Pollen behavior

In the 1963 American Rose Society Rose Annual in an article titled “A Self-Pollination Mechanism And Other Items In Rose Species”, Dr. Eileen W. Erlanson Macfarlane makes the following statement:

Self-pollination mechanism. In may wild roses the petals are past their prime by the third day and the flowers no longer close at night. The stamens may then rise up and their delicate filaments curve over to bring the pollen-bearing anthers onto the receptive stigmatic heads of the ovaries. It was found in one of my earliest studies (1) that the pollen cells mature before the embryo sac and egg cells. Most of the pollen is shed when the petals first open and insects will carry some of it to flowers opening for the second day, which may then be ready for cross-fertilization. However, a few pollen grains remain on the shriveled anthers on the third day and the stamens should still be receptive. The rising and incurving of the stamens could very well provide self-fertilization for any remaining eggs not already cross-fertilized. My experiments showed that the roses are self-fertile."

She gives a table which contains 11 selfing-strongly fertile, 14 selfing-weakly (the actual number is ambiguous to me), and 21 non-selfing (again, the actual number is ambiguous to me). She lists both rugosa and multiflora as selfing-strongly. Of interest is the rugosa classification as the 2 other papers that I mentioned in other threads agree that rugosa belongs in the non-selfing column.

Of interest to me (relative to the virus paper) is the observation that cross pollination gets the first chance.

There is quite a bit of variation within species even for the ability for self-fertilization. For instance, some of my colleages are working with populations of Gaura. They typically are strongly self-incompatible. Selections have been found that are strongly self-fertile within the populations they are studying. For chrysanthemums, “pseudo” self-compatibility has allowed for the development of inbred lines for seed propagated hybrids. This is another species where selection among individuals that are mostly self-incompatible has resulted in some that can set seed from self-pollination.

Self-incompatibility can better be thought of as a loose biological force to encourage out-crossing, but it is a leaky system that can allow for slippage. As I mentioned in another string, I got selfs from a normally self-incompatible diploid in a warm greenhouse. The self-incompatibility proteins are expressed to varying degrees throughout flower development and also can be broken down by high temperature. In some of my lily crosses and selfs I place the long style in a test tube of relatively hot water for a few minutes. Self-incompatibility proteins are degraded and I can obtain selfs or crosses with other lilies sharing the same self-incompatibility alleles. In addition, very early or late pollinations can allow for pollen tube growth in normally self-incompatible crosses or selfs because the proteins involved have not developed fully or are being degraded. The phenomenon of old rose flowers having the filiments continue to elongate and then curl over the stigmas to deposit whatever little bit of pollen may be in them can allow for at least some seed set if earlier cross pollination did not occur. At this time the self-incompatibility proteins are degrading and depending on their strength in the particular variety self fertilization may be possible.



P.S. It would be interesting to compare self-fertility within the same varieties of roses when grown in the colder North compared to warm regions of the South.