MSc

The study entitled “Varietal screening and management of anthracnose of
black pepper using new generation fungicides” was conducted at Department of Plant
Pathology, College of Agriculture, Vellayani during 2018 - 2020 with the objective to
screen KAU varieties and most popular local cultivar Karimunda for resistance
against anthracnose of black pepper caused by Colletotrichum gloeosporioides (Penz.)
Penz. and Sacc. and evolve management strategy using new generation fungicides.
As a part of the study, diseased samples were collected from three black
pepper growing tracts of Kerala viz., Thiruvananthapuram, Wayanad and Idukki.
Sample collections were made from two locations from Thiruvananthapuram
(Kowdiar and Vellayani), Wayanad (Meenangadi and Ambalavayal) and Idukki
(Myladumpara, Pampadumpara, Kattapana and Kambilikandam). Disease incidence
and severity were assessed from the surveyed locations. The highest percentage
disease index was observed in Myladumpara (50.28%) followed by Kattapana
(48.62%). Weather parameter viz., temperature, relative humidity and rainfall were
recorded during the survey period. The weather parameters viz., low temperature, high
relative humidity and heavy rainfall favoured the incidence of anthracnose. The
symptoms of the anthracnose appeared as small necrotic spots with a yellow halo on
the leaf lamina. Several lesions coalesce together resulted in leaf blight and
defoliation. In Pampadumpara, spike infection was also observed along with leaf spot.
Colletotrichum cultures were isolated from the diseased sample by tissue isolation
technique and eight pure cultures of Colletotrichum sp. (C1 to C8) were obtained. The
pathogenicity of the eight isolates of Colletotrichum sp. from different locations were
proved by Koch postulates.
The morphological characters of the eight different isolates were studied in
potato dextrose agar (PDA) medium. The isolated cultures of Colletotrichum sp.
produced whitish with yellowish orange centre to light pink, off white to greyish
coloured colony having fluffy, cottony to sparse mycelial growth with regular
margins. Days taken to grow the entire petridish ranged from 7.25 to 9.75 days. The
mycelium of the fungus was hyaline and septate, and its width ranged from 2.21 - 3.45
μm. The septal distance of the different Colletotrichum isolates ranged between 8.50 -
21.23 μm. The conidia were single celled with an oil globule at the centre. The
conidial shape was either cylindrical, oblong or dumbbell. The conidial and
appressorial size varied from 9.4 - 12.1 μm x 3.6 - 4.6 μm and 8.5 – 11.2 μm x 3.5 –
4.3 μm respectively. The isolates were identified as Colletotrichum gloeosporioides.
The pathogenic variability of the eight C. gloeosporioides isolates were
assessed on three black pepper varieties viz., Panniyur 1, Panniyur 3 and Karimunda
by virulence rating. The isolate C7 was identified as the most virulent isolate which
produced lesion size of 1.92 cm, 2.40 cm, and 3.22 cm on Panniyur 1, Panniyur 3 and
Karimunda respectively at 5 days after inoculation (DAI). The isolate C7 produced
symptoms within two days after artificial inoculation in the three varieties tested with
a higher rate of lesion development of 0.40 (Panniyur 1), 0.49 (Panniyur 3) and 0.66
(Karimunda) cm day-1.
KAU varieties (Panniyur 1 to 8) and local cultivar Karimunda were screened
against the most virulent isolate of C. gloeosporioides. Among the varieties screened,
Panniyur 4 was found to be highly susceptible with highest PDI of 51.43 (7 DAI),
whereas Panniyur 2 had the lowest PDI of 14.28 (7DAI) followed by Panniyur 8 with
PDI 20.00 % (7DAI) and were found to be tolerant to anthracnose infection. Panniyur
1, Panniyur 7 and Panniyur 5 were also found to be moderately susceptible. The
pathogen produced symptoms in susceptible varieties within 2 DAI, whereas the
tolerant varieties took 3-4 days to initiate the infection.
In vitro screening of new generation fungicides revealed that kresoxim methyl
of strobilurin and tebuconazole of triazole were the most effective in inhibiting
mycelial growth of C. gloeosporioides (80.37% and cent percent respectively). The
combination fungicide carbendazim 12% + mancozeb 63 % completely inhibited the
mycelial growth at 25, 50 and 100 ppm. The combination fungicides azoxystrobin
11% + tebuconazole 18.3% SC and trifloxystrobin 25% + tebuconazole 55% WP were
also effective against the pathogen at 100 ppm. The contact fungicide copper
oxychloride was ineffective against the pathogen @ 10, 25, 50 and 100 ppm.
The present study revealed the use of tolerant varieties along with need based
application of new generation fungicides to keep the destructive disease under control.
The future line of work should include screening of more black pepper varieties under
field condition to assess their reaction to anthracnose, elucidation of the factors
governing resistance to the disease and the efficacy of new generation fungicides
under field condition.