POSSIBLE INVOLVEMENT OF ALTERED GIBBERELLIN METABOLISM IN THE INDUCTION OF TOMATO IRREGULAR RIPENING IN DWARF CHERRY TOMATO BY SILVERLEAF WHITEFLY

External and internal tomato irregular ripening (TIR) symptoms were as sociated with the feeding of silverleaf whitefly (SLW), Bemisia argent ifolii Bellows and Perring. Four experiments consisting of various soi l drench applications of GA(3) (100 ppm) and cycocel (CCC, an inhibito r of GA biosynthesis; 1,000 and 2,000 ppm) were applied to dwarf cherr y tomato cv. Florida Petite in the presence and absence of SLW in an a ttempt to mimic the disorders induced by the SLW. The application of G A(3) induced external and internal TIR symptoms similar to the SLW-ind uced disorder. Minimal TIR-like symptoms also occurred in the control and CCC treatments. Internal TIR symptoms in GA(3), GA(3) plus SLW, an d GA(3) plus CCC treatments ranged from 66% to 97% throughout the expe riments. The incidence of external TIR symptoms was highest in the GA( 3) plus SLW treatment compared with the other treatments. CCC reduced the incidence of external TIR symptoms induced by GA(3) or GA(3) plus SLW treatments, However, CCC-treated plants also attracted more ovipos ition and higher populations of SLW and consequently induced a greater incidence of TIR symptoms than SLW treatment alone. Furthermore, alth ough low SLW populations may be associated with low external TIR sympt oms, internal TIR symptoms almost always remained high in infested pla nts. The results suggest that the TIR disorder in dwarf cherry tomato which is induced by the SLW may be a gibberellin-regulated disorder.