EPIDEMIOLOGY AND MANAGEMENT OF LATE BLIGHT OF TOMATO
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Date
2019-04
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UHF,NAUNI
Abstract
ABSTRACT
Late blight caused by Phytophthora infestans (Mont.) de Bary has been recorded as one of the most
destructive disease of tomato among various other diseases. It appeared in moderate to severe form in different
tomato growing areas of Solan, Sirmaur, Shimla and Kullu districts of Himachal Pradesh. The different isolates
of fungus collected from infected leaves and fruits of diseased plants revealed of white to creamish white,
submerged to densely arial mycelium on OMA. Mycelium was coenocytic with sympodial branching of
sporangiophores bearing ovoid to limoniformsporangia. The molecular identification revealed a PCR product of
900bp using ITS1 and ITS4 primers. Thus, based upon morphological, cultural characters and molecular
characters the causative fungus was identified as Phytophthora infestans (Mont.) de Bary. The pathogenicity
tests revealed peculiar symptoms on leaves as water soaked lesions which later enlarged rapidly and turned to
black necrotic spots bearing mildew like downy growth covering most of leaf surface. Dark olivaceous greasy
spots covering fruit surface were also observed. The variability study of different isolates of Phytophthora
infestans (Mont.) de Bary collected from different tomato growing localities of H.P had manifested varied
cultural, morphological, pathogenic and molecular characters. Epidemiological studies revealed that the
temperature of 20ºC, relative humidity of 100%, leaf wetness period of 24 h and inoculum concentration of
5x104 sporangia/ml were optimum for the rapid progression of disease reflecting significant higher infection rate
under artificial epiphytotic conditions. Under field conditions, disease was affected by variation in weather
variables, as cool (16-20°C) and wet weather coupled with high relative humidity (>90%) favoured the
progression of late blight disease. The screening of twenty seven genotypes using detach leaf and whole plant
assay revealed Arka meghali, Solan Lalima, Him Sona, EC-526146 and BT-1012 as moderately susceptible
against the disease. In vitro and in vivo evaluation of fungicides indicated Sectin 60 WG (fenamidone 10%+
mancozeb 50%) and Curzate M8 (cymoxanil8%+mancozeb64%)) as potent inhibitors of P.infestans while garlic
and neem extracts were most promising amongst different botanicals. Trichoderma harzianum had proved the
most efficacious antagonist. Field evaluation studies inferred the soil application of Trichoderma harzianum @
2.5 Kg/50 FYM/ha in combination with six periodic spray of fungicides including fenamidone 10%+ mancozeb
50% @ 0.2% followed by copper oxychloride @ 0.3% and mancozeb @ 0.25% at ten days interval started with
the initiation of disease to be most efficacious in limiting late blight of tomato and enhancing the fruit yield
(532,75q/ha) with ICBR ratio of 1:16.50.
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