Characterisation of the ‘C’ morphotype of the pine pathogen Sphaeropsis sapinea

Abstract

Sphaeropsis sapinea is an opportunistic pathogen of Pinus spp. and other conifers. Infection occurs when host trees are predisposed by adverse environmental conditions or mechanical damage. Initially two morphotypes, A and B, were described for S. sapinea and these were defined based on cultural characteristics, texture of conidial walls and virulence. The existence of these two morphotypes has, furthermore, been confirmed through the use of RAPDs and DNA sequencing of the ITS region of the rRNA operon. A third RAPD group, including isolates from Indonesia and Mexico, has recently been reported and was designated as a C morphotype based on differences in conidial size. The objective of this study was to characterise isolates of the C morphotype of S. sapinea based on cultural characteristics, conidial morphology, growth rate and pathogenicity. Cultural and conidial characteristics of isolates belonging to the A and C morphotypes were more similar to each other than to those of the B morphotype. The growth rates of isolates belonging to the three different morphotypes were not significantly different. Artificial inoculation of both Granny Smith apples and Pinus patula seedlings revealed that isolates of the C morphotype were considerably more virulent than those of the A and B morphotypes. The discovery of the more virulent C morphotype of S. sapinea could have serious implications for management of this pathogen, as well as quarantine practises in countries that import pine seeds.