Root Colonization by Inoculated Plant Growth-Promoting Rhizobacteria

Certain rhizobacteria referred to as 'plant growth-promoting rhizobacteria' (PGPR) can contribute to the biological control of plant pathogens and improve plant growth. They enhance root development either directly by producing phytohormones, or indirectly by inhibiting pathogens through the synthesis of different compounds. PGPR are likely to be of great interest in sustainable crop protection and have drawn much attention in recent years. However, the use of these bacteria to protect crops sometimes fails because rhizobacteria are unable to recolonize the rhizosphere of inoculated plants. The colonization of roots by inoculated bacteria is an important step in the interaction between beneficial bacteria and the host plant. However, it is a complex phenomenon influenced by many biotic and abiotic parameters, some of which are now apparent. This paper summarises knowledge on rhizosphere colonization by PGPR.     

Influence of Methyl Bromide Fumigation on Microbe-induced Resistance in Cucumber

Field experiments were conducted to evaluate growth promotion and induced systemic disease resistance (ISR) in cucumber mediated by plant growth-promoting rhizobacteria (PGPR) with and without methyl bromide soil fumigation. In both fumigated and nonfumigated plots, numbers of cucumber beetles, Acalymma vittata (F.), and the incidence of bacterial wilt disease, caused by the beetle-transmitted pathogen Erwinia tracheiphila , were significantly lower with PGPR treatment compared with the nonbacterized control. However, in PGPR-treated plots, the incidence of bacterial wilt was more than 2-fold lower in the nonfumigated treatments compared with fumigated treatments, indicating that the level of PGPR-mediated ISR was greater without methyl bromide fumigation than with methyl bromide. Cucumber plant growth at 21 days after planting was greater in fumigated plots than in nonfumigated plots; however, plant height values in the nonfumigated, PGPR treatments and the fumigated, PGPR treatments were equivalent. This suggests that PGPR treatment compensated for delayed plant growth that often occurs in nonfumigated soil. These results indicate that, in cucumber production systems, withdrawal of methyl bromide will not negatively impact PGPRmediated ISR, and also that PGPR may have potential as an alternative to methyl bromide fumigation.