Potato Research, 55(1): 27–40 (Mar 2012)
The Effect of Photoperiod on Tuberisation in Cultivated x Wild Potato Species Hybrids
P. Kittipadukal, P. C. Bethke, S. H. Jansky

Interpretive Summary: The major limitation to the use of wild Solanum relatives for potato improvement is their poor adaptation to major potato production areas. Most wild Solanum species produce tubers at photoperiods of about 12 hours. When grown under the long photoperiods of temperate regions, wild Solanum species typically do not tuberize. Significantly, however, crosses between wild species and cultivated potato clones produce offspring that segregate for the ability to tuberize under long summer photoperiods in temperate regions. The tuberization response to photoperiod is a complex, multistep process. It is influenced by environmental factors such as night temperature, day/night temperature differential, and nitrogen availability. Consequently, it seems logical that this would be a quantitative trait. However, this study provides additional confirmation of previous research which suggested that a few major genes are responsible for the adaptation of tropical wild potato germplasm to temperate zone production regions. Another counterintuitive result of this study is that selection for photoperiod response genes is much more effective in cultivated than wild species. Cultivated potato segregates for dominant genes that control the tuberization response at a 14 hour photoperiod, while wild species are homogeneous for recessive alleles that inhibit tuberization. The identification of S. tuberosum haploids that are homozygous for one or both of the long day tuberization genes will allow the efficient utilization of valuable genetic diversity in diploid wild Solanum species. When used as females in crosses, they will produce a high proportion of offspring that tuberize in temperate zone field conditions.

Technical Abstract: Wild Solanum species offer a valuable source of genetic diversity for potato improvement. Most of these species are found in equatorial South and Central America and they do not tuberize under long day photoperiods typical of those in the major potato production areas of North America, Europe and Asia. Crosses between two haploids of S. tuberosum Chilotanum Group as females and two wild Solanum species clones generated four hybrid families. The parents and progeny were subjected to two greenhouse trials to evaluate tuberization at 20, 14, 8-hour photoperiods. Parents and offspring tuberized most readily at the 8-hour photoperiod, and poorly or not at all at the 20-hour photoperiod. Segregation for tuberization in hybrids was apparent at the 14-hr photoperiod and depended on the cultivated parent not the wild species parent. The data support previous studies and suggest that tuber production under long photoperiods is controlled by two dominant genes in cultivated x wild species hybrids.