we can monitor the growth of U. virensat any time, which provides much convenience to investigate the early process ofU. virensinfection. Our serial observations at different infection time confirmed that 
hyphae colonize the inner upper spaces of spikelets from the apex and grow downward to infect the pistil and stamens. We did not observe the case in which hyphae infect pistil and stamens first but not appear in the inner upper part of the spikelets.