The comparison of oxalic acid production in vivo and in vitro by virulent and hypovirulent Cryphonectria (Endothia) parasitica

Abstract

The relation between oxalic acid production in liquid broth and in infected apple tissue during virulence assays was determined for Michigan and Italian strains of Cryphonectria parasitica with or without cytoplasmic double-stranded RNA (dsRNA). Two strains without dsRNA and considered virulent produced more oxalic acid in broth than did their dsRNA-containing near-isogenic counterparts. In contrast, five dsRNA-containing strains produced more oxalic acid per gram of infected apple fruit than did the dsRNA-free strains even though the lesion size produced by most of the dsRNA-containing strains was relatively small when compared to their dsRNA-free counterparts. One dsRNA-containing isolate (M14), judged virulent, produced a relatively large lesion in the apple fruit virulence assay, but oxalic acid production by this strain was similar to that of dsRNA-free virulent strains in both culture and apple fruit. Thus, the presence of dsRNA did not consistently confer avirulence, and the amount of oxalic acid production was positively associated with virulence only in broth, not in diseased plant tissue.