Growth-Promoting and Growth-Retarding Substances in Pollen from Diploid and Triploid Apple Varieties

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Abstract
The material studied was pollen from 4 vars. of apple: James Grieve (2n), Graastener (3n), Tompkins King (3n), and Belle de Boskoop (3n). The numbers of pollen grains per anther were 6.38, 0.75, 1.26, and 2.42 thousands, respectively. The percentage germination was much higher in pollen from the 2n- than from the 3n- vars. In no case was germination improved by addition of indoleacetic acid. Samples of dried pollen were extracted with wet ether. From a given sample, extracts were collected for growth-substance assay (Avena test) after 1, 2, 24, and 168 hrs., the ether being renewed each time. A neutral and an acid growth-promoting substance and a neutral growth inhibitor were found. After 1 and 2 hrs. the growth-promoting and the growth-retarding activities of the extracts were almost equal; later an excess of growth-promoting activity developed. This excess was considerably smaller in pollen from the diploid than in pollen from the triploids. The results of the detns. of growth-promoting and growth-retarding substances do not explain the differences in germinability and pollinating value of pollen from the 2n- and 3n-vars.