The effect of temperature (18˚C -30˚C), water activity (0.85 -1) and pH (4 -9) was studied by dual culture technique on the antagonism of Bacillus amyloliquefaciens and Trichoderma harzianum to Colletotrichum acutatum, responsible of strawberry (Fragaria x ananassa (Weston) Duchesne ex Rozier) anthracnose. The antagonistic bacteria's strains behave significantly and differently according to the parameters studied. These results reveal useful information about the applicability of their biocontrol in agricultural culture with the change of environmental factors.

Biological control of plant diseases makes extensive use of the antagonists. The effectiveness of the control depends on the choice of an effective antagonist strains from criteria of implying a good knowledge of biological peculiarities of the material used. In this study, the antagonistic activities of nine isolates of Bacillus amyloliquefaciens and one isolate of Trichoderma harzianum were tested in vitro against seven strains of Colletotrichum acutatum, the causal agent of strawberry anthracnose. It was found that T. harzianum and B. amyloliquefaciens strains showed the ability to inhibit the mycelial growth of the pathogen by dual culture technique by more than 50 percent. The nonvolatile substances produced by the antagonists showed high inhibition percentages that are more than 99 percent, meanwhile their volatile compounds inhibited the mycelial growth of C. acutatum strains with low inhibition percentages starting from 30 percent except the substances produced by B. amyloliquefaciens Bc2 that showed a high inhibition percentage of more than 70 percent.

The increasingly strict regulation of the use of phytosanitary products and the will of the populations to move towards sustainable development allow bio-sourced products and more particularly for biocontrol in the field of pesticides to progress. The study carried out here concerns the evaluation of the potency of Bacillus amyloliquefaciens Bc2 and Trichoderma harzianum to fight against strawberry cultures infected with anthracnose (Fragaria × ananassa Duch.). The studies were carried out in the laboratory and in the field. The results indicate that B. amyloliquefaciens Bc2 and Trichoderma harzianum TR are effective for the biological control of anthracnose, gray mold and powdery mildew on strawberries grown in field conditions. The increase in plant size and the number of fruits produced with these control agents has also been observed.

Seven Colletotrichum acutatum strains isolated from strawberries were cultivated on various culture media and tested in vitro and in vivo on Fragaria x ananassa for anthracnose symptoms. PDA caused an optimum growth of all isolates, MEA, ML and Strawberry allowed a good but not optimal growth. Czapeck, Sabouraud and the organic medium from potato gave the lowest growth rate of all isolates. PDA allowed a good sporulation of isolates follow-up by strawberry, MEA; in contrast, ML, Czapeck and Sabouraud gave a low sporulation. The fungal development is maximal at 25˚C and 27˚C for all the isolates studied. No growth was observed at 5˚C and 37˚C. The studied strains developed at all pH values. They didn't develop at 0.6, 0.65 and 0.7 aw but mycelial growth was perfect at 1 and 0.95 aw. The in vitro test of the pathogenicity caused by C. acutatum strains on strawberry's leaves showed an increasing percentage of infection with time and different infection rates among C. acutatum strains, strain Ca6 having a pathogenic power very high compared to the other isolates. After in vivo inoculation and incubation of the seedlings, all isolates caused severe symptoms related to anthracnose on leaflets and petioles of the studied strawberry plants.

The effect of nine isolates of Bacillus amyloliquefaciens and one strain of Trichoderma harzianum, TR, on mycelial growth and germination of Colletotrichum acutatum were studied. The nine isolates were identified as Bacillus amyloliquefaciens. The efficacy of isolates was tested, at different concentrations. Results showed that one Bacillus isolates (Bc2) and TR were more effective at the lower concentration tested (3 × 10 5 CFU/ml and 10 5 conidia/ml).