Response of Cowpea, Soya Beans and Groundnuts to Non-Indigenous Legume Inoculants

<p>The use of inoculants is a critical strategy in legume production. In Zambia, inoculants are particularly used for the production of non-promiscuous genotypes of soya beans, but rarely for cowpeas and groundnuts. This study evaluated the response of soya beans, cowpeas and groundnuts to Biofix legume inoculants. Seeds were inoculated at the recommended or double the recommended rate at planting. Plants were grown under greenhouse conditions in a Completely Randomized Design for 7 weeks. Control, non-inoculated seeds were also planted and plants grown under the same conditions. At 7 weeks, nodule number and fresh weight per plant, nodule effectiveness (pinkness/redness), and above ground biomass were determined. Biologically fixed nitrogen was determined using the Nitrogen Difference Method. Nodule number and fresh weight per plant were higher at the recommended rate of Biofix application for soya beans and at both rates for groundnuts, while there was no effect on nodule fresh weight at either rate in cowpeas. All representative nodules assessed were effective. There was no significant benefit in inoculating seeds of the three legumes with Biofix on above ground biomass and biological nitrogen fixation. These results could suggest that possibly, the introduced strains though with a stronger nodulation competitiveness, were not as effective at fixing nitrogen as the indigenous strains in the soils in which soya beans, cowpeas and groundnuts have been repeatedly grown before. This could be an indication that sufficient and appropriate effective strains are already present in this soil. In general, the results suggest that to obtain the full benefits of biological nitrogen fixation, legume growers need to be provided with the correct inoculant, where required. Further work under field conditions is recommended to confirm these findings.</p>

Age of peat-based lupin and chickpea inoculants in relation to quality and efficacy

Extension of the current 12-month expiry of rhizobial inoculants in Australia to 18 months would have commercial benefits for the manufacturers and resellers. The dilemma, however, is that numbers of rhizobia in the inoculants decline over time and individual cells may lose efficacy. The research undertaken in this study shows the effect of lupin and chickpea inoculant age (i.e. 0, 6, 12, 15 and 18 months old) on numbers of rhizobia, rhizobial cell characteristics and efficacy. For the latter, assessments included colony size on plates, survival on inoculated beads, and infectiveness and effectiveness in field experiments at 3 sites. Assessment of commercially produced inoculants at the Australian Legume Inoculants Research Unit (ALIRU) laboratory indicated that, on average, chickpea and lupin inoculants had counts of about log10 9.6 when fresh, delivering >log10 6 rhizobia/seed. At 12 months, the average counts had fallen to log10 9.4, delivering slightly less than log10 6 rhizobia/seed. By 18 months, average counts were log10 9.3, delivering log10 5.9 rhizobia/seed. The lines of best fit indicated decline rates of 0.0005 log10 units/day. We found no evidence that the rhizobia in the older inoculants (i.e. >12 months old) had lost any ability to grow on nutrient agar, survive on inoculated beads, and nodulate and fix nitrogen with the host plant. While the chickpea and lupin inoculants produced currently in Australia are as efficacious after 18 months of storage at 4°C as they are when fresh, efficacy of other inoculant types may fall below acceptable levels at <12 months.

The legume inoculant industry and inoculant quality control in Australia: 1953 - 2003

Fifty years have passed since the first commercial inoculants were manufactured in Australia. Before 1953, various Government Agencies supplied mostly agar cultures with New South Wales Department of Agriculture issuing the first peat-based inoculants. There are no data to indicate the quality of these inoculants, but in the early commercial cultures rhizobia were often outnumbered by contaminants and field failures were widespread. A comprehensive system of quality control was developed from discussions between CSIRO and the University of Sydney. Succeeding quality control bodies have continued on the basis of the original scheme. It set inoculant standards, approved and supplied mother cultures to manufacturers annually, tested all batches of peat inoculants before sale and sampled inoculants at the point of sale. In this paper we describe the history of Australian legume inoculants, list the commercial firms and key people involved and the period during which they were active. We tabulate the strains involved, indicate the period of their use and highlight some of the problems encountered with them and with inoculant production. We indicate the personnel who have been particularly active in the quality control of inoculants, the funding bodies who have supported the work and stress the reliance of the control laboratories on the help of many agricultural scientists in Australia. An important part of the control scheme has been the implementing of standards without resort to legislation. This has depended on the cooperation of the manufacturers involved and has allowed flexibility in applying the standards.

Levels and identities of nonrhizobial microorganisms found in commercial legume inoculant made with nonsterile peat carrier

Sixty samples of commercial North American legume inoculants manufactured for sale in 1994 using nonsterile peat as carrier were tested for Rhizobium (or Bradyrhizobium) content and nonRhizobium biological contaminant load. Products of three major producers of such inoculants for sale in Canada were examined. Viable Rhizobium content varied from 5.6 × 105 to 8.1 × 109 cells/g, while the contaminant load varied from 1.8 × 108 to 5.5 × 1010 cfu/g. Most of the inoculants contained more nonrhizobial organisms than they did rhizobia. Identifications were made of the most numerous nonrhizobial bacteria occurring in 100 samples of inoculants collected in 1993 and 1994. The most commonly identified contaminant was Xanthomonas maltophilia. Pseudomonas aeruginosa, Klebsiella pneumoniae, and Enterobacter cloacae were also found at high levels in some products. Contaminant organisms capable of inhibiting rhizobial growth in plate culture were found in the products of all three manufacturers.Key words: Rhizobium, contaminant, inoculant.