Rhizobacterial growth and yield promotion of cucumber plants inoculated with Pythium aphanidermatum

Abstract

The potential of rhizobacterial strains to reduce the adverse effects of Pythium aphanidermatum on plant growth and yield was examined under in vitro and greenhouse cropping conditions. Rhizobacterial cultures of 10 strains of Pseudomonas putida, 24 strains of Bacillus subtilis, 4 strains of Enterobacter aerogenes, 1 strain of Bacillus cereus, and 1 unknown bacterial strain were evaluated for antagonism against P. aphanidermatum in laboratory and greenhouse conditions. In a dual culture test on potato dextrose agar, only AG-1 of B. subtilis and strains 2xyta75 and B8 of E. aerogenes were antagonistic to P. aphanidermatum. Under sterile in vitro conditions in pouches, 40 bacterial strains were tested for growth promotion of cucumber (Cucumis sativus) seedlings in the absence of P. aphanidermatum. All bacteria except strain PPG-7-1 of P. putida, strains AGS-3 and AGS-1 of B. subtilis, and strain AG-0 of an unidentified bacterium increased root length of cucumber compared with the P. aphanidermatum inoculated controls. Of the 16 bacterial strains evaluated for antagonistic activity against P. aphanidermatum under greenhouse conditions, only one strain (BACT-0) of B. subtilis increased shoot growth by 9% and weight of cucumber plants by 29% compared with the P. aphanidermatum inoculated controls. The same strain increased the fruit yield by 14% and fruit number by 50% of cucumber plants compared with the P. aphanidermatum inoculated controls. This study has demonstrated that the strain BACT-0 of B. subtilis has the potential to increase growth, fruit yield, and fruit number of cucumber plants inoculated with P. aphanidermatum in soilless culture under near commercial greenhouse conditions.

Keywords:

• plant-growth-promoting rhizobacteria
• PGPR
• Bacillus subtilis
• Pseudomonas putida
• Enterobacter aerogenes
• Kluvera cryocrescens
• Enterobacter agglomerans