Controle biológico de Rhizoctonia solani, agente causal do tombamento do tomateiro, com Trichoderma spp.

Abstract

Several crops, including vegetables such as tomatoes, are subject to various diseases that may limit its production. In particular, inhabiting fungi soil are responsible for important losses in all types of agricultural crops. Species of the genus Trichoderma have antagonistic properties capable of controlling a large number of plant diseases such as damping off of seedlings caused by the pathogen Rhizoctonia solani. The objective of this study was to evaluate the potential antagonist Trichoderma spp. in the control of tomato damping-off in terms of green-house. The isolates of Trichoderma spp. were provided by the Collection of Microorganisms of Interest agroforestry INPA. While, R. solani was obtained from the stem necrosis of tomato plants with characteristic symptoms of damping off, collected in the field of Horticultural Experimental Station Alejo van der Pahlen city of Manaus, AM. For selection of the antagonists, with potential to control R. solani, two experiments were conducted: the first in December 2010 using 40 isolates, and the second in January 2011 with the five most efficient in the first experiment. Both experiments in green-house. After preparation of the suspension of antagonists and pathogen inoculum promoted himself to artificial soil infestation. This infestation was selected by 24 g the amount of R. solani/100 g soil adjusted quantity to cause damping off in tomato. In a plastic tray mixed 24 g of mycelium of R. solani cultivated in rice grains /100 g soil and applied 1.0 mL of the suspension of 108 conidia mL-1/100 g soil. After the revolving of mixtures, these were transferred to glasses of 500 ml plastic. The material was incubated for 15 days, for the initial establishment of fungi. Later, proceeded to plant the seeds of tomato cultivar Kada. The results showed that 12 isolates had a similar effect to the control group without pathogen, significantly reducing the incidence of damping off in tomato seedlings. Among the 12 selected antagonists were five isolates of Trichoderma (1.611, 2.121, 1.439-B, 2.130 and 1.599) and the latter showed that the percentage of surviving seedlings showed no significant difference among themselves by Tukey test at 5% probability compared with the control treatment without the pathogen. Have the isolate 1.599 resulted in 100% of seedlings survivors similarly the witness without the pathogen. For the evaluation of the in vitro mechanism of action of the antagonist was used in cultivation method paired with five disk BDA antagonistic isolates 1.611, 2.121, 1.439-B, 2.130 e 1.599 against the pathogenic strain 2.329. The results showed that the isolates 1.611, 2.121, 1.439-B, 2.130 and 1.599 showed excellent antagonistic action to the test of direct confrontation in which all had grade 1 according to the scale of Bell. The five selected isolates antagonist with potential antagonist were identified by macroscopic and microscopic observation, grown on plates and incubated at 25 °C. The results showed the identification of fungi using the taxonomic keys: 1.611 (T. pseudokoningii), 2.121 (T. virens), 1.439-B (T. aureoviride), 2.130 (T. harzianum) and 1.599 (T. aureoviride). To obtain the sporulation of the best strain 1.599, selected as antagonistic fungus was used 3% of calcium carbonate, different moisture contents (60 mL, 100 mL e 140 mL) and 36 polypropylene bags, containing 200 g of substrate of rice grains previously moistened autoclaved for twice, on alternate days, to 120 0C during 25 minutes. The results showed that the isolate 1.599 produced statistically more conidia, when grown in substrate of rice grains in closed bags, include 100 mL water, and addition of calcium carbonate.