Effects of Chryseobacterium soldanellicola T16E-39 and Bacillus siamensis T20E-257 on Biocontrol against Phytophthora Blight and Bacterial Wilt and Growth Promotion in Tomato Plants

Abstract

Soil borne diseases caused by Phytophthora capsici and Ralstonia solanacearum have threatened growth and productivity of tomato (Solanum lycopersicum), which is one of the most important vegetable crops in the world. It has been reported that plant growth-promoting bacteria (PGPB) enhance disease resistance and plant growth. In this study, we selected two bacterial strains to suppress soil-borne diseases caused by P. capsici and R. solanacearum in tomato plants and investigated the effects of the strains on plant growth and fruit productivity. To this end, we pre-selected 17 potential biocontrol strains out of 363 bacterial strains based on reduction of disease incidence by P. capsici in a radicle assay; and then through a plant assay, two strains, T16E-39 and T20E-257, were selected as biocontrol agents against P. capsici and R. solanacearum in tomato plants. We found that strains T16E-39 and T20E-257 increased plant growth; especially strain T16E-39 significantly increased fruit fresh weight in a plastic-house test and strain T20E-257 had antifungal activity against Sclerotinia sclerotiorum, Botrytis cinerea, P. capsici, Fusarium oxysporum, Alternaria alternata, and R. solanacearum. The two selected strains had ACC deaminase and nitrogen fixation activities; produced indole-acetic acid (IAA) and siderophore, but they could not produce HCN. Based on 16S rRNA gene sequence analysis, T16E-39 and T20E-257 were identified as Chryseobacterium soldanellicola and Bacillus siamensis, respectively. These findings implied that both strains T16E-39 and T20E-257 play important roles in suppressing two soil-borne disease and inducing growth promotion; both can act as biocontrol agents and bio-fertilizer in sustainable agriculture. (C) 2020 Friends Science Publishers