Macroscopic and microscopic phenotypes of barley inoculated with Magnaporthe host (TH6772) or nonhost (CD180) isolates. A) Macroscopic disease symptoms on primary leaves of barley cv. Vada at five days after inoculation with isolate TH6772, CD180 or mutant ∆pmk1 as indicated. Some of the plants were treated with the fungicide Beam prior to inoculation with isolate TH6772 or CD180. B) In the same experiment primary leaves of treated plants were harvested at 96 h p.i. for microscopic analysis. Interaction sites on plants were grouped into six categories according to the development of fungal infection structures as depicted in (C). The ∆pmk1 mutant showed swollen structures at the tip of its germ tubes which were classified, similar to the non-melanized appressoria after Beam-treatment, as non-functional appressoria. From at least three leaves per treatment 100 interaction sites were inspected. The figure shows the mean frequencies for each category and the standard error from one representative experiment. The results were confirmed in two further biological replicates. scale bar: 10 μm; co: conidium; gt: germ tube; nma: non-melanized appressorium; st: swollen structure at the end of germ tube; app: appressorium; ph: penetration hypha; ih: invasive hyphae.