First report of Cucurbit aphid-borne yellows virus in Tunisia causing yellows on five cucurbitacious species.
Virus surveys in 2003 and 2004 were undertaken in all the major cucurbit-growing areas in Tunisia. Large populations of aphids (Aphis gossypii) and severe yellowing symptoms of older leaves of cucurbits were observed in outdoor and under plastic tunnel cultivations, suggesting the presence of cucurbit aphid-borne yellow virus (CABYV). Leaf samples collected from symptomatic and asymptomatic plants of melon, cucumber, squash (Cucurbita pepo), watermelon and ware cucurbit (Ecballium elaterium) were screened for the presence of CABYV using enzyme-linked immunosorbent assay (ELISA) and reverse transcription-PCR (RT-PCR). ELISA tests demonstrated that 91 plants were positive among 160 plants tested with severe yellowing symptoms. All asymptomatic plants were negative. A total of 106 plants were screened with the RT-PCR, including the 91 plants that were positive in ELISA. The 91 plants also were positive after RT-PCR amplification as were 12 more plants. No amplicons were produced from extracts of asymptomatic plants, RNA preparations of cucurbit yellow stunting disorder virus, or beet pseudo yellow virus positive controls. The results of the ELISA and RT-PCR tests showed that CABYV was widely distributed on 5 cucurbit species in the major growing areas of Tunisia, including the northern, Sahel, central and southern regions where it was detected, respectively, in 10 of 25, 11 of 21, 24 of 37 and 58 of 77 samples tested. CABYV was detected at the rates of 63 of 72 on melon, 10 of 21 on cucumber, 17 of 24 on squash, 10 of 25 on watermelon, and 3 of 18 on ware cucurbit. This is thought to be the first report of the occurrence of CABYV in Tunisia on different species of cucurbit and ware cucurbit.