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Publisher: Acharya N.G. Ranga Agricultural University
Language: en_US
Type: Thesis
Pages: 217
Agrotags: null
Keywords: CHARACTERIZATION, MANAGEMENT, Alternaria porri, Ellis Cif., PURPLE LEAF, BLOTCH, ONION, Allium cepa L.
Abstract: Purple leaf blotch caused by Alternaria porri is one of the most destructive diseases of onion causing significant bulb yield losses. Keeping in view the importance of disease, studies were conducted on cultural, morphological, pathological and molecular diversity, in vitro efficacy of fungicides and integrated management of disease at field by using fungicides and bioagents at Horticultural Research Station (HRS), Anantharajupeta. Survey was carried out to understand the disease severity in major onion growing areas i.e YSR Kadapa and Kurnool districts of Andhra Pradesh. Cultural and morphological characters of the native isolate were studied on six different media viz. Carrot agar, Corn meal agar, Czapek’s Dox agar, Host leaf extract agar Potato dextrose agar and Yeast extract agar medium. Out of all the media tested, growth was fast in Czapek Dox medium and slow in corn meal agar medium. Sporulation was best in Host leaf extract agar and potato dextrose agar and less in corn meal agar and Yeast extract agar medium. The pathogen produced septate mycelium. Conidiophores were produced either singly or in small groups. The conidiophores were straight or flexuous some times geniculate, septate, pale or mild brown in colour and measured upto 135μ long and 7-10 μ thick, with one to several conidial scars. xvii Conidia are straight or curved, rostrate, beak generally equal to the length of the body of the conidium pale brown to mild golden brown in colour. Overall length of the conidia ranged from 70-265 μ, 10-21 μ thick in the broadest part with 7-12 transverse and zero to six longitudinal septa, beak flexuous, pale 2-4 μ thick and tapering. A total of 15 Alternaria porri isolates were collected from different locations of Andhra Pradesh, Karnataka and Telangana. Later the isolates were identified and pathogenicity and virulence studies were conducted and found that leaves and the morphological character of the re-isolated organisms confirmed the pathogenicity. Among the isolates, Anantharajupeta (AP-1), Mydukur (AP-3), Gonegandla (AP-4) and Nandikotdur (AP-5) isolates were found highly virulent and potential with highest 41.67 to 56.58 PDI. Cultural and morphological characters of 15 isolates were studied. Conidial length of the isolates ranged from 23-170μ, with an average length of 96.5μ, width from 15-23μ, beak length ranging from 6-29μ and with beak width of 4-9μ. Colour from pale to mild golden brown, horizontal septa ranging from 3-13, with an average of 6-8 between isolates and vertical septa ranging from 0-5, with an average of 2-3 between isolates. Colony growth rate was fast in 8.14 mm in AP-1 and slow in 3.43 mm in KA-2 with an average growth rate of 5.74 mm per day among the fifteen isolates. Molecular characterization was done using 5.8s rDNA specific ITS1 and ITS4 primers. All the 15 isolates of A. porri yielded single PCR amplified product of 560 bp confirming the pathogen identity. Out of 15 isolates, five samples viz., AP-1, AP-4, AP-5, KA-2 and TS1 were sequenced and phylogenic tree was constructed and isolates were divided into two clades. Two groups AP-1 and AP-4; KA-2 and TS-1 were aligned in Clade I and AP-5 alone was grouped in clade II. Genetic diversity studies were carried out to assess the degree of genetic diversity/relatedness among 15 isolates of A. porri. Out of 10 SSR molecular markers used, only four SSR primers i.e., SSR-5 (115 bp) for KA-4, SSR-7 (215 bp) for KA-3, SSR-8 (250 and 340 bp) for AP-2 and SSR-10 (153, 237, 245 and 450 bp) for AP-6, AP-3, AP-6 and AP-4 respectively, produced unique bands. The PIC (Polymorphic Information Content) value ranged between ranged from 1.0 (SSR-1 and SSR 6) to 0.249 (SSR-1 and SSR-4) with an average of 0.826 for all 10 primers among the 15 isolates. In vitro screening of eight fungicides against native pathogen isolate revealed the efficacy of fungicides at varied levels. Hexaconazole was found effective and inhibited cent per cent growth at 1000 and 1500 ppm. Mancozeb was least effective and the mean inhibition per cent was 53.63 among the treatments. The highest toxicity index was observed in hexaconazole xviii (454.85) followed by propiconazole (431.05) on maximum toxicity index of 500. The least toxicity was 268.16 in the treatment of Mancozeb. In vivo evaluation of fungicides revealed that, hexaconazole at 0.1% with 12.50% of PDI and highest CB ratio (2.11) was found significantly superior over other treatments. Increased bulb yield over control and other treatments was observed in hexaconazole. Area under disease progress curve (AUDPC) calculated and yield (t/ha) data were also recorded. The data reveals that in T2 (Hexaconazole 0.2%), lowest AUDPC (399) was observed with highest yield (29.30 t/ha). While in control, highest AUDPC (1008) and lowest yield (9.67 t/ha). Fourteen fungal bioagents viz., Th-1, Tsp-2, Tsp-3, Th-4, Tsp-5, Tkn-6, Th-7, Tlb-8, Trs-9, Th-10, Tsp-11, Tsp-12, Tsp-13 and Tsp-14 comprising of Trichoderma harzianum, , T. koningii, T. reesii and T. longibrachiatum and six bacterial bioagents viz., P. fluorescens-1- Pf- 6 were evaluated against the pathogen and Th4 significantly superior in both in non volatiles (59.97%) and volatiles (57.325%) production over other Trichoderma isolates tested. Evaluation of 28 onion cultivars/ lines under two different agro-climatic conditions i,e., Anantharajupeta and Mahanandi to find the source of resistance, revealed that none of the genotypes was found to be either resistant or immune to the disease . However, the cultivars Bhima Super and Arka Kalyan showed moderately resistant reaction at both the locations. Management studies conducted over two seasons revealed that the integrated strategy with soil application of T.harzianum enriched FYM @ 100 kg/ha + seed treatment with T.harzianum @ 8g/kg of seed + two foliar sprays, one with liquid formulation of T.harzianum @ 5 ml/lt at first appearance of the disease followed by hexaconazole @ 0.2% at fortnightly interval was found significantly effective in reducing the disease intensity by recording a lowest PDI (14.09) with 79.69% disease reduction and yield 29.94 t/ha with 87.81% increased yield over control. This treatment recorded highest (1.99) cost benefit ratio, which was followed by tolerant variety Bhima Super (1.81).
Description: D5732
Subject: Plant Pathology
These Type: Ph.D
Issue Date: 2018
Appears in Collections:Thesis

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