In the present scenario of increasing global human
population, decreasing arable land, predicted increases of water scarcity, soil
salinity, severe diseases, emerging resistance of pests and pathogens to pesticides
and climate change pose significant challenges to modern rice research. The
biotic stresses viz. blast , stem rot, sheath blight, and bacterial blight
diseases cause severe economic losses to rice productivity. Among them Sheath
blight (ShB) is an important fungal disease caused by Rhizoctonia solani Kuhn
causing up to 25% of yield loss and degrades rice quality.
With the increasing application of nitrogenous fertilizers
and the popularization of semi dwarf cultivars with more tillers, ShB is
becoming the most serious disease in many rice-producing areas in the world.
The fungus R. solani Kuhn is soil borne pathogen which survives either as
sclerotia or mycelia in plant debris. After the initial infection, the pathogen
moves on the plant through surface hyphae and develops new infection structures
over the entire plant, causing significant necrotic damage. The architecture of
the canopy and the associated microclimate has strong effects on both the
mobilization of primary inoculums and the further spread of the disease.
In rice because of
availability of high resolution molecular maps, complete sequence information
and extensive germplasm collections, mapping of quantitative trait loci (QTLs)
for disease resistance such as sheath blight is feasible in crop
improvement programme. In this context has reported for the first time the
identification of rice QTL resistant to ShB using RFLP markers. To date, around
50 ShB resistance QTLs (ShBR QTLs) have been detected over all 12 rice
chromosomes in cultivated varieties, deep-water varieties and wild species.
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