Indigenous Rhizobia Research Articles

Correction - Seed pelleting to improve nodulation of tropical and subtropical legumes. 3. A field evaluation of inoculant survival under lime and rock phosphate pellet on Dolichos lablab

Use was made of a soil, in which the indigenous rhizobia are incapable of nodulating Dolichos lablab, to study nodulation of this species resulting from lime pelleted and rock phosphate pelleted seed after storage for one day and one, two, four, six, and eight weeks at 27�C. Cellofas A was used as sticker and two strains of Rhizobium were compared. From each sowing plants were dug at eight weeks of age, and the treatments compared using the criteria : number of plants in row, per cent plants nodulated, number of nodules per plant, per cent of nodules on the crown and yield of dry matter per row. Rock phosphate pelleting was superior to lime pelleting in survival of inoculant on the seed, survival of plants in the row, and promotion of nodulation. Lime pelleting depressed yield at eight weeks of age but not at four months. Both strains of inoculant survived one month's storage satisfactorily when simply applied with sticker. Total nodule number fluctuated greatly with time of planting, and was inversely related to per cent crown nodulation, suggesting chat soil moisture at planting may have had a significant effect on nodulation. Strong interactions of inoculant strain with pelleting treatment and time of planting stressed the difficulty of interpreting nodulation effects resulting from pel!etinp treatments. Rhizobium strain CB756 was greatly superior to CB159 in survival on stored seed, nodulation criteria, onset of N fixation and yield.

Seed pelleting to improve nodulation of tropical and subtropical legumes. 3. A field evaluation of inoculant survival under lime and rock phosphate pellet on Dolichos lablab

Use was made of a soil, in which the indigenous rhizobia are incapable of nodulating Dolichos lablab, to study nodulation of this species resulting from lime pelleted and rock phosphate pelleted seed after storage for one day and one, two, four, six, and eight weeks at 27�C. Cellofas A was used as sticker and two strains of Rhizobium were compared. From each sowing plants were dug at eight weeks of age, and the treatments compared using the criteria : number of plants in row, per cent plants nodulated, number of nodules per plant, per cent of nodules on the crown and yield of dry matter per row. Rock phosphate pelleting was superior to lime pelleting in survival of inoculant on the seed, survival of plants in the row, and promotion of nodulation. Lime pelleting depressed yield at eight weeks of age but not at four months. Both strains of inoculant survived one month's storage satisfactorily when simply applied with sticker. Total nodule number fluctuated greatly with time of planting, and was inversely related to per cent crown nodulation, suggesting chat soil moisture at planting may have had a significant effect on nodulation. Strong interactions of inoculant strain with pelleting treatment and time of planting stressed the difficulty of interpreting nodulation effects resulting from pel!etinp treatments. Rhizobium strain CB756 was greatly superior to CB159 in survival on stored seed, nodulation criteria, onset of N fixation and yield.

WHITE CLOVER AND HILL LAND IMPROVEMENT

As a preliminary step in the development of improved bred varieties an examination has been made of the factors which contribute to the success or failure of white clover (Trifolium repens) in hill land reseeding. Severe restrictions are placed on clover performance and N fixation in many hill areas in Britain by the poor climate, the low pH and exchangeable base status of the soils and the low frequency of effective indigenous Rhizobium strains.Agronomic solutions to some of these problems exist, but experience in mid‐Wales suggests the need for new bred varieties with improved adaptation to the prevailing conditions, particular attention being directed to the limitation of N fixation by low soil temperature.

Rhizosphere relationships of subterranean clover. I. Interactions between strains of Rhizobium trifolii.

A study was made of a number of effective and ineffective strains of Rhizobium trifolii in association with subterranean clover (Trifolium subterraneum L.), variety Bacchus Marsh. Where these were inoculated singly into sterilized soils in pot experiments conducted in the greenhouse, typical effective, ineffective, or intermediate plant reactions were obtained. Where more than one strain was inoculated, competition between strains took place and was reflected in nodule pattern and plant reaction. Some strains consistently failed to produce appreciable nodules in the presence of other rhizobia, some showed modification to varying degrees, and some were unaffected. Such behaviour was found to be closely linked with the ability of the strain to proliferate in the rhizosphere of the host plant, and placement of inoculum was shown to influence plant reaction. The concept of "incursion" as a property of a rhizobial strain is suggested. An incursive strain is one able to migrate from the initial site of inoculation and establish an adequate population in the root zone of the susceptible host despite the presence of active elements of the indigenous microflora and microfauna, including antagonistic and predatory forms. The property of incursion is independent of considerations of efficiency of nitrogen fixation or virulence for the host plant. Strains of rhizobia which are poorly incursive may fail to infect the host upon which they have been inoculated if subject to competition from indigenous rhizobia already established in the soil. The necessity of assessing properties of virulence and incursion as well as efficiency of nitrogen fixation in selecting rhizobia for purposes of commercial inoculation is stressed, and the methods of making such tests are discussed.