Potential of Trichoderma spp. isolates and Trichoderma bioactive metabolites for biological control of aphid pests of cereals

Different species of the genus Trichoderma have been reported to be effective biocontrol agents of a wide range of important soil-borne and air-borne plant pathogens. Our studies show that some Trichoderma species also have a potential for biocontrol of aphids. Aphids are a major cause of loss of agricultural production and reduction of its quality. They induce a direct noxious effect on crop health, caused by subtraction of sap, and an indirect effect related to the spread of insect-transmitted virus diseases. Cultures of four fungal isolates belonging to different species of the genus Trichoderma had a fagodeterrent effect on the aphid Schizaphis graminum (Rondani), one of the most important pests of cereal crops, in feeding preference tests. All of the tested fungal isolates restrained winged morphs of S. graminum from visiting treated leaves, but only one isolate of T. citrinoviride influenced the preference of wingless morphs as well. Cultures of the isolate of T. citrinoviride showed a significant fagodeterrent activity towards different species of aphids besides S. graminum, including the polyphagous Myzus persicae (Sulzer) and Rhopalosiphum padi (L.), another widespread pest of cereal crops. Trials carried out with supernatants obtained by centrifuging aqueous suspensions of the fungal cultures showed that the feeding preference of aphids was maintained in the absence of fungal spores and mycelia, supporting the hypothesis that at least part of the effect was due to fungal metabolites. Further investigations, aimed at identifying the fungal compounds with fagoterrent activity produced by the isolate of T. citrinoviride led to the isolation and structure determination by spectroscopic methods (essentially by NMR and MS techniques) of four distinct groups of structurally related metabolites with fagodeterrent activity. The first two are novel metabolites, which have been named citrantifidiene and citrantifidiol. and characterized as a symmetrical disubstituted hexa-1,3-dienyl ester of acetic acid and a tetrasubstituted cyclohexane-1,3-diol, respectively. Other two compounds belong to the chemical family of bisorbicillinoids, namely bislongiquinolide and dihydrotrichodimerol. The fourth group, showing a distinctly high fagodeterrent activity, consists of different primary alcohols of the general formula R-OH, wherein R is a long, unbranched, unsubstituted linear aliphatic group. These compounds, have no chiral centers and therefore can be obtained in good yields through chemical synthesis, besides natural sources. For the active compounds an international patent (PTC IB2012/052383) has been filed.