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1 Rice diseases and their management


Hello everybody, welcome to the third week of this course. In the previous two weeks we talked about the principles and components of plant disease development and principles and components of plant disease management. In this week we’ll be talking about diseases of field crops and their management. So in the first talk we will be talking about diseases of rice and their management. Although, rice is infected by many different types of plant pathogens causing different diseases some of them are significant and most widely occur around the world. So they are Blast, Bacterial Leaf Blight, Brown spot, Sheath Blight and False smut.

Let us take the example of blast at the beginning. It is a fungal disease caused by the organism Magnaporthe oryzae. The infection can be in the leaf, causing Leaf blast, may be at the nodal level, Nodal blast or at the neck it is known as Neck blast. And the disease is caused by the fungus Magnaporthe oryzae which produces tree cell spores. It is very important to know where this pathogens survive so that we can design a proper management practice for management of this particular disease. The pathogen may survive in Collateral hosts like sugar cane, Digitaria, Dinerba, Panicum, and so many other grassy plants. At the same time the pathogen may also survive in rice plants where continuous rice cultivation takes place. The pathogen may also survive in leftover disease seedlings in nursery beds. So these are the places where this particular pathogen survives and disease management strategies should involve taking care of this survival mode. So IPM Practices that needs to be adopted for management of this particular pathogen includes Cultural Practices, Application of fungicides, Use of resistant cultivars and Biological Control. Among the cultural practices it is very important to have Field sanitation where destruction of weed and collateral hosts are very very essential. We should avoid application of excessive nitrogen and mostly nitrogen should be applied in split form (50% through FYM and 50% in the form of urea). So application of fungicides then include seed treatment with copper sulfate. Copper is a very good compound for management of Blast of rice and copper oxychloride along with Blitox, Hinosan, Carpropamid are some of the other chemical compounds which give effective control for this particular pathogen. Use of resistant cultivars should be adopted wherever resistant cultivars are recommended for local regions. Then Biological control has also proved to be effective where Pseudomonas fluorescens can be applied along with Pseudomonas putida. This organisms gave good biological control for this pathogen.

The next disease is Brown leaf spot. It is caused by Bipolaris oryzae . This is again the pathogen which caused Bengal famine in 1943 to 45. So the disease is very easy to detect where you can see leaf spots on the leaves and the spots can also be seen on the seeds. The pathogens survived both in soil and seed. So management of the pathogen includes its Survival mode. IPM practices includes Cultural practices, Application of fungicides, Use of resistant cultivars and Biological Control. These are the four major approaches which needs to manage this particular pathogen. Cultural practices include field sanitation where destruction of rice stubbles is very very important, removal of collateral hosts like Setaria, Leersia, Echinochloa etc. Then hot water seed treatment at 55o C for 10 minutes it is very very good method for management of this particular pathogen. We can also apply calcium silicate in silica deficient soil so that disease can be taken care of. Some of the good fungicides which are recommended for management of this particular pathogen includes seed treatment by Captan and Thiram. It may be applied at the rate of 4 gram per kg of seed. Seed treatment with tricyclazole along with spraying of Mancozeb + (plus) Tricyclazole and tillering and late booting stage are also helpful. Then we can also go for it. Use of resistant varieties because resistant varieties are available for this particular pathogen and using resistant varieties will also give good control. Biological control has also proven effective where Pseudomonas fluorescens application and the rate of 10 gram per kg of seed was recommended. Foliar spray of conidial suspension of Trichoderma is also giving good control for this particular pathogen.

Then next disease is Bacterial leaf blight – it is caused by a bacterial pathogen Xanthomonas oryzae pv. Oryzae The disease is very easy to diagnose in the leaf where you can see that the margins of the leaf getting blighted and it is seen from a distinct odd places. Can also be served through exudation on the leaf surface where these are the bacterial exudates that is particularly seen in the early morning time.

The pathogens survive in the seeds, weed host, volunteer rice and infected stubbles. So these are the mode of survival of the pathogen. The IPM Practices for management of the disease include Cultural practices, Chemical applications, Use of resistant cultivars and Biological control. In cultural practices application of nitrogen is very very important. A Split application of nitrogen is recommended and maintaining shallower water in nurseries is also proving useful. A good drainage system in the rice field is also recommended. Clean cultivation and drying the fallow fields is also recommended and removal of collateral weeds is very very important. Chemicals that are used for management of this disease include seed treatment with 1.1 grams Streptocycline plus 0.1 gram Copper Sulfate then we can also use Agrimycin or copper oxychloride in combination followed by foliar spray of Streptocycline and Copper Sulphate. So these are some of the chemicals that are recommended for management of this particular pathogen. Resistant varieties are available for this particular disease and it should be used wherever it is available. Biological control has not proved very effective so biological control agents are not recommended for management of this particular disease.

Next important pathogen is Rhizoctonia solani which causes Sheath Blight in rice. From the name we can understand that the blight is caused in the sheet region of the rice plants where blighted portions are very distinct from a distant place.

The pathogens survives as sclerotial bodies which are left in the field from the previous crop and weeds. Mycelium also they can be present on the plant debris. So the Management Practices include Cultural, Chemical, Resistant Varieties and Biological Control. So Cultural Practices again here also nitrogen is very very important. So nitrogen should be applied in split doses and last form of application of nitrogen can also be avoided if the field is infested with seed blight pathogen. Chemical Control include seed treatment with carbendazim then spraying of fungicides of carbendazim is also proved useful in the later stage or mancozeb that is also recommended along with hexaconozole and Propiconazole. This all chemicals are proving effective against this particular pathogen. Although there is no highly resistant varieties available for management of this particular disease there are certain moderately resistant varieties are available and one should go for application or use of this moderately resistant varieties for management of this pathogen. Biological Control agents like Pseudomonas fluorescens, Trichoderma viride and Bacillus subtilis. These all proved very very effective in lowering the sclerotial inoculum in the field. The last disease of rice is caused by False smut and known as all false smut it is caused by Ustilaginoidea virens. Diseases can easily be diagnosed in where you can see that the grains are initially converted into spore balls which are orange in color later it turned out to be olive green in color.

The pathogens survive in soil and seed it is also air borne in nature. So IPM Practices include Cultural, Use of resistant cultivars and Chemical treatments. Cultural methods are important where we need to keep the field clean, removal of infected seeds, panicles and plant debris after harvest is also very very important. Use of moderate rates of nitrogen is again an essential criteria for management of this disease. Use of certified seeds is very important then see treatment can be done at 52 degrees Celsius for 10 minutes. Resistant varieties are used wherever it is available and chemical treatments can be either preventive or it can be used as a therapeutic along with seed treatment. In case of Preventive chemicals Spray of copper oxychloride is recommended along with Propiconazole. Whereas, Seed Treatment include Carbendazim application at the rate of 2gram/kg of seeds and Therapeutic sprays of Carbendazim and copper[1]based fungicide at tillering and preflowering stage give effective control of the pathogen.

Thank you.



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