All of the species roses that I have encountered have some sort of scent, some much stronger than others (though there are many I have not yet seen). However (at least to my nose) many modern roses have little to no discernible scent.
Which of the modern roses species ancestors brought in the genes for this lack of scent, or is a more complex issue than that?
I think it is more complex. There are many steps (specific genes that code for different enzymes, etc.) that modify multiple kinds of volatile molecules that evaporate to make scent. When we interbreed different roses from different backgrounds I suspect it is easy to get roadblocks in the pathways (that can differ somewhat across different backgrounds). With the possibility for less of certain compounds or lacking of some individual compounds, getting limited scent in the end seems to be a common result. Thankfully with raising lots of seedlings we can get fragrant roses sometimes from even crossing two non fragrant roses in order to get the right mix of genes again to effectively make the critical volatiles.
That does make sense. One distinct advantage of scentless roses here is that they are the ones that the Japanese beetles ignore. Also, scent seems to be quite subjective. Many sources claim Officinalis has a wonderful scent. I find it to have a rather mediocre fragrance. I actually prefer the pine-like scent when I rub the unopened buds to the scent of the flowers themselves. Thank you so much for your response. I like to learn as much as I can.
Unscented ones are also much more enjoyable for highly allergic people to grow, too. My youngest sister is allergic to pretty much everything. When she looks at a plant for the yard, the first requirement is that it doesn’t smell.
Hadn’t thought of the allergy issue…a very good point. I guess a scentless rose is not necessarily a “dud.” But, it is subjective. Some of the scents I like best smell like “old ladies’ perfume” to my wife! 