|Package of Practices
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1. The disease is characterized by general chlorosis, with pronounced stunting and profused tillering. The chlorotic leaves are uniformly pale yellow. The young infected plants usually produce either no panicle at all or a few small panicles with unfilled grains. Plants infected during later growth stages may not develop symptoms before harvest. 2. This disease is caused by phytoplasmas and these are generally Observed in phloem tubes of yellow dwarf infected rice plants. These are pleomorphic bodies measured from 80-800 mm, devoid of cell walls and bound by unit membrane. 3. The disease is transmitted by leafhopper, Nephotettix virescens. The insect can acquire the pathogen by feeding on diseased plant by half an hour and require long incubation period (20 days) to transmit the phytoplasma. 4. The insects remain infected until they die. A combination of low temperature and high humidity favours the leafhopper population resulting in higher disease incidence. The ratoon plants growing from stubble may be diseased and act as inoculum sources for later infections. The yellow dwarf of rice may be reduced by: • Field sanitation • Seed treatment with Carbofuran and subsequent soaking in Carbofuran solution (75% WP) for 36 hours prior to transplanting (by effectively controlling the vector) • Spraying Dimecron (0.03%), Carbofuran (0.04%), Dimethoate (0.025%) and Methyl Dometin (0.025%) Spraying of ch lorotetracycline at 100 ppm
1. The disease occurred in an epidemic form in NE states during 1969 and 1970.This is one of the most damaging diseases. Tungro ischaracterized by stunting ofthe plant and leaf colours range from various shades of yellow to orange, the discolouration and rusty blotchesspreading downwards from the leaftip. 2. The young leaves may show a mottled appearance and slightly twisted whereas older leaves appear rusty coloured. 3. Tungro is the result of concurrent infection by two viruses -the single stranded RNA virus, rice tungro spherical virus (RTSV) and thedouble stranded DNA virus, rice tungro bacilliform band virus (RTBV) Both viruses are transmitted by several leafhopper species, more particularly Nephotettix virescens in semi-persistent manner. 4. The insect can become infective after feeding on diseased plants for 30 minutes and can transmit the virus almost immediately after feeding. 5. The females are more efficient in transmission than the males. Wild rice, rattoning stubble and grassy weeds may serve as source of virus between rice crop. 6. Use of resistant varieties controls the disease.
1. This is a bacterial foliar disease. The disease first starts on the leaves as small water-soaked to translucent interveinal streaks of 1-10 cm long. They elongate parallel to the veins and turn yellowish brown, which often coalesce to form large blotchy lesions covering the entire leaf Surface. Minute, yellowish orange beads of bacterial exudates appearing all along the lesions is a characteristic feature of this disease. This disease is caused by Xanthomonas campestris pv. oryzicola. The bacterium is a rod shaped, 1.0-2.5 x 0.5-0.8\ in size and motile by single polar flagellum. It is gram negative and non-spore forming bacterium. To eradicate the disease, following steps should be taken 1. Procurement of seeds from authentic source to minimize the seed borne inoculums. 2. Soaking ofthe seeds in 0.025% Streptocycline and hot water treatment at 52°e for 30 minutes . 3. Use of resistant varieties.
1. Spraying with copper fungicides (Blitox 0.3%) alternately with Streptocycycline (250 ppm).
2. Application of moderate dose of nitrogenous fertilizer (80 kg/ha) and use of wider spacing (30 x 15 cm) .
3. Growing resistant varieties to the disease .
1. This disease occurs mostly in low altitude areas of Tripura, Meghalaya and Arunachal Pradesh during July to September. The disease is caused by Xanthomonas campestris pv. Oryza.
2. The bacterium induces either wilting of plants or leaf blight. Leafblight phase is most commonly seen and typical symptoms are yellow to straw coloured stripes with wavy margins, generally on both edges of the leaves. These stripes start from the tips, extend downward and cover the entire leaf. The blighting may extend to the leaf sheaths and culms, killing the tiller or whole clump.
