Real-time analysis of Polymyxa betae GST expression in infected sugar beet

SUMMARY We have tested and developed protocols for both sequence-independent and hybridization probe real-time PCR for the detection of Polymyxa betae glutathione-S-transferase transcripts in infected sugar beet roots. When using the test on P. betae-free plants, no signal above the level of the non-template control was observed. Real-time PCR analysis of both serially diluted zoospore suspensions and infected root material demonstrated a close relationship between the threshold cycle and the amount of P. betae. Hybridization probe real-time analysis of infected plants sampled sequentially over 20 days from sowing showed that the levels of the transcript rose steadily after initial infection to a peak and then declined. Comparative time-course analyses of infection in susceptible plants and a resistant wild Beta species indicated that, whilst transcript levels in susceptible plants showed a continuing upward trend, in the resistant species they were detectable only at an extremely low level.