Abstract
Cucumber is one of the vine crops widely consumed in Iran both as fresh fruit and in preparing different sorts of salads and cucumber pickles. Cucumber root and crown rots are the main constraints of the plant cultivation worldwide. Due to the nature of being soilborne the disease agents, their chemical control is not only ineffective but also destroys the environment. Biological control and resistance induction in plants are the combat approaches to these diseases. In the research, the biocontrol influence of Trichoderma harzianum, T. virens, Pseudomonas fluorescens and Bacillus subtilis were investigated against cucumber root and crown rots caused by Fusarium oxysporum f.sp. radicis-cucumerinum, Pythium aphanidermatum and Phytophthora melonis in both laboratory and greenhouse. Dual- culture and volatile compounds tests were used to evaluate the antagonistic power of these strains in the laboratory. The results showed that the highest inhibition zone with a diameter of 18 mm was induced by B.subtilis versus P. aphanidermatum. T. harzianum, which had the highest rate of inhibitory growth in the laboratory, was used for greenhouse studies. In different treatments, the disease severity and cucumber yield components of greenhouse grown cucumber, Negin variety, was evaluated in a completely randomized design with four replicates. Statistical analysis of the data was carried out using the SAS software and the averages were compared with healthy control plants by Duncan test at 5% probability level. The results revealed that this antagonistic agent had the highest and lowest disease control on F. oxysporum f.sp. radicis-cucumerinum and P. melonis with 32.81 and 18.75 percentage, respectively. Treatment related to Trichoderma-inspired healthy plants had the greatest effect on the increase of yield components in cucumber, while the infected plants with F. oxysporum f.sp. radicis-cucumerinum had the lowest yield. The disease severity index and root fresh weight showed a high correlation in different treatments. There is a high correlation between Trichoderma's antagonistic mechanisms under laboratory conditions and their biocontrol ability in greenhouse conditions in the case of F. oxysporum f.sp. radicis-cucumerinum.