Conidial Germination and Appressorial Formation ofColletotrichum capsidandC. gloeosporioidesIsolates from Pepper

Abstract

Conidial germination and appressorial formation of Colletotrichum capsici and C. gloeosporioides were examined on pepper fruits and in association with some inorganic and organic compounds. Conidial germination and appressorial formation were greater on immature green or ripe red fruits of pepper (Capsicum annuum) variety Long Fruit than in water droplets on glass slides. Conidial germination was significantly (P= 0.05) higher for both fungi as concentrations of either sucrose of KCl increased. Appressorial formation for C. capsici was highest when sucrose was 10 mM and for C. gloeosporioides at 0.1 mM. Appressorial formation was reduced and mycelia formed for both fungi at higher sucrose concentrations, but not at 1-100 mM of KCl. Among six compounds tested for induced conidial germination and appressorial formation, CaCl 2 and sucrose caused a significant (P = 0.05) increase, KCl an intermediate one, and AlCl 3 was lowest. β-resorcilic acid did not stimulate conidial germination and appressorial formation, and Fe-resorcilic acid stimulated conidial germination only for C. capsici. Three test melanin biosynthesis inhibitors at 1 μm per milliliter stimulated conidial germination but varied in causing appressorial formation for both fungi. Appressorial formation of C. capsici was completely inhibited by tricyclazole and stimulated by fthalide and isoprothiolane; appressorial formation of C. gloeosporioides was completely inhibited and stimulated by isoprothiolane and tricyclazole, respectively, and only slightly inhibited by fthalide. Inorganic and organic compounds that affect conidial germination and appressorial formation may play a role in the preinfection process of Colletotrichum spp. on pepper fruits