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The study entitled “Evaluation of beneficial fungal root endophytes against
Fusarium rot in small cardamom” was conducted at College of Agriculture, Vellayani
and Cardamom Research Station, Pampadumpara during 2020-21 to evaluate the
colonisation and interaction of two beneficial fungi, Piriformospora indica and
Glomus fasciculatum, in cardamom and their potential to manage Fusarium rot disease
of cardamom and elucidation of the role of gibberellic acid in the endophytic fungimediated disease tolerance.
Fusarium infection in small cardamom is characterised by root rotting, eye
shaped lesion on pseudostem and panicle rot. Fusarium oxysporum Schledt was isolated
from the infected roots of the farmer’s field of Pampadumpara in Idukki district. Koch’s
postulate was proved by inoculation of the pseudostem of one year plants using pinprick
method where the isolate produced the typical eye shaped lesion within two weeks.
A pot culture experiment was conducted at CRS, Pampadumpara to assess the
interactive effect of the fungal root endophytes P. indica and G. fasciculatum on the
vegetative growth of small cardamom seedlings and suckers using four treatments and
five replications. Both individual and combinatorial effects of the endophytes on the
vegetative characters like plants height, number of leaves, leaf length, leaf width, root
parameters, biomass etc. were evaluated. Successful root colonization was observed in
P. indica and G. fasciculatum treated roots at six and seven days after their inoculation
respectively. This is the first report of colonization of P. indica in small cardamom. The
study revealed that the endophytes inoculated plants were superior to control plants in
which maximum shoot growth was shown by the dually colonized plants followed by
the P. indica-colonized which was then followed by G. fasciculatum colonised plants.
The root parameters were higher for P. indica-colonized plants compared to the
combined or G. fasciculatum colonized plants in cardamom seedlings whereas dually
colonized plants had better root growth in cardamom suckers. P and K analysis of the
whole plant clearly indicated the enhanced nutrient uptake to root, shoot and leaf in the
endophytes-colonized plants. The IAA analysis of root samples also revealed a higher
IAA content in the endophytes colonized seedlings compared to the control seedlings
with P. indica colonized plants recording the maximum value of 83.80 µg g-1
in
seedlings and 94.30 µg g-1
in suckers; and least value being observed in control plants
recording 44.80 µg g-1
in seedlings and 94.30 µg g-1
in suckers. This study stipulate a
scope of better establishment of cardamom in field especially in the case of seedlings
during transplantation due to well established root system. There was also a reduction
in nursery period by two months in the P. indica and G. fasciculatum dually colonized
seedlings compared to the non-colonized seedlings.
In vitro evaluation of P. indica against F. oxysporum and in vivo evaluation of
both the bioagents against F. oxysporum in small cardamom was carried out to appraise
the effect of bioagents in the management of Fusarium rot disease of cardamom. In in
vitro evaluation, dual culture assay of P. indica with F. oxysporum was performed in
PDA in which a percent inhibition of 64.4 (%), antagonism index of 20.53 and an
obscure lysis zone was observed. There wasn’t any presence of inhibition zone,
antibiosis, coiling, overgrowth, sporulation etc. In in vivo evaluation, a pot culture
experiment was laid out at CRS, Pampadumpara with seven treatments and three
replications including a bio agent check of 2% Pseudomonas fluorescens and chemical
check of 2 % carbendazim as basal drench. The study revealed that the beneficial
interaction with bioagent successively decreased the disease severity and lesion size,
among which P. indica treated plants showed the best result having the least disease
severity of 38.07 (%) and 31.48 (%) in seedlings and suckers respectively. The disease
severity of the control plants were the highest, recording 86.62 (%) and 76.77 (%) in
seedlings and suckers respectively. Combinatorial and P. fluorescens treatments were
the other treatments showing promising results in disease management.
Total Gibberellic acid was estimated from leaf samples of challenge inoculated
experimental plants to elucidate the role of GA in endophyte mediated disease tolerance
and the authors couldn’t interpret any role of GA in disease development. Moreover,
the GA content was higher in P. indica colonised recording 18.60 µg g-1
and 10.65 in
µg g-1 in seedlings and suckers respectively; and dually colonised plants recording
18.00 µg g-1 and 9.71 µg g-1 in seedlings and suckers respectively.
Thus, the present study proclaims a very pronounced plant growth promotion in
cardamom seedlings and suckers by the beneficial fungal root endophytes viz., P. indica
and G. fasciculatum just before transplanting to the field and therein advocating better
development and establishment in the field condition. Furthermore, the results also
indicates an effective management of the destructive Fusarium rot disease in small
cardamom using endophyte colonization especially in P. indica colonized and dually
colonized plants.