Ultrastructural Studies of Greenbug (Hemiptera: Aphididae) Feeding Damage to Susceptible and Resistant Wheat Cultivars1

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Abstract
There were two types of cell damage by biotype C greenbug, Schizaphis graminum (Rondani), in susceptible plants. (1) All identifiable structure was lost by the organelles in a few phloem cells as early as 1 h postinfestation. (2) A slower degeneration of cell organelles occurred in mesophyll adjacent to aphid feeding tracks. Chloroplast membranes were disrupted, leaving enlarged osmiophilic granules. Mitochondrial degeneration was slower, with vesicle formation within cristae. Nuclear vesicles occurred at 10 days postinfestation. Densely staining salivary sheath material occurred near feeding sites. A resistant wheat showed no macroscopic damage at 10 days postinfestation. There were patches of collapsed dried mesophyll in samples 2 days postinfestation; these were surrounded by unaffected cells. Saliva sheath material was observed at 2 days postinfestation, but not later. In susceptible wheat, feeding tracks were primarily intercellular in phloem. Damage in resistance tissue was to mesophyll. Resistance in wheat was physiological and biochemical.