Screening and risk assessment of biological control agents against bacterial wilt of ginger

Abstract

Bacterial wilt caused by Ralstonia pseudosolanacearum race 4 is a highly destructive disease in ginger. To screen for biological control agents of the disease, 118 bacteria were isolated from different cultivating soils. First, the suppressive activity of soil bacteria on lesion development by R. pseudosolanacearum was evaluated using ginger leaves. Subsequently, a tobacco hypersensitive reaction test was performed for risk assessment in plants. After the clonality test by repetitive element sequence-based PCR, 12 screened isolates were inoculated into silkworm larvae as a preliminary risk assessment in animals, and we observed that five isolates did not cause a lethal effect. Finally, based on the results of the disease suppression test in infested soil, Pseudomonas sp. 008 was selected as the most suitable isolate for biological control. To ascertain the taxonomic position of the isolate, biochemical and physiological tests, multilocus sequence analysis, and average nucleotide identity with related species analysis were performed. Our results suggest that Pseudomonas sp. 008 is a novel species belonging to the P. mandelii subgroup of the P. fluorescens group. Risk assessment and taxonomic approaches with robust resolution demonstrated in the present study are expected to contribute to the efficient screening of biological control agents.