Rice False Smut Fungus, &amp;lt;i&amp;gt;Ustilaginoidea virens&amp;lt;/i&amp;gt;, Inhibits Pollen Germination and Degrades the Integuments of Rice Ovule

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

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.

Highlights

Rice false smut is a severe and widespread disease in major rice-growing areas of Asia, Africa and America [1,2,3,4]
We reasoned that if U. virens caused a systemic disease in rice, at least we would observe traces of fungal infection in the pedicel of the spikelet which was state of vascular bundle in the pedicels from the infected and uninfected spikelets. These results indicated that U. virens was not able to go through the pedicel from the infected spikelets to the adjacent spikelets, rice false smut is not a systemic disease
Rice false smut has emerged as one of the major diseases worldwide; its impact on rice production has increased in importance over time and attracted much concern of researchers

Summary

Introduction

Rice false smut is a severe and widespread disease in major rice-growing areas of Asia, Africa and America [1,2,3,4]. It has been in the Unite States since at least 1906 [5]. In China, rice false smut has long been considered a minor disease in rice production, and farmers even called smut balls the harvest fruits, meaning the harbinger of a big harvest for rice yield. With the wide use of high-yielding varieties and heavy application of nitrogen fertilizer in rice cultivation, rice false smut has emerged as the most devastating grain disease in rice production [1,7]

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