Employing a rapid agglutination test, serogroups of Rhizobium japonicum were distinguished by using homogenized nodule suspensions as antigens. Most of the nodules obtained from soybeans on Iowa soils were in one of four serogroups: 123, 135, 31, and 3. Serogroup 123 was dominant, averaging 52% in all soils except a few highly alkaline soils dominated by 135. Serogroups 3 and 31 were found in small percentages in many soils. Serogroups 71a, 110, and 117 were rarely found. Generally, variability between soil sites on the same soil type was less than variability between soil types. Serogroup 123 occupied from 79 to 100% of the nodules in 4 soybean fields on Webster, and was present in about 40% of the nodules from Clarion, Winterset, Shelby, and Lagonda soils. In a soil toposequence grading from Clarion (pH 5.9) to Harpster (pH 8.3), 80% of the nodules from Clarion were serogroup 123, but 92% of the nodules from Harpster contained serogroup 135. The predominance of serogroup 123 or 135 seemed related to soil pH. In sterile soil, serotype 123 grew well at pH values from 6.1 to 8.2; in liquid culture, it had a lower pH limit of about 4.0. In sterile soil, growth of serotype 135 appeared best around pH 8.2; in liquid culture, it had a lower pH limit of 5.5. Cropping with soybeans appeared to increase the percentage of 123, but soil type had a greater influence on the distribution of serogroups than did previous cropping history. The factors which affect the dominance of a serogroup in soybean nodules need further evaluation.

Twenty‐four isolates of Actinomycetes were taken from soil of an experimental soybean field. Susceptibility of eight Rhizobium japonicum strains to antimicrobial action of the Actinomycete isolates on yeast extractmannitol agar was tested. Twenty of the isolates produced no inhibition of rhizobia. Isolate E1 antagonized only R. japonicum strain 76 and isolate E8 was antagonistic to all strains. Two other isolates showed slight inhibition of strains 122 and 123. Infectivity of rhizobia on soybean variety Kent was evaluated in the presence of selected Actinomycete isolates. In autoclaved soil, reductions in nodule numbers produced by rhizobial strains were 35% and 53%, when Actinomycete E8 was introduced into the soil at the time of planting and 28 days before planting, respectively. Generally, similar results were obtained in sterilized sand jars. The results suggest that anti‐rhizobial soil microorganisms in a particular soil play a role in the establishment of specific rhizobial strains.

No abstract

Dnrr.rncr, S.lI-ru M., Coor, F. D. eNo WEssrE,n, G. R some Alberta soils. 19'16. Alfalfa disease in Attempts were made to evaluate the potential biological factor causing poor growth (stunting) of alfalfa (Medicago sativa L.) on some soils in central Alberta.Paratylinchus projectus which associates with stunted alfalfa was extracted from an affected soil. Alfalfa seedlings grown in sterilized sand culture assemblies were inoculated with P. projeclas alone and in combination with dilutions from sterilized and non-sterilized affected and normal soils. Other studies included the effects of various sterilized and non-sterilized soil dilutions from an affected soil on plant growth and incidence of alfalfa stunting symptoms. Results indicate that P. projectus is not the biological factor causing alfalfa stunting. Typical stunting symptoms were observed on plants receiving non-sterilized This experiment was conducted under growth chamber conditions with light intensity of 279lx (3,000 ft-c), l6-h day length, day temperature 21 C and night temperature 16 C. The purpose was to determine whether there was an indigenous organism(s) which is primarily responsible for the incidence of stunting.Ancther objective was to determine the appropriate level of intensity or inoculum load required to produce stunting.A special glass culture tube assembly was used (Fig. 1)

Alfalfa seedlings were grown in soil collected from a field depicting "alfalfa sickness." A vigorous line (resistant) and a less vigorous line (susceptible) were selected for study. Both lines were grown in sterilized sand subjected to three treatments: control; inoculated with the fungal isolate; inoculated with a soil suspension from alfalfa "sick" soil. Both inocula severely stunted growth and produced severe root lesions on the susceptible line but had no effect on the resistant line, indicating good resistance to the disease.A disease of alfalfa in central Alberta, known as "alfalfa sickness," has been reported and described by Webster et al. (1967). Recently, Damirgi et al. (1976, 1978)