Diseases of lettuce and kai choy induced by Bemisia tabaci
Bemisia tabaci (EPPO A2 quarantine pest) has been associated with a reduced growth, yellowing and stem blanching of lettuce and kai choy (Brassica campestris). As experiments in Hawaii (US) showed the weight of lettuce was reduced by 41% when the plants were colonized by 200 whiteflies and their offspring for three weeks. At the same colonization rate kai choy plants were reduced by 21%. Exposure to 50 whiteflies plus nymphs induced yellowing in lettuce, while exposure to ; 10 whiteflies with nymphs induced stem and midvein blanching and leaf curling in kai choy. Weight losses in both plant species was positively correlated with the immature density. Infestation by adults alone did not result in weight loss or symptom development in kai choy. The removal of whiteflies and their offspring led to a recovery of the plants. The authors suggested that the recovery of the plants is an indication that the symptoms are caused by a toxin or toxins and that they are phytotoxic disorders.
Costa, H.S.; Ullman, D.E.; Johnson, M.W.; Tabashnik, B.E. (1993) Association between Bemisia tabaci density and reduced growth, yellowing and stem blanching of lettuce and kai choy.
Plant Disease 77, 969-972.