ACCUMULATION OF MANSONONE-E AND MANSONONE-F IN ELM CALLUS-CULTURES INOCULATED WITH OPHIOSTOMA-ULMI

The accumulation of mansonones E and F in relation to susceptibility o f elm to Dutch elm disease, caused by Ophiostoma ulmi, was investigate d in callus cultures of Ulmus americana (susceptible), U. pumila (resi stant), U. carpinifolia (intermediate resistant) and U. x 'Pioneer' (r esistant). Callus cultures of each elm species were maintained on modi fied B5 or modified Murashige and Skoog media in petri dishes, inocula ted with either an aggressive or a nonaggressive isolate of O. ulmi, a nd analyzed for mansonone content 12, 24, and 48 h later. Mansonone ac cumulation in elm callus cultures depended on the medium, the host spe cies, the fungal isolate, and time. Only mansonones E and F were obser ved, and in measurable concentrations only in U. americana and U. pumi la grown on modified B5 medium. Manosonones were detected soonest in c allus cultures inoculated with the nonaggressive isolate (after 12 h i n U. pumila and after 24 h in U. americana). At 48 h, mansonone concen trations reached their highest level, were higher in U. pumila (322-40 0 mug/g) than in U. americana (29-31 mug/g), and were not significantl y affected by the isolate of O. ulmi. There was no relation between ma nsonone accumulation in callus cultures and resistance of elm to Dutch elm disease.