Ph.D

The research work entitled “Management of Banana bract mosaic virus using
beneficial fungal root endophyte, Piriformospora indica” was carried out at the
Department of Plant Pathology, College of Agriculture, Vellayani,
Thiruvananthapuram during the academic year 2018-2022. The objective was to
evaluate the beneficial fungal root endophyte, P. indica for the management of
Banana bract mosaic virus (BBrMV); and to elucidate the role of antioxidants and
plastids in this tripartite interaction.
The characteristic symptoms of BBrMV viz., reddish spindle shaped streaks
on pseudostem, black necrotic streaks on peduncle, chlorotic spindle lesions on
leaves and underdeveloped fruits were observed during the survey conducted in five
agro-climatic zones (ACZ) of Kerala. Percent disease incidence (PDI) and
vulnerability index (VI) of the disease recorded from different zones showed the
highest in banana var. Nendran (PDI - 61.66 & VI – 44.03) from southern zone and
lowest in var. Poovan (PDI – 7.29 & VI – 6.29) in central zone. Serological and
molecular detection confirmed the presence of BBrMV in banana var. Nendran. The
sequence similarity analysis of the coat protein (CP) gene of BBrMV southern zone
isolate (Vellayani) showed 99.12 percent genetic closeness to its Tamil Nadu isolates
compared to the Kerala isolates (98.38 percent).
Screening of the most virulent strain of BBrMV from five different ACZ of
Kerala was done based on early symptom development in TC banana plants var.
Nendran. The BBrMV strain from southern zone could produce the symptoms on
var. Nendran within 30 days (lowest) followed by central zone (55 days) on artificial
inoculation with viruliferous aphids, Pentalonia nigronervosa. The cross-infection
study of virulent strain of BBrMV (southern zone) of Nendran on Nendran
developed chlorotic spindle lesions on leaves at 30 days after inoculation followed
by Nendran on Robusta (75 days).
P. indica-colonization in banana var. Nendran was carried out using
standardized medium. The chlamydospores of the fungus were observed in roots at
20 days after colonization (DAC). In both in vitro and in vivo experiments, P. indicacolonized
plants showed reduced disease severity irrespective of the virusinoculation stage with a vulnerability index of 6.7 percent in BBrMV (+Pi / +V);
and 20.0 percent in the virus-infected plants post-colonized with P. indica (+V / +Pi)
compared to 53.3 percent in the virus alone infected plants. Further, PCR analysis
with BBrMV coat protein specific primer yielded amplicon of low intensity in P.
indica-colonized plants inoculated with the virus compared to the control plants
indicating the ability of the fungus to inhibit the virus. Further, P. indica precolonized
plants inoculated with BBrMV had improved growth and yield parameters
compared to non-colonized plants.
Field trial was laid out with two treatments (P. indica-colonized and noncolonized
banana plants var. Nendran) at Instructional Farm, College of Agriculture,
Vellayani. P. indica-colonized plants recorded a drastic reduction in the severity of
BBrMV by 33 to 58 percent compared to non-colonised control plants. Enhanced
plant height (30 percent), collar girth (45 percent), number of leaves (25 percent),
leaf length (30 percent), leaf width (27 percent), fresh weight of shoot (34 percent),
number of secondary roots (62 percent), number of tertiary roots (76 percent) and
root weight (86 percent) were observed in P. indica-colonized plants at 90 days after
treatment. P. indica-colonization also improved the bunch weight (32.9 percent) and
fruit quality.
Biochemical detection of superoxides using nitroblue tetrazolium (NBT) and
H2O2 with diamino benzidine (DAB) stains at 5, 10, 15, 30 and 45 days revealed a
reduction in reactive oxygen species (ROS) accumulation in both P. indica-colonized
plants challenged with BBrMV (+Pi / +V) and virus infected plants post-colonized
with P. indica (+V / +Pi) compared to BBrMV alone. The decrease in ROS
production and disease severity in the endophyte-colonized plants inoculated with
the virus were attributed to the increased activities of antioxidant enzymes viz.,
peroxidase, superoxide dismutase, catalase, glutamate synthase and ascorbic acid
oxidase.
