Growth rate and trapping efficacy of nematode-trapping fungi under constant and fluctuating temperatures

The effect of temperature on radial growth and predatory activity of differ ent isolates of nematode-trapping fungi was assessed. Four isolates of Dudd ingtonia flagrans and one isolate of Arthrobotrys oligospora were inoculate d on petri dishes containing either cornmeal agar (CMA) or faecal agar and then incubated for 14 days under three different constant and fluctuating t emperature regimes. The radial growth was similar on the two substrates at each temperature regime. All fungal isolates showed a higher growth rate at a constant 20 degrees C. At 10 degrees and 15 degrees C, all D. flagrans i solates showed very similar patterns of radial growth at both constant and fluctuating temperatures. At 20 degrees C, they grew significantly faster a t constant than at fluctuating temperatures. A. oligospora grew significant ly faster than all D. flagrans isolates except when incubated at a fluctuat ing 20 degrees C. Spores of each fungal isolate were added to faecal cultur es containing eggs of Cooperia oncophora at a concentration of 6250 spores/ g faeces. The cultures were incubated for 14 days at the same temperature r egimes described above. Control faeces (without fungal material) were also cultured. More larvae were recovered from the fungus-treated cultures incub ated at a constant 10 degrees or 15 degrees C than from those incubated at the respective fluctuating temperatures, except for one D. flagrans isolate . Incubation at 20 degrees C showed the opposite effect. The general reduct ion observed in the number of nematode larvae due to fungal trapping was 18 -25% and 48-80% for a constant and fluctuating 10 degrees C, 70-96% and 93- 95% for a constant and fluctuating 15 degrees C, and 63-98% and 0-25% for a constant and fluctuating 20 degrees C, respectively.