The cause and control of wilt symptoms in Calceolaria multiflora and Senecio cruentus cultivars

Abstract

Phytophthora erythroseptica Pethy. was isolated from acutely wilted calceolaria (Calceolaria multiflora) Cav. and cineraria (Senecio cruentus D.C.) cultivars. Two species of Pythium were also frequently isolated from diseased roots and crown tissues of both hosts and were found to be associated with an unthrifty growth condition. Isolates from plants grown at the Wellington City Council's Parks and Reserves Berhampore Nursery were identified as Pythium irregulare Buisman and isolates from plants grown at Botany Department, Victoria University of Wellington were identified as Pythium debaryanum auct. non Hesse . Tissues cultured from acutely wilted plants often produced both Phytophthora and Pythiurn, indicating the presence of a disease complex. Pythium debaryanum was shown to cause a marked growth.reduction in calceolaria plants and damping-off in germinating seed and young seedlings. P. irregulare was not tested for pathogenicity. Symptoms of Pythium infection in calceolaria plants included unthrift, stunting, epinasty of lower leaves and a chronic wilt condition. Similarly, Pythium was often the sole pathogen isolated from diseased roots of unthrifty cinerarias. Although the pathogenicity of Pythiurn on cineraria was not studied, it would appear that a similar growth reduction is caused in both subjects. The presence of Pythium was demonstrated in a glasshouse water-trough, in detritus from a hose-end and in prepared peat. It was not found in baled peat. The ease with which pasteurised media are reinfected with Pythium is also demonstrated. Phytophthora erythroseptica was isolated from and found to cause an acute wilt of healthy calceolarias and cinerarias when potted into a medium inoculated with this pathogen. This is the first instance of this pathogen being recorded on these hosts in New Zealand. P. erythroseptica having previously been recorded here only on potato (Solanum tuberosum) cvs. Identification was confirmed by the Commonwealth Mycological Institute, Kew, England. Satisfactory control of both pathogens was attained by the incorporation of Bayer 5072 or Terrazole fungicides into potting media prior to use.