ULTRASTRUCTURAL RESPONSES OF RESISTANT AND SUSCEPTIBLE WHEAT TO INFESTATION BY GREENBUG BIOTYPE-E (HOMOPTERA, APHIDIDAE)

Biotype E greenbugs, Schizaphis graminum (Rondani), were allowed to fe ed for at least 1 h on leaves of resistant and susceptible wheat, Trit icum aestivum L. Cellular responses were studied using transmission el ectron microscopy. Greenbugs caused severe degenerative changes in vas cular cells of susceptible plants as early as 1 h after aphid removal. In mesophyll tissue, cells adjacent to the stylet path were most affe cted, and amount of cellular damage decreased as distance from the sty let path increased. Ultrastructural damage included disruption of chlo roplast and cellular membranes and enlargement of the plastoglobuli wi thin chloroplasts. Cell wall appositions occurred in susceptible tissu e 1 d after infestation, and they became more pronounced by 4 d. By 7 d, cellular organelles had degenerated, and it was impossible to disti nguish their primary structural features. In contrast, few mesophyll c ells of resistant plants were damaged; however, cellular debris was fo und in intercellular spaces. Bacterial cells were observed among cellu lar debris at the feeding sites in some resistant plants. Moreover, ap hid salivary sheaths, which were prominent in susceptible plants, did not persist in resistant plants beyond 4 d after infestation. Resistan ce in wheat to biotype E greenbug appears to depend on ability of the host plant to resist cellular alterations induced during the feeding p rocess rather than on differences in feeding site location or mechanic al damage.