Recognising ceratocystis disease symptoms in a Eucalyptus pellita nursery

Abstract

Early recognition of symptoms of infection is essential to prevent diseases from spreading through nurseries and into planted systems. In plantations, symptoms of Ceratocystis manginecans infection are typically wilt and canker but symptoms may differ at the nursery stage and as yet have not been described for Eucalyptus pellita. In this study, disease symptoms were recorded over a three-month period in an E. pellita nursery and isolates trapped. Then, to clearly identify those relating to ceratocystis disease and any related mortality, two C. manginecans isolates were re-inoculated by either spraying or dipping of healthy plantlets raised by tissue culture and mini-cuttings. Many disease symptoms were observed in the nursery but only perithecia on the leaves and stems was a clear indication of the presence of a Ceratocystis pathogen. Nine pathogenic fungal species, including C. manginecans, were isolated and identified by DNA analysis. Koch’s postulates indicated that leaf blight associated with C. manginecans was black-brown in colour, irregular, with uneven edges and surrounded by a yellow margin or halo on the upper leaf surface. Mortality following inoculation of plantlets by spraying immediately after planting was > 70%; by contrast, mortality of mini-cuttings was < 50% if spraying was done just before transplanting but < 20% if done 7 or 14 days after transplanting. Isolate EP313C caused significantly greater mortality than isolate EP106C. The research showed that C. manginecans and other pathogens were present in the nursery environment and must be identified and managed as part of good nursery practice.