1. Diseases of rice

A detailed description of rice diseases has been furnished in an easy manner

1. Diseases of Rice N . H. SHANKAR REDDY Ph.D., Plant Pathology Annamalai University

2. Important diseases of rice DISEASES CAUSAL ORGANISM FUNGAL DISEASES Blast Pyricularia oryzae Brown spot or Sesame leaf spot Bipolaris oryzae ( Helminthosporium oryzae ) Sheath blight Rhizoctonia solani Sheath rot Sarocladium oryzae Stem rot Sclerotium oryzae Foot rot or Bakanae disease Fusarium moniliforme False smut Ustilaginoidea virens Udbatta disease Ephelis oryzae Grain discolouration Complex disease

3. BACTERIAL DISEASES   Bacterial leaf blight(BLB) Xanthomonas oryzae pv . oryzae Bacterial leaf streak Xanthomonas oryzae pv . oryzicola VIRAL DISEASES Tungro Rice tungro virus [RTV] Grassy stunt Rice grassy stunt virus Dwarf Rice dwarf virus Yellow dwarf Phytoplasma like organisms Rice khaira Zn deficiency

4. 1. Rice blast - Pyricularia oryzae ( Magnaporthe grisea ) Symptoms Typical spindle to diagonal, both end pointed (different from brown spots), reddish brown margin and the center is grayish white ( strw colour ).   The pathogen produces three different symptoms viz., leaf blast , nodal blast and neck blast .

5. Leaf blast Susceptible at Seedling stage Tillering stage Panicle initiation stage On the leaves, spindle shaped spots are formed with whitish grey centre and dark brown margin. These spots coalesce together and cause quick death of leaves

6. Nodal blast/ culm bblast On nodes, blackish to brown lesions on node which gradually spread to node, in severe cases leads 100 % yield loss.

7. Neck blast/ panicle blast The infected neck region of the panicle show dark brown to black spots and shriveled . The affected plants develop chaffy grains/ light weight grains . The fungus infects the grain also and the infected grains become dark brown.

8. Mode of spread The secondary spread of the disease is through air borne. Survival The pathogen survives as dormant mycelium and conidia in the infected straw and seeds. Also, collateral hosts like Panicum repens , Leersia hexandra , Echinochloa crusgali also harbour the pathogen Epidemiology Intermittent drizzles, cloudy weather, high RH (above 92 per cent), low temperature

9. Management Suceptible varieties are mansuli , jumli Seed treatment with [ Captan / thiram / carbendazim @ 2g / kg (or) P.fluorescens @ 10g / kg of seed]. Seedling root dipping can also be followed with P.fluorescens . Avoid closer spacing of seedlings in the main field and excess dose of nitrogenous fertilizers. Grow resistant varieties like CR 1009, Co 43 & 44, ADT 36, ADT 39 and 40. Spray with Pseudomonas fluorescens @ 2% or Iprobenphos @ 500 ml/ha or Tricyclazole @ 400g/ ha can be followed.

10. Fungi produces two toxins - α - Picolinic acid, Pyricularin Fungus produce pyriform conidia (2 septate and 3 celled)

11. 2. Brown leaf spot - Helminthosporium oryzae / Bipolaris oryzae Symptoms Numerous brown, round to oval spots (sesame shaped sports) appear on the leaves and leaf sheaths. The spots appear like sesame and hence the name sesame leaf spot. The grains also become infected and dark brown spots can be seen on the glumes. The disease is responsible for the Bengal famine of 1942-43.

12. Mode of spread The primary spread is through infected seeds and the secondary spread is through air borne conidia Epidemiology 28-30 C with RH 90 – 92 %

13. Management Use disease free seeds. Seed treatment either with chemicals viz ., Captan / thiram / carbendazim @ 2g / kg (or) bio control agent P. fluorescens @ 10g / kg of seed. Grow resistant varieties [Co 44, Bhavani ] Spray the crop with Carbendazim @ 250 gm/ha or Mancozeb 1 kg/ha.

14. 3. Sheath blight - Rhizoctonia solani Symptoms The fungus affects the crop from tillering to heading stage. On the leaf sheath oval or elliptical or irregular greenish grey spots are formed. As the spots enlarge, the centre becomes greyish white with an irregular blackish brown or purple brown border. In the advanced stages brown colour sclerotia (Irregular shaped) are formed in the infected tissues.

