In vitro Evaluation of Antagonism between Trichoderma spp.and Rhizoctonia solani causing black scurf disease on potato

Abstract

The fungus Rhizoctonia solani causes black scurf disease in potato crops, which results in lower yield and quality of ware and seed potatoes. This study was under taken to evaluate in vitro the inhibitive effect of two antagonistic Trichoderma species on the fungus pathogen Rhizoctonia. Apure isolate of the pathogen R.solani was recovered from certified tubers imported from Holland, while the two antagonists, T.harzianum and T.koningii Pers that have been used in biological control of several pathogenic fungi were obtained from University of Tushreen, Syria. The percent inhibitive capability of the two antagonists was assessed in both solid potato dextrose agar (PDA) and liquid potato dextrose broth (PDB) media, and in turn the underlying mechanism of the antagonistic behavior involved was inferred. Bothe species of Trichoderma antagonists inhibited Rhizoctonia growth significantly compared to the control, with extensive growth and sporulation over the pathogen. Isolates of T. koningii showed higher growth rates and more proliferative sporulation on the pathogen colonies than T.harzianum. The direct parasitism of Trichoderma could be inferred from the observation under the light microscope of the coiling of the antagonist mycelium around that of the pathogen with external malformation on its hyphae. Also, the culture filtrates of the two antagonist species (at 1:1 and 2:1 concentration) displayed high competitive efficacy of growth inhibition of the pathogen Rhizoctonia isolates in PDA, indicating secretion of inhibitive substances to Rhizoctonia(pathogen). There were no significant differences between the two concentrations of T. koningii, while the higher concentration was more efficacious in T.harzianumthan the lower one for inhibition or secretion of inhibitive substances to Rhizoctonia.