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Résumé :
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Biotype E greenbugs, Schizaphis graminum (Rondani), were allowed to feed for at least 1 h on leaves of resistant and susceptible wheat, Triticum aestivum L. Cellular responses were studied using transmission electron microscopy. Greenbugs caused severe degenerative changes in vascular cells of susceptible plants as early as 1 h after aphid removal. In mesophyll tissue, cells adjacent to the stylet path were most affected, and amount of cellular damage decreased as distance from the stylet path increased. Ultrastructural damage included disruption of chloroplast and cellular membranes and enlargement of the plastoglobuli within chloroplasts. Cell wall appositions occurred in susceptible tissue 1 d after infestation, and they became more pronounced by 4 d. By 7 d, cellular organelles had degenerated, and it was impossible to distinguish their primary structural features. In contrast, few mesophyll cells of resistant plants were damaged; however, cellular debris was found in intercellular spaces. Bacterial cells were observed among cellular debris at the feeding sites in some resistant plants. Moreover, aphid salivary sheaths, which were prominent in susceptible plants, did not persist in resistant plants beyond 4 d after infestation. Resistance in wheat to biotype E greenbug appears to depend on ability of the host plant to resist cellular alterations induced during the feeding process rather than on differences in feeding site location or mechanical damage.
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