Biological inoculants in Australia: from rhizobia for legumes to PGPR and disease-suppressive products

Abstract

Australian farmers embraced rhizobial inoculants for legumes during the early part of the 20th century. The soils that they farmed were generally low in plant-available N and the use of fertiliser N was not an affordable option. Thus, the legumes grown had to supply N for themselves; that is they had to be capable of effective N2 fixation. Currently, Australian farmers inoculate legume seed sown on about 2.5 million hectares annually using a variety of products from a number of manufacturers. Following decades of relative stability, the Australian inoculants industry has seen substantial changes during the past six years. There are now four major manufacturers, two of which are multi-national. They collectively produce and market peat, liquid and granular products for use on-seed and in-furrow. Two of the manufacturers market inoculants for legumes containing rhizobia and a second microorganism (co-inoculants). Pre-inoculated seed has also emerged as a major market. The longstanding relationship between the manufacturers and the independent, government quality testing laboratory has been affected by these changes as has the issue of industry-wide quality assurance (QA). In response, a new initiative aims to bring a degree of coordination within the industry through the formation of a peak body - the Microbial Manufacturers & Marketers Association (M3A). There is also potential in Australian agriculture to increase the occurrence of specific, beneficial microorganisms in the soil by applying them as inoculants, similar to the way that rhizobia is applied to the soil with sown legume seed. Australian farmers are receptive to biological alternatives to chemical inputs, particularly related to the control of plant pathogens. Soil and stubble-borne diseases of cereals can decimate yields with annual losses estimated to cost farmers hundreds of millions of dollars annually. New projects aim to develop bacterial and fungal inoculants that may have one of a number of modes of action, eg plant disease suppression through production of antibiotics or other means, plant root stimulation through production of phytohormones etc. To comply with the registration requirements, associated research is focussed on efficacy and modes-of-action, the ecology of the microbes once introduced into the soil and related to the target host plant and existing soil biota, toxicology, and, finally, commercial manufacture, QA and formulation.