Rice blast disease caused by pyricularia oryzae: epidemiology, characterization and yield loss in major rice growing areas of Tanzania
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Date
2016
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Sokoine University of Agriculture
Abstract
This study was conducted in Mbeya, Morogoro, Kilimanjaro, Shinyanga and Dar es
Salaam regions. The overall objective of the study was to establish the magnitude of rice
blast disease in Tanzania and its contribution to yield losses. Rice is an important staple
food crop and is affected by blast disease with suspected high yield losses of up to 100%.
Surveys were conducted in two years (2012 and 2014) to observe disease prevalence of
rice blast disease in two different ecosystems in Mbeya, Morogoro, Kilimanjaro and
Shinyanga regions of Tanzania. Results showed that the incidence and severity of blast
disease varied considerably across the surveyed regions. The highest rice blast incidence
(74.38%) and severity (87.62%) were observed in the rainfed ecosystem in Mbeya and
Morogoro, respectively. The lowest rice blast incidence (19.38%) and severity (41.5%)
occurred in the irrigated ecosystem in Kilimanjaro region. Another study was conducted in
the screen-house to assess yield loss caused by Pyricularia oryzae using ten rice varieties
Jaribu 220, Supa, Kalamata, Shingo ya mwali, Mwarabu, Mbawambili, Kihogo, IR 64,
TXD 306 and TXD 85. The varieties were sown in completely randomised design and
inoculated to evaluate the effect of rice blast disease on yield. Results showed that most of
the rice varieties were susceptible to P. oryzae and caused grain yield losses of between
11.9 and 37.8% per hectare. Identification and characterization of pathogenic variation of
P. oryzae causing rice blast disease were conducted in the laboratory and screen-house at
Sokoine University of Agriculture, Morogoro. Ten P. oryzae isolates collected from
Shinyanga, Kilimanjaro, Mbeya and Morogoro were tested with a set of ten rice blast
differentials viz; IRBLk-Ka, IRBLkm-Ts, IRBLb-w/co, IRBLkp-K60, IRBLz-Fu, IRBLa
C, IRBLi-F5, IRBLta2-Pi), St and IRBLt-K59. The experiment was laid out in a
completely randomized design with three replications. Twenty one-day-old seedlings
grown in pots were inoculated with a P. oryzae spore suspension (2 x 105 ml -1) with the
hand sprayer in the evening. Disease assessment was done in seven to ten days after
inoculation. Considerable pathogenic variations among the tested isolates were observed.
The International rice blast disease differentials IRBLk-Ka, IRBLkp-K60, IRBLa-C,
IRBLi-F5, IRBLta2-Pi, St and IRBLt-K59 were resistant to all isolates, except that
IRBLb-w/co, IRBLkm-Ts and IRBLz-Fu (Piz) were susceptible. Further studies were
conducted in the biotechnology laboratory at Mikocheni Research Institute in Dar es
Salaam to characterize P. oryzae using molecular techniques. DNA was extracted from
seven isolates of P. oryzae. Polymerase chain reaction (PCR) amplification was carried
out in a thermocycler. The results of DNA amplification showed that the isolates collected
from Morogoro, Shinyanga, Mbeya and Kilimanjaro regions were genetically similar. The
study recommends that research on diversity of P. oryzae pathotype should be conducted
further in order to develop rice varieties resistant to the disease.
Description
THESIS SUBMITTED IN FULFILMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY IN CROP SCIENCE
SOKOINE UNIVERSITY OF AGRICULTURE.
MOROGORO, TANZANIA. 2016
Keywords
Rice blast disease, Pyricularia oryzae, Epidemiology characterization, Yield loss, Rice growing, Tanzania