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The primary growth of both Erysiphe graminis de Candolle and E. pisi de Candolle on the same cell or adjacent cells of barley coleoptiles was observed by light microscopy to determine factors conditioning host cells toward susceptibility. Erysiphe pisi never successfully penetrated (0% efficiency) when it was the sole inoculum. By contrast it penetrated with varied efficiencies when initiation of cytoplasmic aggregates induced by it followed that of E. graminis by 4.0–19.0 h on the same coleoptile cells. When E. graminis induced a cytoplasmic aggregate 4.0–9.0 h earlier than E. pisi in a single coleoptile cell, induced susceptibility was minimal around the E. graminis penetration site, within 100 μm of the site, in the cell. When the time intervals were 9.25 – 14.0 h, induced susceptibility was maximal around the E. graminis penetration site, within 100 μm, and minimal when the fungi were more than 200 μm apart. When the time intervals were more than 14.0 h, induced susceptibility was evenly dispersed throughout the entire cell and transfer of susceptibility to laterally adjacent cells occurred only under these time conditions. Erysiphe pisi penetrations on coleoptile cells were influenced by its growth or the host cell's response before actual penetration occurred.

From October 2016 to March 2019, 83 tomato leaf mold fungal strains (Passalora fulva) were isolated from 15 greenhouses in Mie prefecture, Japan. Their susceptibility to succinate dehydrogenase inhibitor (SDHI) fungicides was investigated. The occurrence of boscalid-and penthiopyrad-resistant strains was confirmed, and all penthiopyrad-resistant strains had acquired cross-resistance with boscalid. We also confirmed that several fungal strains had developed resistance to the SDHI fungicidal agents isopyrazam and pyraziflumid, neither of which had been used in the field from which the leaf mold fungus was isolated.Consequently, it was suggested that cross-resistance might have developed due to previous boscalid and penthiopyrad treatment.The frequency of boscalid-and penthiopyrad-resistant strains increased significantly as the frequency of SDHI fungicide spraying increased. Significant differences were also observed between the fungicides in terms of changes in resistance rate; boscalid treatment resulted in more resistance than penthiopyrad treatment.

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