Results from hypocotyl and layer tests of soybean plant introductions PI273483 to PI427107, in maturity groups 000 to IV, following inoculation with P. sojae are outlined in Table 3. Of the 1,015 soybean plant introductions evaluated for new sources of Rps genes in this study, 159, or approximately 16%, were susceptible to all three races 7, 17, and 25, indicating that they either had Rps7 or there were no Rps genes present.
In contrast, 162, or 16%, were resistant to all three races 7, 17, and 25 of P.sojae. Of these 162, 32 were resistant to an additional five races of P.sojae (Table 3). These additional races (30-T, 30, 31, 33, and 38) have a susceptible interaction with many 2-Rps gene combinations (Table 2). These five isolates of P.sojae do not have a susceptible interaction with four 3-Rps gene combinations Rps1c, Rps3a, Rps4; Rps1c, Rps3b, Rps4; Rps1c, Rps2, Rps3a; and Rps1c, Rps2, Rps3b (Table 3).
Therefore, the 130 of the 162 soybean plant introductions that had a susceptible interaction with these five additional isolates potentially have more than one Rps gene. The possibility also exists that an unidentified Rps gene could have a susceptible interaction with these additional races with a previously unidentified virulence pathotype.
Forty-nine accessions had mean root-rot ratings of <3.0, and 438 had ratings from 3.1 to 4.0, indicating very high levels of partial resistance in the 877 soybean plant introductions that were inoculated with a race of P.sojae that had a susceptible hypocotyl interaction (Table 3). These levels of partial resistance were equal to or better than the standard cultivar Conrad which has a partial resistance score of 3.5 with most isolates.
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