Constructionandoptimizationofaculturesystemforgrowthandbioassayof<italic>Ustilaginoideavirensinvitro</italic>

Rice false smut is an important fungal disease at the rice heading stage, which causes severe loss to yield production and rice quality. Due to insufficient growth performance of Ustilaginoidea virens in vitro, screening and observation of effective fungicides in bioassay have been restricted. In this work, selection, combination and optimization of various carbon, nitrogen sources and coagulants have been carried out, an optimized culture system for U. virens growth was developed. The growth rate of U. virens in 5 representative types of commercial media was only from 0.7 to 2.3 mm/d, while the significant growth promotion effect on U. virens was observed in 77% of 18 types of compound media. Especially, maximum growth rate of 3.4 mm/d was observed in the peptone sucrose gellan gum (PSGG) medium. Interestingly, growth promotion effect of this medium was also observed on different strains of U. virens collected from rice grown in geographically diverse regions. Moreover, supplementation of 0.02% MgSO₄ into the media solidified using gellan gum could enhance the solidification degree of the culture system, but did not affect the growth of U. virens. This indicated that peptone and sucrose were ideal nitrogen and carbon sources, respectively, in the PSGG medium, and gellan gum was a favorable coagulant. Our results would improve the growth rate of U. virens in vitro, and advance the understanding of underlying mechanism involved in the growth of U. virens, and also serve as an basis for the efficiency improvement of the bioassay system for U. virens.