Host Response to Meloidodera spp. (Heteroderidae)

Host responses to Meloidodera floridensis Chitwood et al., 1956, M. charis Hooper, 1960, and M. belli Wouts, 1973 were examined on loblolly pine, peony, and sage, respectively, with light, scanning, and transmission electron microscopy. In each case the nematodes induce a single uninucleate giant cell. The giant cell is initiated in the pericycle and expands as it matures. The mature giant cell induced by M. floridensis is surrounded by vascular parenchyma, whereas that caused by M. charts and M. belli coutacts xylem and phloem. The cell wall of giant cells induced by all three Meloidodera spp. is generally thicker than that of surrounding cells, with the thickest part adjacent to the lip region of the nematode. The thinner portion of the wall includes numerous pit fields with plasmodesmata, but wall ingrowths were not detected in a thorough examination of the entire wall. The nucleus of a giant cell induced by M. goridensis is highly irregular in shape with deep invaginations, whereas those caused by M. charis and M. belli include a cluster of apparently interconnected nuclear units. Organelles, including mitochondria, endoplasmic reticulum, and plastids of giant cells caused by Meloidodera, are typical of those reported in host responses of other Heteroderidae. The formation of a single uninucleate giant cell by Meloidodera, Cryphodera, Hylonerna, and Sarisodera, but a syncytium by Atalodera and Heterodera sensu lato, might be considered in conjunction with additional characters to determine the most parsimonious pattern of phylogeny of Heteroderidae.