Soil salinity has become a serious threat to crop growth and productivity and has aggravated the gap between sustainable food supply and population growth. Application of plant growth-promoting rhizobacteria (PGPR) has emerged as a novel way of alleviating the harmful effects of salt stress and improving soil nutrients. The aim of this study was to study the effects of exposure cucumber seedlings at one co-inoculation of Bacillus licheniformis and B. subtilis, a mitigation of salt stress in cucumber seedlings. In this study, we isolated salt tolerant (NX-3 and NX-4) and growth-promoting (NX-48, NX-59, and NX-62) bacteria from the rhizosphere of cucumber. NX-3 and NX-59 were identified as B. licheniformis, and NX-4, NX-48 and NX-62 were identified as B. subtilis. Under salt stress, relative to non-inoculation, co-inoculation with B. licheniformis and B. subtilis increased stem diameter and plant fresh weight. Moreover, the concentration of substrate available phosphorus increased (except for NX4-59). The catalase and sucrase activities of NX4-62 were the highest. Meanwhile, NX3-62 and NX3-59 had the highest phosphorus content and NX3-59 had the highest urease activities. Comprehensive analysis indicated that NX4-62 and NX3-59 showed the best effect on promoting cucumber seedlings growth, activating substrate nutrients, and alleviate salt stress in seedlings of cucumber.

Aims:The effect of Bacillus strains combined with fish protein hydrolysates (FPHs) on cucumber root rot disease, seedlings growth and substrate nutrients was investigated. Methods and Results:We isolated three strains capable of mitigating cucumber root rot disease, XY-1 and XY-13 strains were identified as B. amyloliquefaciens, and XY-53 strain as B. subtilis. In the absence of bacteria, The 200×dilution (5 ml L −1 ) of FPHs was the optimum concentration for improving cucumber seedlings growth.In vivo antibiosis tests showed that combined bacteria alongside FPHs inhibited the pathogen growth by 85%~90%, higher than individual bacteria. The FPHs combined either with XY-1 and XY-53 strains or with XY-13 and XY-53 strains promoted seedlings growth under infection, whereas FPHs combined with a mixture of XY-1, XY-13 and XY-53 strains showed the highest total phosphorus and organic matter content in substrate. Moreover, FPHs combined with XY-53 strain increased urease activity, while combined either with XY-13 and XY-53 strains or with XY-1, XY-13 and XY-53 strains increased sucrase activity under infection. Conclusions: FPHs combined with B. amyloliquefaciens and B. subtilis had great potential to suppress growth of root rot and promote cucumber seedlings and increase substrate nutrient content.Significance and Impact of the Study: Co-inoculation of B. amyloliquefaciens and B. subtilis with addition of FPHs is a good strategy for maintaining healthy crops.