벼 品種의 잎집무늬마름病 抵抗性 硏究 Ⅴ. 感染器官形性과 發病정도와의 관계

Studies on varietal resistance to sheath blight disease in rice Ⅴ. Relationship between infection structure formation and disease severity

Twenty rice varieties were tested to know their levels of resistance to sheath blight disease and degree of infection structure (IS) formation on plant surface by Rhizoctonia solani at seedling and adult plant stages, and to find the relationship between IS formation and disease severity(DS). Varietal differences of degrees of IS formation and DS were found at seedling and adult plant stages. More IS were formed and higher disease scores were found when isolate Ia or Ic was inoculated compared with isolate Ⅲ. Disease susceptible rice varieties, Labelle and S2, formed more IS and showed higher DS, and resistant cultivars, Zenith and Gayabyeo, formed less IS and showed lower DS on seedlings and adult plants inoculated by three different fungus isolates separately. Positive relationships were found between scores of hypha growth, lobate appresorium formation and disease severity at seedling stage, and between degrees of hypha growth, lobate appresorium and infection cushion formation, and disease scores observed at 20 to 30 days after inoculation to adult plants under field condition. Rice varieties showing different reactions in IS formation and/or DS were also found between inoculation stages or fungus isolates inoculated.