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Inheritance of Stem Canker Resistance in Soybean Cultivars Crockett and Dowling

Texas A&M Univ. Res. & Ext. Ctr., Rt. 7, Box 999, Beaumont, TX 77713
National Grain Legume Program, P.O. Box 11635 Kinshasa 1, Zaire
Dep. of Soil & Crop Science, College Station, TX 77843.

^* Corresponding author.

Stem Canker caused by Diaporthe phaseolorum (Cooke & Ellis) Sacc. var. caulivora K. L. Athow & R. M. Caldwell (Dpc) has become a serious disease of soybean [Glycine max (L.) Merr.] throughout the southeastern USA. Sources of resistance have been identified and information on the inheritance of resistance is needed for each source. The objective of this work was to study the inheritance of resistance to stem canker in ‘Crockett’ and ‘Dowling’ soybean. Crockett, Dowling, and ‘Tracy-M’ were crossed with each other and with two susceptible cultivars, Coker 338 and Johnston. Disease reactions of parent and progeny populations were studied in the greenhouse following artificial (toothpick) incoculation with a southern isolate of Dpc. Crosses between either Dowling or Crockett and the two susceptible parents resulted in segregating F₂ populations that fit a 3 resistant : 1 susceptible ratio, and F_2:3 families that fit a 1 resistant : 2 segregating : 1 susceptible ratio. The cross between Crockett and Dowling resulted in a 15:1 ratio in the F₂ and a 7:8:1 ratio in the F₃ generation. Crosses between Tracy-M and Crockett or Dowling resulted in segregation ratios of 63:1 in the F₂ and 37:26:1 and F₃. These results suggest that Crockett and Dowling each have a major dominant gene, and that these two genes are different from RdC1 and RdC2 found in Tracy-M. The gene symbols Rdc3 and Rdc4 are proposed to identify genes controlling resistance to stem canker in Crockett and Dowling, respectively.

Received for publication April 14, 1992.