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**Chapter 7**

**Abstract**

disease control, and assay.

mycotoxin, sclerotium

**1. Introduction**

Rice False Smut: An Increasing

Threat to Grain Yield and Quality

*Wen-Ming Wang, Jing Fan and John Martin Jerome Jeyakumar*

Rice false smut (RFS) is the most important grain disease in rice production worldwide. Its epidemics not only lead to yield loss but also reduce grain quality because of multiple mycotoxins generated by the causative pathogen, *Villosiclava virens* (anamorph: *Ustilaginoidea virens*). The pathogen infects developing spikelets and specifically converts individual grain into a RFS ball that is established from mycelia covered with powdery chlamydospores, sometimes generating sclerotia. RFS balls seem to be randomly formed in some grains on a panicle of a plant in the paddy field. However, epidemics differ largely among varieties, fields, and seasons. This chapter introduces current understanding on the disease, mycotoxins, the biology of the pathogen, pathogenesis of RFS, rice resistance, the disease cycle, the

**Keywords:** basal defense, biotroph, effector, epiphytic growth, grain filling gene,

rice false smut (RFS) disease that is a threat to yield and grain quality.

Rice production plays a crucial role in our food security. Rice security is not only an economic issue but also an important parameter to determine social and political stability [1]. Thus, rice research has to be geared up to develop strategies for alleviating losses due to pests and diseases. In the past decades, a number of minor diseases have attained the status of major importance in rice. One such disease is the

RFS was previously recorded as a minor disease of rice and considered as a symbol of good harvest in old times. In recent years, increasing occurrence of RFS has been reported in most major rice growing regions throughout the world, such as China, India, and USA [2–5]. The emergence of this disease is believed to be partially due to wide application of hybrid rice varieties, which are mostly susceptible to the RFS. The causative agent of RFS is an ascomycete fungal pathogen *Villosiclava virens* (anamorph: *Ustilaginoidea virens* [Cooke] Takahashi) [6], which specifically infects rice flowers and transforms the latter into RFS balls [3]. RFS balls are small at first growing slowly and enclosing the floral parts. The early balls were found to be slightly flattened and smooth and were covered by a thin membrane. As the pathogen growth intensifies, the RFS ball bursts with chlamydospores and becomes orange then later yellowish-green or greenish-black (**Figure 1A**–**C**). The RFS balls generate sclerotia (**Figure 1D**) when the temperature difference between day and night is large in autumn [3]. RFS ball is the only visible symptom of RFS disease.
