Screening of Rice Germplasms for Their Resistance against Sheath Rot Disease (Sarocladium oryzae) at Fogera, Ethiopia

Abstract

Sheath rot, caused by Sarocladium oryzae (Sawada) is one of the major diseases of rice. The pathogen mainly infects the upper most flag leaf sheaths that enclose the emerging young panicle during the boot stage. The lesions are oblong or irregular oval spot and usually expressed as a reddish-brown discoloration of the flag-leaf sheath. Early or severe infection affects the panicle so that it only partially emerges. The unmerged portion of the panicle rots, turning florets red-brown to dark brown. Grains from damaged panicles are discolored reddish-brown to dark brown and may not fill the affected grains, are known as chaffy grains and the disease is appropriately known as “empty head” and is familiar as “rice abortion” [1]. Moreover, the pathogen is mostly observed on the entire seed (about 46%) and on the lemma and/or palea (about 31%) [2]. Sheath rot is one of the most serious and devastating rice diseases in wetland rice growing regions [3]. The pathogen attacks flag leaf sheaths and grains and yield losses result mainly from poor panicle formation and exertion, spikelet sterility (80-100%), reduced grain filling, and losses in milling [4]. Quality is also affected as severe attacks lead to chaffy, discolored grains and affect viability and nutritional value of the grains followed by a decrease in the protein and starch contents of infected seeds [5]. Seeds from infected panicles become discolored and sterile, thereby reducing grain yield and quality significantly. Since the pathogen attacks the crop at maturity starting from panicle initiation stages; its impact is direct to minimize the crop yields. There was a yield loss report ranging from 20% to 85% in Taiwan and 30 to 80% in Vietnam, the Philippines and India [6]. Variability in yield loss depends upon prevailing favorable conditions under which rice is grown and the level of susceptibility of the grown cultivar [7]. In Ethiopia, diseases of rice in general, and sheath rot in particular is not well studied. This is because rice cultivation in the country is at infant stage, and that associated production constraints are not well known along with the fact that importance of diseases of newly introduced crops are expanding and manifesting them gradually with the time. However, now a day sheath rot becomes major rice disease especially in Fogera plains with prevalence, incidence and severity of 100, 47 and 44%, respectively (unpublished). Therefore, unless effective management measure is taken, the disease will cause high yield loss with the consequence that leads the rice crop to be out of production in the area. Thus, there is a need to establish