whitefly-borne cl osteroviruses (lettuce infectious yellows virus [LIYV], cucurbit yellow stu nting disorder virus [CYSDV], and beet pseudo-yellows virus [BPYV]) were st udied in cucurbits collected from several distinct geographic locations. Of 498 samples analyzed, none were found to be infected by LIYV. Sixty-nine s amples collected in the Middle East and Mediterranean Europe were found inf ected by CYSDV, and twelve samples from Crete and Italy were infected by BP YV. Reverse-transcription polymerase chain reaction of a portion of the hea t shock protein 70 homolog coding region, followed by single-strand conform ation polymorphism and nucleotide sequence analysis, was used to estimate t he intra- and inter-isolate molecular variability. These analyses showed th at each BPYV and CYSDV isolate was composed of a population of sequence var iants with a nucleotide identity greater than 98%. CYSDV isolates could be divided into two divergent groups. Group I was only composed of isolates fr om Spain, Jordan, and Turkey, and group II isolates were predominantly foun d in Saudi Arabia. Nucleotide identity between isolates of the same group w as greater than 99%, whereas identity between both groups was less than 92% . All BPYV isolates showed a nucleotide identity greater than 98%.