Diseases of castor by SACHIN R KONDAGURI.pptx

Diseases of castor and its management

1. Diseases of Castor Groundnut is an important oilseed crop in India which occupies first position in terms of area and second position in terms of production after soybean. The contribution of groundnut to total oilseeds and edible oil produced in the country is immense and quantified to the tune of 27% and 16% respectively.

2. Fungal Diseases SL No. Disease Causal Organism 1. Seedling blight Phytophthora parasitica 2. Rust Melampsora ricini 3. Alternaria blight Alternaria ricini 4. Brown leaf spot Cercospora ricinella 5. Powdery mildew Leveillula taurica 6. Botrytis Grey mold/Pod rot Botrytis ricini 7. Wilt Fusarium oxysporum f.sp. ricini 8. Stem rot Macrophomina phaseolina Bacterial Disease SL No. Disease Causal Organism 1. Bacterial leaf rot Xanthomonas compestric pv ricinicola Nematode disease SL No. Nematode Causal Organism 1. Reniform nematode Rotylenchulus reniformis Diseases of Castor

3. Grey mold/Grey rot/Blossom blight – Botrytis ricini ( Amphobotrys ricini ) (Sexual stage : Sclerotinia ricini ) Symptoms Symptoms can be seen on leaves, stem, flowers and capsules, being prominent on spikes. (mainly target inflorescence and capsules). Initially water-soaked lesions form on the male flowers at the base of the spike. These flowers rot and are covered by characteristic grey or ash colored growth of the fungus subsequently the disease spreads upward infecting all flowers and capsules which are covered by the fungus thereby involving the entire spike. This is followed by development of cottony white growth which later converts into grey colour due to sporulation. The infected capsules rot.

4. Epidemiology Night temperatures below 22 C followed by rains. Disease cycle The fungus survives through sclerotia on infected seed and crop debris. The fungus attacks first the male flowers because the anthers , being soaked with the rain water or dew, easily retain the fungus spores carried by the wind.

5. Management Adjust sowing time in such a way that crop maturation occurs during dry season. Adopt wider spacing (90 x 60cm). Remove diseased spikes and destroy them. Grow varieties like Jwala with non-spiny capsules and less compact inflorescence. Seed treatment with Carbendazim@3g/kg of seeds. Spray Carbendazim / Thiophanate methyl @1g/L before the onset of cyclonic rains based on weather forecast followed by second spray soon after rains have receded. Application of 20kg urea and 10kg of muriate of potash after removal of diseased panicles may be useful for the growth of panicles that subsequently develop.

6. Wilt - Fusarium oxysporum f.sp . ricini Symptoms When seedlings are attacked cotyledonary leaves turn to dull green colour , wither and die subsequently. Leaves droop and drop off leaving behind only top leaves. Diseased plants are sickly in appearance. Wilting of plants, root degeneration, collar rot, drooping of leaves and necrosis of affected tissue and finally leading to death of plants. Necrosis of leaves starts from margins spreading to interveinal areas and finally to the whole leaf

7. Etiology The fungus produces macroconidia, microconidia and chlamydospores. Macroconidia are falcate shape, hyaline and 5-9 celled. Microconidia are hyaline, thin walled, unicellular and ovoid. The dark walled chlamydospores are also produced. Disease cycle The fungus survives in the soil in the infected plant debris. It is also seed-borne and primary infection occurs through infected seeds or through chlamydospores in soil. Infected seeds play an important role in the perpetuation and spread of the pathogen The secondary infection may be caused by conidia disseminated by rain splash and irrigation water.

8. Management Select disease free seeds for planting. Rogue out and burn disease affected plants and crop debris regularly. Follow crop rotation for 2-3 years with non-host plants like pearl millet, finger millet or other cereals. Follow intercropping with redgram . Seed treatment with Trichoderma viride@10g/kg or Carbendazim@2g/kg seed . Multiplication of 2 kg T. viride formulation by mixing in 1 tonne FYM. Sprinkle water and cover with polythene sheet for 15 days and then apply between rows of the crop. Cultivate wilt resistant varieties, viz., Jyoti, Jwala , Harita , GCH-4, DCH-32, GCH-5, DCH-177, 48-1 and DCH-519

9. Stem rot - Macrophomina phaseolina Symptoms Sudden wilting of plants in patches under high soil moisture stress coupled with high soil temperatures is a common symptom. The plants show signs of water shortage. Within a week, the leaves and petiole droop down and within a fortnight the infected plants dry up. Dark brown lesions are seen on the stem near the ground level. The taproot shows signs of drying and root bark sheds off easily. Fruiting bodies (pycnidia) of the fungus are seen as minute black dots on woody tissues and in pith region.

