Characterization of a novel plant growth-promoting bacteria strain Delftia tsuruhatensis HR4 both as a diazotroph and a potential biocontrol agent against various plant pathogens

Abstract

A novel, plant growth-promoting bacterium Delftia tsuruhatensis, strain HR4, was isolated from the rhizoplane of rice ( Oryza sativa L., cv. Yueguang) in North China. In vitro antagonistic assay showed this strain could suppress the growth of various plant pathogens effectively, especially the three main rice pathogens ( Xanthomonas oryzae pv. oryzae, Rhizoctonia solani and Pyricularia oryzae Cavara). Treated with strain HR4 culture, rice blast, rice bacterial blight and rice sheath blight for cv. Yuefu and cv. Nonghu 6 were evidently controlled in the greenhouse. Strain HR4 also showed a high nitrogen-fixing activity in N-free Döbereiner culture medium. The acetylene reduction activity and 15N 2-fixing activity (N 2FA) were 13.06 C 2H 4 nmol ml −1 h −1 and 2.052 15Na.e.%, respectively. The nif gene was located in the chromosome of this strain. Based on phenotypic, physiological, biochemical and phylogenetic studies, strain HR4 could be classified as a member of D. tsuruhatensis. However, comparisons of characteristics with other known species of the genus Delftia suggested that strain HR4 was a novel dizotrophic PGPB strain.