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

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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

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