Rhizosphere Microorganisms: Application of Plant Beneficial Microbes in Biological Control of Weeds

Abstract

Weeds usually result in average ~ 20–37% losses of the world’s agricultural output, and therefore, weed control is indispensable in every crop production system. For weed management, usually chemical herbicides are applied, but their indiscriminate use causes environmental problems and human health hazards. Moreover, continuous use of herbicides may lead to evolution of resistant weed biotypes and shift in the weed flora. Thus, biological control of weeds is an alternate eco-friendly method of weed management, in which microorganisms or their products are used to suppress the growth of weed species. Many rhizosphere microorganisms including Pseudomonas aeruginosa, P. fluorescens, Erwinia herbicola, Alcaligenes sp., strains of Xanthomonas campestris pv. poannua, Pseudomonas syringae pv. tagetis, Serratia plymuthica, and S. marcescens as well as the fungi including Colletotrichum gloeosporioides, Aeschynomene virginica, Phoma chenopodicola, and Exserohilum monoceras have been characterized as bioherbicides. These rhizosphere microorganisms have been found to suppress the growth of weeds by reducing weed density, biomass, and its seed production. Various metabolites produced by microorganisms such as cyanide, organic acids, secondary metabolites (antibiotic 2, 4-diacetylphloroglucinol), and plant growth regulators, including auxins (indole acetic acid and δ-aminolevulinic acid), have been found to inhibit seed germination, seedling growth, and suppression of weed plant growth. Bacterial and fungal microbes also produce a wide array of phytotoxins that may cause mortality of weed plants. Many of the microorganisms have been released as commercial bioherbicides for different crops. Thus, there are immense possibilities for characterizing and developing novel microbial bioherbicides that could reduce the application of chemical herbicides for weed control in sustainable agriculture.