Influence of root treatment with S. plymuthica IC1270 on M. oryzae -induced cellular responses in rice. (A) Intact leaf sheaths of the susceptible cv. CO39 and its resistant near-isogenic line C101LAC were challenged by injecting a conidial suspension of M. oryzae VT7. Left, Micrographs depicting representative interaction phenotypes (48 hpi): (I), Vigorous invasion of living tissues in the absence of visible host responses (CO39; Control treatment). (II), Fungal arrest in the first-invaded cell associated with browning of anticlinal cell walls (black arrowheads) and enhanced vesicular activity (asterisks) [CO39; Control treatment]. (III), Abrupt arrest of fungal invasion in hypersensitively reacting epidermal cell as indicated by dense cytoplasmic aggregation (C101LAC; Control treatment). Ap, appressorium or appressorial site. IH = invading hyphae. Scale bars = 20 μm. (B) Frequencies of abovementioned interaction phenotypes at 36 and 48 hours post inoculation. Each bar represents the mean and SD of six replications stemming from three plants. At least 50 single-cell interaction sites originating from representative sheath sections were examined per replication. Data from one experiment is presented. Repetition of experiments led to results very similar to those shown.