Rhizobacteria: Influence of cultivar and soil type on plant growth and yield of potato

The influence of potato cultivar and soil type on effectiveness of plant growth-promoting rhizobacteria (PGPR) was examined. Rhizobacteria were isolated from potato roots and tubers obtained from fields with a history of high potato yields. Fluorescent pigment-producing rhizobacteria. identified as strains of Pseudomonas putida and P. fluorescens, were selected for their antibiosis against Erwinia carovotora ssp. carotovora and growth-promoting activity on potatoes. In greenhouse tests, treatments of potato seedpieces and stem cuttings increased shoot dry weight from 1.23- to 2.00-fold and root dry weight from 1.27- to 2.78-fold. Survival of PGPR in the rhizosphere was monitored using antibioticresistant strains. Populations of these strains decreased from 3.6 × 10⁹ cgu g^?1 dry root weight to 4.5 × 10⁵ cfu g^?1 dry root weight 4 weeks after treatment. In field trials, PGPR strains were applied to seedpieces of cultivars Kennebec, Pungo, Red Pontiac and Superior and planted in Cape Fear loam. Plymouth loamy sand or Delanco sandy loam. Significant yield increases of 1.17–1.37-fold over controls were observed in two of three field trials. Variability in plant growth-promoting activity was observed between greenhouse and field trials, and no given treatment combination of PGPR strain, potato cultivar and soil type was consistently better than another.