Variation Among South African Isolates ofSphaeropsis sapinea

Abstract

Swart, w. J., Wingfield, M. J., PaJmer, M. A., and Blanchette, R. A. 1991. Variation among South African isolates of Sphaeropsissapinea. Phytopathology 810489-493. Ten isolates of Sphaeropsis sapinea (syn. Diplodia pinea) obtained from various natural!y 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 isoJates had distinct pits over the entire outer surface of 30m-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 ,.-ilhsmaJ1 indentations that were not distinct pits and occurred on only parts of individual conidia. Three isolates grew more slowly (P = O.OJ) on five culture media tested and at 20 and 25 C on malt Additional keywords: isozyme analysis, Pinus radiata. 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.wa!Jed 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.