MICROBIOLOGICAL ASPECTS IN RHIZOSPHERE OF HORTICULTURAL PLANTS CULTIVATED ON VARIOUS GROWTH SUBSTRATES IN GREENHOUSE PUBLISHEDGabi-Mirela MATEI(1),) S.MATEI(1) , Elena Maria DRĂGHICI(2
Abstract: The goal of the present paper was to present microbial aspects in rhizosphere of four horticultural plants grown on various substrates based on use of perlite and its combinations with peat, as easily biodegradable material and to reveal the interrelations between natural antagonists and potential plant pathogenic species. A better control of pathogens developed in greenhouse, due to the ease of perlite substrate disinfection and its recycling was signaled as beneficial for yields and its quality, with cost benefits and important advantages for the health of consumers. Samples from rhizosphere of tomato, pepper, cucumber and lettuce plants cultivated in soilless systems on substrates from perlite or perlite-peat mixture were analyzed from a microbiological point of view comparatively with non-cultivated substrates for assessing the bacterial and fungal density and taxonomic composition of community. Peat-perlite substrate was more favorable to bacterial microflora than perlite alone, with highest values in the rhizosphere of pepper plants. Cucumber roots found good aeration conditions in the perlite from nutritive mattresses and its exudates stimulated the increase of microbial community number and diversity more than in pepper or tomato rhizosphere. Microbial counts and global physiological activity were determined in lettuce rhizosphere cultivated on perlite-peat mixt substrate and showed doubled values comparatively with samples from extra-radicular substrate in mattress. Dominant rhizosphere fungal species belonged to genera Penicillium, Trichoderma, Fusarium, Aspergillus and bacteria to genera Psedomonas, Bacillus, Arthrobacter, both accompanied sometimes by actinomycetes. The existence of antagonistic species (e.g. Trichoderma viride strains D2, D6 and D11 with proved in vitro effect on the pathogenic isolates of Fusarium and Penicillium) indicated a good relationship antagonist-pathogen in rhizosphere of horticultural plants. The possibilities of biological control of pathogens by natural antagonists, beneficial influence of plant root exudates and rhizosphere effect similar to soil conditions recommend perlite-based substrates as environmental friendly for using in greenhouse soilless systems for horticultural plants.
Key words: perlite, rhizosphere, antagonism, Trichoderma, growth substrate