Rice: Blast, Brown spot, Bacterial blight
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Sexual stage (लैंगिक अवस्था):- Magnaporthe grisea
- In Japan, it is believed to have occurred as early as in 1704.
- In Italy the disease called “brusone ” was reported in 1828 and in USA in 1876.
- The disease was first recorded from Tanjore district of Tamil Nadu in 1918.
i. Leaf blast (पर्ण ब्लास्ट):-
- On the leaves, the lesions start as small water soaked bluish green specks, soon enlarge and form characteristic spindle shaped spots with grey centre and dark brown margin.
- The spots join together as the disease progresses and large areas of the leaves dry up and wither.
- Similar spots are also formed on the sheath.
- Severely infected nursery and field show a burnt appearance.
- In infected nodes, irregular black areas that encircle the nodes can be noticed.
- The affected nodes may break up and all the plant parts above the infected nodes may die (Node blast).
- At the flower emergence, the fungus attacks the peduncle which is engirdled, and the lesion turns to brownish-black. This stage of infection is commonly referred to as rotten neck/neck rot/neck blast/panicle blast.
- In early neck infection, grain filling does not occur and the panicle remains erect like a dead heart caused by a stem borer.
- In the late infection, partial grain filling occurs.
- Small brown to black spots also may be observed on glumes of the heavily infected panicles.
Etiology (इटीओलोजी):-
- The causal organism was first detected by Cavara in 1891 from Italy.
- Mycelium of the fungus is hyaline to olivaceous, septate and highly branched.
- Conidia are produced in clusters on long septate, olivaceous slender conidiophores.
- Conidia are pyriform to obclavate or somewhat top shaped, attached at the broader base by a hilum.
- Conidia are hyaline to pale olive green, usually 3 celled. - The perfect state of the fungus is M. grisea. It produces perithecia. The ascospores are hyaline, fusiform, 4 celled and slightly curved.
- The pathogen produces few toxins namely, α-picolinic acid, Pyricularin and pyriculol.
2. Brown Spot of Rice (धान का भूरा धब्बा):-
Introduction (परिचय):-
Helminthosporium oryzae (Syn: Drechslera oryzae)
[Sexual stage (लैंगिक अवस्था): Cochliobolus miyabeanus]
In India, this disease is the principal cause of Bengal famine of 1942-43. The first report of the disease in India was made by Sundararaman from Madras in 1919, and now is reported from all of the rice growing states. Under highly favourable conditions, the disease causes a reduction in yield ranging upto 90 per cent.
(भारत में यह रोग 1942-43 के बंगाल अकाल का प्रमुख कारण है। भारत में इस रोग की पहली रिपोर्ट 1919 में मद्रास के सुंदररमन द्वारा की गई थी, और अब यह सभी चावल उत्पादक राज्यों से रिपोर्ट की जाती है। अत्यधिक अनुकूल परिस्थितियों में, इस रोग के कारण उपज में 90 प्रतिशत तक की कमी आ जाती है।)
Symptoms (लक्षण):-
- The fungus attacks the crop from seedling in nursery to milk stage in main field.
(कवक नर्सरी में अंकुर से लेकर मुख्य खेत में दूधिया अवस्था तक फसल पर हमला करता है।)
- Symptoms appear as lesions (spots) on the coleoptile, leaf blade, leaf sheath, and glumes, being most prominent on the leaf blade and glumes.
[लक्षण कोलोप्टाइल, पत्ती के ब्लेड, पत्ती के आवरण और ग्लूम्स पर घाव (धब्बे) के रूप में दिखाई देते हैं, जो पत्ती के ब्लेड और ग्लूम्स पर सबसे प्रमुख होते हैं। ]
- The disease appears first as minute brown dots, later becoming cylindrical or oval to circular.
(यह रोग पहले सूक्ष्म भूरे धब्बों के रूप में प्रकट होता है, बाद में बेलनाकार या अंडाकार से गोलाकार हो जाता है।)
- The several spots coalesce and the leaf dries up.
(कई धब्बे आपस में जुड़ जाते हैं और पत्ती सूख जाती है। )
- The seedlings die and affected nurseries can often be recognized from a distance by their brownish scorched appearance.
(अंकुर मर जाते हैं और प्रभावित नर्सरी को अक्सर उनके भूरे रंग के झुलसे हुए रूप से दूर से पहचाना जा सकता है। )
- Dark brown or black spots also appear on glumes which contain large number of conidiophores and conidia of the fungus.
