I don’t know how I missed this one called, “Seed Dormancy in Rosa as a function of climate” by Von Abrams and Hand American Journal of Botany 43:7-12. They looked at germination of several crosses repeated for 5 years in a row (mainly hybrid teas, but some species too). They had detailed weather data and monitored the temperature the last 30 and 60 days before a Nov. 1st hip harvest. They found a very clear, linear trend for warmer average daily temps the last 30 days before harvest contributing less dormancy to seeds and resulting in greater/earlier germination.
They also divided some plants up one year that were pollinated at the same time and let some mature their fruit outside and some finish maturing their fruit in a greenhouse where temperatures were warmer than outside. The seeds that matured at a warmer temp had less dormancy and germinated better at any stratification regime.
Attention in recent years has been given to Gudin’s work reported in the early 1990’s looking at temperatures right after pollination and during early embryogenesis influencing the endocarp thickness and future germination of rose achenes. Relatively warmer temperatures result in faster growing embryos that have a thinner endocarp and better germination.
By combining the information from both sources, warm temperatures early in the season as well as later in the season results in less dormancy in seeds to be overcome. Here in the far north (MN) I have a limited growing season with cool springs and falls. Cooler weather at both ends seem to increase dormancy and therefore can make germination more challenging. Perhaps cool conditions just trigger plants to know they are in a climate where greater dormancy is beneficial so young seedlings don’t germinate at an inopportune time of the year.
Sincerely,
David