Bacillus amyloliquefaciens subsp. plantarum KC-1 inhibits Zantedeschia hybrida soft rot and promote plant growth

Abstract

Soft rot disease caused by Pectobacterium carotovora subsp. carotovora (Pcc) is one of the most destructive diseases of Zantedeschia species. The purpose of this study was to manage the disease by using biocontrol agents in the form of Bacillus sp. Successive screenings of 600 isolates yielded strain KC-1 as the best antagonist against Pcc. The strain KC-1 with displayed effective biocontrol activity against phytopathogenic bacteria (Pcc) in in vitro conditions and significantly reduced the soft rot disease in Z. hybrida was identified as belonging to Bacillus amyloliquefaciens subsp. plantarum. When test in vitro, it was able to produce indole-3-acetic and to solubilize inorganic phosphate and potassium. This strain also inhibits pathogen growth in co-culture assay. While applied to soil, KC-1 populations persisted on the leaves of Z. hybrida up to 30 days (103–104 CFU/g leaf fresh weight). Spraying KC-1 with concentration of 3 × 107 CFU/ml has maximum inhibition activity in greenhouse prior to pathogen inoculation. Minimum disease severity index were recorded in plants treated with KC-1 five days before pathogen inoculation. In addition, maximum protective value (PV) for KC-1 were achieved five days before pathogen inoculation, whereas, the minimum PV was observed for biocontrol applications which were used after five days of pathogen inoculation. Moreover, healthy Z. hybrida tubers pre-treated with strain KC-1 demonstrated significantly higher levels of growth and greater number of progeny tubers compared to untreated ones, and lower levels of disease index than treatment of inoculation of pathogen alone. This finding revealed that B. amyloliquefaciens strain KC-1 has great potential as a promising growth promoting and biocontrol agent in Z. hybrida due to its multiple beneficial traits.