Trichoderma spp. como agentes de biocontrole de Cylindrocladium scoparium e como promotores de crescimento em mudas de eucalipto

Abstract

A brief survey of leaf pathogens in a commercial production area of eucalyptus seedlings in a commercial nursery in the municipality of Luziânia (GO) showed the occurrence of five pathogens: C. scoparium, Pleospora sp., Hainesia sp., Pestalotiopsis sp. and Rhizoctonia solani (Chapter I). Among these pathogens of eucalyptus (Eucalyptus spp.), leaf spot caused by Cylindrocladium spp. Morgam (Teleomorph: Calonectria sp. de Not) stands out. This disease is especially important in nurseries that produce eucalyptus seedlings, especially in the cloning of hybrid species. Control of the disease has been based mainly on treating plants with fungicides at all stages of eucalyptus cloning. In Chapter II, liquid culture media SG (Sucrose-Glucose), BD (Potato-Dextrose) and SDY (Yeast extract) were tested to produce spores of C. scoparium. The SG liquid medium enabled the production of conidia of two pathogen isolates, which were showed to be infective in eucalyptus leaves. To draw up a biological control program against plant diseases, it is necessary and appropriate to select well adapted antagonists with a high degree of control against the plant pathogens and, preferably, to promote growth and rooting of the minicuttings. In this study five isolates of Trichoderma were selected through in vitro and in vivo tests. The biological control of two isolates of Cylindrocladium scoparium in detached leaves was evaluated, as well as the ability of the antagonist isolates to produce indoleacetic acid (IAA) growth hormone and for endophytic colonization in seedlings of hybrid clones (G-100) of eucalyptus. The promotion of plant and root growth was studied in Eucalyptus urophillla seedlings obtained from seeds and in the hybrid G-100 (Eucalyptus urophilla x Eucalyptus grandis) obtained by cloning. The capacity of Trichoderma isolates to sporulate in two solid substrates, grains of parboiled rice and millet, was also studied. The in vitro experiments consisted of pairing colonies and exposing the pathogen to volatile and non-volatile metabolites produced by Trichoderma spp. Morphological changes were observed in hyphae and inhibition of micelial growth of C. scoparium. On detached eucalyptus leaves, the five Trichoderma isolates gave protection against the disease, and isolate CEN 517 of C. scoparium proved to be more aggressive than CEN 494 of C. scoparium, when the levels of incidence of leaf spot were quantified. The results obtained for sporulation of antagonists in grains of parboiled rice and millet showed great variation between these isolates. The isolate CEN 262 (T. harzianum) showed higher production of spores in both substrates, at 07 and 11 days of incubation (Chapter III). In experiments to evaluate growth promotion, using five isolates of Trichoderma selected in laboratory tests, isolate CEN 262 (Trichoderma harzianum) showed a significant increase in dry roots, shoots and height of the seedlings. In vitro, the production of IAA was observed in the following isolates: CEN 209, CEN 500 and CEN 262. Isolate CEN 262 presented concentration of the hormone that was 19 times greater than that of CEN 209. CEN 162, CEN 262 and CEN 498 isolates demonstrated capacity to colonize roots of eucalyptus (Chapter IV).