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Leaf rot disease of coconut, which occurs superimposed on root (wilt) disease of coconut in about 65 % of the cases, is an important disease prevalent in Kerala State of India. Colletotrichum gloeosporioides and Exserohilum rostratum are the main fungal pathogens of the disease, which disfigure the leaves and reduce yield substantially. Several biocontrol agents have been identified which reduce the disease development by these fungal pathogens. Pseudomonas spp. exhibit a host of mechanisms, which act in concert to bring about biocontrol activity. Bacillus spp. work mainly through production of antibiotics and other non-volatile metabolites. Mycoparasitism was the main contributing factor for actinomycetes group. INTRODUCTION Micro-organisms are central to our understanding of biological control of plant diseases and their potential in reducing disease incidence and severity is well demonstrated in many crops worldwide, leading to their practical applications in agriculture. The surface of aerial plant parts provides a habitat for epiphytic micro-organisms, many of them are capable of influencing the growth of pathogens, thus, paving the way for biological control on foliar surfaces (Blakeman and Brodie, 1976; Blakeman and Fokkema, 1982). These saprophytic organisms play an important part in control of foliar pathogens thus reducing the incidence of foliar diseases on crops in the field. In recent times, bacterial antagonists have received considerable attention mainly because of their ability to reduce the inoculum’s density of the pathogen, which is effected through several means. An efficient bio-control agent may affect pathogens by a combination of mechanisms (Chet, 1987). Hence, to devise ways of enhancing the antagonistic effects of foliar micro-organisms against pathogens, it is necessary to understand the mechanisms responsible for biological control. The production of volatile and non-volatile secondary metabolites, siderophores, hydrogen cyanide (HCN), antibiotics, etc. have been implicated in the control of plant pathogens (McKeen et.al., 1986; Fravel, 1988; Droby et al., 1989; Chet et. al., 1990; Thomashow and Weller, 1990; Ferriera et.al., 1991). Mycoparasitism / hyperparasitism by microbial antagonists can also be distinguished, which involve hyphal interference, penetration of host mycelium and hyphal lysis (Amer et. al., 1997; Gupta et al., 2001). Leaf rot disease, which occurs in the Southernmost District (Kerala) of India, is an economically important disease of coconut plantation crop. The disease is caused mainly by fungi Colletotrichum gloeosporioides and Exserohilum rostratum, which produce lesions on innermost tender leaves. These lesions coalesce rotting a large leaf area, which falls off after drying. Each successively emerging leaf gets infected, thus, reducing the photosynthetic area to a great extent and the yield of the palm is adversely affected. Several microbial antagonists have been identified against the fungal pathogens of this disease. Out of this, seven bacterial / actinomycetal anta-gonists were selected for further studies. 1 Central Plantation Crops Research Institute, Regional Station, Kayangulam, Krishnapuran, India.

IMPORTANT BIOCONTROL TRAITS OF MICROBIAL ANTAGONISTS OF LEAF ROT DISEASE OF COCONUT