Exogenous Inoculation of Seed with Plant Growth-promoting Rhizobacteria Effectively Enhanced Growth of Cucumber in a Greenhouse

Abstract

Cucumber (Cucumis sativus L.) production in most countries remains unprofitable due to poor growth and low yields resulting from low soil fertility. Concern over environmental contamination and human health hazards posed by increased use of chemical fertilizers requires the development of an alternative strategy to increase food production. The study was conducted to assess the effectiveness, and consistency, of plant growth-promoting rhizobacteria (PGPR) strains in enhancing growth promotion of cucumber plants in a greenhouse. The in-vitro germination bioassay was conducted on eight potential PGPR strains. The effectiveness of the two most efficacious PGPR strains (Pseudomonas aeruginosa OG04 and Bacillus subtilis MO07) on cucumber plants was repeatedly evaluated in the greenhouse for three trials using seed bacterization and soil inoculation methods. Data on plant heights, leaf lengths, leaf numbers, number of branches, root weights and shoot weights were collected and analysed. The seed germination bioassay showed that cucumber seeds inoculated with potential PGPR strains had significantly higher percentage germination rate (16.20% - 53.30%) and vigour index (18.30% - 114.70%) than un-inoculated seeds. Inoculation of cucumber with P. aeruginosa and B. subtilis significantly (p ≤ 0.05) increased the plant heights (4.40 – 28.70%), leaf numbers (9.10 – 33.30%), leaf lengths (5.60 – 42.50%), fresh root weights (20.90 – 62.40%), dry root weights (29.50 – 113.30%), fresh shoot weights (13.20 – 54.30%) and dry shoot weights (46.40 – 100.0%) over un-inoculated plants in all trials. Pseudomonas aeruginosa OG04 and Bacillus subtillis MO07 could be exogenously applied as microbial inoculants to promote growth of cucumber under greenhouse conditions.