Studies on the geographical distribution of lettuce infectious yellows crinivirus, cucurbit yellow stunting disorder crinivirus and beet pseudo-yellows closterovirus
Lettuce infectious yellows crinivirus (LIYV - EPPO A1 quarantine pest), cucurbit yellow stunting disorder crinivirus (CYSDV- EPPO Alert List), and beet pseudo-yellows closterovirus (BPYV) are transmitted in a semipersistent way by whiteflies. LIYV is transmitted by Bemisia tabaci (poorly transmitted by biotype B), CYSDV by B. tabaci (including biotype B), BPYV by Trialeurodes vaporariorum. These viruses have overlapping host range and can cause similar symptoms, for example on cucurbits. LIYV has been reported from limited regions in USA, CYSDV from some parts of Europe and the Middle East, and BPYV is more widespread. 498 cucurbit samples (Citrullus lanatus, Cucumis sativus, Cucumis melo, Cucurbita pepo) showing yellowing symptoms or infested by whiteflies were collected from field or glasshouse crops in California (US), Middle East (Jordan, Saudi Arabia, Turkey) and Europe (Spain, Crete (GR), Italy). Samples were specifically tested for the presence of these 3 viruses and molecular variation between virus isolates was also studied. LIYV was not found in any sample (this virus is now reported to be very rare in California). CYSDV was found in 69 samples from the Middle East and Europe: 49 from Spain, 9 from Jordan, 5 from Saudi Arabia*, 6 from Turkey. BPYV was found in 12 samples: 9 from Italy and 3 from Crete. The authors noted that in Europe the geographical distribution of CYSDV and BPYV is not overlapping. In Spain, the displacement of BPYV by CYSDV has been correlated with the increase of B. tabaci (and of the B biotype) populations replacing T. vaporariorum. Similarly the disappearance of LIYV in California has been associated with the displacement of certain biotypes of B. tabaci by the B biotype which is a very poor vector of this virus. Studies on the molecular variation among virus isolates showed rather high homogeneity. CYSDV isolates could be divided into two groups: one group was only composed of isolates from Spain, Jordan and Turkey and a second group was predominantly composed of isolates found in Saudi Arabia.
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* The EPPO Secretariat had previously no data on the occurrence of CYSDV in Saudi Arabia.
Sources
Rubio, L.; Soong, J.; Kao, J.; Falk, B.W. (1999) Geographic distribution and molecular variation of isolates of three whitefly-borne closteroviruses of cucurbits: lettuce infectious virus, cucurbit yellow stunting disorder virus, and beet pseudo-yellows virus.
Phytopathology, 89(8), 707-711.