Resistance to the soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is difficult to evaluate in soybean [Glycine max (L.) Merr.] breeding. PI 437.654 has resistance to more SCN race isolates than any other known soybean. We screened 298 F6∶7 recombinant-inbred lines from a cross between PI 437.654 and 'BSR101' for SCN race-3 resistance, genetically mapped 355 RFLP markers and the I locus, and tested these markers for association with resistance loci. The Rhg 4 resistance locus was within 1 cM of the I locus on linkage group A. Two additional QTLs associated with SCN resistance were located within 3cM of markers on groups G and M. These two loci were not independent because 91 of 96 lines that had a resistant-parent marker type on group G also had a resistant-parent marker type on group M. Rhg 4 and the QTL on G showed a significant interaction by together providing complete resistance to SCN race-3. Individually, the QTL on G had greater effect on resistance than did Rhg 4, but neither locus alone provided a degree of resistance much different from the susceptible parent. The nearest markers to the mapped QTLs on groups A and G had allele frequencies from the resistant parent indicating 52 resistant lines in this population, a number not significantly different from the 55 resistant lines found. Therefore, no QTLs from PI 437.654 other than those mapped here are expected to be required for resistance to SCN race-3. All 50 lines that had the PI 437.654 marker type at the nearest marker to each of the QTLs on groups A and G were resistant to SCN race-3. We believe markers near to these QTLs can be used effectively to select for SCN race-3 resistance, thereby improving the ability to breed SCN-resistant soybean varieties.

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Soybean [Glycine max (L.) Merr.] cultivars in the USA, which are resistant to soybean cyst nematode (SCN) (Heteroderag lycines Ichinohe), have resistance derived from only a few plant introductions (PIs). Many other SCN resistant PIs have been identified which could be used as sources for broadening the diversity of resistance genes in cultivars. The objectives of this research were to study the relationship among PIs with SCN resistance using restriction fragment length polymorphism (RFLP) markers and to assess their resistance response to five races of H. glycines. Thirty‐eight PIs previously reported as being resistant to one or more SCN races were evaluated for resistance to H. glycines Races 1, 2, 3, 5, and 14 in a greenhouse and were tested with 201 genomic DNA clones. PI 437654 and PI 438489B were resistant to all five SCN races. Four PIs were resistant to four SCN races, nine resistant to three races, four resistant to two races, four resistant to one race and the remainder had only moderate resistance or moderate susceptibility to one or more races. The PIs were polymorphic for 138 clones which revealed 301 polymorphic DNA fragments. The groupings of the PIs for both cluster analysis and principal component analysis (PCA) were associated with resistance responses to races of H. glycines. One major group of PIs was distant from all previously used sources of resistance. These PIs had only moderate resistance to Race 3 but could potentially provide new genes for resistance to this race. The other PIs were in groups that included Pls with resistance sources previously used by breeders. This information on the relationship of the PIs should help researchers developing resistant soybean cultivars to identify sources of SCN resistance which are not closely related to previously used sources.

Inheritance of resistance in soybean [Glycine max (L.) Merr.] soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is complex. The objectives of this study were to determine (i) inheritance Race 3 resistance in ‘Peking’ and PI 90763 and (ii) the relationship Rhg4 and of any other genes occurring in Peking to those genes found in PI 88788 for SCN resistance. The F1, F2, and F3 plants from five different crosses among resistant (R) and susceptible (S) cultivars evaluated for SCN resistance in the greenhouse. Individual plants were categorized as resistant or susceptible based on the index of parasitism. The chi‐square test was used to determine goodness of fit between observed and expected ratios. The results indicated that SCN Race 3 resistance was conditioned by one dominant and two recessive genes in each parent. Peking and PI 90763 have all three resistance genes in common. Two genes, Rhg4 and rhgz, in both Peking and in PI 90763 were also in P1 88788. An additional dominant gene in PI 88788 and a second recessive gene in Peking and in PI 90763 provided nonallelic interaction.

Six sugarbeet (Beta vulgaris L.) lines (GWI-248, SPB-11, MonoHy 55, SMS-1, EL45 and FC607) were tested for regeneration. Shoot cultures were initiated in vitro from naked, sterilized embryos obtained from mature seed. Excised petioles from cultured shoots were plated on Gamborg's B5 medium and four modified Murashige and Skoog (MS) media. A medium containing MS inorganic salts supplemented with 0.4 mg/1 N(6)-benzyladenine, 0.1 mg/1 indole-3-butyric acid, ten vitamins and six amino acids, termed RV, was superior for both adventitious shoot and callus formation. Callus was observed only on RV medium and only on petioles that did not develop adventitious buds directly. Rooting of regenerated shoots and development of complete plants was accomplished by transfer to Gamborg's B5 medium with 5 mg/l indole-3-butyric acid as the sole phytohormone. The complete process of regeneration through adventitious shoot production took from 4 to 6 weeks from explants to rooted plants. The callus that formed on nonorganogenic petioles was regenerative when transferred to fresh RV medium. Regeneration from callus occurred mainly by shoot organogenesis but also by somatic embryogenesis at a low frequency.