CHARACTERIZATION OF Colletotrichum gloeosporioides (Penz.) Penz. and Sacc. CAUSING TWISTER DISEASE OF ONION AND ITS MANAGEMENT 3456
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Date
2022-04
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JAU JUNAGADH
Abstract
The present investigation was undertaken on “Characterization of Colletotrichum
gloeosporioides (Penz.) Penz. and Sacc. causing twister disease of onion and its
management”. Nowadays, disease is quite destructive in onion growing regions and
management of disease can be achieved by adopting proper strategies. It is grown in
three seasons i.e., Kharif, Rabi and Summer. About 20 per cent of total area of onion is
under kharif season. It is cultivated round the year but maximum during rabi season in
India and grown under wide range of Agro-climate conditions.
Onion plant showing typical symptoms of twister disease were collected from
farmer’s fields and isolated on PDA medium. Based on cultural i.e. colony cottony to
dirty white to yellowish pink, flat to fluffy growth with regular to irregular margin,
mycelial colour changed grey to black on formation of acervuli and morphological i.e.
conidia hyaline, one celled, ovoid to oblong, curved to dumbbelled with bunt end,
measured, 10.2-17.3 L X 3.3-6.6 W µm and size of seate, 46.1-163.4 L X 3.6- 5.6 W µm
and molecular (NCBI accession No. MW931723) characteristics, it was identified as
Colletotrichum gloeosporioides (Penz.) Penz. and Sacc. It was found pathogenic in
pathogenicity test. The pathogen produced symptoms were curling, twisting and
chlorosis of leaves. The necrotic lesions developed on neck and bulb, destroyed before
maturity. The black acervuli were formed on infected plant parts carry over disease in
next season.
Survey was conducted to identify twister hot spots and disease free area in major
onion growing tracts of Bhavnagar and Amreli (rabi 2020-21) and Junagadh and Rajkot
(kharif 2021) districts of Gujarat. Among these districts, the highest twister disease was
observed in Bhavnagar (36.36%) and Rajkot district (48.77%), while in Amreli (28.09%)
and Junagadh (39.13%) district it was found less in rabi and kharif season, respectively.
Among talukas, maximum disease was found in Palitana (53.66%) followed by Savar
Kundla (51.60%) in rabi season whereas in kharif, maximum disease was found in
Gondal (56.87%) followed by Visavadar (56.25%). Total 69 and 46 onion fields were
visited in kharif and rabi seasons, out of which 89.13 and 78.26 per cent fields were
found infected, respectively with disease in range of 0.0 to 86.00 per cent.
Abstract
Mostly prevalence of disease found in accordance with climate conditions.
Hence, role of weather parameters on twister disease of onion were checked at
Junagadh and Talaja locations. The correlation coefficient results indicated that twister
disease was found highly significant negative correlation with evening relative
humidity, whereas PDI positively correlated with morning relative humidity and wind
speed was non-significant, while maximum and minimum temperature, bright sunshine
hours and evaporation were found highly significant at Junagadh. At Talaja, the
correlation coefficient indicated a highly significant negative correlation with morning
and evening relative humidity, whereas PDI was positively correlated with maximum
temperature was non-significant and minimum temperature, wind speed and
evaporation were found highly significant with positive effect on disease. The
coefficient of multiple regression (R2
) was 0.930 in Junagadh and 0.942 in Talaja,
indicating 93.00 and 94.20 per cent of the variation in twister disease development
explained by the set of variables.
The more emphasis is given on use of potential biocontrol agents for
management of plant diseases to reduce risk of toxic chemicals. Among ten fungal
antagonists evaluated in vitro by dual technique, the maximum inhibition of C.
gloeosporioides was recorded in Trichoderma harzianum Rifai (JAU isolate) (45.79%)
with mean colony diameter of 26.83 mm and among six bacterial antagonists screened
by spreading method, Pseudomonas fluorescens JAU isolate-3 showed maximum
inhibition (86.30%) of pathogen with fungal colony diameter of 12.33 mm.
Though resistant varieties are cheap method to eliminate the disease, rational use
of agrochemicals are necessary to avoid disease. Different fungicides were tested in vitro
by poisoned food technique against C. gloeosporioides viz., six non-systemic, eight
systemic and eight ready-mixed fungicides. Among non-systemic fungicides, copper
hydroxide 53.8% DF and mancozeb 75%WP, systemic fungicides, carbendazim 50%
WP and tebuconazole 255.9 EC and ready-mixed fungicides, carbendazim 12% +
mancozeb 63% WP and metiram 55% + pyraclostrobin 5%