TOWARDS AN UNDERSTANDING OF THE EXPRESSION OF STEM RUST RESISTANCE GENE SR5

In an attempt to determine the timing and expression of stem rust resi stance gene Sr5, infection structure development of Puccinia graminis f. sp. tritici race 2SA2 in a resistant line (ISr5Ra) and a susceptibl e line (ISr8Ra) was compared quantitatively using a fluorescence micro scopy technique. The results indicated that there were no significant differences in numbers of pre-primary haustorium infection structures observed in the two near-isogenic lines at 48 hours post inoculation, however the resistant line housed fewer colonies with higher numbers o f secondary haustorial mother cells. It was concluded that Sr5 is expr essed once primary haustorium formation has been initiated, and result s in a limitation of the number of secondary haustorial mother cells.