DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 1-2/1966 str. 115 <-- 115 --> PDF |
the morphology of the flowers, the time of flowering, and the incompatibility* of species. It is understandable that species that are genetically distant from each other usually cannot be crossed. In such a case the difficulties are very great and much effort will be required to surmount them, if they can be surmounted at all. If there is an essetial difference in the structure of flowers, the crossing generally cannot be performed with success. Likewise, if there is a difference in the flowering time between two species, there is difficulty in hybridization, but the overcoming of these difficulties is much easier. In such a case it is nacessary to speed up or retard the time of flowering of male or female flowers so that the pollination can be carried out in due time. The most suitable method consists of storing the pollen and using it when the female flowers are ready for pollination. The difficulties are also great, in incompatible species but we are of the opinion that in some cases they can be surmounted. In order to determine the phase of development after pollination is the pollen, egg cell, zygote or proembryo, it is necessary to carry out embryological investigations as presented in the works of Buc h hol z (7), McWilliam (36), Ha gm an and M i k kola (21), and Hyun and Yim (23). Such investigations should indicate to us how far the pollen tube has penetrated, wheter fertilization has occured, and what happened to the zygote after fertilization. When we get a clear idea about these processes in the crossing of two incompatible species, we shall perhaps be able to overcome more easily the difficulties due to resistence to crossing. In addition, in the crossing of incompatible species it is necessary to work out suitable methods of hybridization. We consider the method of preliminary vegetative approach and the bringing of the stigma fragments of father tree on to the stigma of mother tree pistils interesting, as recommended by J a b 1 o k o v (24). According to our incomplete investigations (55) of the hybridization of incompatible species, pollination of female flowers of one species with the irradiated polen of another species provides a possible new way of solving this problem. In this connexion it is interesting to point out — although the results are incomplete — that after pollination of Austrian pine with Scots pine pollen irradiated with 800 and 1000 r the ovule shows a degeneration in fewer cases than when the pollen of Scots pine was not irradiated. At the end of this report I will take the liberty to make a suggestion. Previous work on hybridization within and especially between species gave conspicuous results. Many heterotic hybrids were obtained. Today we possess much information on different cross combinations. Our experience and theoretical knowledge about the possibilities of crossing two species are constantly improving, and regardless of the fact that many problems still lie ahead, mass production of hybrids deserves full consideration, as Righte r * By incompatibility we mean the inability of pollen to fertilize the egg cell, and if it is fertilized, the inability of the zygote to survive, or the subsequent degeneration of the proembryo. |