MSc

The study entitled ‘Integrated management of fruit rot of jackfruit incited by
Athelia rolfsii’ was conducted during 2021-23 at College of Agriculture, Vellayani
and IFSRS, Karamana with an objective to assess the factors influencing growth of
A. rolfsii and development of an integrated disease management strategy against fruit
rot of jackfruit.
A survey was conducted in four agro-ecological units of Kerala viz., AEU 4,
8, 9 and 14 covering Thiruvananthapuram, Alappuzha, Pathanamthitta, Kollam and
Kottayam districts.Fruit rot affected jack fruit samples were collected from a total of
eight locations i.e., 2 from each AEU during 2021-23. Six out of the eight fruit rot
affected fruit samples were observed atsoil level whereas the remaining two were
above soil level. The disease was manifested as white, fan shaped mycelial growth
with presence of cream coloured sclerotia on fruits.Gradually, discolouration and
rotting were observed on the fruits. The natural incidence of thedisease was observed
at slightly acidic to neutral pH, at soil temperature of 24 to 34℃ and 21 to 50.40 per
cent soil moisture level.
Pathogen isolation was undertaken from each fruit rot affected jack fruit
sample collected from the eight locations and pathogenicity of the isolates was
confirmed individually. The mycelia of all the isolates appeared as white with fan
shaped growth except for a cottony appearance in the case of Kunnumma isolate. All
the isolates produced round shaped sclerotia with colour variations ranging from light
cream to dark brown. Among all the isolates, Karamana isolate took the least days
for completion of mycelial growth (3 days) and formation of sclerotia (5 days) in
vitro. The pattern of growth of sclerotia appeared as scattered (Venganoor, Chavara,
Alappuzha, Kunnumma and Pathanamthitta isolates), ring like at centre (Karamana
and Koodalisolates) and aggregated at the centre (Kottayam isolate). The hyphae of
all the isolates were septate with size ranging from 0.02 to 0.03 μm. The size of the
sclerotia of the isolates rangedfrom 1.02 to 2.00 mm. Karamana isolate was
revealed to be the most virulent isolate with 195.84 cm2
of infection area within
three days of artificial inoculation on fruits. The virulent isolate of the pathogen was
selected for identification. Morphological and cultural characters including presence
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of fan shaped mycelia and clamp connections confirmed it as A. rolfsii. Further,
molecular characterization using ITS primers conclusively confirmed the fungus as
A. rolfsii.
Evaluation of chemicals for their antifungal potential against A. rolfsii by
poisoned foodtechnique revealed that dithane M-45 75%WP, tebuconazole 25%WG,
propineb 70% WP andhexaconazole 5% EC completely inhibited the fungus at
recommended and half the recommended dose. The chemicals viz., dithane M-45
75% WP, tebuconazole 25% WG and hexaconazole 5% EC were effective even at
one fourth of the recommended dose.
In vitro evaluation of biocontrol agents by dual culture technique revealed
that Trichoderma asperellum (KAUT6) and Trichoderma viride (NBAIR) were the
most effectivebio agents which resulted in 80.55 and 51.77 per cent inhibition of the
mycelial growth of the fungus respectively.
Studies on the compatibility between effective chemicals and biocontrol agents
revealedthat T. asperellum (KAUT6) was completely compatible with hexaconazole
5% EC (0.025%, 0.05%, 0.1%) and dithane M-45 75% WP at recommended dose,
half as well as quarter of therecommended dose. Tebuconazole 25% WG showed
compatibility with T. asperellum (KAUT6) at quarter of its recommended dose only.
In vitro assessment of the influence of various environmental factors on the
growth of the fungus on artificially inoculated fruits was conducted. Exposure to
varying light intensitiesrevealed that alternate cycles of light and darkness promoted
mycelial growth of A. rolfsii compared to continuous darkness and other varying
levels of light intensity. Evaluation of influence of different levels of temperature
demonstrated that high temperature levels of 37 and 40˚C inhibited the growth of the
fungus when artificially inoculated on to the fruits. The pH range for optimum growth
of mycelium and production of sclerotia was revealed to be within a range of 5.5 to
6.5. High soil moisture percentage was revealed to inhibit the growth of the fungus.
Pre and post application of the best effective contact fungicide, bio agent and
their combination on artificially inoculated jack fruits revealed that pre application of
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dithane M- 45% WP (0.3%) resulted in complete (100%) inhibition of the growth of
the fungus on fruits upto one week period wherein the untreated inoculated fruit got
completely rotten. Studies onpost-application of dithane M-45% WP (0.3%) at 24 h
after artificial inoculation resulted in complete (100%) inhibition of the growth of the
fungus followed by post application of talc based formulation of T. asperellum
(KAUT6). However, subsequent observations revealed that,beyond 72 hours after
artificial inoculation, the virulent isolate of the fungus continued to growon the fruits,
revealing that neither the chemicals nor the biocontrol agents, alone or in
combination, was effective in controlling the fungus on artificially inoculated fruits.
Thus, the present study could identify A. rolfsii as a predominant fungal
pathogen causing fruit rot of jackfruit in Kerala. The disease incidence was revealed
to be influenced bythe prevailing weather conditions. It was revealed that pre
application of dithane M-45 75% WP (0.3%) before artificial inoculation as well as
post-application of dithane M-45 75% WP (0.3%) within 72 hours of artificial
inoculation were the most effective treatments followed bydithane M-45 75% WP
(0.3%) combined with talc based formulation of T. asperellum (KAUT6). Further
validation through multi-seasonal field trials need to be undertaken to identify the
cardinal environmental factors resulting in disease incidence as well as to develop a
holistic approach for the integrated management of the disease.