Integrated biological and chemical control of grapevine trunk diseases using bacteria and fungicides

Abstract

The grapevine trunk disease (GTD) caused by Fusarium solani isolate GR and Neofusicoccum parvum isolate GR3 have a real threat on grape crops. This study aimed to evaluate and compare the efficiency of biological control agents in combination with low concentration of fungicides to prevent growth of fungi caused GTDs in vitro conditions. Five bacterial isolates, Pseudomonas fluorescence isolate ORS3, Pseudomonas fluorescence isolate PFL, Pseudomonas aeruginosa isolate SH1, Pseudomonas fluorescence isolate 1.2 and Bacillus artophaous isolate BAT demonstrated to be antagonistic against F. solani isolate GR and N. parvum isolate GR3. The isolated bacteria were evaluated as biocontrol agents alone and in combination with the fungicide Strubilurin (Azoxystrobin). In vitro, biocontrol agents were highly tolerant to the fungicide Azoxystrobin, commonly used to control GTD diseases. Azoxystrobin reduced disease symptoms by over 75% at 250 µg/ml, but it had little effect at lower concentrations on F. solani. Combination of the bacterial isolates and Azoxystrobin for N. parvum gave significant control of the disease up to 85% in vitro conditions. e.g: Application of Azoxystrobin at a low concentration (50 µg/ml) in combination with P. fluorescence isolate ORS3 inhibited disease symptoms to 84% on N. parvum, compared with a reduction of 66% obtained with the fungicide alone at 50 µg/ml and about 20% with the biological control alone for N. parvum. However, biological control alone inhibited F. solani to 50%. In this experiment, the treatment was also applied by volatiles produced by the different isolates of 2 bacteria, they gave a good inhibition on F. solani and slightly inhibition on N. parvum. Trichoderma was also experimented as a biocontrol against GTD disease in vitro conditions, The results showed a good efficiency in both dual cultures assay and production of volatile antibiotics in inhibition of mycelium growth of F. solani and middle effect on N. parvum. The average inhibition of fungus caused GTD by Trichoderma in dual culture assay about 70% for F. solani isolate GR and N. parvum isolate GR3 and 42% from volatile antibiotics by Trichoderma for F. solani but N. parvum didn’t have any effect from volatile antibiotics.