Nickelson, R. L. and T. M. Currence.
A program has been under way in an attempt to incorporate male sterility, potato leaf, and green stem into the variety Firesteel. Combining ability for early, total, and marketable yield, and for fruit size has been emphasized.
The results of repeated backcrosses to Firesteel, using as the nonrecurrent parent a numbered selection, NC-1-48 F2, have been presented previously by Honma and Currence. In that study, the F3 generation of the cross NC-1-48 F2 x Firesteel was noted as equal to Firesteel in transmitting earliness, yield, and fruit size. In the present report, individual plants of the F3 and F4 generations of that cross were progeny tested in order to select for combining ability.
Eight psps cc aa plants of the F3 generation were pollinated by two tester varieties, and at the same time were selfed. The sixteen testcrosses were grown with crosses of Firesteel by the two testers.
It was apparent from the data that crosses of F3 plant 4 were superior to the Firesteel crosses for early and total yield. In marketable yield, the difference favored plant 4 and approached significance. In fruit size the difference was toward Firesteel and was close to significance. Compared with the crosses of the other seven F3 plants, plant 4 was significantly higher in early yield and not significantly different for the other three characters.
Plant 4 was therefore selected for further inbreeding and testing. From selfing number 4, ten F4 plants were grown and pollinated with two tester hybrids. The twenty testcrosses and the crosses of Firesteel by the two hybrids were grown in a field design similar to that of the previous year. Although differences between the F4 plants were noticeably smaller than those of the F3, or F4 plant was identified which was significantly superior in fruit size, but not significantly different for any other character.
Self progeny of this plant were grown and selfed, but not selected for two additional generations. It is thought that the psps cc aa line is now relatively homozygous and probably equal to or superior to Firesteel in transmitting earliness, yield, and fruit size to F1's. _________ Paper No. 3491 of the Scientific Journal Series of the Minnesota Agricultural Experiment Station.