Induced susceptibility and enhanced resistance at the cellular level in barley coleoptiles. II. Timing and localization of induced susceptibility in a single coleoptile cell and its transfer to an adjacent cell

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Abstract
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.