It was reading an old Annual from the 50’s and the hybridizer noted “it is well accepted that the length of time it takes seeds to germinate is determined by the pollen parent.” Is that still an accepted generalization?
From my experience it seems to be both. The female has a huge role in my experience and then out of different males with the same female there appears to be differences, so that suggests the male plays a role too. In Gudin’s research years ago there was evidence that the thickness of the endocarp of the rose “seed” (achene) plays a role in degree of dormancy and ease of germination later. Right after fertilization and early growth of the embryo there seemed to be an especially critical time for determining how thick that layer would be and ultimately strength of dormancy. Layer thickness was affected by temperature if I remember right with cooler conditions at that time of early embryo development leading to a thicker endocarp and ultimately more dormancy later. I suspect if the male parent leads to slower growing embryos initially, that can lead to a similar result and may be a strong component in differences in seed germination between different males. Perhaps a male may generally contribute to thicker endocarps in its offspring possibly due to slower initial growth, or maybe just in particular combinations with certain females that may result. The endocarp is female tissue and those cells do not contain DNA from the male parent in the recent cross.
I usually assume that traits come from both parents unless there’s reason to think otherwise. In this case, the obvious example of achenes which take forever to germinate would be R. canina, yet if one puts pollen on a canina, there is very little male contribution to the offspring. I can’t say that I ever timed germination between achenes of pure caninas versus canina x something, but I’d be kind of surprised if there were much difference between the two. They’re hard enough to tell apart as adult plants!
That’s not to say that pollen parents can’t have a big impact on seed, anyone who has ever grown a hot pepper next to a bell pepper, then experienced fiery hot bell pepper seeds, knows this to be true. I just can’t think of an example with roses where it really applies, since the canina section are so oblivious to pollen in general, and I don’t know of any other roses that have such clearly anomalous germination times that anyone would notice the difference.
I recently finished processing my rose seeds.
I noticed that the seeds derived from crosses of the same seed parent when
crossed with different pollen parents seem to produce seeds of different sizes.
Viz; it look like the seed weights between the same cross was uniform in size,
where as the weight between different crosses of the same mother and different pollinators seen to very.
The female parent is not very fertile and there is always lots of room the the pod of all crosses.
Is this possible?
Chuck, anything is possible. It is relative likelihood that matters. I would say it depends on species amongst plants in general. With maize both embryo and endosperm (most of the grain) definitely show contribution from the male parent. With a rose, most of the seed is the embryo. The hard coat of the acheme is contributed by the mother, solely. But hormone production in the early embryo could alter the growth, hence size, of the woody outer coat.
The dog roses are special because they have an imbalance of chromosomes favoring the mother. For simple tetraploids like most HT and fl, a given mother may well have offspring that germinate differently depending on pollen parent. It was E.B. Risley, living in New England who wrote a little article, in American Rose magazine, Oct 1958, in which he showed that “male controls sprouting”. He used various pollen parents on Skinner’s Rambler and saw that kordesii crosses germinated about twice as quick as Queen’O Lakes.
I suppose in my germination studies I have enough examples of one female crossed by several males to get some estimates of whether this holds true for other female parents. Maybe that will be a theme for next year’s studies.
Reference to Larry’s comments about Risley experiment:
Risley was onto something important, but got a bit confused in his terminology. Many species have a seed dormancy that must be broken, often by chilling. But “sprouting” can mean the moment when the seedling emerges from the ground. In this case the differences between sprouting time is probably related to the ability of the seedling to grow at low temperatures.
The slowest seeds to germinate in his study were (Skinner’s Rambler x Queen of the Lakes). The latter is one of Brownell’s “Sub Zero” roses. Another slow group was (SR x Diamond Jubilee). In this case the pollen parent was derived from ‘Marechal Niel’, a variety that thrives on heat. I suggest that the hardiness of ‘Queen of the Lakes’ is due, at least in part, to its refusal to grow at low temperatures. In this way it would avoid late frosts in the Spring.
The differences could be due to different fatty acids produced in the embryos. A preponderance of saturated fatty acids favors rapid growth at higher temperatures; unsaturated fatty acids allow the seedlings to grow faster at lower temperatures.
Ngamau (2006) found that seeds of Zantedeschia aethiopica ‘Green Goddess’ which sprouted first at low temperatures were also able to grow and flower at lower temperatures when they matured. On the other hand, seeds that germinated faster at high temperatures retained this heat-tolerance as adults.
There is no doubt that the pollen parent will contribute to the fatty acid balance in the seedlings, and thus to their growth rate at different temperatures. This, of course, has nothing to do with any aspect of seed dormancy that relies entirely on maternal contributions, such as the thickness of the seed coat.
Excellent and useful information! Thank you!
Thank you for that piece of information regarding low temp germinations being more capable of enduring lower temps and warmer germinations being more heat tolerant, Karl. That seems to tie in with Ralph Moore’s statements that the faster germinating seedlings after planting are the more dwarf, heavier repeating types and those germinating the second season tended to be more climbing, once-flowering and more cold hardy types. That’s my hope with the Banksiae seedlings which germinated as quickly as four months after sowing rather than requiring the two years so often quoted.
That’s an interesting observation. There may be at least two explanations for the differences.
- Certain pollen parents may contribute to larger embryos. It would be useful to compare the results of crosses using the same pollen parents on different seed parents to see if there is a correlation between pollen parent and size of seeds.
- There is evidence from other plants (e.g., Mirabilis jalapa) that the seed parent “decides” what quantity of resources to allocate to seeds based on the diversity of genotypes of the pollen tubes competing for the ovules. If the mother approves of her daughters’ “gentleman callers”, she devotes more resources to the seeds that form.
BTW, have you tried repeated pollination?
Pollen and pollination experiments. X. The effect of repeated pollination on fruit and seed set in crosses between the hybrid tea rose CVS. Sonia and Ilona.
Euphytica 32(3): 685-689 (Nov 1983)
D. P. Devries, Lidwein A. M. Dubois
To improve fruit and seed set in roses, the Hybrid Tea-cultivar Sonia was pollinated with the cv. Ilona 0, 1, 2, 3, 4, 5, 6, and 7 times at 24 h intervals. Unpollinated flowers did not yield fruits. The number of achenes per fruit increased up to 3, fruit weight and weight of achenes increased up to 4, and the number of seeds per pollinated flower (PI) increased up to 5 pollinations.
Both between and within pollination treatments, highly significant correlations occurred between fruit weight, number of achenes per fruit, and weight of achenes. Effects of repeated pollination in rose and apple are compared. The effect of a relatively low fertilization level in rose crosses is discussed.
In my experience the variability of seed size within a single cross is the same as that between crosses. A lot depends on environmental factors.
Also, in my experience embryo sizes don’t necessarily correlate with achene size although sometimes they do. The largest embryos I’ve personally ever seen are from moyesii and its kin praelucens. Their seeds are big although not the biggest. Embryo sizes do correlate with ploidy, somewhat.
There is also the matter of precocity vs juvenility.
The age of seeds also influences the length of the vegetative period. Van Mons (1835) found that by collecting unripe fruit of pears he was able to shorten the juvenile (non-flowering) period. The effect is partially hereditary and cumulative. Wild pears grew 10-12 years before flowering. After 5 generations of his method, he had trees flowering in just 3 or 4 years from seed. Arthur (1899) did the same with tomatoes.