Evaluation of plant-derived preparations and microorganisms as seed treatments for control of covered kernel smut of sorghum (Sporisorium sorghi)

The agents studied included three commercial plant-derived preparations (Tillecur, Milsana and Quillaja), water extracts of different plant parts from 11 plant species, the active microbial ingredients of three commercial microbial products (Bacillus amyloliquefaciens strains MBI 600 and QST 713; Trichoderma harzianum strain T 39) and seven other experimental microorganisms. In the first step, the effect on the germination of teliospores of Sporisorium sorghi was evaluated on agar media. The observed antifungal activity was particularly pronounced for Quillaja, the water extracts from walnut, rhubarb, garlic, and Tillecur and the culture filtrates of Streptomyces (one isolate), Bacillus (two isolates) and Trichoderma (two isolates). In pot tests with sorghum grains inoculated with S. sorghi, full control of kernel smut was obtained by seed treatment with Tillecur, Quillaja and T. harzianum T39. In two field experiments, seed treatment with these preparations and with a second isolate of T. harzianum provided 84–100% control of the disease. In the pot tests, the level of control was assessed not only based on the presence of infected panicles at maturity but also using diagnostic microscopy and PCR of young plants. The results obtained with the different methods were in very good agreement. It is concluded that diagnosis of young plants by microscopy or PCR can significantly speed up screenings for new seed treatments with activity against covered kernel smut. Assuming that only agents with a high level of efficacy are of interest for further development, examination of a relatively small number of plants should yield sufficiently accurate data to identify promising candidates.