Diurnal Alternating Temperature Improves Germination of Some Wild Potato ( Solanum ) Botanical Seedlots

Potato has about 100 wild species relatives that are multiplied in the form of botanical seed populations by genebanks and distributed for use in research and breeding, so understanding factors that affect seed germination is valuable. This is especially true for problematic seedlots that have slow and low (“trickle”) germination even when subjected to germination techniques that give optimal results in most other seedlots in the genebank. Twelve seedlots with trickle germination even after at least 2 years of storage and 2 robustly-germinating positive control seedlots encompassing 9 species were germinated in petri plates, and subjected to day/night = 10 h/14 h = 20C/6C alternating temperature (AT) trials along with constant room temperature (RT) controls, in the spring of 2015 and 2016. When Relative Area Under the Germination Progress Curve (RAUGPC) was calculated, normal germinating seedlots’ germination in AT was not significantly different from RT control. Some species’ seedlots’ RAUGPC germination in AT was nearly zero, some were about 50% of RT control, and some in AT germination had RAUGPC double or even triple that of RT control. In a separate trial in 2017, four seedlots most responsive to AT were shown to germinate significantly better in constant cold than their RT controls, but not as well as seeds germinated under AT. Also in 2017, two seedlots known to be very dependent on gibberellin pretreatment were tested. RT germination without gibberellin had RAUGPC of only 13% of RT control, but AT without gibberellin pretreatment increased this to 65%, showing AT substantially substitutes for gibberellin pretreatment in these seedlots. AT could be a useful application to all seed germination assays in the genebank if it facilitated a better assessment of the potential viability of trickle-germinating seedlots. But one would need to identify and exclude those seedlots for which alternating temperature greatly depresses germination.