The molecular analysis of genes involved in the symptom development
indicated the beneficial effect of P. indica on BBrMV infection in banana. P. indica
reduced the symptoms by up-regulating chlorophyll biosynthesis gene (chlorophyll
synthase-CHLG) and down-regulating chlorophyll degradation genes (chlorphyllase
CLH1 & CLH2; and pheophytin pheophorbide hydrolase - PPH), carotenoidbiosynthesis genes (phytoene synthase-PSY1 and PSY2), carotenoid degradation
gene (Phytoene desaturase - PDS) and the virus specific genes responsible for
symptom development (Hc-Pro and P3). Thus, the present study reveals that P.
indica enhances tolerance against BBrMV in addition to improved growth
promotion, yield and fruit quality in banana plant.
േവരിൽ അ􀅵ർവ􀅖ാപനേശഷിയു􀆄 മി􀅗തകുമിളായ
പിരിേഫാർേമാ􀅏േപാറ ഇൻഡി􀅚 ഉപേയാഗി􀅢് വാഴയിെല െകാ􀅚ാൻ ൈവറസി􀅀െറ
നിയ􀅗􀅵ണം” എ􀅹 വിഷയെ􀅮 ആ􀅏പദമാ􀅚ി തിരുവന􀅵പുരം െവ􀆄ായണി കാർഷിക
േകാേളജിെല സസ􀅖 േരാഗ വിഭാഗ􀅮ിൽ 2018 – 2023 കാലയളവിൽ ഗേവഷണ പഠനം
നട􀅚ുകയു􀅪ായി. വാഴയിെല െകാ􀅚ാൻ േരാഗ (ബനാന 􀅗ബാ􀄭􀆃് െമാൈസ􀄭 ൈവറ􀅏 􀇦􀀃 ബി
ബി ആർ എം വി􀈌􀀃 നിയ􀅗􀅵ണ􀅮ി􀅀 􀅗പേയാജനകരമായ മി􀅗തകുമിളായ പി. ഇൻഡി􀅚െയ
വിലയിരു􀅮ുകയും􀇢􀀃 വാഴ - മി􀅗തകുമിൾ - ൈവറ􀅏 (􀅗തിക􀅜ി) ഇടെപടലിൽ നിേരാ􀄭സീകരണ
എൻൈസമുകള􀆧െടയും 􀆗ാ􀆊ിഡുകള􀆧െടയും പ􀅠് മനസിലാ􀅚ുകയുമാ􀄻 ഈ പഠന􀅮ി􀅀െറ
ല􀅜􀅖ം.
േകരള􀅮ിെല അ􀅦് കാർഷിക-കാലാവ􀆉ാ േമഖലകളിൽ (􀀄􀀆􀀝􀈌􀀃 നട􀅮ിയ സർേവയിൽ􀇡
െകാ􀅚ാൻ േരാഗ􀅮ി􀅀െറ വിവിധ ല􀅜ണ􀅡ളായ ത􀅪ിൽ ചുവ􀅹 കതിർ ആകൃതിയിലു􀆄
