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Studies on seed borne aspects of Alternaria porri (Ellis) Cifferi, the causal agent of purple blotch of onion, its molecular characterization and disease management

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Title Studies on seed borne aspects of Alternaria porri (Ellis) Cifferi, the causal agent of purple blotch of onion, its molecular characterization and disease management
 
Creator Nainwal, Deepa
 
Contributor Vishunavat, Karuna
 
Subject seed borne diseases, molecular biology, characterization, onions, disease control, alternaria porri, fungal diseases
 
Description Thesis-PhD
Purple blotch (A. porri) in conjuction with Stemphylium blight (S. vesicarium) is the
most destructive foliar and seed stalk pathogens of onion which cause significant qualitative and
quantitative losses both in bulb and seed crop. Thrips are found to aggravate the incidence of
purple blotch. Keeping in view, the significance of these diseases, the present study was carried
out in foot hills of Tarai and Bhabar regions of Uttarakhand to investigate the severity of
diseases, morphological, molecular and culture characterization of pathogens, seed quality
losses due to these plant pathogens, detection and location of infection in seed, transmission of
pathogen, effect of pathogen on germination and longevity of pathogens in seed during storage
and their effective management. For effective management of both the diseases, seed treatment
and foliar spray of bioagents and fungicides were carried out under field conditions. To analyze
the molecular characterization of 14 isolates of A. porri were collected and studied from
different regions of Uttarakhand.
The symptoms of purple blotch appeared as small, elliptical, water-soaked, whitish and
orange coloured lesions surrounded by yellow hallow in the initial stage. As, the disease
progressed the lesions enlarged and became eye shaped having purplish concentric rings which
resulted in the development of necrotic patches. Initially, Stemphylium blight showed small,
yellow to tan water-soaked lesions with elongated spots turnning dark olive brown to black. The
leaves and flower stalks of onion showed completely blighted appearance as the lesions
coalesce. The infestations of the thrips observed on the onion leaves reflected characteristic
longitudinal streaking which gave the appearance of rasping damage.
The best growth of the fungus was reported in Malt Agar medium at 27±10C. The deep
freeze method was found to be the best for maximum recovery of pathogen from onion seed. The
histopathological studies of infected onion seed revealed the presence of mycelium in or on the seed
coat and pericarp but not in embryonic tissues. The maximum percent germination was maintained
in seeds stored in cold and dry conditions. The longevity of pathogens (A. porri and S. vesicarium) in
seed was higher in cold and dry condition as compared to ambient storage conditions.
The seed treatment with CMC + T. harzianum @ 10g/kg of seed was found effective
for enhancing percent germination and reducing seed rot. Amongst chemicals used for seed
treatment, thiram @4g/kg is found the most effective followed by bio control agents, T.
harzianum against A. porri. In vitro, propiconazole at all the concentrations 25ppm, 50ppm,
100ppm, 250ppm) followed by tebuconazole at 250 ppm concentration completely inhibited the
growth of pathogen (A. porri) however, out of eleven treatments tried in foliar spray for
management of both the diseases mancozeb (@ 0.3%) + monochrotophos (@ 0.05%) followed
by neembicidine (@ 0.03%) at every 15 days interval was found to be very effective in reducing
the diseases and increasing the yield including the management of thrips population.
To assess the degree of genetic diversity and relatedness, 14 isolates of A. porri collected
from different locations of Uttarakhand were subjected to molecular characterization using 9 SSR
markers (selected on the basis of polymorphism pattern). A total of 36 loci were obtained. Allelic
diversity was found ranging from 0.0531-0.3707. The isolates A.p.B4 and A.p.B1 showed maximum
similarity coefficient (92%). Based on UPGMA cluster analysis, genetic similarity coefficients was
observed between pair wise isolates ranging from 0.61-0.91. The PIC value (0.2978) was recorded to
be maximum for D. N. alt-14 while minimum (0.0495) for D. N. alt-5.
 
Date 2016-06-08T16:19:32Z
2016-06-08T16:19:32Z
2013-11
 
Type Thesis
 
Identifier http://krishikosh.egranth.ac.in/handle/1/67049
 
Language en
 
Format application/pdf
 
Publisher G.B. Pant University of Agriculture and Technology, Pantnagar-263145 (Uttarakhand)