*2.1.3 Pathogen*

Rice sheath rot is a complex disease that can be caused by various fungal and bacterial phytopathogens. Major phytopathogens associated with the disease are *Sarocladium oryzae* and *Fusarium fujikuroi* species complex (*Fusarium* 

**Figure 1.** *Infected leaf sheath.*

**Figure 2.** *Severe infection.*

**Figure 3.** *Infected grains.*

**Figure 4.** *The panicle turned chaffy.*

*fujikuroi, Fusarium verticilloides* and other *Fusarium* spp.). Bacterial pathogen like *Pseudomonas fuscovaginae* is associated with the disease. Among these pathogens, *Sarocladium oryzae* is the major pathogen which was originally identified as *Acrolyndrium oryzae* when it was first reported from Taiwan in 1922 [28]. Later in 1975, the genus *Sarocladium* was established [29] and the pathogen was renamed

*Emerging Minor Diseases of Rice in India: Losses and Management Strategies DOI: http://dx.doi.org/10.5772/intechopen.99898*

as *Sarocladium oryzae*. The genus Sarocladium currently comprises of 16 species including plant pathogens, saprophytic microbes, endophytes, mycoparasites and some of the potential human pathogens [30]. The pathogen grows slowly on Potato Dextrose Agar (PDA) at 2.5 mm per day at 28°C. It produces sparsely branched white mycelium with yellow pigmentation underside. It also produces numerous microsclerotia which are round in shape and orange colored. The pathogen produces simple or branched conidiophores. The conidia are cylindrical, septate./ aseptate and hyaline measuring 4–7 X 1–2 μm in size (**Table 1**).

#### *2.1.4 Epidemiology and integrated disease management*

The disease is reported from moderate to severe form in almost all the rice growing countries. The disease is very common and severe in Monsoon/rainy season and reported in low to moderate form in summer months [31]. Sharma et al. [32] observed that, the disease incidence in Nepal was found below 1250 M altitude at a temperature of 20-30°C and relative humidity of 65–85%. Similar observation found by [33]. The sheath rot pathogen survives in infected seeds (having seed borne nature), plant residues like straw, stubble, chaffy grains. It can also found in soil, water when environmental conditions become favorable. The pathogen may attack the plants at various growth stages. The fungus enters through stomata, wounds and found to be most destructive during booting and grain developmental stages [34]. The nature of entry and extent of damage also facilitated by insect and mites damage by weakening of the plants [34]. Secondary transmission of the pathogen may be by wind and rain splash.

#### *2.1.5 Integrated management*

Though the disease can be managed through number of measures, breeding for resistance is the best option for its management. Breeding for disease resistance is bit difficult and challenging as the disease is caused by a number of pathogens. Many researchers have identified few resistant varieties. Hemalatha et al. [35] developed method of screening for resistance against. *S oryzae* based on a crude toxin preparation. Pathogen variability, its virulence pattern, geographical location and cultivars growing are the points to be considered while breeding for diseases resistance. Select suitable resistant varieties for sowing: Jalmagna, Latisali, Rasi, Pankaj etc., Apart from resistance breeding other management practices should also be followed [36]. Use of healthy seeds, limiting insect pest population, avoiding densely planting, balanced application of chemical fertilizers especially nitrogen and increased application of potassic fertilizers. Similarly adoption of field sanitation, weed control, crop residue management is the some of the recommended cultural practices. Treat the seeds with carbendazim 50% WP @ 2 g/kg or biological control agents like *Trichoderma* or *Pseudomonas* talc based formulations @ 8–10 g/kg of seeds. Soil application of *Pseudomonas fluorescens* @ 2.5 kg/ha after 30 days of transplanting mixing with 50 kg FYM. Removal and destruction of weeds, infected stubbles should be done at critical periods. Application of potash at tillering stage is helpful in disease reduction. At booting stage, spray fungicides like carbendazim 50% WP @ 500 g/ha or mancozeb 75%WP @ 1 kg/ ha or Iprobenphos 48EC @ 1 kg/ha or Thiophanate methyl 70%WP @ 500 g/ha or Isoprothiolane 40%EC @ 750 ml/ha. During grain maturity stage, spray systemic fungicides like Ediphenphos @ 500 g/ha or a combination of Tridemorph 80% EC (fungicide) + phosphamidon 40% SL (insecticide) to give better control of sheath rot. Foliar spray of calcium sulphate and zinc sulphate is effective against sheath rot.


#### **Table 1.**

*Pathogens associated with rice sheath rot disease and their characteristics.*
