|Phyllosphere and Phylloplane, and Rhizosphere and Rhizoplane Regions
Phyllosphere is the immediate vicinity of leaf surface, as rhizosphere is the zone of immediate vicinity of roots, where microbial communities are constantly in dynamic state due to exo-and endogenous sources of nutrients. As rhizoplane denotes root surface, similarly phylloplane refers to leaf surface of plants. Nutrients stimulatory for microorganism on phyllosphere and phylloplane regions consist primarily of plant materials (e.g. pollen grains, old petals, etc.) or insect excreta. Stimulation of necrotrophic (destructive) fungi by pollen grains (Fokkema, 1981) and aphids honey dews (Fokkema et al, 1983) is well documented. Rai and Singh (1980) have investigated the antagonistic activities of some phylloplane fungi (of mustard and .barley) against Alternaria brassicae and Drechslera graminea. The antagonists are Aureobasidium pullulans, Epicoccum purpurascens, Cladosporium cladosporioides and Alternaria alternata. The most significant effects were observed when the spores of leaf surface fungi or their metabolites were sprayed on leaves prior to inoculation of the pathogens.
Pandey et al. (1993) studied the antagonistic activities of some phylloplane fungi of guava against its fungal pathogens i.e. Colletotrichum gloeosporiodes and Pestalotiapsidii. They found a pronounced inhibition in lesion development after application of spore suspension (3 x 105 propagutes/ml) of A. pullulans, C.cladosporioides, E. purpurascens, F. oxysporum and Trichoderma harzianum against C. gloeosporioides, and A niger, A. terreus, C. roseo-griseum and T. harzianum against P. psidii.
Similarly, a variety of soil microorganism are present in the rhizosphere and rhizoplane regions of a plant. Their number remains many times more than the non-rhizosphere one. The increase in microbial number and their activity have been referred to as 'rhizosphere effect'. It is caused by secretion of growth promoting substances (root exudates) and casting of sloughed off root tissues by plants in soil during their growth phases (Baker and Sayder, 1965; Rovira, 1965).
Dubey and Dwivedi (1988) have studied the population dynamics of micro fungi in root region of soybean during different growth stages of the plant. They recorded a gradual increase in numbers of soil fungi, both qualitatively and quantitatively, from seedling to flowering stage, thereafter their frequency declined at the senescence stage. Nowadays, manipulation of soil environment has become a tool for biological control of soil borne plant pathogens.
Several methods have been developed which bring about artificial manipulation of rhizosphere, phyllosphere and soil environment. Consequently number of antagonistic microorganism is increased. This can be done by (i)
artificial introduction of antagonists in soil or spraying these antagonists on the aerial parts of plants, (ii)
modification of soil environment by organic amendments, (iii)
green manuring, changing soil pH, C : N ratios, temperature, and (iv)
adding the selective chemicals or heat treatment of plant tissues (Garrett, 1965; Baker and Snyder, 1965; Baker and Cook, 1974).