The cultivar 'Tracy' had been extensively used as a parent in breeding programs even before Laviolette and Athow (1977) reported that it was resistant to all nine of the identified races of Phytophthora megasperma Drech. var. sojae Hildeb. Kilen (1977) reported that Tracy had two major genes for resistance to race 1 of the pathogen. His data, based upon segregation of the F2 generation, also suggested that the two genes occupied loci different from Rps1 and Rps2. This paper is a report on the reaction of (1) F2 populations from the crosses 'Pickett 71' x Tracy and Tracy x D60-9647 inoculated with race 1; and (2) F3 lines from the crosses Tracy x Pickett 71 and Pickett 71 x Tracy inoculated with races 1 and 2 of the pathogen.
Kilen, Thomas C.
"Research notes: Studies on Phytophthora rot in soybeans,"
Soybean Genetics Newsletter: Vol. 6
, Article 47.
Available at: http://lib.dr.iastate.edu/soybeangenetics/vol6/iss1/47