Plant-associated bacteria in nitrogen nutrition in crops, with special reference to rice and banana

Abstract

Associative and endophytic bacteria that fix atmospheric nitrogen (diazotrophs) are promising alternatives to synthetic nitrogen (N) fertilizers. Application of those diazotrophic bacteria substantially supplements the N requirement and promotes the growth of crop plants. A large body of literature reveals that bacteria from diverse genera such as Acetobacter, Azoarcus, Azospirillum, Bacillus, Burkholderia, Herbaspirillum, Klebsiella, Rhizobium, and Pseudomonas are capable of N 2 fixation and thus exert beneficial effects on N nutrition, enhanced uptake of other essential nutrient elements, promotion of root growth, and other physiological activities in economically important nonlegume crop plants like rice and banana. Review of literature on the effects of associative diazotrophic bacteria (e.g., Azospirillum sp.) on rice, wheat, and maize indicates that substantial amount of N can be incorporated into these plants by the bacterial inoculants. Similarly, biofertilization by associative bacteria has been found to promote root growth, nutrient uptake, dry matter yield, and fruit quality of bananas (Musa sp. cv. Berangan, AA type). This chapter reviews recent findings on N nutrition, root stimulation, plant growth, and yield by associative and endophytic bacteria in rice and banana. Recent progress in understanding underlying molecular mechanism of N nutrition of plants by the help of diazotrophic bacteria and molecular tools for incorporating N 2 fixing gene into plant associated bacterium or plant will create excellent opportunity for increasing crop productivity of economically important nonlegume crops such as rice, wheat, maize and banana.