15. Mode of spread The pathogen spreads through irrigation water Survival The pathogen can survive as sclerotia and mycelium

16. Management Avoid flow of irrigation water from infected to healthy fields. Summer ploughing helps to reduce soil borne sclerotia . Avoid excess dose of nitrogenous fertilizers. Spray with Carbendazim @ 250g / ha or chlorothalonil @ 1kg / ha or Propiconazole @ 0.1 % during tillering stage can be followed

17. 4. Sheath rot - Sarocladium oryzae Symptoms The disease affects the boot leaf covering the panicle. The affected areas shows grayish brown, oblong lesions on the upper most leaf sheath with a grey centre and brown margins. In severe conditions the whitish mycelial growth can be observed in the panicle inside the sheath. The young panicles if affected remain inside the sheath or emerge partially.

18. Survival and Mode of spread The pathogen survives in the infested seeds and spreads through air borne conidia. The infected seeds also spread the disease

19. Management Avoid excess dose of nitrogen fertilizers. Adopt optimum spacing. Spray with carbendazim @ 250g/ha or mancozeb @ 1kg / ha or chlorothalonil @ 1kg / ha or NSKE (5%), or Ipomoea / Prosophis leaf powder extract at booting stage controls the disease.

20. Write differences between Sheath rot and Sheath blight diseases Sl.no Sheath rot disease Sheath blight disease 1 Caused by Sarocladium oryzae and its perfect stage is Acrocylindricum oryzae Caused by Rhizoctonia solani and its perfect stage is Thanetophorus curcumeris 2 The disease affects the boot leaf covering the panicle or the upper most leaf sheath Affects the crop at the collar region or the base of the plants at the water surface 3 The fungus produces conidia The fungus produces sclerotia 4 The fungus spreads through air borne conidia and pathogen is also seed borne The pathogen is soil borne and spreads through irrigation water 5 The disease is severe during boot leaf stage The disease is severe during maximum tillering stage 6 The pathogen survives in the infected plant debris The pathogen survives as sclerotia in soil

21. 5. Stem rot - Sclerotium oryzae Symptoms Small, black, irregular lesions appear on the outer leaf sheath. Theses spots enlarge and reach the inner leaf sheath. Finally the infected leaf sheath rots and sclerotia are formed in the host tissues.

22. Mode of spread The pathogen spreads through irrigation water. Survival The pathogen survives as soil borne sclerotia in the infected stubbles and straw

23. Management Summer ploughing and burning the stubbles left in the infested fields. Balanced fertilizer application. Avoid flow of irrigation water from infected field to healthy field.

24. 6. Foot rot or Bakanae disease – Fusarium moniliforme / Gibberella fujikuroi Symptoms Infected plants several inches taller than normal plants in seedbed and field Thin plants with yellowish green leaves and pale green flag leaves Reduced tillering and drying leaves at late infection Partially filled grains, sterile or empty grains for surviving plant at maturity In the seedbed, infected seedlings with lesions on roots will die, which may die before or after transplanting .

25. Management Seed treatment with captan or carbendazim or thiram @ 2g / kg of seed. Seed treatment using fungicides such as thiram or thiophanate -methyl or benomyl is effective before planting or Benomyl at 1-2% of seed weight may be used as dry seed coating

26. 7. False smut - Ustilaginoidea virens It is also called as Green smut or Lakshmi disease as the farmers believe that the lakshmi disease affected fields normally results in a bumper harvest. Symptoms The disease appears on the ears and converts individual grains in to greenish smut balls. The infected ovaries are transformed in to large, velvety green masses. Usually only few grains are affected in a panicle.

27. Mode of spread The chlamydospores are air borne spores but do not free themselves from the spore balls easily because of the presence of the sticking material. Survival The pathogens survives as sclerotia and chlamydospores in the soil

28. Management Seed treatment with carbendazim 2 g/kg of seeds. Spraying of copper oxychloride @ 2.5 g/litre or Propiconazole @ 1.0 ml/litre at boot leaf and milky stages will be more useful to prevent the fungal infection. At tillering and preflowering stages, spray Hexaconazole @ 1ml/lit or Chlorothalonil 2g/lit.

29. 8. Udbatta disease - Ephelis oryzae Symptoms The affected panicle emerges from the leaf sheath as a slender dirty grey coloured, cylindrical spike, rod like hard structures . They very much resemble as ‘’ udbatta ’’ hence the name is given as udbatta disease. No grains are formed in the affected panicles

30. Mode of spread and Survival The pathogen is externally seed borne and survives in the infested seeds. Epidemiology A soil temperature of around 28 C and abundant soil moisture favour the disease.

31. Management Use disease free seeds for sowing. Seed treatment with Captan or Thiram . Hot water treatment of the seeds at 50-54 C for 10 minutes before sowing gives effective control of the disease.  Solar treatment of seeds is effective in killing the pathogen carried in the seeds, if any

32. 9. Grain discolouration –Fungal complex disease Symptoms Dark brown to black spots appear on the grains. The infection may be external / internal causing discolouration [Red, yellow, orange, pink] of the glumes / kernels or both. Many fungi are found involved in the disease depending on the locality.

