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Response surface methodology study of the combined effects of temperature, pH, and a w on the growth rate of Trichoderma asperellum
Author(s) -
Begoude B.A.D.,
Lahlali R.,
Friel D.,
Tondje P.R.,
Jijakli M.H.
Publication year - 2007
Publication title -
journal of applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.889
H-Index - 156
eISSN - 1365-2672
pISSN - 1364-5072
DOI - 10.1111/j.1365-2672.2007.03305.x
Subject(s) - mycelium , growth rate , strain (injury) , water activity , chemistry , food science , incubation , horticulture , biology , biochemistry , water content , engineering , geometry , mathematics , geotechnical engineering , anatomy
Aims: To evaluate the influence of environmental parameters (water activity a w , temperature, and pH) on the radial growth rate of Trichoderma asperellum (strains PR10, PR11, PR12, and 659‐7), an antagonist of Phytophthora megakarya , the causal agent of cocoa black pod disease. Methods and Results: The radial growth of four strains of T. asperellum was monitored for 30 days on modified PDA medium. Six levels of a w (0·995, 0·980, 0·960, 0·930, 0·910, and 0·880) were combined with three values of pH (4·5, 6·5, and 8·5) and three incubation temperatures (20, 25, and 30°C). Whatever the strain, mycelial growth rate was optimal at a w between 0·995 and 0·980, independently of the temperature and pH. Each strain appeared to be very sensitive to a w reduction. In addition, all four strains were able to grow at all temperatures and pH values (4·5–8·5) tested, highest growth rate being observed at 30°C and at pH 4·5–6·5. The use of response surface methodology to model the combined effects of a w , temperature, and pH on the radial growth rate of the T. asperellum strains confirmed the observed results. In our model, growth of the T. asperellum strains showed a greater dependence on a w than on temperature or pH under in vitro conditions. Conclusion: aw is a crucial environmental factor. Low a w can prevent growth of T. asperellum strains under some conditions. The observed and predicted radial growth rate of strain PR11 showed its greater capacity to support low a w (0·93) as compared with other tested strains at 20°C. This is in agreement with its better protective level when applied in medium‐scale trials on cocoa plantations. Significance and Impact of the Study: This study should contribute towards improving the biocontrol efficacy of T. asperellum strains used against P. megakarya . Integrated into a broader study of the impact of environmental factors on the biocontrol agent–pathogen system, this work should help to build a more rational control strategy, possibly involving the use of a compatible adjuvant protecting T. asperellum against desiccation.