Association of a phloem-limited bacterium with a new disease of cucurbits
A new disease has been observed since 1991 on cucurbits in central Texas and Oklahoma (US). This disease called yellow vine causes decline and death of watermelon, melon, courgette and pumpkin. Symptoms are characterized by leaf yellowing, phloem discoloration and plant collapse. Despite many investigations (isolation attempts, transmission tests, serological assays, DNA hybridization) it was not possible to find a consistent relationship between the expression of disease symptoms and the presence of a particular microorganism or virus in the plant. However, electron microscopy consistently show the presence of a bacterium in the phloem. It is a rod-shaped bacterium (0.25 to 0.5 µm width; 1.0 to 3.0 µm length), surrounded by a triple-layered cell envelope. Further studies are needed to better characterize this phloem-limited bacterium and try to clarify its role in the yellow vine disease of cucurbits.
Sources
Bruton, B.D.; Fletcher, J.; Pair, S.D.; Shaw, M.; Sittertz-Bhatkar, H. (1998) Association of a phloem-limited bacterium with yellow vine disease in cucurbits.
Plant Disease, 82(5), 512-520.