中国雲南省のジャポニカ稲栽培地帯では，いもち病の発生が激しく，抵抗性品種の育成・利用が望まれている。いもち病に対するイネ品種の抵抗性は，病斑形成を阻止する真性抵抗性と，病班教や病斑拡大を抑制する圃場抵抗性とに分けられるが，抵抗性品種の育成には，その両方を利用することが望まれる。しかし，圃場では，未知の抵抗性遺伝子をもつ品種の抵抗性検定は困難である。ガラス室で育苗した4葉期の苗にいもち病菌を接種した後，夜間ビニール被覆と加温を行い二次感染を起こさせることによって葉いもち圃場抵抗性を検定できることが明らかになった。以上の結果に基づいてジャポニカ稲および育成系統のいもち圃場抵抗性を評価するとともに，真性抵抗性遺伝子型別に圃場抵抗性比較基準品種を選定した。
インディカ稲81品種・系統のうち，ジャポニカ稲栽培地帯の主要ないもち病菌レースに抵抗性反応を示した19品種は，雲南省のインディカ稲栽培地帯および日本で採集したいもち病菌に対する反応型から9群に類別され，少なくとも5個の未知の真性抵抗性遺伝子を持つと推察された。
以上の結果によりジャポニカ稲の圃場揺抗性検定が可能になるとともに，ジャポニカ稲栽培地帯で有効な真性抵抗性遺缶子がインディカ稲に存在していることを明らかにした。Rice blast disease is very severe in the area cultivated with japonica rice in Yunnan Province, China. The most reliable measure to control this disease has been considered to be the development and use of resistant varieties. Varietal resistance to blast disease is divided into true resistance and field resistance. The former is determined by all-or-none disease response of a certain variety to a certain race of the fungus, and the latter by the severity of a disease on a certain variety caused by the compatible race of fungus. Use and development of resistant varieties harbouring true resistance genes and a high level of field resistance are the most effective measures to control blast. Field resistance of rice varieties with true resistance genes can not be assessed in the test field in the absence of compatible races. Japonica rice varieties were inoculated at the fourth stage by spraying with a spore suspension of compatible races. Inoculated seedlings were warmed with an electric heater at night in the greenhouse. These inoculation and heating techniques resulted in such successful infection that the relative resistance of japonica rice varieties to blast disease could be determined accurately.
Out of eighty-one indica rice varieties tested, nineteen varieties were resistant to all the isolates collected in the japonica rice-growing area in Yunnan Province. These indica varieties were divided into nine groups, on the basis of the reaction patterns to the Japanese isolates or the Yunnan isolates collected in the indica rice-growing area in Yunnan Province. It is assumed that these indica varieties harbour at least five true resistance genes that have not been identified yet.