Detection and Management of Early Blight of Potato Caused by Alternaria alternata

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Potato is the King of vegetables and third most important food commodity in terms of human consumption after rice and wheat. Potato has immense potential for food and nutritional security of the world. India is the second largest producer of potato in the world. Diseases are major constraint resulting in loss in tuber yield of potato.Early blight is one of most important foliar diseases of potato and reported 24 to 54% disease severity in South Eastern Rajasthan. Consequently, the present studies have been undertaken to overcome crop loss by finding suitable disease management. The present investigation on “Detection and Management of Early blight of potato caused by Alternaria alternata.” was carried out at Agricultural Research Station, Agriculture University, Kota during Rabi 2019-20 under laboratory as well as field condition. First symptom of the disease was seen on older leaves as small dark brown, frequently round necrotic spots, the spots enlarged with characteristics in the centre to produce a target board effect and the colour of the spots altered from brown to dark brown. The disease symptoms perceptibly seen on all plant parts viz., leaf, stem and petioles. The contiguous spots eventually coalesced to form large irregular spots primary to drying and defoliation. The diseased plants formed less tuber and size of tuber as compared to healthy plant. Pathogen was isolated by single spore isolation technique from infected potato leaves and pure culture of the fungus was obtained on potato dextrose agar medium after eight days of inoculation which showed brownish colour. The studies on the morphological and colony characters of the isolated pathogen showed its close identify with Alternaria alternata. The mycelium was greyish brown to black producing conidiophores moreover singly or in small groups which were straight or flexuous brown to olivaceous brown. The conidia were solitary straight or muriform or ellipsoidal narrowing to beak, pale or olivaceous brown. For further, identification of pathogen was sent to Indian Type Culture Collection (ITCC), Division of Plant Pathology, IARI, New Delhi-110012. They identified culture as Alternaria alternata with code number 295012. Significantly maximum inhibition of mycelial growth was obtained with Trichoderma viride (57.08%) followed by T. azospirillum (50.00%), T. harzianum (43.26%) and T. virens (37.08%) of the pathogen after 48hours of incubationby dual culture technique. Among the media tested the potato leaf agar and was significantly superior and most effective medium for sporulation as well as potato leaf broth medium for dry mycelial weight followed by PDA. However potato leaf agar was also superior for sporulation of A. alternata. Whereas, the potato stem agar, V-8 juice agar, pea agar, oat meal agar and czapek’s agar medium were least effective in mycelial growth.Screening of twenty eight genotypes/varieties of potatofor resistance to early blightdisease revealed six genotypes viz., CP-3021, 3153, Atlantic, Chip-3, Jx-161 and MS/78-62 as resistant reaction. While thirteen genotypes i.e., NJ-1501, MP-97, NJ-44, NJ-34, MP-97-1606, PS/RI-135, JI-93-77, MS/94-118, JN-1177, Kufri Sindhuri, Kufri Pukhraj, Kufri Khayati and Kufri Pushkar moderately resistant. However, six genotypes viz., NJ-85, NJ-1530, J-92-164, MS/92-2105, J/93-4 and Kufri Bahar susceptible, while three genotypes i.e., MP/94-322, NJ-1 and MS/85- 1663 as highly susceptible. Fungicides viz., Propiconazole 25% EC and Hexaconazole 5% EC @ 10, 20 and 50 ppm concentrations and Mancozeb 75% WP @ 1000 and 1500 ppm and Difenconazole 25% EC @ 50 ppm significantly were recorded 100 per cent inhibition as compared to rest of the fungicides.Next best treatments in order of merit were Difenconazole 25% EC @ 10 and 20 ppm, Mancozeb 75% WP @ 500 ppm and Azoxystrobin 23% SC @ 10, 50 and 100 ppm, Picoxystrobin 22.52% SC andPyraclostrobin 20% WG @ 10, 50 and 100 ppm concentrations against the Alternaria spp. The studies on foliar spray of fungicides against early blight under field condition revealed that the highest per cent reduction over control i.e. 72.3% was recorded in Dinfenconazole 5% EC @ 250 ml/ha followed by spraying of Propiconazole 25% EC @ 500 ml/ha (71.3%) and Azoxystrobin 23% SC @ 500 ml/ha 70.2% after first and second spray. Next best treatments in order of merit were Picoxystrobin 22.52% SC @ 400 ml/ha i.e. 68.2% which was on par with Pyraclostrobin 20% WG @ 500 ml/ha 66.3% disease control after 14 days of each spray, while Hexaconazole 5% EC @ 500 ml/ha gave 63.6% and Mancozeb 75% WP @ 1500 g/ha showed 57.4% disease control 14 days after first and second spray. Significantly maximum percent dry matter was recorded by foliar spray of Azoxystrobin 23% SC @ 500 ml/ha (25.00%). Next best treatments in order of merit were Pyraclostrobin 20% WG (24.03%), Picoxystrobin 22.52% SC (23.87%) and Hexaconazole 5% EC (23.07%), Mancozeb 75% WP (22.23%) and Difenconazole 25% EC (22.00%). Whereas, 21.20% was recorded by Propiconazole 25% EC and 20.13% in control. The highest (269) total tuber no. per plot was observed in Azoxystrobin 23% EC @ 500 ml/ha followed by Picoxystrobin 22.52% SC (260), Pyraclostrobin 20% WG (258), Difenconazole 25% EC (257) and Propiconazole 25% EC (247) which were at par with each other. However, Mancozeb 75% WP (238), while minimum was recorded in untreated checks i.e. (198) tubers.The studies on the effect of foliar sprays of various fungicides on tuber yield revealed that Azoxystrobin 23% SC @ 500 ml /ha gave highest 16.17kg total tuber yield per plot followed by Picoxystrobin 22.52% SC (15.8 kg), Pyraclostrobin 20% WG (15.4 kg), Difenconazole 5% EC (14.93 kg) and Propiconazole 25% EC (13.83 kg), Mancozeb 75% WP (14.63 kg) and least tuber yield in Hexaconazole 5% EC (12.93 kg) as compared to control (10.57 kg). The highest cost benefit ratio was obtained in strobolin group fungicides followed by Mancozeb 75% WP and trizole group fungicides. Cost benefit ratio was least in control.
Detection and Management of Early Blight of Potato Caused by Alternaria alternata