Prevalence and Management of Alternaria Blight of Linseed
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Date
2024
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Birsa Agricultural University, Ranchi
Abstract
Alternaria blight caused by Alternaria lini is an important disease of
linseed and causes severe losses in most linseed growing environments of
Jharkhand. The pathogen generally produces necrotic lesions on the leaves
and rarely on stems and pods of linseed plants. The initial symptom of the
disease appeared on lower leaves as minute dark brown and black target
like lesion on the leaves. Later the spots coalesce and covers the large area
of the leaves. The affected leaves ultimately get dried up and curled.
The morphological characters of the isolated fungus is as follows. The
mycelium growth on PDA as white greyish at the margin with clear light
to dark green zonation radiating from common center. Dark brown conidia
in chains were observed ranging in sizes from 46-49 μm in length and 2.0
to 6.0 μm in width. The Conidia are dark, cylindrical to oblong, muriform
without beak. The transverse septa ranged from 2-6 and vertical septa ranged
from 1-3. Crops sown on 4th November recorded lowest per cent disease
severity of 13.2 per cent. The crop sown on the above date also recorded
highest grain yield of 1052.31 Kg/ ha. Per cent disease index (PDI) were
significantly positively correlated with minimum temperature and evening
relative humidity Whereas Maximum temperature, mean temperature and
wind speed showed non-significantly positive correlated with PDI. PDI
was significantly negative correlation with morning relative humidity,
mean relative humidity and sunshine hours and grain yield.
In-vitro evaluation of fungicides for control of pathogen showed that
the fungicides (T7), Pyraclostrobin plus Metiram (0.1%) recorded lowest
colony diameter of 12.0 mm and colony growth inhibition over control of
86.62 per cent, followed by Mancozeb (0.2%) which recorded colony
diameter of 13.3 mm and colony growth inhibition over control of 85.17 per
cent. The control plates showed colony diameter of 89.7 mm.
In-vivo evaluation of fungicides for control of Alternaria blight of
linseed envisaged that lowest per cent disease index of 8.5 per cent was
recorded when two sprays of Metiram plus Pyraclostrobin (0.1%) was
given. This treatment also recorded highest grain yield of 731.50 Kg/ ha
and increase in grain yield over control of 32.8 per cent. When cost benefit
ratio was taken into consideration then highest B:C ratio (2.60) was recorded
in treatment (T4) i.e., two sprays of Mancozeb followed by two sprays of
Mancozeb plus Carbendazim (1.63). when net return was taken into
consideration then Highest net return was recorded when two sprays of
Mancozeb (0.2%) was given which recorded a net return of Rs. 8738.8
followed by two sprays of Metiram plus Pyraclostrobin (Rs. 7539.9).
In management of Alternaria blight of linseed through plant defense
inducers showed that Lowest percent disease index of 8.6 per cent was
recorded when seed treatment (ST) with Salicylic acid (SA) @ 50 ppm plus
two foliar spray of SA @ 50 ppm at 30 days and 45 days after sowing (DAS)
was given. This treatment also recorded highest grain yield of 787.04 Kg/
ha and increase in grain yield over control of 39.3 per cent.
Linseed varietal screening against Alternaria blight of linseed, out of 23
entries. Six promising entries viz., Rashmi, RLC 164, RLC 92, Divya, RLC
155 and LMS 2016-1-5 showed resistant reaction against Alternaria blight of
linseed under artificial epiphytotics.