The effect of Bacillus subtilis A13 and Streptomyces griseus 2-A24 on the yield of cereals and carrots was studied. The organisms, both antagonistic to Rhizoctonia solani, were applied individually to barley, oats and wheat for sowing at three sites with a known incidence of R. solani. Root disease was not effectively controlled, yet the seed treatments increased grain yield and dry matter production at one site, advanced time of heading at another site and increased tiller number at two sites. Evidence was obtained that the organisms persisted on pericarps in soil for 5 weeks after sowing. In subsequent trials application of B. subtilis and S. griseus in combination with a pellet treatment increased marketable yields of carrots by 48% and 15% respectively over controls. Addition of the organisms to seed without pelleting increased yields by 17% over controls. These results indicate a non-specific effect of B. subtilis and S. griseus, since they increased growth of plants belonging to two different families, the Gramineae and Umbelliferae, in different soils.

Biological control of Rhizoctonia solani on wheat by seed inoculation with microorganisms was investigated. Initially inoculants were selected from bacteria and actinomycetes isolated from two soils and screened for antagonism to R. solani on agar. Of 148 isolates tested on agar, 96 were antagonistic to R. solani and of these 42 were added to pasteurized soil sown with peppers and inoculated with the pathogen. Seven isolates which controlled disease were screened further as seed inoculants of wheat in pasteurized and field soils inoculated with R. solani. Four inoculants, viz. Streptomyces griseus 2-A24 and three Bacillus subtilis isolates 1-B80, 1-B77 and 1-B68, significantly reduced symptoms caused by R. solani and also increased grain yield and dry matter of wheat. S. griseus 2-A24 and B. subtilis 1-B80 increased grain yield by 30% over controls. The magnitude of these differences suggests that biological control and growth stimulation are involved in yield increases.

In two controlled experiments conducted in 1960 and 1961 respectively, the ability of recognized root pathogens to induce premature ripening ("deadheads") of wheat was compared with that of the barley yellow dwarf virus, a hitherto uninvestigated factor in this regard. In both experiments the heads of virus-infected plants ripened earlier than those of plants inoculated with fungal pathogens, and grain in heads which were not completely sterile was extremely shrivelled. However, it was impossible to decide by visual observation when normal ripening commenced. To overcome this difficulty a formula for the classification of prematurely ripened heads, on a weight per floret basis, was used for the statistical analysis of the results. On this quantitative basis it was found that the virus significantly reduced the yield of grain (l% level), but there was no interaction between the virus and any of the root-rot fungi. The fungus, Rhizoctonia solani, Kuehn, also significantly reduced the yield in both experiments (5% level) and Fusarium culmorum (W.G.Sm.) Sacc. caused a reduction (5% level) in the 1960 experiment. There was a significant interaction (5% level) between these fungi in the 1961 experiment. The fungi Ophiobolus graminis Sacc., Helminthosporium sativum Pamm., King & Bakke, and Curvularia ramosa (Bainer) Boed., did not significantly reduce grain yield in either experiment. All fungi were recovered, but to a varying degree, from the roots of inoculated plants.

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