Influence of a Fungus-Feeding Nematode on Growth and Biocontrol Efficacy of Trichoderma harzianum

Abstract

A fungivorous nematode, Aphelenchoides sp., was isolated from field soil by baiting with mycelium of the biocontrol fungus Trichoderma harzianum ThzID1, and subsequently was maintained on agar cultures of the fungus. Interactions between the nematode and the green fluorescent protein-producing transformant, T. harzianum ThzID1-M3, were investigated in both heat-treated (80 degrees C, 30 min) and untreated field soil. ThzID1-M3 was identified in soil by epifluorescence microscopy. When ThzID1-M3 was added to soil as an alginate pellet formulation, addition of the nematode (10 per gram of soil) significantly reduced radial growth and recoverable populations of the fungus, and the effect was greater in heat-treated soil than in untreated soil. Addition of ThzID1-M3 to soil pretreated with the nematode (10 per gram of soil) stimulated nematode population growth for approximately 10 to 20 days, whereas nematode populations decreased in the absence of added Trichoderma sp. When sclerotia of Sclerotinia sclerotiorum were added to soil (10 per 200 g of soil) with ThzID1-M3 (40 pellets per 200 g of soil), addition of Aphe-lenchoides sp. (2,000 per 200 g of soil) reduced the number of sclerotia colonized by ThzID1-M3. These results suggest that fungivorous nematodes may be a significant biotic constraint on activity of biocontrol fungi in the field.

Use of Quantitative Real-Time PCR to Unravel Ecological Complexity in a Biological Control System

“…We previously observed that the presence of A. saprophilus nematodes both reduced radial growth of T. harzia-num ThzID1-M3 colonies, as well as recoverable ThzID1-M3 populations in soil [6], showing a deleterious effect of nematode predation on ability of this potential biocontrol fungus to survive and proliferate in the presence of the fungivorous nematodes. Evidence of this trophic effect was substantiated by the concurrent significant population increase of A. saprophilus in soil to which T. harzianum had been added [6].…”

“…However, we have also demonstrated that the fungivorous nematode Aphelenchoides saprophilus is able to feed on hyphae of T. harzianum in soil [6] (Figure 1).…”

“…Evidence of this trophic effect was substantiated by the concurrent significant population increase of A. saprophilus in soil to which T. harzianum had been added [6]. A trophic cascade effect is implicated, evidenced by a significant reduction in colonization of sclerotia of S. sclerotiorum by T. harzianum, when the fungivorous nematodes were present [6].…”

“…Ability of A. saprophilus to reduce both colony radial growth and recoverable populations of T. harzianum in soil was previously shown [6]. Nematodes (10 nematodes/g of soil, males and females, mixed life stages) were added to soil with pelletized T. harzianum; controls consisted of sterile water.…”

“…Pellets were removed by straining, placed on waxed paper to air-dry at room temperature for 2 days then stored at 4C prior to use. The fungivorous nematode Aphelenchoides saprophilus was obtained from field soil near Moscow, ID, and populations were maintained on agar cultures of T. harzianum [6]. An isolate of S. sclerotiorum was grown on PDA for 7 days, then transferred to carrot discs and incubated 6 -8 weeks at 25 8C.…”