VARIATION IN CONIDIAL MORPHOLOGY AMONG GEOGRAPHIC ISOLATES OF SPHAEROPSIS-SAPINEA

In the U.S.A., Sphaeropsis sapinea is believed to occur in at least tw o distinct forms (type A and B) that can be distinguished by their con idial wall ornamentation. In this study, mature conidia of 50 monoconi dial isolates of S. sapinea from a worldwide collection were examined using SEM to determine whether these two forms occurred more widely. T wenty S. sapinea isolates consistently had conidia with smooth outer s urfaces typical of type A. The remaining 30 isolates had typical pits or similar indentations occurring on between 6 and 38% of conidia exam ined. Pits, or indentations, either occurred uniformly on the outer su rface or only on some parts of individual conidia. Authentic S. sapine a isolates, categorized as type A and type B in previous studies, were chosen for detailed examination of the effect of spore age, nutrition , and pigmentation on surface ornamentation. No distinct differences i n conidial morphology between the two types were discernible between c onidia of different ages, or those produced on media containing differ ent carbon or nitrogen sources. The melanin inhibitor, tricyclazole, w as used to compare melanin-deficient conidia with pigmented conidia. A lthough mature, melanin-deficient conidia were hyaline, this did not a ppear to influence the occurrence of pits on conidia. The results of t hese studies strongly suggest that conidial morphology of S. sapinea i s a variable characteristic and, therefore, a poor taxonomic criterion .