Statistical analysis All statistical analyses were carried out using SPSS 16 software. A fully randomised design with four replications was used for the growth chamber experiments. Critical differences were calculated at p ≤ 0.05 and Duncan’s multiple range tests were employed to test the significant differences between treatments.
Results Evaluation of the colonisation potential of two B. pumilus strains Based on the results of the preliminary experiments, the antifungal activity of two strains including ToIrFT-KC806241 and ToIrMA-KC806242 was confirmed against F. oxysporum f. sp. lycopersici which is the main fungal pathogen of tomato in our area. Chitinase production was recorded as a significant clear zone around both colonies. Moreover, both stains can form biofilm in the relate plate. The strain ToIrMA is a more efficient biofilm producer than another one. The results of the present study also demonstrated that ToIrMA and ToIrFT strains could colonise and survive in tomato rhizosphere with the density of 3.1 × 104 and 2.8 × 104 CFU/g of root, respectively, after one month.
Phytostimulatory effect of B. pumilus strains Amount of auxin production varies between two bacterial isolates (Table 1). The ToIrMA-KC806242 strain produced higher amount of auxin at 1000 μg/ml L-tryptophan.
The pattern of production of indole acetic acid was also determined in ToIrMA and ToIrFT at different times. Their ability to produce IAA increased up to 96 h and thereafter a continuous decrease after 120 h of incubation was observed as shown in Figure 1. Isolates ToIrMA and ToIrFT produced, respectively, 29.7 and 23.76 μg/ml of IAA at the 96 h of incubation. After that time, the range of IAA production decreased in both isolates. Siderophore production was determined by formation of an orange halo on the medium which was positive for ToIrMA on the CAS agar solid medium. None of the isolates were able to solubilise phosphate compounds (TCP, Fe–P) and produce cyanide hydrogen (Table 1).