Inoculant quality and its evaluation

Many factors contribute to high quality legume inoculant products. The most important of these include high numbers of live rhizobia capable of nodulation and nitrogen (N-2) fixation with the target host, and minimal or no contamination, A quality inoculant product is easier to achieve when it is prepared in sterile rather than non-sterile carrier. Current minimum standards vary with country, but range from 5x10(7) to 1x10(9) Rhizobium cells g(-1) of freshly prepared inoculant. The most widely accepted standard for numbers of rhizobia delivered per seed are 10(3), 10(4) and 10(5) rhizobia for small, medium and large seeded species, respectively. Various methods, including microscopic examination, plate counts, most probable number (MPN) plant infection tests, and immunological tests, can be used to evaluate inoculant products and ensure that they meet quality standards. Because many manufacturers are unable or unwilling to institute or enforce rigorous internal quality control procedures, it is desirable that the quality of legume inoculant be protected by some form of governmental regulation. (C) 2000 Elsevier Science B.V. All rights reserved.