Avaliação in vitro e in vivo do potencial de biocontrole de Trichoderma spp. a Fusarium sp. na cultura da melancia.

Abstract

Watermelons are usually affected by root diseases caused by fungi of the genus Fusarium sp. One of the control alternatives is the use of Trichoderma spp. In this sense, the aim of this study was to evaluate the potential in vitro and in vivo biocontrol of Trichoderma spp. over Fusarium sp. in watermelons. The research was carried out from August 2012 to September 2013 in the Centre for Science and Agrifood Technology (CCTA) of the Federal University of Campina Grande (UFCG). Two isolates of Trichoderma spp. (T1 and T2) from soil samples collected in watermelons crops in the counties of Pombal and São João do Rio do Peixe-PB, were confronted with an isolate of a pathogenic Fusarium sp. Mycelial discs with 0.5 mm diameter of the pathogen and the antagonist were plated on potato dextrose agar (PDA) supplemented with antibiotic (A) and incubated in a growth chamber at 28 ±2 °C with 12 h of photoperiod. The transverse and longitudinal diameters of colonies were measured daily for eight days. The inocula of Trichoderma spp. and Fusarium sp. were produced in sandy organic substrates during 15 days. Then, in the greenhouse, were added at concentrations of 4% and 6%, individually and together, in pots with a capacity of 0.5 kg containing commercial sterilized substrate, where two seeds of Crimson Sweet watermelon were sown per pot. The following variables were assessed: antagonism of isolates, incidence of root rot, disease severity, fresh and dry weight of shoots, and gas exchanges. Isolates of Trichoderma spp. showed an antagonistic effect on mycelial growth of Fusarium sp. The disease arose in all treatments with Fusarium sp. and Trichoderma spp. However, Trichoderma spp. reduced the severity of lesions caused by Fusarium sp. The highest values of fresh weight and dry weight of shoots were obtained in treatments with the interaction of pathogen and antagonist (T9 and T10). In the treatments with different concentrations of added Trichoderma spp. (T3 and T4) had higher photosynthetic rates. The highest values of transpiration and stomatal conductance were observed in treatments with 4% of Trichoderma spp. (T3) and 4% of Fusarium sp. (T5). The vegetative growth was more effective when we used a lower concentration of the antagonist and a greater concentration of the pathogen.