Exploitation of abiotic stress tolerant strains of trichoderma spp. for the management of soil borne fungal pathogens
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Date
2018
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Department of Plant Pathology, College of Horticulture, Vellanikkara
Abstract
Soil borne phytopathogenic fungi are known to cause severe yield loss
of several crops. To mitigate these crop ailments, farmers mostly rely on
chemical methods of disease control such as fungicides and other pesticides
which are deleterious to the environment. To date, biological control is an
ecofriendly approach for the effective management of crop diseases. The fungi
belonging to the genus Trichoderma are one among the most exploited
biocontrol agents in the field of agriculture. However, the performance of
Trichoderma spp. gets reduced when it is exposed to abiotic stressed conditions
such as drought, high temperature, salinity, acidity and fungicides. Hence, this
study was proposed to identify and exploit stress tolerant isolates of
Trichoderma spp. with antagonistic potential in Kerala.
Intensive soil sampling surveys were conducted across different stressed
ecosystems of Kerala viz., Palakkad, Alappuzha, Vytilla, Kumarakom,
Wayanad and Thrissur for the isolation and enumeration of native Trichoderma
spp. A total of 24 isolates were obtained from 52 soil samples collected from
different locations. Based on the number of Trichoderma spp. obtained from
each district, they were serially numbered and abbreviated according to the
name of the location. Accordingly, PAT 1 to PAT 6 represents number of
isolates of Trichoderma spp. from Palakkad district, ALT 1 to ALT 3 from
Alappuzha, VYT 1 and VYT 2 from Ernakulam district, KUT 1 from Kottayam
district, WAT 1 to WAT 8 from Wayanad and THT 1 to THT 4 from Thrissur
district. Cultural and morphological identification of these isolates were carried
out under in vitro conditions.
Isolates of Trichoderma spp. were subjected to in vitro screening for
abiotic stress tolerance such as high temperature, drought, acidity, salinity and
also to test their sensitivity towards copper fungicides. The isolates PAT6 and
WAT2 were found as thermotolerant, VYT2 and ALT 1 as drought tolerant,
ALT 3 and ALT 1 as acid tolerant and saline tolerant and the isolates ALT1,
ALT3 and PAT 1 as copper fungicide tolerant. The selected six isolates were
further subjected to biochemical tests and the study showed that the isolates
VYT 2, ALT 3 and ALT 1 showed highest cellulase, β- 1, 3 glucanase and
protease activity. Likewise, isolates PAT 1, ALT 1 and ALT 3 were found as
best producers of ACC deaminase and PAT 1 and ALT 1 as the best cytokinin
producer.
The best performing isolates (ALT 1, ALT 3, PAT 1, PAT 6 and
VYT 2) after enzyme study were subjected to dual culture experiment with five
major soil borne pathogens to test their antagonistic potential. The isolates ALT
3, ALT 1, PAT 6 and PAT 1 showed more than 70 per cent inhibition of R.
solani whereas, isolates ALT1 and VYT 2 showed only 57.78 and 55 per cent
inhibition of S. rolfsii respectively. However, no significant difference was
noticed among the isolates when grown against F. solani. Cent per cent
inhibition of P. aphanidermatum was noticed with Trichoderma isolates PAT 1
and ALT 1. All five isolates showed 100 per cent inhibition on the growth of
pathogen, P. capsici. Among the five, four isolates viz., ALT 1, ALT 3, PAT 1
and PAT 6 with best antagonistic potential were subjected to molecular
characterization at Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram
and the isolates showed homology with the nucleotide sequence of Trichoderma
asperellum.
A pot culture experiment was laid with the selected isolates viz., ALT 1,
ALT 3, PAT 1 and PAT 6 to test the growth promotion of cowpea and biocontrol
efficacy against Rhizoctonia solani. It was observed that the isolate PAT 6 coated
seeds showed 100 per cent germination and also recorded better biometric
characters and yield. Moreover, the lowest per cent disease incidence of 11.11 per
cent was only recorded with both the isolates ALT 3 and PAT 6.
Thus, the study has enlightened our knowledge on the existence of
abiotic stress tolerant isolates of T. asperellum which can be employed in future
for the biocontrol of soil borne pathogens in such conditions.
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