Comparative study on early detection of sugarcane smut (Sporisorium scitamineum) by polymerase chain reaction (PCR) and microscopy

Abstract

Sugarcane smut caused by Sporisorium scitamineum has the potential to result in substantial tonnage loss and significant reduction in sucrose recovery. As early and precise diagnosis is an integral component in the successful management of sugarcane smut, the present study was undertaken to accurately determine the presence of pathogen employing PCR-based methods supplemented with microscopy. Healthy sets of sugarcane cultivars viz., Co 96007 (Susceptible) and Co 6806 (Resistant) were challenge inoculated by hypodermal injection with teliospore suspension of S. scitamineum (containing 1 x 10⁶ teliospores/ml) and planted in sterile soil with appropriate uninoculated controls. Actively growing meristem of the plantlets was sampled at different time points for examination with microscopy and PCR using primers bE4 and bE8 of mating type genes. The whole experiment was conducted for eight weeks and meristem tissue was sampled weekly starting from three weeks post inoculation. Our results show that the PCR assay is more sensitive in early detection of the pathogen (3rd week) in both susceptible and resistant cultivars as compared to microscopic observations of the meristem samples stained with lactophenol cotton blue. However, the pathogen could not be detected from the 4th week onwards in resistant variety Co 6806. In microscopy assay, mycelial colonization was evident only from the 5th week onwards in the susceptible cultivar Co 96007, but not in the resistant cultivar Co 6806 at any of the time intervals until 8 weeks post inoculation. Results of this study suggest that, for the early and precise detection of smut pathogen in sugarcane, the PCR-based assay should be considered as a suitable diagnostic tool rather than microscopy. This could add to effective sugarcane quarantine and successful management of sugarcane smut.

Keywords: Smut pathogen, Saccharum officinarum, cultivars, pathogen detection, light microscopy, host resistance.

African Journal of Biotechnology, Vol 13(51) 4635-4638