Evaluation of different detection assays for use in Leifsonia xyli subsp. xyli assessment programs
Ratoon stunting disease (RSD) caused by Leifsonia xyli subsp. xyli is a major constraint to sugarcane production worldwide. Importation of infected germplasm exposes Nigeria to risk of introduction of the pathogen since it has no unique external and internal symptoms. Therefore, different detection techniques were investigated. L. xyli subsp. xyli inoculated and uninoculated sugarcane varieties comprising susceptible (CP72-1210), moderately resistant (CP80-1743), most commonly grown (Co957, Co997, SP71-6180, Co62175, chewing cane, B47419, Co6806) and locally bred (NCS001, NCS002, NCS003, NCS005, NCS006, NCS007, NCS008, ILS001 and ILS002) were evaluated in the screenhouse for both plant crop and ratoon crop. RSD detection assays of PCR on leaf and stalk saps, evaporative-blot enzyme immunoassay (EB-EIA) on sap from stalk and tissue-blot enzyme immunoassay (TB-EIA) on stalk were carried out using inoculated and uninoculated varieties. L. xyli subsp. xyli was not detected in any of the uninoculated varieties. In inoculated varieties, L. xyli subsp. xyli was not detected by PCR in leaf extracts but was detected by EB-EIA, TB-EIA and PCR in stalk extracts from all the varieties in both plant crop and ratoon crop. Evaporative-blot enzyme immunoassay is recommended for quarantine detection of RSD bacterium in stalk because it is simple, less costly, sap used for detection can be stored for a long time and result read rapidly with a microplate reader compared to counting visually with stereo microscope in TB-EIA. PCR is much more expensive and accurate; it can be used to confirm results that are either questionable or negative from these serological techniques.
Keywords: Ratoon stunting disease, Leifsonia xyli subsp. xyli detection, Sugarcane varieties, Nigeria