VARIATION AMONG SOUTH-AFRICAN ISOLATES OF SPHAEROPSIS-SAPINEA

Ten isolates of Sphaeropsis sapinea (syn. Diplodia pinea) obtained from various naturally infected Pinus spp. in South Africa were screened for differences in cultural characteristics, virulence, and isozyme profiles of five enzymes. Considerable variation among isolates existed in the length and width of conidia, but this did not allow for the separation of isolates into specific groups. Scanning electron microscopy revealed that two isolates had distinct pits over the entire outer surface of 30% of the conidia examined. Three isolates consistently had smooth conidia, and five isolates were considered intermediate. The latter had some entirely smooth conidia and some with small indentations that were not distinct pits and occurred on only parts of individual conidia. Three isolates grew more slowly (P = 0.01) on five culture media tested and at 20 and 25 C on malt extract agar. There was a significant positive correlation between in vitro growth rate and virulence of the 10 isolates in growth chamber and field inoculations. The isozyme banding patterns of the three isolates with smooth-walled conidia and four intermediate isolates were identical to those of a typical smooth-spored isolate of S. sapinea from the north central United States for each of the five enzymes tested. The banding patterns of the two isolates with pitted conidia and one intermediate isolate were identical to those of isolates that had smooth conidia for all enzymes except malic dehydrogenase. None of the 10 local isolates displayed banding patterns associated with a typical isolate of S. sapinea having pitted conidia from the north central United States.