Fungistatic Activity Mediated by Volatile Organic Compounds Is Isolate-Dependent in Trichoderma sp. “atroviride B”

Abstract

<i>Trichoderma</i> spp. produce multiple bioactive volatile organic compounds (VOCs). While the bioactivity of VOCs from different <i>Trichoderma</i> species is well documented, information on intraspecific variation is limited. The fungistatic activity of VOCs emitted by 59 <i>Trichoderma</i> sp. "<i>atroviride</i> B" isolates against the pathogen <i>Rhizoctonia solani</i> was investigated. Eight isolates representing the two extremes of bioactivity against <i>R. solani</i> were also assessed against <i>Alternaria radicina</i>, <i>Fusarium oxysporum</i> f. sp. <i>lycopersici</i> and <i>Sclerotinia sclerotiorum</i>. VOCs profiles of these eight isolates were analyzed using gas chromatography-mass spectrometry (GC-MS) to identify a correlation between specific VOCs and bioactivity, and 11 VOCs were evaluated for bioactivity against the pathogens. Bioactivity against <i>R</i>. <i>solani</i> varied among the fifty-nine isolates, with five being strongly antagonistic. All eight selected isolates inhibited the growth of all four pathogens, with bioactivity being lowest against <i>F</i>. <i>oxysporum</i> f. sp. <i>lycopersici</i>. In total, 32 VOCs were detected, with individual isolates producing between 19 and 28 VOCs. There was a significant direct correlation between VOC number/quantity and bioactivity against <i>R</i>. <i>solani</i>. 6-pentyl-α-pyrone was the most abundant VOC produced, but 15 other VOCs were also correlated with bioactivity. All 11 VOCs tested inhibited <i>R. solani</i> growth, some by >50%. Some of the VOCs also inhibited the growth of the other pathogens by >50%. This study demonstrates significant intraspecific differences in VOC profiles and fungistatic activity supporting the existence of biological diversity within <i>Trichoderma</i> isolates from the same species, a factor in many cases ignored during the development of biological control agents.