Management of False Smut Disease of Rice: A Review

*Mathew S. Baite, Mukesh K. Khokhar and Ram P. Meena*

#### **Abstract**

Rice (*Oryza sativa* L.) is the most important food crop of the developing world. Among the biotic stresses of false smut is an emerging disease caused by *Ustilaginoidea virens*. The disease reduces both the quality and quantity of rice. The pathogen produces mycotoxins that are harmful to animals and humans. The disease is severe when favorable environmental conditions like high humidity (more than 80%) and temperature ranging from 25 to 30°C, late sowing and high soil fertility as well as using high amount of nitrogen. It has gained the status of a major disease of rice and causing varying yield loss depending on the weather conditions during the crop-growing period and the genotypes. Therefore, the primary concern of the farmers is the disease management methods, which are effective, simple and practical. Since, there is no single effective management strategy for false smut, we have discussed about the potential management options available depending upon the economic status and adoption capacity of the farmers. In the Plant Pathologists point of view, eco-friendly methods of disease management like cultural, biological and use of resistant variety should be advocated for sustainability of agriculture and human being.

**Keywords:** Management, false smut, rice, disease, *Ustilaginoidea virens*

#### **1. Introduction**

Rice is one the most important food crop of India. It is cultivated in all states from North to South and East to West. India is the second largest producer of rice in the world after China. In 2018–2019 India produced 116.47 million tonnes of rice with an average productivity of 2638 kg/hectare (Indiastat.com). However, rice is constantly attacked by biotic stresses namely pathogens, insects and weeds etc. False smut of rice is a destructive inflorescence disease caused by *Ustilaginoidea virens* (Cooke) Takahashi (teleomorph: *Villosiclava virens*). It was a minor disease with sporadic occurrences. However, it has recently become emerging disease in the majority of rice-growing areas of the world due to planting of high-yielding varieties and hybrids and climate change [1, 2]. The disease caused yield losses of rice by 2.8–81% depending on the disease intensity and genotypes [3, 4]. The disease caused grain quality reduction and mycotoxins produced by the pathogen is poisonous to livestock and humans [5]. The pathogen converts individual grains of the rice panicle into greenish spore balls (false smut balls) of a velvety appearance [6], the surface of which are covered by powdery dark-green chlamydospores during maturity (**Figure 1**).

**Figure 1.** *Rice panicle infected with false smut.*

The chlamydospores survive the winter in the soil and act as primary source of infection in the succeeding rice plants. Therefore, the pathogen is primarily soil and air-borne. The pathogen is a slow-growing fungus that forms abundant conidia in cultures which are globose in shape and echinulated under scanning electron microscope [7, 8]. False smut of rice can be managed using appropriate fungicides, cultural practices, bio-agents, plant extracts, resistant cultivar and integrated disease management techniques which are briefly discussed.

### **2. Management through fungicides**

The most common method of plant disease management is by use of chemical pesticides. It is popular with farmers probably due to easy availability and quick action. The control of rice false smut is mostly relied on fungicides. However, they are harmful to environment and increase the cost of cultivation and hence are highly discouraged whenever possible. Therefore, it should be used judiciously as prevention but not as curative measure. The timing and dose of application of fungicides are also important to control the disease. Crop loss is common where fungicide application timing is incorrect or an inadequate concentration of the material is applied [9, 10]. Therefore, need based applications are highly advisable for their usage.

Various fungicides such as Wenquning (a suspension of *Bacillus subtilis* in a solution of validamycin), copper oxychloride, cuproxat, simeconazole, tebuconazole, copper hydroxide, difenoconazole and hexaconazole have been reported for the control over 70% of rice false smut disease [11–16]. Field tests were conducted [17], to determine the effect of fungicide applications to flooded paddy water to control false smut. The results showed that the application of simeconazole granules to the paddy water two to five weeks prior to the heading stage of rice was highly effective against false smut and the fungicide application at three weeks was the most effective. Application of prochloraz + carbendazim followed by chlorothalonil were efficacious in controlling the false smut of rice [18]. There is a report that propiconazole 25EC (0.1%) recorded lowest disease severity than other treatments, followed by trifloxistrobin + tebuconazole 75 WG when sprayed at booting or 50% panicle emergence [19]. Higher yields were obtained when propiconazole 25 EC was sprayed at booting stage and also trifloxystrobin + tebuconazole 75 WG at booting. Spray of propiconazole and hexaconazole were effective in managing the rice false smut [20].

*Management of False Smut Disease of Rice: A Review DOI: http://dx.doi.org/10.5772/intechopen.97329*

The eventual goal of reducing fungicide use in rice production will be accomplished by using different broad-spectrum, bio-rational fungicides in rotations with traditional fungicides as preventive or need based applications. Further studies are desirable to explore the best fungicide that is specific and effective against *U. virens*, their use as potential, economical phytochemical molecule against false smut of rice.
