Rice False Smut Fungus, Ustilaginoidea virens, Inhibits Pollen Germination and Degrades the Integuments of Rice Ovule

Wenlu Li, Luoye Li, Aiqing Feng, Xiaoyuan Zhu, Jianxiong Li

Key Laboratory of Plant Resources Conservation and Sustainable Utiliza-tion, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China.
Plant Protection Institute, Guangdong Academy of Agricultural Sciences, Guangzhou, China.

DOI: 10.4236/ajps.2013.412284                

Abstract

Ustilaginoidea virens is a flower-infecting fungus that forms false smut balls in rice panicle. Rice false smut has long been considered a minor disease, but recently it occurred frequently and emerged as a major disease in rice production. In vitro co-cultivation of U. virens strain with young rice panicles showed that U. virens enters inside of spikelets from the apex and then grows downward to infect floral organs. In response to U. virens infection, rice host exhibits elevated ROS accumulation and enhanced callose deposition. The secreted compounds of U. virens can suppress rice pollen germination. Examination of sectioning slides of freshly collected smut balls demonstrated that both pistil and stamens of rice flower are infected by U. virens, hyphae degraded the contents of the pollen cells, and also invaded the filaments. In addition, U. virens entered rice ovary through the thin-walled papillary cells of the stigma, then decomposed the integuments and infected the ovary. The invaded pathogen could not penetrate the epidermis and other layers of the ovary. Transverse section of the pedicel just below the smut balls showed that there were no fungal hyphae observed in the vascular bundles of the pedicel, implicating that U. virens is not a systemic flower-infecting fungus.

Keywords

Flower-Infecting Fungi; Integuments; Pollen Germination; Oryza sativa; Rice False Smut

Conflicts of Interest

The authors declare no conflicts of interest.

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