Cytological aspects of events occurring after the formation of primary haustoria in barley leaves infected with powdery mildew

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Abstract
Cellular responses occurring after the formation of normal primary haustoria were examined in barley leaves inoculated with Erysiphe graminis f. sp. hordei, race 1 or IX. Collapsed mesophyll cells that fluoresced appeared specifically in incompatible combinations (infection types 0'', 0-1, 1, and 1-2). In moderately resistant combinations (infection types 1 and 1-2), conidia were produced 4-5 days after inoculation in spite of the extensive collapse of mesophyll cells, suggesting that fungal development was not completely suppressed by this cell collapse. In highly resistant (infection type 0'') and resistant (infection type 0-1) combinations, most of the epidermal cells that were subject to secondary penetration attempts prevented the formation of normal secondary haustoria by collapsing hypersensitively. The appearance of fluorescent mesophyll cells was correlated with the race-specific expression of .**GRAPHIC**. .**GRAPHIC**. JMlr12, and JMlh, which are major genes for resistance identified in cultivar H.E.S.4, Turkey 290, Russian No. 12 and Hanna, respectively. Further, the appearance of fluorescent or browned epidermal cells associated with secondary penetrations was also correlated with the race-specific expression of .**GRAPHIC**. .**GRAPHIC**. and JMlr12. These 3 genes apparently control both epidermal and mesophyll responses.