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Abstract
To aid the development of compatible biocontrol inocula, a prescreening method for the prediction of compatibility of fungal antagonists was developed. Compatibility between 18 Clonostachys isolates with known antagonistic capabilities against Phytophthora palmivora was tested using intra- or interisolate pairings (dual cultures) on water agar plates, a hyphal interaction experiment and a modified double host-range experiment. Almost all inter- or intraisolate pairings of Clonostachys isolates showed growth inhibition zones and did not show free hyphal intermingling. A hyphal interaction experiment on water agar demonstrated that the aggressiveness of a Clonostachys isolate and its susceptibility to mycoparasitism were unrelated phenomena. However the level of aggressiveness and/or susceptibility of an isolate were largely dependant on the isolate with which it was challenged. The degree of growth-inhibition caused by an isolate was unrelated to the hyphal damaged it caused or received. In the double host-range experiment all possible pairs from four Clonostachys isolates were inoculated in different ratios (10 000-fold range) on plates precolonized with one of two P. palmivora isolates. The results showed that antagonistic capabilities of certain combinations were affected by the Clonostachys isolates. The primary host, P. palmivora, did not affect antagonistic capabilities; whereas inoculum ratio did. Of note, it was not possible to predict the outcome of the double host range on the basis of the results of the hyphal interaction experiment. In conclusion the competitive abilities of Clonostachys isolates depend on the partner with which they are applied and less on resource availability. The double host-range test as developed here might provide the most representative tool to date to test compatibility of fungal antagonists to be used in biocontrol inocula. However the link between the results of the double host-range test and field efficacy of biocontrol inocula remains to be investigated.
This work was financially supported by USDA-ARS and Directoraat Generaal Internationale Samenwerking (DGIS) and was managed by CABI and CATIE. We thank the Universidad de Costa Rica and the University of Bath for support through their student placement program; the latter was financially supported by Cocoa Research UK and the British Society for Plant Protection (BSPP). Ghiselle Alvarado, Claudio Arroyo, Johnny Garcia, Armando Portuguéz, Isa Royo and Miguel Sanabria provided technical and administrative assistance. Keith Holmes supplied isolate Dis105g. We thank Hans-Joseph Schroers for patiently sharing his insights into Clonostachys and Zoltán Naár for useful discussion on fungal interactions.