(ग्लूम्स पर गहरे भूरे या काले धब्बे भी दिखाई देते हैं जिनमें बड़ी संख्या में कवक के कोनिडियोफोर्स और कोनिडिया होते हैं।)
- It causes failure of seed germination, seedling mortality and reduces the grain quality and weight.
(यह बीज के अंकुरण में विफलता, अंकुर की मृत्यु का कारण बनता है और अनाज की गुणवत्ता और वजन को कम करता है।)
- The disease is associated with a physiological disorder known as akiochi in Japan.
(यह रोग एक शारीरिक विकार से जुड़ी है जिसे जापान में अकिओची कहा जाता है।)
- Abnormal soil conditions (Deficiency of potassium) predispose the plants to heavy infection.
(असामान्य मिट्टी की स्थिति (पोटेशियम की कमी) से पौधों में भारी संक्रमण होने का खतरा रहता है।)
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- H. oryzae produces greyish-brown to dark brown septate mycelium.
- The perfect stage of the fungus is C. miyabeanus. It produces perithecia with asci containing 6-15 septate, filamentous or long cylinderical, hyaline to pale olive green ascospores. It produces C25 terpenoid phytotoxins called ophiobolin A, (or Cochliobolin A), ophiobolin B (or cochliobolin B) and ophiobolin I. Ophiobolin A is most toxic. These result in the breakdown of the protein fragment of cell wall resulting in partial disruption of integrity of cell.
- The fungus overwinters mainly in the infected plant parts.
- It is not soil borne.
- The infected seeds are the most common source of primary infection.
- Diseased seeds (externally seed borne) may give rise to the seedling blight, the first phase of the disease.
- Pale yellowish brown spots appear on the coleoptiles, spreading to cover the other tissues of the seedling.
- The fungus reproduces on the spots and is disseminated by air currents.
- The fungus also survives on collateral hosts like Digitaria sanguinalis, Leersia hexandra, Echinochloa
colonum, Pennisetum typhoides, Setaria italica and Cynodon dactylon.
- The symptoms of potassium deficiency are somewhat similar to that of brown spot making it often difficult to ascribe the symptoms to fungus attack or nutrient deficiency.
- Use disease free seeds.
- Field sanitation - removal of collateral hosts and infected debris in the field.
- Crop rotation.
- Adjustment of planting time.
- Proper fertilization.
- Use of slow release nitrogenous fertilizers is advisable.
- Good water management.
- Use of soil amendments.
- Grow disease tolerant varieties viz., Bala, BAM 10, IR-20, Jaya, Ratna, Tellahamsa and Kakatiya.
- Treat the seeds with Thiram or Captan at 4 g/kg and with Mancozeb @0.3%. Dissolve 3gm in 1 litre of water to make 0.3%.
- Spray the crop in the main field twice with Mancozeb (DIthane M45) @ 0.2%, once after flowering and second spray at milky stage.
3. Sheath Blight (शीथ ब्लाइट):-
Introduction (परिचय):-
Rhizoctonia solani
[Sexual stage (लैंगिक अवस्था): Thanetophorus cucumeris]
Symptoms (लक्षण):-
- The fungus affects the crop from tillering to heading stage.
(कवक पौधे को टिलरिंग से लेकर हेडिंग स्टेज तक प्रभावित करता है।)
- Initial symptoms are noticed on leaf sheaths near water level.
(प्रारंभिक लक्षण पानी के स्तर के पास पत्तियों की शीथ पर देखे जाते हैं।)
- On the leaf sheath oval or elliptical or irregular greenish grey spots are formed.
(पत्ती की शीथ पर अंडाकार, दीर्घवृत्ताकार या अनियमित हरे-भूरे धब्बे बनते हैं।)
- As the spots enlarge, the centre becomes greyish white with an irregular blackish brown or purple brown border.
(जैसे-जैसे धब्बे बढ़ते हैं, उनका केंद्र ग्रे-व्हाइट हो जाता है और सीमा अनियमित काले-भूरे या बैंगनी-भूरे रंग की हो जाती है।)
- Lesions on the upper parts of plants extend rapidly coalesing with each other to cover entire tillers from the water line to the flag leaf.
(पौधे के ऊपरी हिस्सों पर घाव तेजी से फैलते हैं और एक-दूसरे के साथ मिलकर पूरे टिलर को पानी की रेखा से ध्वज पर्ण तक ढक लेते हैं।)
- The presence of several large lesions on a leaf sheath usually causes death of the whole leaf, and in severe cases all the leaves of a plant may be blighted in this way.
