Effects of Bacillus amyloliquefaciens Pb-4 on growth and physiological characteristics of tomato under the condition of plug seeding

Objectives Bacillus amyloliquefaciens Pb-4, as a kind of bacillus strain, can antagonize the fusarium wilt of tomato and promote plant growth. The objective of this study was to investigate the promotion effect of Pb-4 on plant growth and its appropriate application dosage.

Methods The experiment consisted of 5 treatments, including 0, 20, 60, 100 and 200 mL/L matrix according to the dosage levels of the fermentation broth. The seedling growth index, physiological parameters and their relationship were investigated and analyzed using conventional physiological techniques.

Results 1) The application of Pb-4 fermentation broth promoted the tomato growth. The highest tomato height, stem diameter, leaf area and shoot dry weight were observed in the 100 mL/L treatment and were increased by 28.5%, 23.9%, 57.4% and 42.4% compared to CK, respectively. The largest root surface area and volume were observed in the 20 mL/L treatment, and were increased by 16.9% and 34.2%. 2) The Pb-4 application increased the contents of chlorophyll, GA₃ and IAA. Compared to CK, the chlorophyll content was increased by 12.6% in the T100 treatment, followed by 9.4%, 7.6% and 5.8% in the 60, 200 and 20 mL/L treatments compared to CK, respectively. The IAA and GA₃ contents in stems and leaves of tomato seedlings were increased by applying fermentation liquid but those in roots were not significantly affected. 3) Correlation analysis showed that the tomato height, stem diameter, leaf area and shoot dry weight were significantly correlated with leaf photosynthetic pigment contents, the contents of IAA and GA₃ in stems, and GA₃ in leaves. The root dry weight was significantly correlated with photosynthetic pigment contents, and IAA contents in stems. The root surface area was significantly correlated with the contents of IAA in leaves and GA₃ in roots. The root volume was significantly correlated with the IAA contents in leaves.

Conclusions Bacillus amyloliquefaciens Pb-4 could promote shoot and root growth of tomato seedlings, improve their photosynthetic pigment, IAA and GA₃ contents. The appropriate concentration is 100 mL/L fermentation broth of Bacillus amyloliquefaciens Pb-4 for plug seedings in tomato.