Background:

In recent years, afforestation programmes have been accelerated to augment their demand in social forestry and commercial plantations. A large number of nurseries are established to grow both native and exotic tree saplings. Among several natural constraints in raising nurseries, diseases and pests constitute major limiting factors to have inexpensive seedling stock. Seedling health largely determines their successful establishment in out plantings while epidemics in nurseries may upset the planting programme. Forest nursery diseases-Collar rots, Damping –off, root rots and foliar diseases are known to cause losses to important species such as Eucalyptus, Acacia, Bamboo, Dalbergia , Albizia, Tectona and other species. Several diseases cause either total damage to seedlings in the nursery or weaken them to different degrees so that the nursery initiated diseases are carried over to the main field resulting in disease spread and severe loss (Sharma et al. 1985).

Collar rots and root diseases affect most forestry species including bamboo raised in nurseries. Many fungal pathogens are involved with the diseases. Species of Rhizoctonia, Fusarium, Rhizostilbella, Scerotium, Pythium, Phytophthora, Cyclindrocladium etc. are associated with the diseases either alone or in combinations.

Soil is a dynamic environment in which diverse microbial communities survive together affecting growth of plants. Certain microorganisms have the ability to control plant pathogens and are always instrument in keeping plants healthy. This phenomenon is nothing but antagonism. Most of the antagonist are saprophytes; fungi like Gliocladium or Trichoderma or bacteria like Pseudomonas or Bacillus have been used to control plant pathogens. These microorganisms may act directly or indirectly. Direct mode of action is broadly categorized into competiton, parasitism and hyperparasitism. All of these mechanisms may operate together or independently and their activities can result in suppression of plant pathogens. Indirect mode of action is also called immunization or induced resistance. Systemic resistance can be induced by using non-pathogenic or avirulent or pathogenic and or saprophytic microorganisms. Plant growth promoting fungi like Phoma and other sterile fungi have also been studied for their ability to induce systemic resistance (Meera et al., 1994; hivanna et al, 1996). Due to the activity of biocontrol agents, certain biochemical changes re-exhibited in host plant, which are inturn associated with plant defence mechanism. Of late, there has been a large upsurge in the interest on biological disease control, reflecting increase in environmental concern over the use of pesticide. Protection of seedlings in forest nurseries against diseases has been much relied on chemical pesticides, because of the assured results. However, widespread and indiscriminate applications of chemical pesticides, because of the assured results. However, widespread and indiscriminate applications of chemical pesticides in forest nurseries have resulted in the emergence of problems related to pesticide resistance in pathogens, toxicity to non-target organisms, environmental contamination etc. which have greatly reduced the desirability of chemical pesticides.

Antagonistic activity of numerous microbial populations in the rhizosphere influence plant growth and health (Weller, 1998; Weller et al., 2002). These beneficial fungi include plant growth promoting fungi (PGPF) and biological control agents (BCA). The detection of PGPF and BCA depend on efficient methods of screening, which often involve the analysis of thousands of isolates, only to find a few useful ones. An improved knowledge of the diversity and structure of fungal contamination of the rhizosphere soil can lead to a better understanding of their roles in soil ecosystem including the balance of pathogen population. The most important property of an antagonist has to be the saprophytic ability and their capacity to reside up to a depth 5-15 cm. much emphasis has been given to isolate soil borne saprophytic microorganisms and to study their antagonistic ability. The chances of colonization of the root system of grasses grow, are rich in humus, undisturbed in nature and are by the large free from pesticide contamination. Hence, this reason that the current proposal aims to forest soil and five perennial grass species in Western Ghats are Choris barbata, Dactyloctenium aegyptium, Eragrostis unioloides, Digitaria bicornis, Heteropogon contortus have been selected to isolate potential PGP and antagonistic microbes and to test for their biocontrol ability against bamboo nursery diseases and hence the study is taken up.