(पत्ती की शीथ पर कई बड़े घावों की उपस्थिति से आमतौर पर पूरी पत्ती की मृत्यु हो जाती है, और गंभीर मामलों में इस तरह से पूरे पौधे की पत्तियाँ ब्लाइटेड हो सकती हैं।)
- The infection extends to the inner sheaths resulting in death of the entire plant.
(संक्रमण आंतरिक शीथों तक फैल जाता है, जिससे पूरे पौधे की मृत्यु हो जाती है।)
- Older plants are highly susceptible.
(पुराने पौधे अत्यधिक संवेदनशील होते हैं।)
- Five to six week old leaf sheaths are highly susceptible.
(पांच से छह सप्ताह पुरानी पत्तियों की शीथ अत्यधिक संवेदनशील होती है।)
- Plants heavily infected in the early heading and grain filling growth stages produce poorly filled grain, especially in the lower part of the panicle.
(शुरुआती हेडिंग और ग्रेन फिलिंग वृद्धि अवस्था में भारी संक्रमित पौधे खराब तरीके से भरे हुए दाने उत्पन्न करते हैं, विशेष रूप से पैनिकल के निचले हिस्से में।)
Etiology (रोगजनन):- The fungus produces usually long cells of septate mycelium which are hyaline when young, yellowish brown when old. It produces large number of globose sclerotia, which are initially white, later turn to brown or purplish brown.
(कवक आमतौर पर लंबी कोशिकाओं वाला विभाजित कवकजाल उत्पन्न करता है, जो तरुण होने पर पारदर्शी होता है और परिपक्व होने पर पीले-भूरे रंग का हो जाता है। यह गोलाकार स्क्लेरोशिया की बड़ी संख्या उत्पन्न करता है, जो प्रारंभ में सफेद होते हैं, बाद में भूरे या बैंगनी-भूरे रंग में बदल जाते हैं।)
Disease cycle (रोग चक्र):-
- The pathogen can survive as sclerotia or mycelium in dry soil for about 20 months but for 5-8 months in moist soil.
(रोगजनक शुष्क मिट्टी में स्क्लेरोशिया या कवकजाल के रूप में लगभग 20 महीने तक जीवित रह सकता है, लेकिन नम मिट्टी में 5-8 महीने तक।)
- It infects more than 188 crop species in 32 families.
(यह 32 कुलों की 188 से अधिक फसल प्रजातियों को संक्रमित करता है।)
- Sclerotia spread through irrigation water.
(स्क्लेरोशिया सिंचाई के पानी के माध्यम से फैलता है।)
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Management (प्रबंधन):-
- Avoid excess doses of fertilizers.
(उर्वरकों की अधिक मात्रा से बचें।)
- Adopt optimum spacing.
(उचित दूरी अपनाएं।)
- Eliminate weed hosts.
(खरपतवारों को नष्ट करें।)
- Apply organic amendments.
(जैविक संशोधनों का उपयोग करें।)
- Avoid flow of irrigation water from infected fields to healthy fields.
(संक्रमित खेतों से स्वस्थ खेतों में सिंचाई के पानी के प्रवाह से बचें।)
- Deep ploughing in summer and burning of stubbles.
(गर्मियों में गहरी जुताई करें और ठूंठ को जलाएं।)
- Grow disease tolerant varieties like Shiva (WGL 3943).
[शिवा (WGL 3943) जैसी रोग प्रतिरोधी किस्में उगाएं।]
- Spray Propiconazole@0.1% or Hexaconazole@0.2% or Validamycin@0.2%.
(प्रोपिकोनाज़ोल @0.1% या हेक्साकोनाज़ोल @0.2% या वेलिडामाइसीन @0.2% का छिड़काव करें।)
- Seed treatment with Pseudomonas fluorescens @ of 10g/kg of seed followed by seedling dip @ of 2.5 kg of product/ha dissolved in 100 litres and dipping for 30 minutes.
(स्यूडोमोनास फ्लोरेसेंस के साथ बीज उपचार @ 10 ग्राम/किलो बीज और फिर पौध डुबाना @ 2.5 किलो उत्पाद/हेक्टेयर को 100 लीटर में घोलकर 30 मिनट तक डुबाना।)
- Soil application of P. fluorescens @ of 2.5 kg/ha after 30 days of transplanting (This product should be mixed with 50 kg of FYM/Sand and then applied).
