SUMMARY Cytokinins are implicated in a wide variety of devel- opmental and physiological processes in plants includ- ing host-pathogen interactions. The effect of cytokinin benzyl amino purine (BAP) on Phytophthora colocasiae mycelium growth was investigated in vitro and in planta. BAP inhibited the growth of P. colocasiae under in vitro conditions and a corresponding decrease in endo b-1,3 glucanase (EBG) activity was observed in a dose-de- pendent manner. The BAP mediated inhibitory effect of P. colocasiae mycelium growth was overcome by supply- ing the media with an external source of EBG. Results also showed that BAP has inhibitory effect on disease development in taro leading to a reduction in disease severity which correlated with increasing BAP concen- trations. It is concluded that the use of BAP could be an important strategy in the control of taro leaf blight. Key words: Benzyl amino purine, b-1,3 glucanase, cy- tokinins, taro, Phytophthora colocasiae, taro leaf blight. INTRODUCTION Taro (Colocasia esculenta (L.) Schott), a tropical aroid is an important staple or subsistence crop for millions of people in developing countries, especially in Africa and south east Asia. Leaf blight of taro, caused by Phytoph- thora colocasiae is the most destructive disease of Colo- casia. It has become a limiting factor for taro production in all taro growing-countries causing yield loss of 25-30 % (Jackson et al., 1980; Thankappan, 1985; Misra and Chowdhury, 1997). Taro leaf blight symptoms appear as small, water soaked spots, which increase in size and number. Under cloudy weather conditions with inter- mittent rains and temperature around 28ºC, the disease quickly spreads across entire fields giving them a blight- ed appearance. Metalaxyl- and mancozeb-based fungi- cides have proved effective in controlling taro leaf Corresponding author: R.S. Misra Fax: +91.471.2590063 E-mail: rajshekharmisra@gmail.com blight but the waxy leaf surface and the occurrence of the disease during rainy season makes fungicidal sprays ineffective (Misra, 1999). Moreover, these treatments are costly, soil microorganisms rapidly degrade meta- laxyl, contaminanting the surrounding water and soil, and development of resistance against the fungicides is a possibility. Thus, there is a need to develop integrated management strategies to combat this disease using nat- ural and environmentally friendly mechanisms. The role of plant growth regulators in pathogenesis has not been widely studied but there is some evidence that both the pathogen and host plant have the capacity to synthesize various growth regulators whose level varies as a result of plant-pathogen interactions (Jameson, 2000; Serezhkina et al., 2004). For example, fluctuations in the level of growth regulators are related to disease suscepti- bility or resistance in wheat cultivars infected with pow- dery mildew (Serezhkina et al., 2004). It was shown that some fungal pathogens are not only able to increase the level of indole-3-acetic acid in their respective hosts, but are themselves capable of producing this auxin which is directly released into soil (Agrios, 1997). Furfurylamine, 1, 2, 3, 4 tetra-o-acetyl-b-D-glucopyranse, adipic acid mo- noethyl ester (FGA), a mixture of three analogues of plant growth regulators has direct anti-microbial activity against filamentous fungi like Alternaria solani and Botry- tis cinerea, and the oomycetes P. capsici and P. citrophtho- ra (Flors et al., 2004). Naphthalene acetic acid reduces disease severity of Sclerotinia sclerotiorum (white mold) attacks to bean and cucumber plants (Al-Masari et al., 2002). It was also shown that exogenous cytokinins at high concentrations can effectively suppress the growth of the barley powdery mildew pathogen and induce ab- normalities in the morphology of fungal growth tubes and appressoria (Mishina et al., 2002). These findings clearly suggest that phytohormones play significant role in ontogeny of pathogens. Never- theless, no evidence is available supporting a direct role of growth regulators in inhibiting mycelium growth and necrotic lesions development in taro plants during in- fection caused by P. colocasiae. Therefore, it seemed im- portant to analyse the role of growth regulators in the context of taro leaf blight pathogen. The present study was aimed at investigating the role of BAP, a synthetic Journal of Plant Pathology (2008), 90 (2), 191-196 Edizioni ETS Pisa, 2008 191 EFFECT OF BENZYL AMINO PURINE ON THE PATHOGEN GROWTH AND DISEASE DEVELOPMENT OF TARO LEAF BLIGHT CAUSED BY PHYTOPHTHORA COLOCASIAE A.K. Mishra, K. Sharma and R.S. Misra Central Tuber Crops Research Institute, Thiruvananthpuram, Kerala, India 695017 005_JPP_66RP_191 21-07-2008 10:15 Pagina 191