Antifungal potential of Trichoderma against Penicillium mononematosum agent responsible of white yam (Dioscorea rotundata Poir.) rot

Post-harvest rot generated by Penicillium mononematosum is a key issue that restricts the
healthy development of yam industry. To compensate for this deterioration, farmers rely
mainly on chemicals pesticides. However, theses not only cause environmental pollution, but
also increase the amount of pesticide residues in agricultural products, which is potentially
harmful to human health and capable of inducing the appearance of resistant microorganisms.
In the face of these adverse effects, research of beneficial microorganisms such as
Trichoderma is a biological alternative to resolve the problem. The aim of this study was to
evaluate in vitro and in situ potential of Trichoderma species as bio-control agents against
Penicillium mononematosum. In vitro activities were evaluated by pair culture and by
antibiosis (cellophane membrane). In situ tests were conducted by direct inoculation of
Trichoderma sporal solutions at different concentrations (105 to 107
conidia/ml) on yam discs.
In vitro, T. asperellum and T. harzianum inhibited radial growth of Penicillium
mononematosum respectively from 50±1.72 to 51.03±1.38 percent for pair culture and
100±0.00 to 64.33±0.06 for antibiosis. The inhibition observed during different test is
explained by the fact that Trichoderma can produce enzymes and antimicrobial secondary
metabolites. In situ, their sporal suspensions in a curative test reduced necrosis diameters to
107
conidia/ml from 16.7±0.00 to 30.6±0.00 percent and induced total protection in a
preventive test. Trichoderma asperellum and Trichoderma harzanium have been shown to be
effective in conserving yam tubers against Penicillium mononematosum, significantly
reducing mycelial growth and necrosis diameter on the tuber. These results show that
Trichoderma could be used as an alternative to control post-harvest rot of yam tubers caused
by fungi pathogens.
KEYWORDS: Dioscorea rotundata, Penicillium mononematosum, post-harvest rot,
Trichoderma spp.