EFFICACY OF PENICILLIUM-FUNICULOSUM AS A BIOLOGICAL-CONTROL AGENT AGAINST PHYTOPHTHORA ROOT ROTS OF AZALEA AND CITRUS

Penicillium funiculosum was evaluated in the greenhouse for its ability to suppress Phytophthora root rots of azalea (Rhododendron spp.) and sweet orange (Citrus sinensis) as measured by increased shoot and root growth. The antagonist was grown in a wheat bran-peat moss (1:1) medium, which was then mixed into a peat-perlite (3:1) planting mix at a concentration of 0.7% (wt/vol). Rooted azalea cuttings or sweet orange seedlings were transplanted into the planting mix, which was inoculated with Phytophthora 5 to 7 days later. In most of the tests, P. funiculosum effectively increased the shoot growth and root weight of azalea in media infested with P. parasitica and those of sweet orange in media infested with P. citrophthora. It also reduced, to some degree, root rots caused by P. cinnamomi on azalea and by P. parasitica on sweet orange. Three subisolates of P. funiculosum (T327H, T327L, and T327S) exhibited different degrees of root rot suppression; T327S provided the best control. The population density of each of these subisolates increased in the planting mix during the first 4 weeks and decreased thereafter. Mixing the P. Suniculosum bran-peat inoculum into the planting mix was a more effective method for delivering the biocontrol agent than dipping the plant root systems into a P. Suniculosum spore suspension before transplantation. P. funiculosum was also effective in increasing plant growth when the bran-peat inoculum was used at concentrations lower than 0.7%. P. funiculosum inoculum applied at a concentration of 0.35% twice during a 12-week period was more effective in the biocontrol of azalea root rot caused by P. cinnamomi than when it was applied only once. P. funiculosum also reduced sweet orange root rot caused by P. citrophthora in some other planting mixes.