Streptomyces toxytricini, a biocontrol plant growth-promoting bacterium against smut of broomcorn millet (Panicum miliaceum L.)

Smut disease is one of the significant threats to broomcorn millet. It is essential to find a safe method to control this disease for sustainable agricultural development. To address this issue, we isolated various strains from the rhizosphere soil of broomcorn millet. Among these, 18 strains exhibited inhibitory effects on smut, with the v-3 strain demonstrating the best control effect. The morphological characteristics of the v-3 strain showed that the colony was cinnamon pink, and the surface was rough and opaque. The spores were light pink, and the aerial hyphae were well-developed. This strain was found to produce protease, hydrogen sulfide, and melanin. Finally, 16S rDNA sequencing confirmed that the strain is closely related to Streptomyces toxytricini. From 2021 to 2022, the v-3 strain was prepared as spore suspension (SS) and sterile fermentation broth (SF) for field experiments. The results showed that the disease plant rate of broomcorn millet smut was reduced by 39.55%∼55.29% and 50.91%∼63.14% after using SS and SF, respectively. Similary, the control rate increased 39.46%∼59.05% and 50.96%∼62.99%, respectively. Furthermore, the v-3 strain significantly promoted the growth of aboveground traits (plant height and stem diameter) and underground traits (root fresh weight, root length, and root surface area) of broomcorn millet. It also improved the activity of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) in the leaves, and reduced the malondialdehyde content. These findings preliminarily indicate that the v-3 strain has biocontrol potential against broomcorn millet smut and could promote the growth of broomcorn millet.