Inoculation experiment
A schematic overview of the experiment design is shown in Figure 1a.
When plant clones were two months old, three replicates of each of the
five genotypes, in total 15 plants, were exposed to single P.
plantaginis strain (Lammi_3) by brushing spores gently with a fine
paintbrush onto six test leaves and two positive control leaves.
Similarly, three replicates of each genotype, in total 15 plants, were
mock inoculated by brushing leaves without mildew spores. Both powdery
mildew and mock-inoculated leaves were marked with a piece of masking
tape. Inoculated and mock-inoculated plant clones were placed in two
separate growth chambers (Panasonic MLR-352) at 20 ± 2 °C (day) and 16 ±
2 °C (night) with 16:8 light-darkness (L:D) photoperiod, and were
randomly organized to minimize potential variation in microclimatic
conditions. We collected two inoculated or mock-inoculated leaves from
every plant at 24, 48 and 72 hours post inoculation (hpi), snap froze
the leaves in liquid nitrogen, and stored samples in glassine bags in
-80 °C until RNA was extracted. Control leaves in whole plants were
screened until 14 days post inoculation to detect putative powdery
mildew infection to confirm the phenotypic response of the plants,
resistant or susceptible. Viability of spores used in the experiment was
confirmed by inoculating detached leaves of a susceptible genotype.