Systematic Screening Strategies for Identifying Elite Plant Growth Promoting Rhizobacteria for Coconut (Cocos nucifera L.)

Abstract

Elite strains of plant growth promoting rhizobacteria were proficiently selected based on the strategic screening approaches. These included in vitro testing for plant growth promotion attributes, seedling bioassay under controlled and under greenhouse conditions. A total of 483 morphologically distinct bacteria [156 rhizosphere fluorescent Pseudomonas spp. (RSF), 206 rhizosphere Bacillus spp. (RSB) and 121 endophytic Bacillus spp. (EB)] were isolated from the roots and rhizosphere soil of coconut palms growing in different states of India. These were characterized for various plant growth promotion traits that have direct and indirect effects on plant growth. All the isolates were assessed and given scores based on their in vitro assay of plant growth promotion traits. A total of 129 isolates, which secured more than 11 points, were further selected for seedling bioassay under controlled conditions. Greenhouse trial was conducted with 72 isolates and results further proved the efficiency of screened isolates for plant growth promotion. This strategic screening helped in shortlisting a total of 20 best PGPR (7 fluorescent Pseudomonas spp. and 13 Bacillus spp.) out of 483 isolates. The present study clearly showed that the rhizosphere of coconut palms harbour varied populations of fluorescent pseudomonads and Bacillus spp. that possess diverse plant growth promotion properties, and some of the efficient ones could be developed in to bioinoculants for use in coconut nurseries and plantations.