[30 दिनों के बाद स्यूडोमोनास फ्लोरेसेंस @ 2.5 किलो/हेक्टेयर मिट्टी में डालें (इस उत्पाद को 50 किलो FYM/रेत के साथ मिलाकर डाला जाना चाहिए)।]
- Foliar spray at 0.2% concentration commencing from 45 days after transplanting at 10 days interval for 3 times depending upon the intensity of disease.
(45 दिनों के बाद से 0.2% सांद्रता पर 10 दिनों के अंतराल पर 3 बार पत्तियों पर छिड़काव करें, रोग की तीव्रता के आधार पर।)
Introduction (परिचय):-
The disease was first observed in Japan (1884). In Indonesia, Kresek disease was reported to kill young seedlings completely in 1950. In India, BLB was first reported in 1959 and it is believed that it is introduced from philipines. A severe outbreak of the disease occurred in Bihar and Uttar Pradesh in 1963. In the tropics the disease is usually referred as bacterial blight as it often kills entire young seedlings.
Symptoms (लक्षण):-
- The bacterium induces either wilting of plants or leaf blight.
- Wilt syndrome known as Kresek is seen in seedlings within 3-4 weeks after transplanting of the crop.
- Kresek results either in the death of whole plant or wilting of only a few leaves.
- The bacterium enters through the hydathodes and cut wounds in the leaf tips, becomes systemic and cause death of entire seedling.
- The disease is usually noticed at the time of heading but in severe cases occur earlier also.
- In grown up plants water soaked, translucent lesions appear usually near the leaf margin.
- The lesions enlarge both in length and width with a wavy margin and turn straw yellow within a few days, covering the entire leaf. As the disease progresses, the lesions cover the entire leaf blade which may turn white or straw coloured.
- Lesions may also be seen on leaf sheaths in susceptible varieties.
- Milky or opaque dew drops containing bacterial masses are formed on young lesions in the early morning. They dry up on the surface leaving a white encrustation.
- If the cut end of leaf is dipped in water, bacterial ooze makes the water turbid.
Etiology (रोगजनन):-
- The bacterium is strict aerobe, gram negative, non spore forming, rod shaped with monotrichous polar flagellum of at one end.
- The bacterial cells are capsulated and are joined to form an aggregate mass. Colonies are circular, convex with entire margins, whitish yellow to straw yellow and opaque.
- The bacterium has many strains that differ in ability to infect rice plants.
- Strains in tropical countries are usually more virulent than those in temperate areas like Japan.
Disease cycle (रोग चक्र):-
- The bacterium enters the plant through water pores (hydathodes) along the edges of the leaf and through injuries in roots or leaves.
- It does not enter through stomata.
- BLB is primarily a vascular or systemic disease.
- Bacterial cells move along the vascular tissues causing wilting.
- Rain storms and typhoons help in the spread of the disease.
- Irrigation water also carries the organism from field to field.
- The primary source of infection is through bacterium overwintering in seed (husk and endosperm).
- Bacteria may survive in soil, plant stubbles and debris.
- The pathogen also survives on collateral hosts like Leersia hexandra, Leersia oryzoides, Zizania latifolia, Cyprus rotundus, Cyprus deformis, Phalaris arundinacea, Cyanodon dactylon, etc.
-The bacterial ooze serves as secondary inoculum and cause secondary infection.
Management (प्रबंधन):-
- Grow resistant cultivars like MTU 9992, Swarna, Ajaya, IR 20, IR 42, IR 50, IR 54, TKM 6, Mashuri, IET 4141, IET 1444, IET 2508, Chinsura Boro, etc.
- Resistant donors: Tetep, Tadukan, Zenith, etc.
- Affected stubbles are to be destroyed by burning or through ploughing.
- Judicious use of nitrogenous fertilizers.
- Avoid clipping of tip of seedling at the time of transplanting.
- Avoid flooded conditions or drying of the field (not at the time of flowering).
- Avoid flow of irrigation water from infected to healthy field.
- Seed treatment with Streptocycline (100ppm) along with foliar spray in combination with COC (100 ppm + 500 ppm) gave the best result against bacterial blight.
Important Definitions (महत्वपूर्ण परिभाषाएँ):-
1. Hyperplasia Vs Hypertrophy (हाइपरप्लासिया बनाम हाइपरट्रॉफी):-
