Recent works suggest that the combination of several PGPRs could be more effective than individual strains as a horticultural product. LS213 is a product formed by a combination of two PGPRs, Bacillus subtilis strain GB03 (a growth-promoting agent), B. amyloliquefaciens strain IN937a (an inducer of systemic resistance) and chitosan. The aim of this work is to establish if the combination of three PGPR, B. licheniformis CECT 5106, Pseudomonas fluorescens CECT 5398 and Chryseobacterium balustinum CECT 5399 with LS213 would have a synergistic effect on growth promotion and biocontrol on tomato and pepper against Fusarium wilt and Rhizoctonia damping off. When individual rhizobacterium and the LS213 were put together, the biometric parameters were higher than with individual rhizobacterium both in tomato and pepper, revealing a synergistic effect on growth promotion, being the most effective combination that of B. licheniformis and LS213. When P. fluorescens CECT 5398 was applied alone, it gave good results, which could be due to the production of siderophores by this strain. Biocontrol results also indicate that those treatments that combined LS213 and each of the bacteria (Treatments: T7 and T8) gave significantly higher percentages of healthy plants for both tomato (T7: 65%) and pepper (T7: 75% and T8: 70%) than the LS213 alone (45% of healthy plants for tomato and 60% for pepper) three weeks after pathogen attack. The effects in pepper were more marked than in tomato. The best treatment in biocontrol was the combination of P. fluorescens and LS213. In summary, the combination of microorganisms gives better results probably due to the different mechanisms used.
The ability of six putative plant growth promoting rhizobacteria, isolated from the rhizosphere of Nicotiana glauca L., to stimulate growth and induce systemic resistance against Xanthomonas campestris CECT 95 in Arabidopsis thaliana L. Col-0 was evaluated. The six bacterial strains significantly reduced the disease symptoms caused by the pathogen compared to the controls, with the best results obtained with the Bacillus strain N11.37 and the Stenotrophomonas strain N6.8. These two strains were tested on A. thaliana NahG plants and jar1-1 and etr1-1 mutants, to elucidate whether the salicylic acid (SA)-dependent or SA-independent pathway was involved in the induction of systemic resistance. The results indicate that N6.8 induces the SA-dependent pathway. For N11.37 it is as yet not clear as in the etr1-1 mutants and NahG plants ISR is not expressed, while in jar1-1 it is. In addition, levels of SA were measured in Col-0 plants treated with N6.8 and N11.37 to confirm whether or not the two strains produced an increased level of SA. N6.8-and N11.37-induced plants showed higher levels of SA than the controls. It is concluded that N6.8 induces a SA-dependent pathway while N11.37 induces a pathway that is both ethylene (ET)-and SA-dependent.
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