Inoculant formulations are essential for successful inoculation with plant growth-promoting bacteria and business opportunities

Abstract

Inoculation of plants with plant growth-promoting bacteria (PGPB/PGPR) either rhizoplane, endophytes and plant symbionts to enhance performance of plants is centuries old. The majority of field inoculations done today are on cereals and legumes. Yet, numerous other crops are inoculated mostly in developing countries. In general, shortly after suspensions of bacteria, the most primitive inoculant, are inoculated into the soil without a proper carrier, the bacterial population declines rapidly for most species of PGPB/PGPR. This phenomenon, combined with production of bacterial biomass, the need to sustain activity in the rhizosphere, and the physiological state of the bacteria at application time, can prevent the buildup of a sufficiently large PGPB/PGPR population in the rhizosphere. These unprotected, inoculated bacteria must compete with the often better-adapted native microflora and withstand predation by soil microfauna. Consequently, a major role in the formulation of inoculants is to provide a more suitable microenvironment, combined with physical protection for prolonged periods to prevent a rapid decline of bacteria introduced into the soil. Inoculants for field-scale use have to be designed to provide a dependable source of bacteria that survives in the soil and become available to the plant, when needed. The first goal when considering inoculation of cereals with PGPB/PGPR is to find the best strain of bacteria or a microbial consortium for the intended effect on the target crop. The next step is to design a specific inoculant formulation for specific target plants and a method of practical application, considering the limitations of the growers. Currently, many inoculants are in the market place, some that substantially improve yield. This inoculation strategy opens significant business opportunities in Asia in general and India in particular.