MSc

The research work entitled “Beneficial fungal root endophytes for the management of
cardamom mosaic disease” was done at the College of Agriculture, Vellayani and
Cardamom Research Station, Pampadumpara during 2020-22, to evaluate the individual
and interaction effects of two beneficial fungal root endophytes (Piriformospora indica
and AMF) for the management of Cardamom mosaic virus and study the biochemical
mechanisms involved in the disease management. The survey for the cardamom mosaic
disease was conducted in two major cardamom growing agroclimatic zones of Kerala
– AEU 16 (Kumali hills) and AEU 14 (Southern high hills) during 2020-22 and disease
incidence in the surveyed area were recorded as 61 per cent (AEU 16) and 63 per cent
(AEU 14). The disease severity assessed as vulnerability index in the surveyed area
were recorded as 53 and 55 at AEU 16 and AEU 14 respectively. A pot culture
experiment was conducted at CRS, Pampadumpara for the evaluation of endophytescolonized seedlings of Njallani, the popular variety of small cardamom against
Cardamom mosaic virus. Both individual and combinatorial effects of the endophytes
on the vegetative characters, virus titre as well as the induction of biochemical
mechanisms in plants against the virus were elucidated in the study. Successful root
colonization with P. indica and AMF was observed in plants individually and in
combination. All the endophyte colonized plants showed promising vegetative
characters compared to control plants. Among the treatments, seedlings pre inoculated
with P.indica before virus transmission showed maximum plant height (46.50±0.707
cm) followed by seedlings pre treated with both AMF and P.indica (45.25±0.354 cm).
Plants treated with AMF followed by P.indica prior to viral infection showed maximum
leaf area (48.17±0.240 cm2 ). Treatments such as pre application of P.indica, AMF ,
AMF followed by P.indica , as well as post application of P.indica followed by AMF
and sole application of P.indica showed the highest number of leaves and the effect of
these treatments were statistically on par. Based on the immunodetection studies (DACELISA) it was observed that plants colonized with P.indica prior to viral transmission
showed lower most virus titre value (OD value 0.95±0.071) compared with the absolute
control. Virus inoculated control plants showed highest virus titre with an OD value of
4.55±0.071. On the basis of immune-molecular detection studies, plants treated with
P.indica , AMF individually and in combination before virus transmission showed least
virus load. PCR amplification was carried out using specific primers for conserved
regions of coat protein of CdMV had an amplicon lenght of 127 bp. Viral RNA isolated
from the first emerged leaves of pre and post- inoculated treatments revealed that,
treatment such as pre colonization of P. indica (T1), AMF (T2) as well as AMF and
P.indica (T4) showed best results in disease management (Plate 4). Control plants
showed least amplification of viral RNA (T9) The biochemical analysis of defence
enzymes was conducted at monthly interval for three times for the best two treatments.
Among the treatments, plants pre treated with P. indica showed highest ascorbic acid
oxidase(1.115±0.007), glutamate synthase(0.255±0.007 )and peroxidase(89.50±0.707 )
activity followed by plants pre treated with both AMF and P. indica. Highest PAL and
SOD activity was observed in plants pre treated with AMF and P. indica in combination
followed by pre treatment with P. indica alone. Highest catalase activity was observed
in plants pre treated with P.indica at first and second month after virus transmission
followed by plants pre treated with AMF. A field experiment was also laid out at CRS,
Pampadumpara farm to evaluate the performance of endophytes colonized varieties of
cardamom (PV3, PV5 and Njallani ) against natural incidence of Cardamom mosaic
virus. Endophyte colonized plants were planted in hot spot area for the disease. Among
the treatments P.indica colonized PV5 had highest plant height and number of leaves
followed by AMF colonized PV5. Highest number of tillers was observed in P. indica
colonized PV5 plants followed by P.indica colonized Njallani plants (14.0±2.282 and
11.5±3.536 cm respectively). Highest leaf area was recorded for AMF colonized PV3
plants followed by PV5 plants colonized by the same bioagent. P.indica colonized PV5
gave least virus titre value followed by P.indica colonized PV3 plants (OD value0.89±0.578 and 0.93±0.189 respectively) and these two varieties were considered to be
the best treatments in alleviating the virus inoculum development. In response of
endophyte colonization among the varieties and treatments evaluated, the variety PV5
and the endophyte P.indica respectively gave least virus titre. Positive control plant
having the characteristic symptoms showed higher virus titre with 9.8 fold increase in
OD value than negative control. Among the treatments highest PAL(527.75±0.354) and
superoxide dismutase activity was found in P.indica colonized PV3 plants. Highest
peroxidase and glutamate synthase activity was observed in PV3 plants colonized with
both P. indica and AMF followed by PV5 plants colonized by both bioagent. Highest
ascorbic acid oxidase (1.115±0.007) activity was recorded on the variety PV5 colonized
with both P. indica and AMF followed by PV3 plants colonized with P.indica alone .
Highest catalase (856.15±0.21) activity has been shown by the variety PV5 colonized
with P.indica at first and second month after inoculation followed by PV3 colonized
with P.indica and AMF in combination. Thus, the present study affirms that, the
beneficial association of fungal root endophytes like P. indica and AMF significantly
improve the plant growth of cardamom in controlled (pot) and field conditions. Further
more the results also suggest an effective management strategy against Cardamom
mosaic virus by the reduction of virus load as well as enhancement of defense enzymes
or antioxidants in plants in response to endophyte colonization.