Occurrence of rice blast in two agro-ecologies of Burundi and assessment of varietal resistance and diversity of pyricularia oryzae strains
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Date
2022
Authors
Niyonkuru, Estella
Journal Title
Journal ISSN
Volume Title
Publisher
Sokoine University of Agriculture
Abstract
In Burundi, rice is a very important staple food, generating income for smallholder
farmers and the business community. Unfortunally constrained by rice blast disease
cause by fungus Pyricularia oryzae, which can cause up to 100% loss if not managed.
The present study was conducted in middle and high altitudes agro-ecologies of Burundi
with an overall objective to increase rice productivity by identifying resistant rice
cultivars for management of the disease. Occurrence of blast disease on rice cultivars
was caary out in a triplicated split plot experiment in a Randomized Complete Block
Design (RCBD) in middle and high altitudes zones. Rice blast disease incidence and
severity were significant different between locations (P =0.000). The high altitude agro
ecological zone had the higher disease incidence (68.68%) and severity (77.53%), than
the disease incidence (3.42%) and severity (20.74%) recorded in Middle altitude agro-
ecological zone. When compared between rice growth stages, the disease occurrence and
severity were significantly different (p < 0.05). In high altitude, rice blast incidence
(74.12 - 90.89%) and severity (48.15 - 100%) were recorded at the booting stage and
dough stage. In middle altitude, incidence of disease was recorded at tillering (2.49 -
9.67%), booting (3.07 - 9.83%) and dough (0.49 - 1.68%) stages and blast severity was
observed at tillering (11.11 - 33.33%) and booting stage (11.11- 48.155%). The Area
Under the Disease Progress Curve (AUDPC) showed that the disease progress in all
cultivars increased exponentially from tillering to the dough stage, but at this dough
stage the disease progress plateaued in some cultivars.
Another study was conducted in the both laboratories in IRRI-Burundi and Plant
Molecular Biology at Sokoine University of Agriculture to establish genetic relatedness
of rice blast (Pyricularia oryzae) isolates from two agro ecologies of Burundi. For the thirty five (35) Pyricularia oryzae isolates for two AEZ, a set of five primers were used
for molecular markers targeting the International Transcribed Spacer (ITS) and
Translation Elongation Factor (EF) regions by using polymerase chain reaction (PCR)
followed with Sanger sequencing. The results showed differences in banding patterns
between isolates: ITS1 and 2R, ITS3F and 4R, ITS1F and 4R, ITS4F and 5R and EF1-
983F and EF1-2218R showed bands size of 220bp, 350bp, 390bp, 550bp and 1235bp
respectively. Phylogenetic analysis confirmed the narrow genetic diversity between
Pyricularia oryzae isolates collected in high and middle altitudes regions of Burundi.
Phylogenetic analysis showed that the isolates used from Burundi belong to Pyricularia
oryzae and that the isolates vary considerably depending on the specific hosts. Some
isolates were from hosts other than rice, Ryegrass, millet, wheat and Graminis-tritici for
different locations.
A screen house experiment in a Complete Randomized Design (CRD) with three
repetitions was conducted in IRRI-Burundi to evaluate 10 cultivars for resistance to a
particular artificially inoculated Pyricularia oryzae isolates. The results indicated a
significant difference between isolates and cultivars in incidence and severity. Of the ten
rice cultivars, only three were resistant (R) (Mugwiza, Rufutamadeni and V18) to all
isolates of Pyricularia oryzae.
Rice blast disease is distributed in middle and high altitudes agroecologies of Burundi.
The study recommends more studies in different season to evaluate the incidence and
severity of rice blast in relation to paddy yield and the genetic diversity of isolates for
other locations in Burundi, not yet covered by the current study.
Description
Dissertation
Keywords
Rice blast, Agro-ecologies, Burundi, Varietal resistance assessment, Pyricularia oryzae Strains