Descriptions and Comparative Morphology of Cactodera milleri n. sp. (Nematoda: Heteroderidae) and Cactodera cacti with a Review and Key to the Genus Cactodera.

A new species, Cactodera milleri n. sp., is described and illustrated from specimens obtained from roots of common lambsquarter, Chenopodium album L., from Mattawan, Michigan. Cactodera milleri can be differentiated from other Cactodera species by the presence of punctated egg shells and a second-stage juvenile (J2) stylet length averaging 21.8 mum as measured from freshly killed specimens in water mounts. Thirty-four plant species, including 11 weed species, 18 agronomic crop species, and 5 cactus species were tested as potential hosts of C. milleri. The new species reproduced only on Chenopodium album, C. amaranticolor Cofte. Reyn., and C. quinoa Willd. Cactodera cacti (Filipjev &Schuurmans Stekhoven, 1941) Krall &Krall, 1978, a morphologically similar species, is reexamined. A description of the female and additional morphometric and morphologic data of cysts, males, J2, and eggs are provided for several populations of C. cacti. A review of the morphometrics of all species of Cactodera and a taxonomic key to the seven species are presented.

Life Cycle of Heterodera zeae Koshy, Swarup, and Sethi on Zea mays L. Axenic Root Explants.

Monoxenic cultures of Heterodera zeae, the corn cyst nematode (CCN), were established on root explants of corn Zea mays L., cv. Kenworthy. The life cycle of H. zeae was determined from light anti scanning electron microscopic observations of the root explants grown in the dark at 29.5 +/- .5 C under gnotobiotic conditions. The life cycle, from the time the explants were inoculated with second-stage larvae (L2) to the first appearance of newly hatched second-generation L2, required 22 days. The occurrence of males was rare suggesting that reproduction in H. zeae is parthenogenetic.

Development of Heterodera glycines Ichinohe on Soybean, Glycine max (L.) Merr., under Gnotobiotic Conditions.

The life cycle of the soybean cyst nematode, Race 3 (SCN 3), Heterodera glycines Inchinohe was determined from observations of the developmental stages on soybean Glycine max cv. Kent root explants under gnotobiotic conditions at 25 C. Approximately 51% of the second-stage larvae penetrated the root l day after inoculation (DAI). Third-stage larvae appeared 4 DAI, became sexually differentiated 5 DAI, and protruded from the root tissues 6 DAI. Fourth-stage males and females were observed 7 DAI. Ensheathcd adult males were observed at 9 DAI and exsheathed to free adults at 11 DAI. The fourth-stage female became an adult at l0 DAI, Males entwined arotmd the gelatinons sac of the female at 12 DAI and were assumed to be mating. Some males actually penetrated and were enveloped by the gelatinous sac. The female-to-male sex ratio ranged from 2.3 to 9.5:1. First- and second-stage larvae were observed in the egg 17 and 19 DAI, respectively. The life cycle of the SCN 3 was completed 21 DAI upon hatching of the eggs and emergence of second-stage larvae. The average number of eggs in the cyst body and gelatinous sac, was 210 and 187, respectively. Key words: reproduction, soybean cyst nematode, scanning electron microscopy.

Screening Soybean for Resistance to Heterodera glycines Ichinohe Using Monoxenic Cultures.

A simple, rapid, and inexpensive method for evaluation of host-parasite interactions, based on monoxenic cultures, is described. Axenic root explants of Glycine max (L.) Merr., cultured on a holidic agar medium, were inoculated with axenic second-stage larvae of Heterodera glycines Ichinohe, Race 3. A clear separation of susceptible and resistant cultivars, based on numbers of mature female nematodes present after 3 wk at 25 C, was observed. The method described should aid researchers in the evaluation of the host response to infection by H. glycines.