INDUCTION OF TOMATO POLYPHENOL OXIDASES IN RESPONSE TO COMMON CUTWORM (Spodoptera litura) AND JACK BEARDSLEY MEALYBUG (Pseudococcus jackbeardsleyi) INFESTATIONS

Our objectives were to evaluate the induction of polyphenol oxidases (PPOs) and expression patterns of PPO A, B, D, E, and F genes upon infestations by common cutworm (Spodoptera litura) and Jack Beardsley mealybug (Pseudococcus jackbeardsleyi). After common cutworm infestation at leaf node 4, PPO activities increased 10.2-fold locally, leading to systemic increase in PPO activities at upper leaf nodes 1-2 (3.0-fold) and lower leaf node 6 (1.7-fold). While infestation at leaf node 6 locally induced PPO activities 14.5-fold, and systemically induced PPO activities 3.0-fold at leaf node 4. By contrast, no significant induction of PPO was observed at any leaf nodes when either leaf node 4 or 6 was infested by mealybug. When common cutworm fed on PPO B::GUS fusion tomatoes, induced PPO B expression was observed locally particularly in mature leaves at veins, petioles, and abscission zones. However, PPO D::GUS fusion tomatoes showed locally induced expression especially in older leaves at veins and petioles. Systemically induced expression was also observed. Mealybug feeding also locally induced PPO B and PPO D expression in vascular tissues but at lower levels.