Smut disease assessment by PCR and microscopy in inoculated tissue cultured sugarcane cultivars

By using PCR to amplify the bE mating-type gene of Ustilago scitaminea, it is possible to detect this pathogen in sugarcane. Different parts of smut inoculated tissue cultured plantlets were assayed to determine whether plant resistance to smut infection could be effectively evaluated by PCR or microscopy. The PCR assay was extremely sensitive in detecting the presence, of the pathogen and yielded a positive response in plantlets inoculated with as few as 10 sporidia, 12h post-inoculation, irrespective of parental disease rating. The PCR assay also detected the presence of sporidia of the single mating-type in plantlets individually inoculated with each mating type. Although easily visible in the first week of inoculation, fungal hyphae were difficult to locate in areas beyond the point of inoculation by microscopy, four weeks post-inoculation. After 8 weeks the convoluted hyphae, characteristic of U. scitaminea, was again evident within the culms of all three sugarcane cultivars under investigation. At the 95% confidence level, the PCR assay was significantly better for smut detection than microscopy. Whilst the PCR assay and microscopy may be used to detect the smut pathogen in plantlets not exhibiting symptoms of infection, there was no relationship between the presence of the pathogen and plant resistance. (C) 2004 Elsevier Ireland Ltd. All rights reserved.