Evaluation location: Illinois, United States
Seeds of the perennial Glycine species were scarified by scoring seed coats on the opposite side of the hilum with a razor blade. Seeds were then germinated on moist filter paper inside petri dishes under light at 25C for 4 to 6 d. Germinated seedlings were planted in a 1:1 steam-sterilized soil:sand mix (1:1 v/v) at pH 7. The soil was a Drummer silt loam. All plants were grown in greenhouses under a photoperiod of 16 h of daylight at 24 +/- 3C/18 +/- 3C day/night temperature. For all evaluations, transplanted seedlings were grown for 2 to 3 wk before being inoculated. Seeds of the soybean checks were sown when the perennial accessions were transplanted. The seedlings were grown in a greenhouse and watered daily for 10 to 14 d before inoculating. Five plants of each accession were screened once in a series of 8 non-replicated runs. The cultivar Spencer was used as a susceptible check in each run. A selected set of 67 accessions, which were based on the result of the non-replicated runs with some accessions representing most species, was further screened in 2 replicated trials with 5 plants/per each of 4 replications. A final selected set of 15 accessions, which were based on those 67 accessions that performed well within some of the species, was screened in 2 trials with 3 replications each. A F. solani f. sp. Glycines isolate, Mont-1, was subcultured on 2% (w/v) water agar for 3 wk before infesting sorghum seed. Two hundred cm3 of sorghum seed were soaked in distilled water in a 1-L Erlenmeyer flask overnight, drained, and autoclaved on 2 consecutive days for 20 min at 121C. Ten mycelial plugs (4-mm diameter) were transferred from the water agar colonies. Cultures on sorghum grains were incubated under a 12 h-photoperiod with fluorescent light for 10 to 14 d at 25C. Nine entries of 5 seedlings or seeds were sown in 20- by 30-cm trays. Soil was infested by placing colonized sorghum seed below transplanted Glycine spp. and beneath soybean seeds at planting. A template was used to make 3 furrows that were 30 cm long, 2 cm deep, and 3 cm apart. 5 cubic centimeters of infested sorghum seed was evenly distributed in each furrow and about 800 cm3 of soil mix was added to cover the infested seed to a depth of 2 cm. Transplanted seedlings or seeds were added to each furrow directly over the infested sorghum seeds. Trays were placed in a greenhouse at 20 to 30C and watered daily. Disease severity was rated for each plant 21 d after planting.