DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 1-2/1966 str. 109 <-- 109 --> PDF |
hybrids between Abies concolor and A. grandis, Gath y (19) concluded that there is a relationship between these two species and A. loviana Wright (58) has dealt with these problems in spruce. For a successful crossing the structure and number of chromosomes are important. In a general way the rule is valid that species with a similar structure and equal number of chromosomes cross more easily than species that are dissimilar in these respects. However, we also know cases where the number of chromosomes is different, and yet some of them can cross with each other as in the genus Betula, in which there are species with 28, 56, 70 and 84 chromosomes. The second step is the production of a small number of hybrids, verification by repetition of the experiment and the testing of the hybrid. When producing a small number of hybrid plants it is not always necessary to pay attention to the particular trees which are chosen for parent pairs. If the because various genotypes and especially different races may give positive result is negative, one should attempt to take different trees for parents, results. The third working step is to ascertain the possibility for mass production of hybrids. Mass production of hybrids depends in the first place upon the character of the parental species. It is well known that the pines yield large quantities of seeds, but in interspecific hybridization this is usually not the case. At present the hybrid P. rigida x P. taeda is mass produced in Korea under the direction of H y u n (22). In the genus Larix, mass interspecific hybridization can also be carried out in seed plantations, as was recommended by S. C. L a r s e n and performed in Denmark. In many species of the genus Populus and in the genus Salix there are no difficulties, because they can be propagated readily by cuttings and rooted cuttings. In Denmark — according to L a r s e n´s scheme — the hybrid of Populus tremula x P. tremuloides is also mass produced. The fourth step is to determine what trees answer best for parental pairs. The results are often different if different trees arc used in the same interspecific crossing, because each species has its own range of variation. It has been established that various biotypes belonging to two species may give different results. Therefore such a crossing ought to be carried out with several parental pairs belonging to different biotypes and races in order to attain the desired purpose. The phenomenon of heterosis is well known in many interspecific hybrids. In this report we do not wish to give a detailed survey of individual hybrids but consider it necessary to comment in short on the more important genera. Considering that investigations of the various species of different genera, and even of the various species within one genus, are in different stages of progress, it is difficult to give with certainty a clear appraisal of the success achieved so far. Neiher do we intend to give a special evaluation of each combination, because these investigations are in progress and will be reported by the investigators themselves. Our only objective is to show by examples what has been achieved to date, and that from these achievements the meeting can draw definite conclusions. Data about many interspecific hybrids were taken from the following literature: 10, 14, 46 and 62. |