Photoperiod response and earliness ofS. tuberosum ssp.andigena after six cycles of recurrent selection for adaptation to long days

Between 1963 and 1976 a population of South American Andigena potatoes was subjected to six cycles of recurrent selection at Ithaca, N.Y. for adaptation to North Temperate conditions. This research was undertaken to measure the changes in adaptation and earliness that have taken place in the process of selection. Field experiments with different harvest dates and a controlled daylength experiment in the greenhouse in Ithaca showed: 1) an increase in percent tuberization, tuber weight and size, and harvest index; 2) no change in total fresh weight (haulm + tuber); and 3) a decrease in fresh weight of haulm. Greatest differences among cycles of selection were observed at the early harvest date. Tuberization on cuttings was well correlated with other measures of maturity. Cycles three and four, which were started from open-pollinated seed, tended to “revert” to the form of the original population in terms of late maturity (or low tuberization and yield at the early harvest date) and low harvest index. These results are interpreted as a gain in photoperiod adaptation and earliness with possible effects of mating system and selection pressure on the rate of progress.