PLANT DISEASES TIKKA DISEASE OF GROUNDNUTFUNGAL ANGULAR LEAF

PLANT DISEASES TIKKA DISEASE OF GROUNDNUT(FUNGAL) ANGULAR LEAF SPOT OF COTTON(BACTERIAL) TOMATO LEAF CURL(VIRAL) Presented by JYOTHI N

Disease cycle

TIKKA DISEASE OR LEAF SPOT OF GROUNDNUT Tikka disease is the fungal disease of groundnut crop Infection appears when the plants are one or two months old Seen in the month of september Tikka disease in groundnut

CAUSAL ORGANISM Caused by two different pathogens: Cercospora arachidichola: conidiophores are light olivaceous brown, unbranched, geniculate, septate, no haustoria are produced. conidia are light yellow colour, cylindrical and septate Cercosporidium personatum: septate, haustoria are produced due to which the pathogen does not kill the host cells in advance. Conidiophores develop on a stromata, emerge in groups in rupturing the epidermis, olivaceous brown, small, unbranched, septate, geniculate, conidia are obclavate, coloured septate

SYMPTOMS Cercosporia arachidichola: spots are irregular, surrounded by a yellow halo. On the upper surface the necrotic areas are reddish brown to black, lower surface are light brown. Cercosporidium personatum: spots are smaller, circular, dark brown to black in colour, no halos around spots in early stages of development.

DISEASE CYCLE 1)Perennation 2)Primary infection 3)Secondary infection FACTORS 3 days of high humidity, prolonged low temperature and dew, application of nitrogen and phosphetic fertilizers MANAGEMENT Plant debris of the previous crop must be burnt Rotation of crops and deep burying of debris Early planting, alteration in date of sowing, use of early maturing varieties Seed treatment: seed with shell can be treated by sulphuric acid and seeds without shell are disinfected by soaking them in 0. 5% copper sulphate solution or with ‘Agrosan GN’

ANGULAR LEAF SPOT OF COTTON First reported in tamil nadu(madras) later in AP, MP, UP, Gujarat Gossypium species Cotton crop CAUSAL ORGANISM Xanthomonas malvacearum, pseudomonas malvacearum. Bacterium malvacearum, Bacillus malvacearum, Phytomonas malvacearum It is a rod shaped, uniflagellate, aerobic, gram negative bacterium, occurs in pairs, colonies developed on beef agar medium are circular, raised, smooth and shining.

SYMPTOMS SEEDLING SYMPTOMS: Cotyledons show symptoms. small round water-soaked spots, turn brown to black, drying and withering of the seedlings and death of seedlings occurs(seedling blight) LEAF SYMPTOMS: Small water soaked spots appear first on undersurface and then on upper surface, later the spots become angular(hence the angular leaf spot)brown to black. leaves infected may curl, die and fall off

STEM AND FRUITING BRANCH SYMPTOMS: long dark brown to black sunken lesions covering their whole circumference and this is called ‘black arm’. COTTON BALL OR FRUIT SYMPTOMS: Water-soaked spots which turn dark brown to blackand become sunken. Bacteria invade and rot the balls and cause them to drop.

DISEASE CYCLE 1. 2. 3. PERENNATION PRIMARY INFECTION SECONDARY INFECTION FACTORS High relative humidity, high moderate temperatures, rains accompained with strong winds Primary infection-30 degrees and secondary infection-35 degrees MANAGEMENT Diseased plant debris should be removed, deep ploughing after harvest Crop rotation, late sowing, good tillage, adding potash to soil Seed treatment(externally)with conc. sulphuric acid for 15 min, rinse with water, dry, treat with Agrosan GN. Seed treatment(internally)with antibiotics is recommended. Seeds are soaked in 1000 ppm of streptomycin overnight Use of HC 9, BJA 592, Reba-B 50, DHY 286 etc

TOMATO LEAF CURL Devastating disease in Middle East, Southeast Asia, North and Central Africa, Southern Europe and since 1993 the Carribean Basin islands of Hispanoila and Jamaica In India if plants infected within 20 days the loss ranges upto 92% and if 35 to 50 days old crops result in 74% and 29% loss

CAUSAL ORGANISM Virus belongs to geminivirus group Causal organism is Tobacco virus 16 and Nicotiana virus 10 Genome is single, circular, single stranded DNA SYMPTOMS Infected plants show stunting due to shortening of internodes Leaves are smaller, usually rolled upwards and inwards, become deformed and severly chlorotic The older curled leaves become leathery and brittle Whole plant looks pale and produces more lateral branches resulting in bushy appearance Drop of flowers, fruits fail to set and no more marketable fruit is produced Symptoms are delayed at low temperatures

Chlorosis Inward and upward curling

TRANSMISSION Virus -transmitted in nature and the vector is the whitefly, Bemisia tabaci Virus can be acquired by the vector after feeding on an infected plant for 15 to 30 min Latent period of 6 hrs is seen after which the virus can be inoculated into a healthy plant during feeding Whiteflies remain viruliferous for about 2 weeks

MANAGEMENT Wild tomato(Lycopersicon peruvianum)show high degree of resistance to the virus Use of insecticides such as methyl parathion(0. 02%) and dimethoate(0. 05%) as a spray or carbofuran as soil application Infected plants should be immediately removed from the field 5 to 6 rows of barrier crops should be sown around tomato field atleast 2 months before transplanting seedlings in the field After fruit formation, krishi oil(2%)should be sprayed at 10 days interval

PRINCIPLES OF PLANT DISEASE CONTROL 1. 2. Avoidance of the pathogen Proper selection of geographic area Selection of field Choice of timing of sowing Choice of disease escaping varieties Selection of disease-free seed and plant stock Cultural practices Exclusion of the pathogen Quarantine measures Seed certification Plant disease notification Prevention of sale of diseased plant

3. Reduction or eradication of pathogen inoculum Cultural practices Physical methods Chemical methods Biological methods 4. Resistance or immunity to pathogen BIOLOGICAL CONTROL OF PLANT DISEASES 1. 2. Natural biological control(suppressive soils) Suppressiveness in conducive soil Mode of action of Biological Control Agents(BCA’s) Antagonism-parasitism, predation, competition, antibiosis Hypovirulence Induction of host resistance