EPIDEMIOLOGY, MOLECULAR CHARACTERIZATION AND YIELD LOSS ASSESSMENT OF RICE DUE TO RICE YELLOW MOTTLE SOBEMOVIRUS IN NORTHERN NIGERIA
EPIDEMIOLOGY, MOLECULAR CHARACTERIZATION AND YIELD LOSS ASSESSMENT OF RICE DUE TO RICE YELLOW MOTTLE SOBEMOVIRUS IN NORTHERN NIGERIA
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Date
2012-12
Authors
ALKALI, Goni
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Abstract
Screenhouse and field experiments were conducted between 2008 and 2010 to quantify yield loss
due to Rice yellow mottle virus (RYMV) in some selected rice cultivars; determine the
epidemiology of RYMV in relation to weather factors on the incidence of RYMV and insect vector
population composition and identification studies; identify its alternative hosts; determine serotypes
of the pathogen; and molecular characterization of the strains and their distribution in the northern
states of Nigeria. The screenhouse experiment was arranged in a strip plot design with three
replicates. Significant interaction between the effects of inoculation regimes and rice cultivars were
found between the disease, growth and yield parameters. The critical periods of RYMV infection
for most of the rice cultivars used was within 4 - 8 Weeks after sowing (WAS). Paddy yield losses
of 6.59 - 79.11 % and 3.65 - 81.67 % were recorded on the test cultivars in rainy and dry seasons,
respectively. Keeping the plants RYMV- free for up to 10 WAS resulted in grain yield almost
similar to control. The epidemiology experiment was laid out in a randomized complete block
design (RCBD) with three replicates. Significant positive and negative correlations were recorded
between RYMV incidence and severity index, some insect vectors and weather factors. Insect
species collected in and around the experimental field, included Oxya sp., Locris rubra Fabriculus,,
Chnootriba similis Thunberg, Chaetocnema sp., Cheilomenes sp., Zonocerus variegatus L.,
Paratettix sp., Conocephalus sp., Nezara viridula L. and Dactylispa sp. they transmitted the virus
to different degree. Serological studies showed that some weed species with or without symptoms
collected, across RYMV infected areas in Northern Nigeria tested positive to RYMV. These
included Imperata cylindrica L., Erograstic tenella L., E. Ciliaris L., Digitaria horizontalis Wild.,
Eleusine indica (L) Gaertner., E. corocana L., Cynodon dactylon (L) Pers., Panicum sp.,
Dactyloctenium aegyptium L., Brachiaria lata (Schumach) C.E. Hubbard ex Robyns., Axonopus
compressus (Sw.) P. Beauv., Cyperus rotundus L., C. difformis L., Oryza barthii A. Chev., O.
longistaminata A. Chev.& Roehr. and Pennisetum pedicellatum Trin. Six serological profiles
(Sep.) or serotypes were identified (Sep A to F) in this study. Sep A was found in Gombe, Kaduna,
Kano, Niger, Sokoto and Zamfara states, Sep B was found in Borno, Gombe, Kaduna, and Kano,
states, Sep C was found in Gombe state, Sep D was found in Borno, Sokoto and Zamfara states,
Sep E was found in Borno and Zamfara states and Sep F was found in Kano, Niger and Sokoto
states. The molecular characterization of RYMV isolates revealed that more than two strains of the
virus were present in northern Nigeria. Strain S1 is widespread in Borno, Gombe, Kaduna, Kano,
Niger, Sokoto and Zamfara states. By contrast, strain S2 was only detected in Gombe, Kaduna and
Niger states. Strains SX occurred in swampy sites in Borno, Gombe, Kaduna, Kano and Zamfara
states. The information provided on the vulnerable phase of the plant growth on yield loss to the
pathogen can be useful in integrated pest and production management for rice in RYMV endemic
areas. The relationship established between RYMV incidences, insect vector population and
variation in weather factors data could be used in RYMV disease magnitude prediction. In addition,
Knowledge of weed hosts, potential insect vectors in and around RYMV infected fields, and
distinction between isolates/strains is critical and would provide useful information in
pathogenicity and breeding studies of RYMV in Northern Nigeria.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF
POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY,
ZARIA, NIGERIA
IN PARTIAL FULFILLMENT FOR THE AWARD OF DEGREE OF
DOCTOR OF PHILOSOPHY IN CROP PROTECTION
DEPARTMENT OF CROP PROTECTION
FACULTY OF AGRICULTURE
AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA
DECEMBER, 2012
Keywords
EPIDEMIOLOGY,, MOLECULAR,, CHARACTERIZATION,, YIELD,, ASSESSMENT,, RICE,, RICE YELLOW,, MOTTLE,, SOBEMOVIRUS,, NORTHERN,, NIGERIA.