33. Management Spray the crop at boot leaf stage with mancozeb 1kg/ha or captofal 250 g/ha or Carbendazim 250 g/ha. Store the grain with less than 11 % moisture content.

34. 10. Bacterial leaf blight - Xanthomonas oryzae pv . oryzae Symptoms i . Leaf blight phase Small water soaked streaks appear at the margin of the lamina near the tip which enlarges and become as straw coloured necrotic patch. The inner portion of the diseased leaves also shows wavy margin. Under humid condition, creamy white bacterial ooze characteristics of the disease can also be observed. ii. ‘‘ kresek ’’ or wilt phase Destructive phage with wilting and yellowing of seedlings . No tillering occurs , leaves and wilting hanged downwards. iii. Yellow leaf phase The affected plants show pale yellow discolouration . The youngest leaf in a hill may turn yellow or white.

35. Management Avoid clipping of tip of the seedling at the time of transplanting. Use optimum dose of fertilizers. Hot water treatment of seeds for 10 minutes at 52 – 54 C Grow resistant varieties like IR-20, IR-36, TKM-6 Spray streptomycin sulphate and tetracycline combination @ 300g + copper oxy chloride @ 1.25kg/ha

36. OOZE OUT TEST When affected leaves are cut and immersed in clear water in a test tube, a characteristic turbid ooze of the bacterium streaming from the vascular bundles can be observed.

37. 11. Bacterial leaf streak - Xanthomonas oryzae pv . oryzicola Symptoms The infected leaves shows fine translucent streaks on the veins and the lesions enlarge lengthwise and turn brown. Bacterial exudates appear on the lesions at high humidity which later dry and remain on the lesions as particles.

38. Management Seed soaking with 0.25% streptocycline and hot water treatment at 52 C for 10 min. Spray with Agrimycin @ 100 ppm or streptocycline @100 ppm twice at 10 days intervals.

39. 12. Tungro - Rice tungro virus [RTV] Symptoms The infected plants show yellow to orange discolouration of leaves and rusty blotches spreading downwards from the leaf tip. The infected plants become stunted . The infected plants produce few spikelets and panicles are small with discoloured grains.

40. Vector The disease is spread through green leaf hopper Nephotettix virescens and N. nigropictus in a non-persistent manner Management Summer ploughing and burning diseased plants (Rogueing and Field sanitation). Control insect vectors by spraying systemic insecticide ( Monocrotophos 0.25 %) Growing disease tolerant varieties like CO-45, IR-50.

41. Iodine test to identify RTV Composition of iodine solution [Iodine – 2g, Potassium Iodide – 6g, Water – 100 ml] Dilute 10 ml of the commercial tincture iodine solution available in the medical shops with 150 ml of water

42. 13. Grassy stunt - Rice grassy stunt virus Symptoms Infected plants are stunted and produce excess tillers and have erect growth habit. Leaves are short, narrow, pale green / pale yellow and have numerous rusty brown spots of various shapes.

43. Vector The disease is spread by brown plant hopper ( Nilaparvata lugens ) in a persistent manner. Management Rogueing and Field sanitation Use systemic insecticides to control the vector Grow resistant varieties like IR-28, IR-29, IR-30, IR-32, IR-34 .

44. 14. Rice Dwarf - Rice dwarf virus Symptoms The infected plants show marked stunted growth with chlorotic or whitish specks on the leaves. The number of tillers may be reduced with retarded root growth

45. Vector Leaf hopper Nephotettix nigropictus and Recilia dorsalis. Also weeds like Echinochloa crusgalli harbour the pathogen during off-seasons. Management Rogueing and Field sanitation to destroy the weed host. Spraying with monocrotophos 500 ml / ha to control the insect vector.

46. 15. Yellow dwarf - Phytoplasma disease Symptoms The infected plants are stunted and have yellowish green to whitish green leaves with excessive tillering and leaves become soft and droop slightly. The affected plants are usually sterile.

47. Vector Green leaf hopper Nephotettix virescens and N. nigropictus transmit the disease Management Deep ploughing in summer and burning the stubbles. Grow resistant varieties like IR 62, IR 64. Control of insect vectors with systemic insecticides

48. 15. Rice Khaira Symptoms Initially older Interveinal chlorosis Whitish to yellowish specks present mostly observed in seedling stage (2-3 weeks after transplanting)

49. Management Application of ZnSO 4 @ 20-25 kg/ ha before transplanting. Root dipping @ 2 % ZNO for 1-2 minutes. If pH is 8-9, there is no effect of ZnSO 4

50. Questions ….. ARS/ NET