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Heterodera glycines Ichinohe is a serious pest of soybean [Glycine max (L.) Merr.] in the USA. Several Races of H. glycines occur in the soybean growing areas. Soybean accessions with resistance to Races 3, 5, and 14 have been identified. Data on reaction of these accessions for Races 1 and 2 are not available. Our objective was to bioassay these accessions for resistance to H. glycines Races 1 and 2. Eighty‐six accessions, host differentials, and susceptible control were bioassayed during 1995 to 1996 for each of the two Races in thermoregulated water baths in the greenhouse. The results indicated that 52 accessions had resistance to H. glycines Race 1, and 24 accessions had resistance to Race 2, respectively. Soybean PIs 89772, 90763, 404166, 404198A, 437654, 437690, 438489B, 567491A, and 567516C were either resistant or moderately resistant to both Races. These are potential resistance sources to H. glycines Races 1, and 2 for developing resistant soybean cultivars. These PI lines are being fingerprinted by means of molecular markers to identify the unique lines to allow broadening the diversity of resistance gene utilization.

Phomopsis seed decay (PSD) caused by Phomopsis spp. can be severe when soybean seed producers in the southern United States use the early soybean production system (ESPS) to avoid late-July through early-September drought damage to soybean. The usefulness of this production system would be greater if developing seed could be protected from PSD by foliar application of fungicides or by planting Phomopsis spp.-resistant soybean lines. The objective of this research was to determine the affects of the fungicides benomyl and azoxystrobin applied to soybean, at various times, on percent Phomopsis spp. infection of seed in Asgrow 3834, a PSD-susceptible cultivar, and SS93-6012, a PSD-resistant soybean line, planted in mid-April. The percent Phomopsis spp. infection of Asgrow 3834 seed averaged over years was significantly less for the benomyl (0.28 kg a.i. ha-1) applied at R3 + R5 treatment (48.6% seed infection) than the control (52.8% seed infection) and significantly greater for the azoxystrobin (0.17 kg a.i. ha-1) applied at R3 + R5 treatment (61.6% seed infection) than the control (52.8% seed infection). This method of managing PSD will not be acceptable to soybean growers. The percent of Phomopsis spp. infection of Asgrow 3834 seed averaged over years (52.8% seed infection) was significantly greater than for line SS93-6012 (2.8% seed infection). There were no differences in percent Phomopsis spp. infection of SS93-6012 seed between the control (2.8% seed infection) and benomyl treatment (4.0% seed infection). The most effective method for PSD management was to plant a resistant soybean line. Line SS93-6012 will be useful in breeding programs focused on developing high yielding PSD-resistant cultivars.

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