Studies on factors in sweet potato root which induce spore germination of Ceratocystis fimbriata

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Spore germination of Ceratocystis fimbriata was studied in terms of host-parasite specificity. The sweet potato, coffee and cacao strains of Ceratoqystis fimbriata germinated well in a fraction of sweet potato root water extract which had been passed through a column of cation exchange resin. The results showed that germination of these strains was independent of exogenous cations. On the other hand, the prune, oak, taro and almond strains required for germination both the absorbed and unabsorbed fractions of sweet potato root water extract which were separated from each other with a cation exchange resin column. Divalent cations such as Ca^<2+>, Mg^<2+>, Mn^<2+> and Zn^<2+> were identified as the active principles in the absorbed fraction and Ca^<2+> showed the highest inductive activity for spore germination in the presence of the unabsorbed fraction. The active principle(s) in the unabsorbed fraction has not yet been identified. There was no relationship between the Ca^<2+> and Mg^<2+> contents of the spores and the requirement of exogenous Ca^<2+> for germination. Ca^<2+> appeared to function as a trigger of spore germination, not as a normal nutrient. These results suggest that the divalent cations such as Ca^<2+> and Mg^<2+> in sweet potato contribute to the establishment of host-parasite specificity of this system.