Is sterility sometimes a physical problem, and not genetic?

I’ve become accustomed to thinking that some plants are just incompatible as parents for genetic reasons, but I recall once hybridizing with Orange Triumph, which was a very reluctant mother.

I was just starting with hybridizing at the time, and it didn’t occur to me to blame the plant. And so I rather assumed I was doing something wrong, and studied the flowers carefully. I found that the blossoms on my plant, at least, appeared to have dried stigmas before such time as the flowers opened, so I began monitoring emasculated flowers to see if/when stigmas looked sticky and receptive. It was a good 24 hours or more earlier than one would have expected from the petal opening. So I tried pollinating premature flowers, and I managed to get hips to set.

(Note that this was a very limited experience and in no way bears any statistical significance. It could have been a fluke.)

Upon reflection, I wonder if the ovules themselves could have been receptive at a later point were the pollen tubes to be activated.

Has anyone ever tried moistening the stigma of a flower with very dilute sugar water prior to pollinating? Does it seem likely that a germinating pollen tube would then be able to navigate in the right direction?

Anybody have other thoughts/research as to other barriers to pollination that a persistent hybridizer might overcome?

I observed the opposite with ‘Wasagaming’, the stigmas did not appear ready until the flower started to fade & when they did look right, the window was short. Length of the stigmas were also short/held close to the flower. Repeated pollinations over several days seemed to help, as well as finding pollen which would be accepted.

Interesting. I never thought to worry about going the other direction – I always presumed that pollen would have a “shelf-life” of a few days, and if it was sticking the flowers, it would in good time be induced to germinate a pollen tube. But I suppose the pollen wouldn’t really even “stick” to take?

At least in my climate, conditions and with the pollens I am using, I collect what I want when it’s available then use it throughout the season until I’m either satisfied I’ve generated sufficient quantities of that cross or I run out of either pollen, seed parent blooms or energy. Apparently the pollens remain viable for months in these conditions. If I can raise obvious hybrids between moderns and species using the species pollen that has sat on paper sheeting in my dining room for six to seven months, something is remaining viable.

Years ago I found that ‘Blush Noisette’ never set hips unless I pollinated the flowers by hand. Those little petals covered the stigmas, and most of the stamens.

The excessively double Rosa roxburghii can be pollinated by hand (as I learned by experience) but a bumblebee I once saw visiting such a flower walked around for a little while then flew away in disgust (I’m guessing).

Hybrids and their derivatives can be puzzling. Burbank wrote about an Amaryllis that seemed sterile, but the stigma became receptive only after the petals were fading. Then there was the bigeneric wheat hybrid that was fertile only within a narrow range of temperatures.

Rhododendrons and some of their kin seem to have a time-window that opens when the pollen tubes begin to grow. If they reach the ovary too soon or too late, pollination fails. And in one group of species, those with long styles have fast growing pollen tubes. Species with short styles have slow moving pollen tubes. This keeps the species isolated … unless someone pollinates repeatedly.

Then there are the complicating matters of soil chemistry, air temperature, humidity, and so on.

Did you know that mango trees can thrive in regions with constant high humidity, but refuse to fruit? Most varieties need a period of relatively dry air to be fruitful. Likewise, for avocados.

We’ve grown giant pumpkins in the past where adequate calcium & sufficient plant size was crucial to have fruit set.

I’ve also observed the same with bees preferring the flowers which are easier to access.