What is the maximum temperature that a rose seed can tolerate? I used a different vessel and the temperature on the hot pad escalated to 38C. I know that they should be alright, I am just curious. Anyone know?
Do I actually “know” the magic temp? No, but Semeniuk and Stewart discussed optima for stratification and germination, and the tendency for seeds to go back into dormancy above certain temps, if not fully after-ripened. I just looked back at my review (on this website) and find that they used 29.3 C as their highest temp and it markedly inhibited compared to 18.3 C. The effect varied with the pre-treatments used, and species of rose tested.
Generally for many species of plants 38 C is in the range that induces heat shock protein production. Whether it is somewhat bad or really bad depends on the species, the duration, the rate of approach to temp and other factors such as water stress.
Thank you Larry, what concerns me is that the seeds went from 4C to 38 C in mins but we’re also removed as quickly.
Surprise! After 2 days germination has started on the heat shocked seeds? I think I will read up more of this effect.
What you did is exactly how HSP are induced in crop plants and model plants like arabidopsis. Generally, if the stress is removed soon the plant recovers. In fact it become resistant to an even higher temp, up to some limit. The upper limit even after preparation by inducing HSP is quite species dependent but for the plant as a whole it is often much higher than for pollen. For instance tomatoes can grow in central KS where there can be daily temps of 100 F, near 38 C, and excursions to 42-43 C one or 2 days a week. But you won’t get fruit set under those conditions except with certain cherry tomatoes such as 4th of July. Most CV quit in the range of 30-32 C.
An interesting point that just occurred to me is that I grow roses under these conditions of 100 F days and the maturing seeds have to live with it. I don’t think there is enough evaporative cooling to prevent the rise of the hip to ambient temp. Folk in TX, AZ, CA have it even hotter longer but produce seeds that germinate. Maybe not as well, maybe not for all types, for sure I don’t know. Perhaps some of the RHA members from those states could comment.
Of course a germinating seedling is not a maturing seed and its needs may be quite different. Perhaps that ought to be my next study in germination.
Larry, can’t find your review
Different country but similar 100F+ temps for long periods of time.
No issue with polys/tea/china/moderns/sweet briars/ann endt, get plenty of germinating seed (even with stratification).
May effect some of the colder classes but even then get germination from rugosa, hybrid centifolia/gallica just at a lower rate but that may also be because im crossing them out of class…