VARIABILITY, EPIDEMIOLOGY AND MANAGEMENT OF EARLY BLIGHT OF TOMATO CAUSED BY Alternaria solani (Ellis and Martin) JONES AND GROUT IN HIMACHAL PRADESH
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Date
2020-01
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UHF,NAUNI
Abstract
ABSTRACT
Early blight of tomato caused by Alternaria solani is one of the most important and devastating disease of tomato
which causing extensive yield losses in Himachal Pradesh. Survey of disease was conducted during 2018 and 2019 for two
consecutive crop seasons. Severityof disease ranged from 30.75 to 79.28 and 34.78 to 83.25 per cent during 2018 and 2019 crop
seasons in different locations surveyed and maximum disease severity (81.27%) was recorded in Kaned (Mandi) and lowest
(32.77%) in Shoghi (Shimla) of Himachal Pradesh. The associated pathogen was isolated and on the basis of cultural and
morphological characters, identified as Alternaria solani (Ellis and Martin) Jones and Grout. Incubation period of 144 h was
recorded by spray inoculation method on leaves and 240 h and 192 h on stem and fruits by pin prick method. Twenty isolates of
A. solani collected from different locations of five districts showed variation in morphological and cultural characters. RAPD
molecular markers used to detect the polymorphism among these isolates were informative for detecting genetic variability and
divide all the isolates into five groups, the similarity coefficient among the studied isolates was ranged from 4-67 per cent with
an average of 35 percent. Under in vitro conditions temperature of 30°C and 100 per cent level of relative humidity were most
favorable for germination of conidia, whereas, germ tube length was maximum at 25°C and 100 per cent level of relative
humidity. Under pot culture conditions 30°C temperature and 100 per cent RH level were congenial for disease
development.Simple correlation coefficient between disease severity and environmental factors viz., RH morning, RH evening,
minimum temperature and cumulative rainfall were found positive and significant over the years 2018 and 2019. Partial
correlation coefficient between disease severity and temperature maximum, RH morning and evening was positive but nonsignificant
over two years. Multiple correlation coefficients between disease severity and studied environmental factors
suggested that 87.56 per cent of disease severity was attributed by mean temperature, average relative humidity and cumulative
rainfall collectively. The multiple linear regression equation showed that, a unit change in maximum temperature, relative
humidity evening and morning influence the early blight disease of tomato up to an extent of 6.187, 2.371 and 0.940 in the same
direction followed by -1.682 and 0.030 in opposite direction in case of minimum temperature and rainfall. Among seven bioresources
tested under in vitro conditions, cow urine was highly effective at all the concentrations against the fungus followed by
leaf extract of Roylea elegans (kadu). Under field conditions five foliar sprays at ten days interval of Allium satium (garlic)
extract at 5 per cent concentration after initiation of disease was found most effective and gave 56.12 per cent reduction of
disease. Among different systemic acquired resistance (SAR) inducers evaluated under pot culture conditions, benzothiadiazole
(BTH) and ß-aminobutyric acid (BABA) were found most effective and reduced the disease severity. The activity of defence
related enzymes viz. phenol, PO, PPO and PAL were maximum after 96 h and 72 h, respectively, in tomato plants treated with
benzothiadiazole (BTH) and potassium dihydrogen phosphate (KH2PO4). Under field conditions two foliar sprays of
benzothiadiazol (BTH) and potassium dihydrogen phosphate (KH2PO4)) were found effective against the disease which reduced
the severity of disease to 71.21 and 58.40 per cent. Among different fungicides used in vitro, difenconazole, hexaconazole,
copper sulphate, azoxystrobin + difenoconazole, hexaconazole + zineb, tebuconazole + trifloxystrobin, flupyram +
trifloxystrobin and captan + hexaconazole were found the most effective and resulted in complete mycelial growth inhibition
of the pathogen. Under field conditions foliar spray applications of hexaconazole + zineb (0.2%) and azoxystrobin +
difenoconazole (0.15%), five times at ten days interval after commencement of disease were found effective which resulted in
72.37 and 69.79 per cent reduction of disease. In integrated disease management, two foliar sprays of potassium dihydrogen
phosphate (1.3%) after 15 days of transplanting at seven days interval followed by six alternate foliar sprays of hexa
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