2.8.17
THE EFFECT OF THE STAGE OF FLOWERING ON THE INFECTION EFFICIENCY OF USTILAGO TRITICI ON TRITICUM AESTIVUM

JG MENZIES, PL THOMAS and S WOODS

Cereal Research Centre, Agriculture and Agri-Food Canada, 195 Dafoe Road, Winnipeg, Manitoba, Canada, R3T 2M9

Background and objectives
In general, the inoculation of wheat lines for determining their resistance or susceptibility to Ustilago tritici at the Cereal Research Centre occurs when the plants are at the mid-anthesis stage of spike development. However, it is not always possible to inoculate at mid-anthesis so, occasionally, the wheat spikes are inoculated a few days before or a few days after mid-anthesis. The objective of this study was to determine if inoculation with U. ;tritici of wheat spikes at different stages of development affects the subsequent percentage of smutted plants grown from the inoculated seed.

Materials and methods
Four lines of wheat were inoculated using the partial-vacuum method [1] at three different stages of spike development in the field each year for 5 ;years. The stages of spike development studied were prior to anthesis, which was termed the 'green' stage, mid-anthesis which was when the anthers at either end of the spike were dehisced while those in the middle of the spike were yellow, and the 'late' stage, when all of the anthers had dehisced.

Results and conclusions
Inoculation of the spikes at the late stage of anthesis resulted in a significantly lower percentage of smutted plants (P<0.0001) than when the spikes were inoculated at the green or mid-anthesis stage. There was no significant difference between inoculation at the green or mid-anthesis stage of development of the wheat spikes. There were significant wheat line by stage of inoculation interactions. Significant differences were noted among the four wheat lines for their level of susceptibility to U. ;tritici and among the years of inoculation for the level of smut infection that occurred. We conclude from our data that wheat spikes appear to be the most receptive to infection by U. ; tritici at the mid-anthesis stage, but if one cannot inoculate at this time, the spike appear to be more receptive to the smut pathogen prior to mid-anthesis than after mid-anthesis.

References
1. Nielsen J, 1983. Plant Disease 67, 860-863.