R. Porat et al. (1999) Phytoparasitica 27(3):233-238 Induction of Chitinase and fl-l,3-Endoglucanase Proteins by UV Irradiation and Wounding in Grapefruit Peel Tissue R. Porat, 1 A. Lers, 1 S. Dori, 1 L. Cohen, 1 B. Weiss, 1 A. Daus, 1 C.L. Wilson 2 and S. Droby l* UV irradiation enhanced the resistance of grapefruit against the development of green mold decay caused by Penicillium digitatum, the main postharvest pathogen of citrus fruit, and significantly inhibited the fungus' growth at the fruit wound sites. Immunoblotting analysis using specific citrus chitinase and fl-l,3-endoglucanase antibodies, showed that UV irradiation, wounding of the fruit, or a combination of these two treatments, induced the accumulation of a 25 kD chitinase protein in the fruit's peel tissue. On the other hand, UV irradiation or wounding of the fruit alone was unable to induce the accumulation of 39 and 43 kD fl- 1,3-endoglucanase proteins, but the combination of the two treatments increased these protein levels. It is suggested that both chitinase and/3-1,3-endoglucanase may play a role in the UV-induced resistance of grapefruit against P. digitatum. KEY WORDS: Chitinase; fl-l,3-endoglucanase; grapefruit; Penicillium digitatum; resistance; UV; wounding. INTRODUCTION Green mold decay caused by Penicillium digitatum (Pers.:Fr.) Sacc. invading the fruit through surface wounds, accounts for most of the postharvest losses of citrus fruit (6). This mold is controlled primarily by extensive use of chemical fungicides (7). However, the development of pathogen strains that are resistant to these fungicides, and the increasing health concerns regarding pesticide contamination of food, have led to the search for alternative postharvest control strategies, such as the use of antagonistic microorganisms, natural compounds, and physical treatments that induce resistance against pathogen attacks (17). UV irradiation was first reported to reduce storage rots in onions and potatoes (11,16), and was later shown to induce resistance in a wide array of commodities such as citrus fruit, apples, peaches, bell peppers, carrots, tomatoes and strawberries (reviewed in 15). In citrus fruit, UV induced resistance against the green mold pathogen P digitatum (3). The UV dose required to induce maximum resistance varied along the season and was between 1.6 and 8 kJ/m 2. The resistance in the UV-treated fruit developed to its maximum extent at Contribution from the Agricultural Research Organization,The Volcani Center, Bet Dagan, Israel. No. 403/99. Received April 4, 1999; received in final form May 23, 1999; http://www.phytoparasitica.org posting June 3, 1999. t Dept. of Postharvest Science of Fresh Produce, ARO, The Volcani Center, Bet Dagan 50250, Israel [Fax: +972- 3-9683856; e-mail: samird@netvision.net.il]. ')USDA-ARS,Appalachian Fruit Research Station, Kearneysville, WV 25430, USA. *To whom correspondenceshould be addressed. Phytoparasitica 27:3, 1999 233