　土壌病原菌Fusarium oxysporum f. sp. lactucaeにより発生するサラダナ根腐病の生物的防除法を確立するため，非病原性菌株Fusarium oxysporum corn-3S-nit3によるサラダナ根腐病の抑制効果について検討した。非病原性菌株は，稲わら培養した厚膜胞子の状態でほ場にすき込むことにより，高密度で土壌に定着した。 1作目作付け前の土壌消毒により根腐病菌密度を検出限界以下に低下させた後に，稲わら培地で培養した非病原性菌株をすき込むと，夏～秋期の 4作の間根腐病菌密度の増加を抑え，発病を抑制できた。しかし，土壌中の根腐病菌密度が高い場合は発病抑制効果は低かった。サラダナの根圏土壌中において，根腐病菌の増加にともなって非病原性菌株が減少したことから，サラダナの根圏で両菌が競合していることが推察された。非病原性菌株による生物的防除法を実用化するためには，非病原性菌株の根腐病菌抑制機構の解明による抑制効果の向上と，資材化による接種の省力化が必要と考えられる。

　Microbial Control of Root Rot Disease on Butter Head Type Lettuce with Non-pathogenic Fusarium. NARIYAMA Hideki and WATANABE Toshiro(Fukuoka Agricultural Research Center, Chikushino, Fukuoka 818-8549, Japan) Bull. Fukuoka Agric. Res. Cent., 23: 37 - 42 (2004)

　To establish a method for controlling root rot disease on butter head type lettuce caused by Fusarium oxysporum f. sp. lactucae, the suppressive effect of non-pathogenic Fusarium oxysporum corn-3S-nit3 was studied. Soil was highly enriched with non-pathogenic Fusarium, when the fusarium was cultivated in a straw medium and the straw medium covered with chlamidspore was plowed into soil. After the density of pathogenic Fusarium was lowered by soil steralization as to be undetected and the straw medium covered with non-pathogenic Fusarium was plowed into soil, the density of pathogenic Fusarium and the attributable symptoms were suppressed from summer to autumn. But the suppressive effect was weak when the density of the pathogens was high. It was inferred that the non-pathogens and pathogens competed with each other because the density of the non-pathogens in rhizosphere lowered in proportion to the density of pathogens. To utilize the microbial control by the non-pathogens, it is necessary to improve the suppressive effect by investigating a suppressive mechanism and to reduce the laborious job of inoculation by materializing the inoculum.