BSc-MSc (Integrated)

Several pathogenic diseases have been found to occur on the rice crop
resulting in extensive damage to the grain yield and straw yield. The crop subjected to
attack by many diseases caused by fungi, bacteria, viruses and nematodes which cause
annual loss to the tune of 12-15 per cent of the total production. Major rice diseases
under Kerala conditions are bacterial leaf blight, sheath blight and blast. Among these
diseases, the sheath blight which was earlier considered to be a minor disease is now
causing a major threat to the rice cultivation. Sheath blight is an important soil-borne
fungal disease which causes 10-30 per cent yield loss (Xie et al., 2008). It may reach
up to 50 per cent during favorable years especially when susceptible cultivars are
grown (Prasad and Eizenga 2008). The disease manifests initially as water soaked
lesions on sheaths of lower near water level.
Sheath blight, caused by Rhizoctonia solani Kuhn has become an important
disease of rice, especially in intensive production systems. From the epidemiological
viewpoint, rice sheath blight shares characteristics with other diseases caused by
Rhizocionia spp. In that the primary inoculums is mainly soil-borne while secondary
inoculums does not consist of spores, but is predominantly in the form of mycelia
strands produced by primary lesions that run on the surface of leaves and sheaths to
establish new lesions. As a result, epidemics usually exhibit a very strong spatial
aggregation (Savary et al., 1995).
Objectives of the study were to Study the effect of various weather parameters
and climate change on incidence and development of sheath blight disease of rice and
evaluation of disease forecasting models for sheath blight of rice. The field
experiments were conducted during May 2016 to October 2016 at the Regional
Agricultural Research Station of the Kerala Agricultural University at Pattambi,
Palakkad district, Kerala.
Crops transplanted June showed a higher disease incidence compared to other
dates of planting. Variety Jyothi is more susceptible to sheath blight incidence
compared to Kanchana. The effect of weather on LAI significantly varied with the
variety. The number of grains per panicle was significantly varied with varieties. The
effect weather on grain yield was significant. Under dry land condition the sheath
blight disease incidence was not observed even after artificial inoculation. The effects
of weather and varieties on sheath blight incubation period were significant.
EPRICE model developed by Savary et al., (2012) was used to forecast the
disease severity of sheath blight disease in rice after transplanting. The model works
on daily weather parameters particularly rainfall, maximum and minimum
temperature, morning and afternoon relative humidity. RMSE for Jyothi prediction is
0.248.This shows that the predicted sheath blight severity was in good agreement with
the observed values. So this model can be used for forecasting the rice sheath blight
severity under Kerala conditions.
The future climatic projections have taken from Ensemble of 17 General
Circulation Models (GCMs). The future carbon dioxide concentrations and climate
data has been incorporated into disease simulation model-EPIRICE and predicted the
future disease incidence possibility of sheath blight for the years 2030, 2050 and 2080
in all the 14 districts of Kerala. The impact of climate change on sheath blight severity
in the various districts of Kerala showed an increasing trend. Southern districts are
highly prone to sheath blight disease as compared to northern districts. Considering
the major rice growing tracts of Kerala Alappuzha will be more prone to sheath blight
than Palakkad and Thrissur.