M Sc

The study entitled “Evaluation of Piriformospora indica against Piper yellow mottle
virus (PYMoV) in black pepper” was conducted in Department of Plant Pathology, College
of Agriculture, Vellayani, Thiruvananthapuram during 2019-2021, to evaluate the efficiency
of the root colonizing endophytic fungus P. indica in managing PYMoV in black pepper, and
to elucidate the role of Reactive Oxygen Species and antioxidant enzymes in the tripartite
interaction.
A survey conducted in the instructional farm of College of Agriculture, Vellayani, to
identify and collect PYMoV-infected black pepper plants showed that the surveyed varieties
viz., Panniyur 1 to 7 and Karimunda were moderately to highly susceptible to PYMoV
infection, with the disease incidence ranging from 10 to 91 per cent and disease severity as
vulnerability index from 30 to 58. PYMoV-infected black pepper plants showed symptoms
like chlorotic flecking, mottling, light necrosis, crinkling and distortion of leaves, reduction
in leaf size and stunted growth. Presence of the virus in the samples was confirmed by
polymerase chain reaction (PCR) with oligonucleotide primers specific to open reading
frame III (ORF III) of PYMoV.
P. indica culture obtained from Department of Plant Pathology was maintained in
potato dextrose agar (PDA) and potato dextrose broth (PDB) media. P. indica was mass
multiplied in coirpith-dried farm yard manure (FYM) mixture (1:1) amended with two per
cent gram flour and was allowed to colonize on rooted cuttings of black pepper. P. indica
colonization enhanced different biometric characters at different intervals, compared to the
non-colonized control plants. P. indica colonization resulted in 25 per cent more shoot
length, 23 per cent more root length, 35 per cent more number of leaves, 23 per cent more
leaf area and 27 per cent more number of primary roots than the control plants at 150 days
after co-cultivation (DAC).
A pot culture experiment was laid out to evaluate the efficiency of prophylactic as
well as curative application of P. indica, in managing PYMoV of black pepper. P. indica
colonization significantly reduced the incidence and severity of PYMoD, upon pre- as well
as post- inoculation of the virus, compared to the control plants. Plants colonized with P.
indica and later inoculated with PYMoV as well as plants infected by PYMoV and later
colonized by P. indica, both recovered the loss in biomass caused by the virus infection,
compared to the non-colonized plants challenged by the virus. However, prophylactic
treatment with P. indica resulted in better control of the disease compared to the curative
treatment. Amplification of the virus by PCR also revealed that the virus titer was the least
in P. indica-colonized plants that were post-inoculated with the virus after 30 DAC, followed
by pre-inoculated plants that were later colonized with P. indica. The virus titer was the
highest in the non-colonized plants inoculated with the virus.
In order to evaluate the performance of P. indica in modulating the biochemical
responses of black pepper plants against PYMoV infection, the activity of various enzymes
which are known to play a role in the antioxidant defense systems of plants viz. catalase,
peroxidase, glutathione reducatse, glutamate synthase, phosphatase and superoxide
dismutase were assayed. A significant increase in the activity of these antioxidant enzymes
was observed in the P. indica-colonized plants compared to the control plants, upon pre- as
well as post- inoculation of PYMoV. Thus, the better performance of P. indica-colonized
plants upon PYMoV infection can be correlated to the increased activities of antioxidant
enzymes. PYMoV-infected plants showed increased accumulation of reactive oxygen
species like superoxide anions and hydrogen peroxide, which cause oxidative stress in the
plants. P. indica-colonization was able to mitigate the increase in ROS concentration caused
due to PYMoV infection, thus reducing the symptoms.
Thus the study reveals that, co-cultivation of rooted cuttings of black pepper
(obtained from disease-free mother plants) with P. indica and keeping them under insectproof conditions for around 30 days (for successful establishment of the fungus inside the
root cortex) and then planting them in the main field is a reliable and chemical-free method
to control PYMoD in black pepper. Bio-protective action of P. indica might be attributed to
the increased activity of antioxidant enzymes, which in turn leads to suppression in ROS
accumulation in the colonized plants, upon being challenged by the virus.