Abstract
Pollen materials used for the preparation of the so-called recognition pollen were collected from mutually cross-compatible, different individuals belonging to the same cultivar. Then, ‘crushed’ compatible pollen as a kind of recognition pollen was prepared by grinding the pollen with an agate mortar, and ‘killed’ compatible pollen as another recognition pollen by exposing the pollen to 75% ethanol solution. Immediately after applying these recognition pollens each to the stigmas, it was pollinated further with self pollen. Besides, conventional self pollination was carried out as controls.
Pollen behavior on the stigma was examined to determine the degree their fertility. That is, pistils of treated flowers were collected in the next morning of the pollination day, and fixed and stained in lactic blue. After being differentiated in lactic acid, pollen counts were made in a drop of glycerol. The results obtained are summarized as follows:
In the self pollination alone (controls), a few pollen grains germinated on the stigma. The developed pollen tubes were very short and did not penetrate the barrier of stigma papillae. However, pollen germination was fairly increased by the preceding application of ‘crushed’ compatible pollen. In this case, many pollen tubes penetrated the barrier of stigma papillae. A few emptied pollen grains which had transferred their contents into the developing pollen tubes were recognized. By the preceding application of ‘killed’ compatible pollen, the percentage of pollen germination was increased considerably as compared to that of controls. In general, the length of developed pollen tubes which were affected by applying the ‘killed’ pollen was somewhat shorter than. that produced by the ‘crushed’ pollen application.
As commonly accepted, the effect of recognition pollen on the overcoming of self-incompatibility may be caused by some supposed recognition substances (proteins) contained in the coating (exine) of pollen grains.
It seems that the preceding application of recognition pollen in combination with the following self pollination partially overcome self-incompatibility of Japanese radish.
