PhD

The study on the “Efficacy of ligno-phenolic compost in the suppression of soil borne
plant pathogens” was carried out at College of Horticulture, Vellanikkara during 2011 -2014.
The major objectives were to develop a microbial consortium for rapid composting of lignintannin
rich agrowastes and also to study the effect of these composts on the management of
leaf blight of amaranth and bacterial wilt of tomato.
Sample of soils and partially degraded substrates were collected from 15 sources of 34
locations. Among them, ayurvedic wastes yielded maximum population of cellulose and
lignin degraders whereas, tannin degraders were more in the samples of teak plantation. A
total of 378 microbial degraders were isolated which included 125 cellulose, 133 lignin and
120 tannin degraders. Actinomycetes were the predominant degraders of cellulose and fungi
were dominant among both lignin and tannin with majority belonged to Aspergillus spp. and
Penicilium spp. In vitro evaluation of degraders on respective selective media showed
diffusion zones more than 4cm by 31 cellulose, 39 lignin and 33 tannin degraders. Fungi were
the most efficient degraders of cellulose, lignin and tannin. Thirty five degraders found
effective on their respective selective media showed ability to degrade all the three chemical
components.
In vitro decomposition of 33 degraders on respective host substrates recorded lowest
maturity periods of 40 and 43 days for the degraders isolated from ayurvedic waste and coir
pith. The degraders, ALF-26, CLF-13, CCB-8, ECF-2, ECA-8, TLF-8, CaLF-5 and
ATY-1were most effective on their respective host substrates and also on other tested lignintannin
rich substrates in vivo. All the 22 selected degraders were found mutually compatible.
Based on the ability to degrade all the three chemical components, early maturity of
composting, type and species of organisms and mutual compatibility, 10 degraders viz.
Trichoderma harzianum, Paecilomyces variotii, Penicillium oxalicum, P. chrysogenum,
Talaromyces sp., Streptomyces albus, S. niveus, Arthrobacter sp. and Massilia sp.were
selected for the formulation of microbial consortium.
Screening of selected consortium under in vitro and in vivo condition showed early
maturity of 35 and 43 days in mixed substrate followed by coir pith with 35 and 45 days. In
large scale composting of various agrowastes with microbial consortium, cow dung slurry
and the combination of both, the minimum maturity period was observed with microbial
consortium as compared to other treatments recording 30, 35, 40 and 55 days for mixed
substrate, coir pith, ayurvedic waste and leaf litters respectively. Composting with microbial
consortium resulted in drastic reduction of C:N ratio of the composts with 47 -81 per cent
reduction from the initial and the lowest in ayurvedic compost (10.4:1) .Composts treated
with microbial consortium recorded neutral to alkaline pH and high contents of N, P and K
with maximum N and P in ayurvedic and K in coir pith compost. Traces of lead detected in all
compost samples were below the permissible limits. Composting with consortium showed
reduction in cellulose, lignin and tannin contents with maximum reduction in ayurvedic
(49.38 %), coir pith (49.02%) and leaf litter composts (98.95%) respectively. The degraders
of the consortium were thermophilic and recorded extra cellular enzyme activities of
cellulase, lignin peroxidase, polyphenol oxidase, amylase, catalase, protease and xylanase.
The selected degraders showed antagonism against six major soil borne pathogens viz.
Pythium sp., Phytophthora sp., Rhizoctonia sp., Fusarium sp., Sclerotium sp. and Ralstonia
solanacearum and T. harzianum was the most effective one.
In the field evaluation of various composts in the management of bacterial wilt of
tomato and leaf blight of amaranth, application of ayurvedic compost was effective in
reducing both diseases. In addition, coir pith and leaf litter composts also reduced bacterial
wilt incidence and mixture compost in case of leaf blight.