10. Epidemiology Disease is favoured by soil temperature of 35 C and moisture stress conditions preceding crop maturity and application of more nitrogenous fertilizers. Disease cycle Pathogen survives in soil, plant debris and many cultivated and wild plants as sclerotia and pycnidia. Secondary spread is through sclerotial bodies.

11. Management Burn crop debris containing the sclerotia of the fungus. Seed treatment with Trichoderma viride @4g/kg seed or carbendazim@1g/kg seed. Crop rotation with cereals. Provide irrigation at critical stages of crop growth Soil drenching with carbendazim@ 1g/L, 2-3 times at 15 days interval. Grow tolerant and resistant varieties / hybrids like Jwala , GCH-4 and GCH-6.

12. Bacterial leaf spot - Xanthomonas campestris pv . ricini Symptoms All the above ground parts are attacked by the bacterium. On cotyledons and leaves, water soaked, angular spots are produced. Leaf symptoms are first noticed at the tip which extends to center becoming irregularly angular, dark brown to jet black in colour . Diseased leaves become blighted and plants defoliate. Diseased areas consist of bacterial exudation as small beads on both the surfaces.

13. Management Remove and destroy the infected plant debris. Hot water treatment of seeds at 50-60 C for 10 minutes. Spray Streptocycline @ 0.5 ml/L in combination with Copper oxy chloride @ 3g/L.

14. Seedling blight - Phytophthora parasitica Symptoms The disease appears as circular, dull green patch on both the surface of the cotyledon leaves. It later spreads and causes rotting. The infection moves to stem and causes withering and death of seedling. In mature plants, the infection initially appears on the young leaves and spreads to petiole and stem causing black discoloration and severe defoliation.

15. Etiology The fungus produces non-septate and hyaline mycelium. Sporangiophores emerge through the stomata on the lower surface singly or in groups. The sporangia germinate to produce abundant zoospores. The fungus also produces oospores and chlamydospores in adverse seasons. Epidemiology Continuous rainy weather, low temperature (20-25 C), low lying and ill drained soils.

16. Disease cycle The pathogen is soil borne. The fungus may survive through resistant chlamydospores and oospores and spreads by zoospores carried by rain water. Management Remove and destroy infected plant residues. Avoid low-lying and ill drained fields for sowing. Treat the seeds with Metalaxyl at 3g/kg or T. viride at 10g/kg. Soil drenching with Metalaxyl + Manoczeb @ 2g/L or Copper oxy chloride @ 3g/L. Give need based spray of COC@ 3g/L to avoid further spread of the disease.

17. Rust - Melampsora ricini Symptoms Minute, orange-yellow coloured , raised pustules appear with powdery masses on the lower surface of the leaves and the corresponding areas on the upper surface of the leaves are yellow. Often the pustules are grouped in concentric rings and coalesce together leading to drying of leaves.

18. Etiology The fungus produces only uredosori in castor plants and other stages of the fungus are unknown. Uredospores are two kinds, one is thick walled and other is thin walled. They are elliptical to round, orange-yellow coloured and finely warty. Disease cycle The fungus survives in the self sown castor crops in the off season. It can also survive on other species of Ricinus. The fungus also attacks Euphorbia obtusifolia , E.geniculata , and E.marginata . The infection spreads through air-borne uredospores . Management Rogue out the self-sown castor crops and other weed hosts. Spray Mancozeb 2.5g/L or Propiconazole 1ml/L .

19. Leaf blight - Alternaria ricini Symptoms All the aerial parts of plants viz ., leaves, stem, inflorescences and capsules are liable to be attacked by the pathogen. Irregular brown spots with concentric rings form initially on the leaves and covered with fungal growth. When the spots coaleasce to form big patches, premature defoliation occurs. The stems, inflorescences and capsules also show dark brown lesions with concentric rings. On the capsules, initially brown sunken spots appear, enlarge rapidly and cover the whole pod. The capsules crack and seeds are also get infected.

20. Etiology The pathogen produces erect or slightly curved, light grey to brown conidiophores, which are occasionally in groups. Conidia are produced in long chains. Conidia are obclavate, light olive in colour with 5-16 cells having transverse and longitudinal septa with a beak at the tip. Epidemiology High atmospheric humidity (85-90%) and low temperature (16-20˚C). Disease cycle The pathogen survives on hosts like Jatropha pandurifolia and Bridelia hamiltoniana . The pathogen is externally and internally seed-borne and causes primary infection. The secondary infection is through air-borne conidia.