STUDIES ON PHYSIOBIOCHEMICAL CHANGES, VIRUSVECTOR RELATIONSHIP AND MANAGEMENT OF RICE TUNGRO DISEASE
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Date
2014
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ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY, RAJENDRANAGAR, HYDERABAD
Abstract
Rice tungro disease (RTD) is a major constraint in production of rice (Oryza
sativa L.) not only in India but in all South and Southeast Asia. In Andhra Pradesh, rice
tungro disease (RTD) has been reported to occur in almost all the popular rice cultivars
grown in Khammam, East Godavari, Ranga Reddy, West Godavari, Medak, Nalgonda,
Nellore, Chittoor and Prakasam districts. Keeping this in view, a detailed study on host
range, virus vector relationship, physiological and biochemical changes and
insecticides management of rice tungro disease and its vector was conducted at
Department of Plant Pathology, College of Agriculture, ANGRAU in collaboration with
Directorate of Rice Research (DRR), Rajendranagar, Hyderabad, Andhra Pradesh, India
during the year 2013-2014.
Out of twenty weed host species tested through forced feed inoculation with
viruliferous leaf hoppers (Nephotettix virescens), thirteen weed host species were
found positive reaction for tungro disease viz., Cynodon dactylon, Digitaria
sanguinalis, Echinocloa colonum, E. crusgalli, Leptochloa chinensis, Panicum
repens, Cyperus rotundus, Fimbrystylis miliaceae, Dinebra aratica, Brachiaria
ramosa, Paspalum dilatum, Leersia hexandra and Paspalum hydrophilum and
exhibited leaf yellowing, stunting, reduction in number of tillers and interveinal
chlorosis with typical symptoms of tungro disease as expressed in rice crop. The
virus was also recovered from the seven virus infected weed host species viz., E.
colonum, E. crusgalli, Panicum repens, C. rotandus, Paspalum dilatum, P.
hydrophilum and Leersia hexandra. Weed hosts viz., Paspalum dilatum and Paspalum
hydrophilum exhibited prominent symptoms of the tungro disease.
Physiological and biochemical changes were found to be induced in rice leaves
due to infection by rice tungro disease. Significant differences in chlorophyll ‘a’,
chlorophyll ‘b’, total chlorophyll (a+b), chlorophyll a/ b ratio and carotenoide content
were observed in different rice cultivars and at different days after inoculation (10, 20,
30 and 40). In general in the uninoculated control plants of all the nine rice cultivars,
the contents of photosynthetic pigments were increased with the advancement of the
crop age. In the inoculated plants of susceptible rice cultivars showed highest
reduction in photosynthetic pigments with the advancement of the plant age as
compared to moderately resistant and resistant rice cultivars. Among the nine rice
cultivars tested, the decrease in photosynthetic pigments was highest in T(N)1 (82.5
%), and least in resistant rice cultivar Vikramarya (5.58 %) at 40 days after
inoculation, respectively as compared to all the rice cultivars tested.
The carbohydrate fraction viz., reducing sugars, non reducing sugars, total sugars
and starch content were significantly differed in RTD inoculated and uninoculated
plants irrespective of the rice cultivars. In general in the uninoculated control plants of
all the nine rice cultivars, the contents of reducing sugars were increased with the
advancement of the crop age irrespective of the rice cultivars and days after
inoculation. The inoculated plants of susceptible rice cultivars showed highest increase
in carbohydrate fractions with the advancement of the plant age as compared to
moderately resistant and resistant rice cultivars. Among the nine rice cultivars tested,
the increase in carbohydrate fractions were found high in susceptible rice cultivar
T(N)1 74.5 %, 69.6 %, 71.7 % and 55.5 % at 40 days after inoculation.
The quantities of the phenol contents in healthy plants generally increased with
the age of the plants of all the nine rice cultivars tested. The healthy plants of
moderately resistant and resistant cultivars recorded higher amount of total phenols
than the susceptible cultivars. Total phenol content were decreased in susceptible rice
cultivar T(N)1 (22.9%, 45.3% and 60.5%), CO 39 (21.1%, 41.0% and 59.3%) and
MTU 1010 (19.2%, 37.5% and 53.7%) at 20, 30 and 40 DAI, respectively. But in
moderately resistant and resistant cultivars, total phenol were increased at different
days after inoculation. The maximum decline in phenol content was noticed in
susceptible rice cultivar T(N) 1 (60.50%) samples analysed at 40 DAI.
Biochemical parameters viz., reducing sugars, non reducing sugars, total sugars
and starch content were found high in susceptible rice cultivars (T(N)1, CO 39 and
MTU 1010) as compared to moderately resistant (IR 64, RPBIO 226 and MTU 7029)
and resistant rice cultivars (Vikramarya, Utrirajapan and Nidhi). The phenol content of
susceptible rice cultivars (T(N)1, CO 39 and MTU 1010) was observed to be
decreased over moderately resistant and resistant rice cultivars.
In case of virus- vector and host relationship, resistant rice cultivars (10 -15
days), moderately resistant cultivars (11-13 days) and susceptible cultivars (<10 days)
recorded symptoms after inoculation with RTD . Disease score of 1 or 3 in resistant
rice cultivars, Moderately resistant cultivars (3 or 5) in susceptible rice cultivars ( 7 or
9) were recorded. Resistant rice cultivars, Tjempo Kijik, Utri Merah an Utri Rajapan
showed limited resistance to leaf hoppers but recorded low score to the tungro viruses
as indicating their resistance where as moderately resistant rice cultivars obtained
from IRRI (IR 73546-20-2-2-2, IR 77298-5-6 and IR 81336-39-3-3-3) expressed
resistant reaction with 3 score with varied levels of resistance to the green leafhoppers.
Out of six insecticides evaluated against rice green leaf hopper (Nephotettix
virescens) and RTD infection, buprofezin @1.6 g/L and imidacloprid @ 0.25 ml/L
reduced the insect population by 100 % with 0 % RTD infection in both T(N)1 and
Vikramarya cultivars at one and five days after treatment (1 & 5 DAT) and found
significantly superior over all other treatments. Whereas Difenthiuron @1.2 ml/L and
Dinotefuron @2 g/L controlled insect vector population by 94.0 % with corresponding
decrease in RTD infection of 75.0 %, respectively in rice cultivar T(N)1. The same
insecticides showed 100 % insect mortality and 0 % RTD infection in rice cultivar
Vikramarya at 1 and 5 DAT. All the insecticides treatments were found effective in
controlling the insect vector population and reduction of rice tungro infection.
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Keywords
PHYSIOBIOCHEMICAL, CHANGES, VIRUSVECTOR, RELATIONSHIP, MANAGEMENT, RICE, TUNGRO, DISEASE