Monday June 4, 2018 Q&A

Why do some roses have no smell?


1 Because they aren’t endemic to the region

2 Because they’ve been refrigerated

3 Because they’re missing a gene

When we see a rose, we almost instinctively want to stop and smell it. But sometimes no sweet perfume comes forth. Roses lost their smell in the 1950s when growers wanted to breed varieties with more robust petals that could withstand refrigeration. This eventually spread from cut roses to garden varieties as well. But today the trend is reversing, as rose-lovers want a flower that is just as fragrant as it is beautiful.

Wild roses naturally smell sweet to attract bees so they can be pollinated. But they also produce compounds that repel insects so they won’t be eaten. The flowers’ fragrance is produced by hundreds of volatile compounds that we detect through tiny receptors in our nose. When roses are cultivated in greenhouses, growers both pollinate them and modify them in response to market demand and the latest trends. This selection process, carried out by using cuttings, has eliminated the stamens on some roses – meaning they are sterile and odorless.

Where does roses’ fragrance come from? To find the answer, a team of French scientists compared the genes of roses that do smell with ones that don’t. They found that a gene called Nudix hydrolase or RhNUDX is prevalent in the former group but absent in the latter. What’s more, this gene isn’t specific to roses but can be found in a number of other plants as well as bacteria and even human beings. It usually serves to clear toxins from cells, but in roses it is used to make geraniol – a key component of their fragrance.

Giving roses back their smell without altering their genes will require patiently crossing smell-producing varieties with odorless ones until a breed is found that has both robust petals and a sweet perfume. However, a great deal of research is still needed to pinpoint the two genes involved in this process.