Improved enumeration of Trichoderma spp. on dilution plates of selective media containing a nonionic surfactant.

Addition of Tergitol NP-10 (polyglycol ether), a nonionic surfactant, greatly enhanced enumeration of Trichoderma spp. colonies on three selective media. Colony diameter was restricted 11-47% on dilution plates with Tergitol compared with media without the surfactant. Plates with the surfactant could be incubated up to 2 weeks prior to counting. Colony counts of Trichoderma spp. were not significantly different for surfactant amended or unamended plates on two of the three selective media tested. However, on RBD medium (rose bengal--chloramphenicol--pentachloronitrobenzene (PCNB)--Dexon) with surfactant, significantly fewer colonies were recovered compared with the medium without surfactant.