Status and management of rice blast disease caused by Pyricularia oryzae cav. In upland rice in selected regions in Tanzania
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Date
2020
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Publisher
Sokoine University of Agriculture
Abstract
This study aimed to enhance effective rice blast disease management by the establishment
of the current status of the disease, its effect on yield of selected upland rice genotypes and
the use of environmentally friendly methods such as bio-agents and hot water seed
treatment. Two surveys were conducted in 2017/2018 and 2018/2019 rice growing seasons
to investigate farmers’ knowledge of rice blast disease and its management and to
establish the incidence and severity of rice blast disease in farmers’ rice fields in
Morogoro and Tanga regions. Data were collected through face to face interviews using
semi structured questionnaire. Rice blast disease assessment in farmers’ fields was
conducted by diagonal transect walk using 1.0 x 1.0 quadrant. Results indicated that
about 46.3% of the farmers interviewed were not aware of the cause and means of spread
of rice blast disease. The majority of farmers (92.3%) planted local upland rice varieties
and about 54.0% did not apply any management method due to lack of knowledge,
inability to afford the cost of buying fungicides and unavailability of effective blast
disease control measures. Results from the surveys indicated that the highest rice blast
disease incidence and severity were recorded in the 2017/2018 rice growing season. In this
season, Mvomero and Korogwe districts had higher blast disease severity of 100% and
98.8%, respectively, than Morogoro Rural (88.1%) and Muheza (87.3%) districts. In vitro
evaluation of microbial agents, indicated that Trichoderma asperellum and Bacillus
subtilis had over 75% inhibition of radial growth of P. oryzae compared to fungicide
Linkimil 72 WP (21 - 23%) and the control (0%). In vivo evaluation showed that rice blast
disease incidence was reduced by 70% in plants treated with T. asperellum followed by
51.5% in B. subtilis treated plants and 26.5% in Linkimil 72 WP treated plants. There was
a decrease in blast disease severity by 35.6% in rice plants treated with T. asperellum and
29.1% in B. subtilis treated rice plants, suggesting that T. asperellum and B. subtilis used
in this study had high antagonistic capacity against P. oryzae. Completely randomized
design (CRD) experiments in the laboratory and screen house were conducted to
investigate the efficacy of T. asperellum, B. subtilis and hot water seed treatments on rice
blast disease. Results indicated significant reduction (P ≥ 0.05) of the percentage of
infected rice seeds when T. asperellum, B. subtilis and hot water treatment were used. Rice
blast disease incidence and severity were significantly reduced (P ≥ 0.05) on rice seeds
treated with B. subtilis. Therefore, the use of microbial agents has the potential for
effective management of rice blast disease. Field experiments were conducted twice in
three locations to determine the effect of rice blast disease on grain yield of upland rice
genotypes. A randomized complete block design experiment (RCBD) was used in a paired
block with P. oryzae naturally inoculated and fungicide sprayed blocks. Results showed
that the effect of rice blast disease on grain yield of upland rice genotypes depended on
disease pressure, which differed across rice genotypes, locations and rice growing seasons.
In general, the disease caused 26.6 to 52.1% grain yield reduction in the two rice growing
seasons. Improved rice genotypes such as NERICA 7 and WAB 450 were also found
susceptible to rice blast disease in the study areas. In general, this study, gives highlights
of the incidence and severity of rice blast disease, its management using bio - agents (T.
asperellum and B. subtilis) and the effects of the disease on grain yield of selected upland
rice genotypes grown under rain-fed conditions in Morogoro and Tanga regions. Such
information is important in designing rice blast disease management options.
Description
PhD Thesis
Keywords
Management, Rice blast disease, Pyricularia oryzae, Rice, Tanzania