Summary Significant more left-handed (53.32 %) than right-handed (46.68 %) phyllotactic spirals were found in a population of 2200 tubers from 110 commercial varieties. In some varieties the left-tendency prevailed; others showed a significant surplus of right spirals. For two varieties, i.e. A with prevailing r-tendency and B with a trend for 1-spirals (cf. table 3), the homodromy relations and other characteristics were analysed. In both of them the l-tubers showed a (not significant) tendency to grow larger than r-tubers (table 2, fig. 1). The curves for distribution of eyes per tuber were wider in l-tubers (fig. 2). In variety A and in the typical (7—10-eyed) tubers of the variety B, too, a significant higher percentage of the eyes from left tubers germinated as compared with r-tubers (table 4), the superiority of left-handed tubers being more pronounced in classes with median eye numbers. The left-tending variety B showed for all eye-number classes of r-tubers a clear excess of homodromy; this also is true, but to a much higher degree, for 1-tubers. In the right-disposed variety A, however, only the r-tubers reacted strongly homodromous, whereas the l-tubers behaved antidromous (table 5, fig, 3). In both varieties no difference existed in degree of homodromy between buds from the morphological upper and the lower surface of the tuber. In variety A the median eyes germinated to a higher degree than the apical or basal ones, whereas in variety B a strong apical dominance prevailed. In both cases the superiority of left tubers in respect of germination was most pronounced in the region of highest germination activity (fig. 4). In variety B the homodromy relations were analysed at various stages of germination (cf. fig. 6). At the outset of germination the r-tubers showed a higher rate of homodromy than 1-tubers. As germination advanced, however, the leadership in homodromy changed over to the l-tubers in the basal, median as well as in the apical region (table 7, fig. 7). In tubers of both varieties the average number of turns of the eye spiral was definitely greater in left-handed than in r-tubers (table 8, fig. 8). Both varieties - but A more pronounced than B - showed a tendency for a decreasing average angular leaf distance with increasing number of eyes per tuber (table 9, fig. 9); the greatest significant difference between l- and r-tubers was found in the modal classes for eyes per tuber. Vitality in primary haploid potatoes was correlated with direction of the phyllotactic spiral of the primary shoot as shown in two populations selected for vigour and performance in the field, the l: r-ratio being significantly increased after selection (fig. 10). In haploid potatoes aneuploidy (2 n = 25—27) was correlated with a strong tendency towards right-handed leaf spirals (fig. 11). Plastid numbers in guard cells of haploid potatoes were correlated not only with vitality but also with direction of the phyllotactic spiral. In a population of haploids the fraction with high plastid numbers, as compared with the fractions with medium and low numbers, displayed firstly a considerable decreased vitality and secondly a significant deviation from the normal l: r-ratio with a high number of right-handed seedlings (fig. 12). The teratological phenomenon of „double leaf“ (fig. 13) was found twice in a haploid family with a non-racemic l: r-distribution. In connection with the occurrence of single nodes with double leaves (fig. 14) or with tricotyly (fig. 15), the direction of the leaf spiral often changed a few nodes above. Pairs of axes resulting from dichotomy of stems, tubers (fig. 16), epicotyls, or from cleavage polyembryony may be homodromous as well as antidromous. It is tentatively proposed that the realization of the l: r-ratio and the various correlated physiological and morphological features as readiness for germination of tubers, vigour of haploids, unthriftiness of aneuploid haploids, numbers of plastids in guard cells etc., all of them are influenced from a common physiological system, that of the auxins. Supporting data from the literature for this explanation of the correlations are given. It is further suggested that the number of initials in the vegetative point and their auxin induced helical polarization and trend for unequal division may account for the realized phyllotactic pattern. In species like potato with prohably three initials per germ layer a disperse spiral leaf arrangement may result, whereas in species with four initials per layer like Epilobium a decussate phyllotaxis is realized. The unequal divisions of helical polarized stoma initials are thought to give an impression of forces operating in apical meristems. In the potato an approximate racemic distribution of l- and r-turning division sequences of developing stomata was found.
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Feb 1, 1976
Shigeki Yamashita + 1
Open Access