BIOLOGY, EPIDEMIOLOGY AND MANAGEMENT OF Alternaria spp. CAUSING EARLY BLIGHT OF TOMATO (Lycopersicon esculentum Mill.)

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dc.contributor.advisorKRISHNA PRASADJI, J
dc.contributor.authorRAMA DEVI, P
dc.date.accessioned2017-10-12T06:56:32Z
dc.date.available2017-10-12T06:56:32Z
dc.date.issued2015
dc.descriptionD5198en_US
dc.description.abstractThe present investigation on the biology, epidemiology and management of early blight of tomato caused by Alternaria spp. was carried out in the Horticultural Research Station, Dr. Y. S. R. Horticultural University, Venkataramannagudem, West Godavari district of Andhra Pradesh during 2010-11 to 2013-14. Early blight symptoms on tomato leaves were observed as irregular to regular brown necrotic spots with obscured concentric rings and as brown almost circular necrotic spots with characteristic concentric rings. A. alternata from samples showing first type symptoms and A. solani from samples with second type of symptoms were isolated and pathogenicity of the two Alternaria spp. was proved. The disease incidence was found to range from 31.76 to 70.56% and severity from 20.06 to 54.43%, with highest mean incidence (52.47%) and severity (34.27%) in West Godavari district. Variety of the crop plant, soil type and pH were not found to greatly influence early blight incidence and severity. However, age of the crop was found to have a positively significant correlation with per cent disease incidence and disease severity with r values of 0.79 to 0.87 and 0.62 to 0.85, respectively in the districts surveyed. Colonies of most A. alternata isolates were light grayish to brown while that of A. solani were mostly light grayish brown on potato carrot agar. Differences in radial growth (6.48 to 8.98 cm), time for sporulation (8.00 to 12.23 days), sporulation (9.56 x 104 to 32.44 x 104/ml) and conidial dimensions (27.54 to 59.99 µm length; 9.41 and 18.29 µm breadth and 3.56 to 22.76 µm beak length) among A. alternata isolates were noticed. Such differences were also observed among A. solani isolates (6.89 to 8.08 cm in radial growth; 16.17 to 18 days for sporulation and 0.67 to 2.15 x 104/ml in number of spores). A. solani isolates’ spores were longer (99.89 to 172.35 µm) than A. alternata spores with beak length being the primary determinant of spore length. Incubation period among A. alternata (4.0 to 5.33 days) and A. solani (4.33 to 5.0 days) isolates did not differ significantly. Isolates also exhibited wide and significant differences in the number of spots produced, total spotted area and disease ratings. The twenty isolates i.e., 16 of A. alternata and four of A. solani were grouped into five clusters by Ward’s minimum variance dendrogram using Mahalanobis-Euclidean (D2) distance statistic. The chief characters viz., number of spots produced, per cent spotted area and conidial beak length that contributed the maximum to clustering of isolates were identified by Wilks’ test. Isolates were found to cluster based on the morphological and pathogenicity characters but not on the basis of geographical relationships. The apparent rate of infection (r) varied in both the seasons. The r values ranged between a maximum of 0.440 during 66 and 70 DAT and a minimum 0.006 during 96 and 100 DAT with a mean of 0.075 units/day in 2010-11 crop season. In 2012-13, r values were between a maximum of 0.290 and a minimum of 0.025 with a mean of 0.068 units/day. Regression analysis of PDI with DAT revealed that the age of the plant was an important factor explaining disease development up to 98 to 99%. Maximum temperature ranging between 25.50 C and 32.750 C and morning relative humidity ranging between 68 and 95% were found to be significantly positively correlated (r =0.35 and 0.39, respectively). A regression equation with the data sets of weather and PDI for the two seasons was constructed which revealed that maximum temperature and morning relative humidity would influence early blight development in tomato up to 46%. Y = -239.67 + 5.88 (max temp*) – 3.28 (min temp*) + 1.92 (RH 0800*) N = 46 R2 = 0.46 F value = 12.04 Standard error = 16.30 * significant at 5% Alternaria spp. were isolated from both surface sterilized and unsterilized seeds following blotter paper and agar plate methods indicating both externally and internally seed borne nature of the pathogen. The pathogen was found to exhibit greater survival at deeper depths in soil as isolation frequency of the pathogen from samples stored at different depths (0 to 120 cm) increased from 5.31 to 20.63%. Stemphylium botryosum was found more aggressive in interaction with A. alternata by producing significantly more number of spots. Salicylic acid was not found effective at concentrations between 100 and 500 ppm as a systemic acquired resistance (SAR) elicitor in reducing the severity of early blight. However, significant reduction in number of spots over unsprayed check (35.33/leaf) was recorded in plants treated with Pseudomonas fluorescens (24.50/leaf) and Trichoderma asperellum (27.17/leaf). Tebuconazole, copper oxychloride, chlorothalonil, dimethomorph, mancozeb and azoxystrobin in that order significantly inhibited the radial growth, sporulation and spore germination of A. alternata in vitro. Tebuconazole seed treatment followed by eight foliar sprays of tebuconazole and copper oxychloride alternated with each other recorded the lowest terminal disease severity (PDI=35.39%) that was lesser by 53.17% than that recorded in check (75.57%) and gave the maximum yield (25.71 t/ha) with 86.47% increase over control and with a benefit : cost ratio of 1.60. Significantly higher yield (19.38 t/ha) was also realized with the treatment with P. fluorescens as four foliar sprays preceding four sprays of tebuconazole and copper oxychloride alternated with each other that had significantly decreased disease severity.en_US
dc.identifier.urihttp://krishikosh.egranth.ac.in/handle/1/5810032959
dc.keywordsBIOLOGY, EPIDEMIOLOGY, Alternaria spp., BLIGHT , TOMATO,Lycopersicon esculentum Mill.en_US
dc.language.isoen_USen_US
dc.pages176en_US
dc.publisherAcharya N.G. Ranga Agricultural University, Gunturen_US
dc.research.problemBIOLOGY, EPIDEMIOLOGY AND MANAGEMENT OF Alternaria spp. CAUSING EARLY BLIGHT OF TOMATO (Lycopersicon esculentum Mill.)en_US
dc.subPlant Pathologyen_US
dc.subjectnullen_US
dc.themeBIOLOGY, EPIDEMIOLOGY AND MANAGEMENT OF Alternaria spp. CAUSING EARLY BLIGHT OF TOMATO (Lycopersicon esculentum Mill.)en_US
dc.these.typePh.Den_US
dc.titleBIOLOGY, EPIDEMIOLOGY AND MANAGEMENT OF Alternaria spp. CAUSING EARLY BLIGHT OF TOMATO (Lycopersicon esculentum Mill.)en_US
dc.typeThesisen_US
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