BLAST DISEASE IN RICE - ITS CAUSES & CONSEQUENCES - बाराही अनलाइन खबर

INTRODUCTION

Rice is the major staple food crop for a large part of human population in the world today .About 50% of total agricultural area is utilized for rice production in Nepal. It contributes approximately 1/4th of GDP & more than 75% of the working population is engaged in rice farming for at least six months a year.However it may not be free from diseases of new as well old varieties .

Magnaporthe grisea , also known as rice blast fungus rice rotten neck , rice seedling blight , blast of rice , pitting disease , Johnson spot & neck black is a plant pathogenic fungus that causes a serious disease affecting rice.Among various fungal disease , blast disease is regarded as the prominent emerging disease & widely spreading leading to 10-20% yield reduction in susceptible varieties & upto 80% reduction in severe condition . It is found wherever rice is grown . Rice blast was first identified on California rice in 1996 . As a fungal disease , it causes formation of lesions on leaves , stems, peduncles , panicles , seeds & even roots .It is particularly destructive to upland rice crops produced without irrigation. It has great potential for crop failure as it is threatening so badly & has been ranked as the most important plant diseases of them all.It is because the disease is widely distributed in 85 counties , can be very destructive when environmental conditions are favourable . This disease is a model that demonstrates the seriousness , elusiveness & longevity of some plant.

CONDITIONS THAT CO-OPERATES THE GROWTH & DEVELOPMENT OF BLAST DISEASE

The blast disease is assisted by long periods of free moisture , high humidity ,little or no wind at night & night temperature between 63 & 73°F.Leaf wetness from dew or other sources is required for infection . The Conidia are dispersed in the air & under favourable conditions may cause new infections. Under favourable temperate & moisture condition the fungus can go through many disease cycles & produce a tremendous load of spores by the end of season.

SIGNS & SYMPTOMS

The symptoms of rice blast mainly include

1.Lesions that can be found on all parts , of the plant, including leaves , leaf ,collars, necks ,panicles, pedicels ,rachis , seeds & oven glumes are also affected.

2.Roots has also chance of getting infected.The most significant symptom indicates diamond shaped lesions that occurs on leaves of rice whereas lesions on the sheath are relatively rare.

ITS IMPACTS INCLUDES

Reduction in plant height , no .of productive tillers per plant, grain weight & grain yield are surfacely observable effect seen in rice.
Indirectly , it may increase fossil fuel depletion , ecotoxicity, carcinogens, eutrophication, acidification, global warming potential & ozone depletion.
Reduction on total milling yield by inoculation upto 11% , greatest reduction on average yield.
It increases global price of rice due to maximum reduction in yield upto 80% & lowers consumer welfare & food security.

DISEASE MANAGEMENT THROUGH VARIOUS MEANS : CULTURAL CONTROL , CHEMICAL CONTROL & ,BIOLOGICAL CONTROL.

Rice blast has never been eliminated from a region in which rice is grown. The successful management of rice blast can be made through various strategies.

Improvement of rice through conventional breeding techniques has made great progress.
By destructing infested residue , use of non – infested seed, water seeding , continuous flooding , avoiding excess of nitrogen it can be controlled.
Can be controlled by using resistant cultivars .
Minimizing drought stresses through various means.
Application of simple & effective technique i.e crop rotation.
Proper irrigation facility , maintenance of proper flood level for the rice to grow.
Strategy like genetic resistance must be taken as action.
Monitoring & treatment decisions should be made.
Proper use of seed sampling & testing to identify & avoid the use of blast infested seed in areas where blast is not a problem.
Water transmission can eliminate disease transmission from seed to seedling.

CHEMICAL CONTROL
Use of protectant , fungicide so that panicles is protected as it emerges from the boots.Being a multiple cycle disease , fungicide application can control leaf blast early in the season.

BIOLOGICAL CONTROL

From recent research , it is found that , plant associated bacterial strains assembled from the rice rhizosphere can be used as biocontrol agents for blast suppression .
Employing detachment action with gelatinolytic bacteria. Bacteria inhibiting germling adhesion by phytopathogenic fungi can act as a biological agent.

Writer: Sita Basnet (Student, Bsc. Ag IAAS Paklihawa Campus)