LEAF BLIGHT (Alternaria macrospora Zimm.) OF COTTON AND ITS MANAGEMENT 3634
Loading...
Files
Date
2022-10
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
JAU JUNAGADH
Abstract
The present investigation was undertaken to manage cotton (Gossypium spp.)
leaf blight disease caused by pathogenic Alternaria macrospora Zimm., which is
quite destructive in all the cotton growing areas. During last few decades, the area
and production of this crop has shown a positive trend and it’s a most important
commercial crops of the world. Cotton is attacted by many fungal diseases among
them, leaf blight is most destructive in Saurashtra region of Gujarat.
Cotton plants showing typical symptoms of leaf blight were collected from
Cotton Research Station, Junagadh Agricultural University, Junagadh and pathogen
was isolated on Potato dextrose agar medium. On the basis of cultural and
morphological characters, it was identified as Alternaria macrospora.
Conidiophores were short or long dark brown bearing single but some time
two conidia in chain at the tip and 40-110 × 6.2-12.4 µm in size with 1 to 6 septa.
Conidia were dark to reddish brown with usually 4 to 6 transverse and 2 longitudinal
septa and size measured 16.2-51.4 × 6.8-18.3 µm.
Impact of different meteorological parameters on development of leaf blight
on cotton, first leaf blight symptoms were appeared on 37th and 39th standard
meteorological week during 2020-21 and 2021-22, respectively. In correlation study,
maximum temperature was non-significant with negative effect on leaf blight disease
development in year 2020-21, while maximum temperature was also non-significant
but positive effect leaf blight disease development in year 2021-22. Minimum
temperature was non-significant with negative effect in year 2020-21 and 2021-22,
respectively. Morning and evening relative humidity was significant and highly
significant in both years, respectively and wind speed opposite to RH. Regression
study, in year 2020-21 reflect that one per cent increase in morning relative humidity
and wind speed led to corresponding decrease in per cent disease index of Alternaria
blight in 2020-21 and 2021-22.
Maximum seed cotton yield of 2269 kg/ha was recorded in treatment plot of
hexaconazole + captan (0.1%) at 55, 75, 95 and 115 DAS with maximum percent
disease control (61.10% PDC) and maximum avoidable yield loss (29.44%).
Hexaconazole + captan (0.1%) at 55, 75, 95 and 115 DAS proved the most effective
in controlling the disease in field condition for two seasons with higher yield.
Among different varieties/genotypes were screened against A. macrospora
under natural conditions, none of the entries was found immune at 90 DAS, 31
entries showed resistant reaction, 18 showed moderately resistance or tolerant
reaction and only one entries GBHV 241 was found moderately susceptible. Thirteen
entries were showed resistant reaction, 25 entries showed moderately resistance or
tolerant reaction and 12 entries found moderately susceptible. None of the entries
was found highly susceptible at 120 DAS.
Various fungicides were evaluated under laboratory conditions at different
four concentrations. Among them, maximum mean spore germination inhibition
(90.83%) was found in the treatment of hexaconazole 5% + captan 70% WP which
was at par with propiconazole 25% EC (88.89%).
Among nine plant extracts @ 5, 10 and 15% tested against A. macrospora
under in vitro, growth inhibition ranged from 34.32 to 51.97 per cent. Maximum
radial growth inhibition was found by Datura stramonium (Daturo) (51.97%),
followed by Cascabela thevetia (Karen) (48.27%). Minimum growth inhibition
recorded in Calotropis gigantea (Ankado) (34.32%).
Field evaluation of nine fungicides carried out during Kharif 2020-21 and
2021-22. Among them, hexaconazole 5% + captan 70% WP (0.1%) was found the
most effective fungicide with 16.58 per cent disease intensity and maximum disease
control of 55.42 per cent. Maximum seed cotton yield (2346 kg/ha) and maximum
avoidable yield loss (36.49%) was also recorded in treatment of hexaconazole 5% +
captan 70% WP at 0.1%.
Biochemical analysis of healthy and diseased plant of cotton revealed
decreased amount of total chlorophyll and total phenol content in diseased leaves as
compare to healthy leaves. While in the case of gossypol, increase in diseased leaves
compared to healthy leaves. All the biochemical parameters decrease with increase
the age of plant except phenol