EXPLOITATION OF PLANT PATHOGENESIS-RELATED PROTEINS FOR ENHANCED PEST RESISTANCE IN CITRUS

MCCOLLUM, T. G.

Abstract


Among the various defense mechanisms that plants exhibit in response to attack by pests is the expression of a number of proteins collectively referred to as 'pathogenesisrelated proteins'. We are interested in these proteins in citrus with the long term goal of enhancing resistance to fungal and insect pests by developing improved germplasm and the use of elicitors to induce these proteins on demand. Two classes of enzymes, chitinases and ß-1,3-glucanases, which are known to have antifungal characteristics are active in all citrus tissues studied (roots, leaves, blossoms, and fruit). The amount of activity varies with tissue, tissue age, and in some cases cultivar. Chitinase and ß-1,3-glucanase activities increase with age in leaves whereas chitinase activity decreases and ß-1,3-glucanase activity increases with age in flavedo. Infection of fruit by Penicillium digitatum induced increased activities of these enzymes. Feeding by sugar cane rootstock borer weevil (Diaprepes abbreviatus) larvae induced increased chitinase activity substantially in roots of 2 of 8 cultivars that we examined and in leaves of sour orange; in contrast to chitinase, ß-1,3-glucanase activity is reduced by weevil feeding. Treatment of grapefruit trees with gibberellic acid, salicylic acid, or Keyplex 350 resulted in significant, although transient increases in both enzymes.

Keywords


chitinase; ß-1,3-glucanase; penicillium digitatum; diaprepes abbreviatus; gibberellic acid; salicylic acid; keyplex 350

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283