The origin of new forms inRubus - II. The loganberry,R. loganobaccus bailey
1. Although the loganberry arose as recently as 1881, the details of its origin are in dispute. It has been held (1) that the loganberry is a hybrid, the result of a cross between a blackberry and a raspberry, and (2) that it is not a hybrid but a “direct derivative” of the wild blackberry or dewberry of California,Rubus vitifolius. The present experiments were planned to decide between the two theories.
2. From crossingR. vitifolius, 8x, withR. idaeus, 4x, a hybrid was obtained which in morphology, chromosome number, sex and fertility closely match the loganberry; like the loganberry it is hexaploid and nearly true-breeding.
3. Crosses made betweenR. vitifolius, R. idaeus, 2x, and the loganberry, in whichR. vitifolius andR. idaeus chromosomes were brought together in different proportions, gave results which are also in agreement with the hybrid view.
4. The only conclusion which can be reached from the experiments is that the loganberry is a hybrid as originally supposed, derived from an unreduced male germ cell of a raspberry, which is known to correspond to the diploid type, and a normal reduced germ cell of the blackberry.
5. The breeding data suggest that inR. vitifolius the female is the heterozygous sex.
6. The effects of introducing different proportions of parental chromosomes into hybrids are correlated with differences in morphological and other characters. This results in the intergradation of characters, a common feature of polyploids, and sometimes in a change of dominance.
Volume 101, 2022
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