3. The phase usually appears 4-6 weeks after transplanting. The most destructive phase of the disease is 'kresek' or wilt resulting from early systemic infection. The leaves roll completely, droop and turn yellow and grey and ultimately the whole plant wilts and dies.
4. The kresek affected clumps may be confused with stem borer attack. However, borer affected tillers can be easily pulled out, which is not so in kresek' affected tillers. To distinguish 'krisek'; symptoms from stem borer damage, the lower part of the plant should cut off and squeeze between the fingers. Yellowish bacterial ooze will appear at the cut ends if the kresek is present.
5. Primary infection may result from diseased seeds, stubble, straw, and weed hosts such as Cyprus rotundas, C. deforms and Leticia exedra.
6. Thebacteria enter through hydathodes or wounds of the plant. It multiplies in the plant and becomes systemic in vascular bundles causing plugging of the water-conducting tissue, which results in wilting of plants.
7. The bacteria disseminated through irrigation water and wind-borne rain. The disease spreads fast under favourable weather conditions like incessant rains, strong wind and warm temperature (22-26°C). Plants in shade and close-planted crops supplied with high doses of nitrogen show more disease incidence.
1. Discoluration of rice grains. is becoming a major problem in certain varieties of rice both in upland and lowland conditions. It redUces the germination, causes decay of seedlings, produces chaffy grains and lowers the consumption quality of the grains.
2. The disorder may be limited to individual grains, but in severe cases almost the entire panicle including the rachis becomes discoloured.
3. Drechslera oryzae, Fusarium sp., Nigrospora oryzae, Penicillium sp., Curvularia sp., Sarocladium oryzae and Rhizophus sp. are associated with the discoloured grains. Heavy nitrogenous fertilizers increase the discolouration of grains.
Grain discoluration may be checked by-
• Spraying of 0.1 % Carbendism at the time of panicle emergence
• Clean cultivation
Growing resistant varieties
1. In this disease, a few grains in an ear are affected, the infection being either partly or wholly. The symptoms appear first as minute black Streaks bursting through the glumes at the ripening.
2. If the infected grain is crushed between the fmgers, a black powdery mass of spores emerges. The causal organism of the disease is Tilletia barclayana.
3. The is that develops inside the grain is filled with spores, which are spherical and dark, with a spiny epispore. The spore germinates and produces sporadic. These produce secondary sporadics in large numbers.
4. The teliospores survive in the soil or seed and remain viable for next season. High doses of nitrogen fertilizers make the plant susceptible to the disease.
5. Early maturing varieties suffer more than the late maturing ones. Warm temperature (20-30DC) and high relative humidity (8S% and above) or intermittent rain at the time of ear emergence favours the disease development.
The disease control measures include
• Field sanitation
• Crop rotation
• Use of resistant varieties
1. This is also a minor disease and symptoms are brown coloured to dark coloured linear spots appear on the leaf blades. Spots may also OCCur in the leaf sheath, glume and parts of the stem.
2. Incidence of this disease is due to Cercospora oryzae. The pathogen produces conidia, which are hyaline or dark, filiform and several-celled.
3. Infected plant debris acts as primary source of infection and the disease spreads by means of air-borne conidia produced on the leaves.
• Destruction of infected plant debris by burning
• Spraying of 0.2% Dithane M-4S with the appearance of the disease
1. This is a minor disease and is characterized by appearance of minute, sooty, dull, angular patches on the leaves, which represents the sori. In susceptible varieties, the fungus almost covers the entire leaf surface of the older leaves.
2. The disease is caused by Entyloma oryzae, which produces tel iospores and these are angular to globose, smooth-walled, light brown in colour.
3. The disease perennates through sori lying in infected plant debris.
4. Spores reaching the leaves near the soil level cause infection. High nitrogen enhances the disease incidence.
Control of the disease may be achieved by:
• Clean cultivation
• Growing resistant varieties