Resistance against fusarium wilt induced by non-pathogenic Fusarium in Ipomoea tricolor

The cuttings of morning glory seedlings (Ipomoea tricolor cv. heavenly blue ) were susceptible to Fusarium oxysporum f. sp. batatas (PF), and showed th e typical fusarium wilt symptom. By using the reduction of chlorophyll cont ent in cotyledons as the quantitative index of the disease symptom, we foun d that the pretreatment with the non-pathogenic isolate of Fusarium (NPF; F . oxysporum 101-2), which has been practically used as a biological control agent for fusarium wilt of sweet potato, suppresses the symptom significan tly. Dead NPF bud-cells could not induce resistance. The supernatant of NPF culture after centrifugation at 15,000 x g for 20 min, also induced resist ance. The activity of the supernatant was lost by heating. The factor(s) as sociated with the induction of resistance was considered to be thermolabile chemical component(s) produced by NPF. This experimental model may be faci le and useful for analyzing the chemical basis of the biological interactio n among PF, morning glory and NPF.