DE-NOVO INDUCTION OF ADVENTITIOUS ROOTS IN EXCISED SHOOTS OF TOMATOESBY FUMONISIN B-1, A METABOLITE OF FUSARIUM-MONILIFORME

The de novo induction of roots in tomatoes (Lycopersicon esculentum) M ill. cvs. ''Early-pak-7,'' ''Ace,'' ''Better Boy,'' ''Roma,'' and ''Pa rks' Whopper'') by fumonisin B1, a mycotoxin produced by Fusarium moni liforme J. Sheld., was studied. In graded dosages of fumonisin B1, det ached stems of the cultivars ''Ace,'' ''Better Boy,'' and ''Roma'' wer e induced to produce calluses and roots earlier than controls. The cul tivar ''Ace'' was especially responsive to this mycotoxin, and followi ng a single application, callus initiation was observed to occur withi n a 24-48-h period and roots were produced as early as 72 h with 10 mu g/shoot or as late as 96 h with low dosages. The control plants of all cultivars were completely negative for a rooting response during this time. Some cultivars treated with fumonisin B1 showed either no respo nse or developed signs of phytotoxicity. Those cultivars that were sti mulated to produce roots did not show signs of phytotoxicity, except a t dosages of 0.5 mg/plant and higher. One cultivar did not show any si gns of phytotoxicity nor was it induced to root. The ability of fumoni sin B1 to affect the accumulation of calcium in other systems, and its structural similarity to sphingosine suggest that the induction of ad ventitious roots may be a calcium-dependent process.