GROWTH ENHANCEMENT OF CITRUS-RESHNI AFTER INOCULATION WITH GLOMUS-INTRARADICES AND TRICHODERMA-AUREOVIRIDE AND ASSOCIATED EFFECTS ON MICROBIAL-POPULATIONS AND ENZYME-ACTIVITY IN POTTING MIXES

There have been some scientific reports suggesting that dual inoculati ons with arbuscular mycorrhizal (AM) and saprophytic soil fungi may ca use an additive or synergistic growth enhancement of the inoculated ho st plant. Some Trichoderma spp. have shown antagonistic potential agai nst pathogenic fungi and a beneficial effect on plant growth. Joint in oculations of the mycorrhizal fungus Glomus intraradices Schenck and S mith, isolated from a citrus nursery (Tarragona, Spain) and a strain o f Trichoderma?la aureovir ide Rifai, isolated from an organic compost, were tested on a citrus rootstock, Citrus reshni Hort. ex Tan. The in teractions between both microorganisms and their influence on mycorrhi zal root colonization and plant growth enhancement, the changes produc ed in the soil microbial activity, like esterase, trehalase, phosphata se and chitinase activities, and on microbial populations were evaluat ed in three organic substrates : (1) sphagnum peat and autoclaved sand y soil (1/1, v/v), (2) sphagnum pear, quartz sand and perlite (1/1/1, v/v) and (3) pine bark compost (BVU, Prodeasa Product). Substrate char acteristics were more important than the AM inoculation treatment in t he determination of enzyme activity. In bark compost, the number of ba cterial colonies obtained on soil-dilution plates was significantly hi gher than in pear and sand mixtures. Inoculation with T. aureoviride a lone produced no significant effect on growth enhancement of C. reshni . However, dual inoculation with both, T. aureoviride and G. intraradi ces significantly increased plant growth in two of the substrates used and was the best treatment in pine bark amended compost. The inoculat ion with T. aureoviride did not affect the development of mycorrhizal root colonization. These results show a synergistic effect of G. intra radices and T. aureoviride on the growth of C. reshni in organic subst rates and indicate the potential benefits of using combined inoculatio ns.