A total of seven yeast strains were isolated from rhizosphere soils of soybean plants cultivated at different localities of El-Minia Governorate. Strains were tested for their capability to promote growth of soybean plant in pot experiments containing sterilized soil. Results showed that all the seven tested yeast strains could promote soybean plant growth but with different degrees compared with control. Only two strains of yeast (Saccharomyces cerevisiae and Torulaspora delbrueckii) had high superiority for promotion of soybean growth, therefore, these two yeast species were selected for further studies in field trials.
Results of field trials revealed that Saccharomyces cerevisiae and Torulaspora delbrueckii affected all growth parameters and yield traits of soybean plants significantly. After 30 days from seed germination, they increased plant root and shoot growth, their fresh and dry matter, leaf surrounding, photosynthetic pigments (Chlorophyll a, b, and carotenoids). After 50 days, number of nodules per plant root and its dry weights were also increased.
Also, results revealed that, treatment with S. cerevisiae and T. delbrueckii increased plant height, number of branches, number of fruit clusters, number of pods, number of seeds, weight of seeds, hundred seed weights, and seed production/feddan.
Of interest was the seed quality of treated plants, its total, soluble and insoluble proteins, oil and Tannic acid contents. In vitro indol-3-acetic acid and polyamine production in synthetic medium were detected.
In conclusion, yeast species of Saccharomyces cerevisiae and Torulaspora delbrueckii represent promising candidates for successful biofertilizers and could be used for sustainable agriculture in the future.