Abstract
Around one century ago, a rice disease characterized mainly by rotting of sheaths was reported in Taiwan. The causal agent was identified as Acrocylindrium oryzae, later known as Sarocladium oryzae. Since then it has become clear that various other organisms can cause similar disease symptoms, including Fusarium sp. and fluorescent pseudomonads. These organisms have in common that they produce a range of phytotoxins that induce necrosis in plants. The same agents also cause grain discoloration, chaffiness, and sterility and are all seed-transmitted. Rice sheath rot disease symptoms are found in all rice-growing areas of the world. The disease is now getting momentum and is considered as an important emerging rice production threat. The disease can lead to variable yield losses, which can be as high as 85%. This review aims at improving our understanding of the disease etiology of rice sheath rot and mainly deals with the three most reported rice sheath rot pathogens: S. oryzae, the Fusarium fujikuroi complex, and Pseudomonas fuscovaginae. Causal agents, pathogenicity determinants, interactions among the various pathogens, epidemiology, geographical distribution, and control options will be discussed.
Highlights
Rice is an important crop worldwide, serving as the staple food for half of humanity and being used in industry and for animal feed
Since rice sheath rot symptoms were first described in Taiwan in 1922 and attributed to S. oryzae, various reports of similar or related disease symptoms have been produced in different parts of the world
The principle that “everything is everywhere, but, the environment selects” (De Wit and Bouvier, 2006) applies to rice sheath rot; organisms that can potentially cause rice sheath rot are many and can be found everywhere nowadays, but the environment probably selects the ones that can adapt to the prevailing environmental conditions in a given area
Summary
Rice is an important crop worldwide, serving as the staple food for half of humanity and being used in industry and for animal feed. Rice is grown in various agro-ecological zones in tropical and subtropical areas, especially in Asia, the continent accounting for 90% of the world production (IRRI, 2015a) It faces many production constraints, including pests and diseases. Since the green revolution in Asia in the 1960s, there have been substantial changes in rice farming systems: use of high yielding varieties, increased use of fertilizers, efficient systems of water use, seeding methods, etc. Crop intensification practices such as increased plant density, a high rate of nitrogen fertilizers and the use of semi-dwarf and photoperiod-insensitive cultivars, favor the susceptibility of rice to some diseases and the sheath rot complex is one of them. It is hypothesized that the new photoperiod-insensitive cultivars have lost the capacity of avoiding
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