BIOLOGICAL MANIFESTATION OF RESISTANCE TO SOYBEAN CYST-NEMATODE DEVELOPMENT IN HARTWIG SOYBEAN

'Hartwig' soybean [Glycine max (L.) Merr.] is the first cultivar reported to be resistant to all known races of soybean cyst nematode (SCN), Heterodera glycines Ichinohe; however, the nature of resistance in this cultivar is not known. Resistance to SCN in Hartwig and its donor parent, PI 437654, was studied from observations of the developmental stages of the nematode in the plant roots and compared with the development in susceptible 'Essex'. Soybean seedlings (emerging roots) were exposed to a wild population of SCN for 8 h and transferred to hydroponics. Adult males and females were extracted and the number of immature juveniles in the roots was recorded from stained roots. A greater number of juveniles of SCN penetrated the roots of Hartwig than roots of PI 437654 or Essex. Several immature juveniles were observed in the roots of Hartwig and PI 437654; however, no mature females developed on either of these two lines. There were no immature juveniles in Essex. Many adult males developed in Hartwig and PI 437654. Complete resistance to female development operated in both Hartwig and PI 437654, whereas partial resistance to male development was observed in PI 437654. Hartwig soybean seems to attract more SCN juveniles, resulting in greater initial penetration than occurs in PI 437654 or Essex.