വരകൾ􀇡􀀃 പൂ􀅠ുല􀅮􀅪ിൽ കറു􀅮 െനേ􀅗കാ􀆃ി􀄭 വരകൾ􀇡􀀃 ഇലകളിൽ മ􀅧 നിറ􀅮ിലു􀆄
􀅏പിൻഡിൽ വരകൾ, 􀀃വളർ􀅢 മുരടി􀅢 കാ􀅆കൾ എ􀅹ിവ കെ􀅪􀅮ി. വിവിധ േമഖലകളിൽ
നട􀅮ിയ സർെവ 􀅗പകാരം െകാ􀅚ാൻ ൈവറ􀅏 േരാഗബാധയും (􀀇􀀌􀈌􀇡􀀃 േരാഗ തീ􀅗വതയും (􀀙􀀌􀈌􀀃
ഏ􀆃വും കൂടുതൽ െത􀅚ൻ േമഖലയിെല േന􀅗􀅵ൻ ഇന􀅮ിലും (􀀓􀀇􀀌􀀃􀇦􀀃􀍸􀍳􀇤􀍸􀍸 %􀀃􀆬􀀃􀀙􀀌􀀃􀈂􀀃􀍶􀍶􀇤􀍲􀍵􀈌 ഏ􀆃വും
കുറ􀅌 മധ􀅖േമഖലയിെല പൂവൻ (DI – 7.29 % & VI – 6.29) ഇന􀅮ിലും കാണാൻ സാധി􀅢􀆧.􀀃
. സീേറാളജി􀅚ൽ􀇡􀀃 േമാളിക􀅖ുലാർ വിദ􀅖കളിലൂെട വാഴയിൽ െകാ􀅚ാൻ ൈവറ􀅏
േരാഗ􀅮ി􀅀െറ സാ􀅹ിധ􀅖ം 􀆉ിരീകരി􀅢􀆧. െത􀅚ൻ േമഖലയിൽ നി􀅹ും േന􀅗􀅵ൻ ഇന􀅮ിൽ
കെ􀅪􀅮ിയ െകാ􀅚ാൻ ൈവറ􀅏 ഐെസാേല􀆃ിൻ്െറ (െവ􀆄ായണി) േകാ􀅨് േ􀅗പാ􀅨ീൻ (സി􀀃 പി)
ജനിതക ഘടന വിശകലനം െച􀅆തതിൽ നി􀅹ും􀀃 ഈ􀀃 പഠന􀅮ിെല െകാ􀅚ാൻ ൈവറ􀅏, ബി
ബിആർ എം വി േകരള ഐെസാേല􀆃􀆧കെള അേപ􀅜ി􀅢് (98.38􀀃 􀎨) തമി􀅋നാ􀄷
ഐെസാേല􀆃􀆧കള􀆧മായി 99.12 ശതമാനം ജനിതക അടു􀅼ം കാണി􀅚ു􀅹ു എ􀅹ു വ􀅖􀅛മായി. 􀀃
ടിഷ􀅖ൂ കൾ􀅢ർ വാഴെ􀅢ടികളിെല േരാഗല􀅜ണ􀅡െള അടി􀆉ാനമാ􀅚ി􀀃 നട􀅮ിയ
പഠന􀅮ിൽ നി􀅹ും േകരള􀅮ിെല അ􀅦് വ􀅖ത􀅖􀅏ത കാർഷിക-കാലാവ􀆉ാ േമഖലകളിൽ
നി􀅹ു􀆄 ഐേസാല􀆃􀆧കളിൽ, ഏ􀆃വും തീ􀅗വതേയറിയ 􀅏െ􀅗ടയിനിെന കെ􀅪􀅮ി. െത􀅚ൻ
േമഖലയിൽ നി􀅹ു􀆄 ബി ബി ആർ എം വി 􀀃 􀅏െ􀅗ടയിൻ 30 ദിവസ􀅮ിനു􀆄ിലും (ഏ􀆃വും
കുറ􀅌 സമയം) തുടർ􀅹് മധ􀅖 േമഖലയിൽ നി􀅹ു􀆄 􀅏െ􀅗ടയിൻ 55 ദിവസതിനു􀆄ിലും േരാഗ
ല􀅜ണ􀅡ൾ കാണി􀅚ുകയു􀅪ായി. േരാഗ വാഹകരായ മു􀅧􀇡􀀃 (െപൻ്റേലാണിയ
ൈനേ􀅗ഗാെനർേവാസ) ഉപേയാഗി􀅢് കൃ􀅗തിമ േരാഗ സം􀅗കമണ പഠനം നട􀅮ി. അതിൻ 􀅗പകാരം
െത􀅚ൻ േമഖലയിൽ നി􀅹ു􀆄 ബി ബി ആർ എം വി 􀀃􀀃 ൈവറൽ 􀅏െ􀅗ടയിനിൻ കൃ􀅗തിമ േരാഗ
സം􀅗കമണ􀅮ി􀅀 േശഷം േന􀅗􀅵ൻ ഇന􀅮ിൽ 30 ദിവസ􀅮ിനു􀆄ിലും േറാബ􀆊യിൽ 75
ദിവസ􀅮ിനു􀆄ിലും െകാ􀅚ാൻ േരാഗ􀅮ി􀅀െറ ല􀅜ണ􀅡ളായ ഇലകളിൽ മ􀅧 നിറ􀅮ിലു􀆄
വരകൾ രൂപെ􀅼ടു􀅹􀄼 നിരീ􀅜ി􀅢􀆧. 􀀃