A Question for David Zlesak

Howdy David;

I was just reading an article you wrote titled (Natural Selection of Pollen and Pollen Competition). Very interesting article and enjoyed reading it, but what made me sit up was the section regarding pollen tube length.

I have been trying for years to get a hybrid from a Modern X R. laevigata without any success. But after reading your article, R. laevigata pollen tubes may be to short. It was used to create R. fortuniana, but when I saw the structure of R. banksia’s styles they are alot shorter than what would be in a modern rose, therefore making it easier to fertilize. With Spring breeding around the corner for us in Australia, looking at diploid Tea roses will have to put on the back burner and go looking for something with shorter styles.

cheers Warren

Someone was writing about cutting them off or shorter to fertilize.

Hi Neil; I dont think that would work as it be altering the physical structure to much, plus there is a fluid ( I have forgotten whats its called) secreted by the styles which germinate the pollen grains. I think the solution might to cross them with Cinnamomae roses or Microphyllae roses or hybrids of both which have very short styles. I will see what Dave Z has to say about short pollen tubes being a possible problem.

cheers Warren

Cutting styles is done commonly to make wide crosses with lilies, and presumably would work with roses as well, though I’ve never tried it. With lilies, they either collect the stigmatic exudate from another style and put on the end of the cut style, or make basically a sugar water substitute.

Hi Joseph; Quite honestly I have never heard of cutting styles before. Cutting the style of a Lily would be easy as there is usually only one, I have never counted the styles in a rose bloom before but there are a few and small, imagine cutting them in half. I use a pair of Artery dissecting scissors when cutting off anthers, suppose you would have to use something similar.

Talking about the stigma exudate, saw a technique for testing pollen viabilty by placing pollen in a 20% sugar solution, and see if the pollen swells or germinates. Of course you will need a microscope.

Hi Warren!!

Great questions and points. Rose pollen tubes tend to grow fast in culture. In two hours in sugar water with a little boric acid they can be 30x the pollen diameter long! It is a great way to ascertain pollen viability. We can look at stained pollen and assume the dark plump ones are viable, but actually observing a sample and seeing the rate that actually germinates really is convincing for the rate of viability.

My suspicion is that even though the style length can differ across species, that given enough time, if it is a compatible cross, in general the pollen is likely to grow down to the ovule. Other factors surrounding the s alleles and interspecific barriers are a different story. Roses have gametophytic self incompatibility (when it is expressed- mainly at the diploid level and some species have it stronger than others). For instance, when a pollen grain has the same S allele as the female parent the pollen tube is slowed and often ruptures in the style and doesn’t make it all the way down to fertilize the egg.

We can often overcome self-incompatibility with heat to denature and deactivate the proteins involved. I overcame self-incompatibility with some polyanthas in a hot greenhouse (over 100F). Like Joseph said, cut styles in lilies are a well utilized tool and in my tissue culture class I teach for instance we developed some LA lilies (Easter lily x Asiatic hybrids) this spring that are still small seedlings. Beyond the self-incompatibility alleles there are some more broad barriers that can fall under the umbrella of incongruity. Julie Overom has a great RHA article on that from a number of years ago. With divergence in species, it is difficult for the sequence and control of genetic events to occur and be well orchestrated for things to progress as normal. It is basically the biochemical signals are getting confused some. By reducing the length of the style, there is hopefully the opportunity for pollen tubes to grow long enough to reach the ovule before things get so chaotic and confused the tubes rupture and stop growing. Of course, with wide crosses there is the possibility for failure and incongruity and miscommunication for additional steps in the journey to becoming a viable plant. For instance, most of my rugosa x polyantha seedlings failed not at the point of fertilization, but soon after germination.

For the cut style method, cut the styles shorter, take another bloom with sticky stigmatic exudate that you can transfer over the cut styles and then pollinate. Things are disrupted, but in some cases if that is where the barrier is occurring, it can be overcome hopefully at a good frequency allowing for some seeds. For the LA lilies, we cut the style to a quarter to half inch above the ovary in the Easter lily female parent, cut the style down the middle lenthwise, opened it putting pollen and exudate inside. We wrapped parafilm around the cut style with pollen inside to keep it moist. In a couple weeks we put the ovary in small slices in culture. The endosperm of the seeds fail (source of nutrition) due to th wide crosses and incongruity, but the embryos are generally viable. By putting the little chunks with several ovules at a time onto media, we can nourish the embryos and keep them growing instead of starving to death from lack of viable endosperm on the parent plants and get viable hybrids.

In order to work through crossing barriers with the roses you want to cross, the key will be to know where the failure is occurring and then trying to do something to overcome that critical limitation if possible. Trying cut styles sounds like a great step to see if pollen tube length is the critical factor.

Please let us know what you learn!!

Sincerely,

David

Wow! David, your lily experiment is quite incredible! It will be interesting to see your hybrids blooming.

Jim Sproul

Have you tried the following?

http://home.roadrunner.com/~kuska/sprayingthehip.htm

Link: home.roadrunner.com/~kuska/sprayingthehip.htm

Hi Jim :0)

People are sure making great advances with lily breeding crossing intersectional barriers. People have successful crosses with martagons and Asiatics / Asiatics and Orientals, etc. Some are much harder to get than others. Many of the current LA lilies are backcrosses with Asiatics in order to get richer flower colors, but still maintain the size and other great traits. People have moved up to the tetraploid level with many intersectional lilies via chromosome doubling or 2n gametes are are reshuffling the genes more. As time goes by I suspect with lilies the classes will become more and more blurred- kind of like complex rose hybrids. It is fun to see the great lilies coming out. The orienpets sure are amazing. It is fun that they are more durable / perennial in at least the climate I live in than either of the parents that make them up (Oriental and Aurelian trumpets).

Intersectional peonies often have better, longer lasting foliage than either parent.

Dave Z , this is not rose related , but one year I crossed Agapanthus with Clivia. All was going well, the seedpods grew untill some one came and deadheaded all the spent blooms with my cross included. I must try this again one day.

warren