DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 1-2/1966 str. 131 <-- 131 --> PDF |
that it is in this hybrid progeny that heterotic individuals are most likely to be found. The progeny which had the highest mean height (1) has a small variability and the hybrid progeny form the cross P. pyramidalis x P. nigra varied least. At the same time, however, within the same section Aigeiros a cross between the American P. angulata and European P. nigra offers the greatest chance of obtaining heterosis. When breeding for trees which will be later propagated vegetatively it is necessary to aim at producing a small number of heterotic individuals, which could be used as new cultivars. Under these conditions the widest possible variability in the characters of economic interest is desirable. The result obtained with P. angulata x P. nigra is all the more interesting since it appears to be analogous to the excellent results obtained with the Euroamerican poplars (P. deltoides x P. nigra). CONCLUSIONS 1. On the basis of the available data it is difficult as yet to establish a definite relation between the parental affinity and the heterosis of the progeny, however, it does appear that this relation has no simple dependence on the systematic position of the parents. 2. Within a systematic unit (species or section), heterosis among hybrids appears to be greater the greater the heterogeneity of the parental forms. 3. This heterogeneity is best explained by the geographic isolation of the parental sites of origin which presumably have different ecological conditions, and also — as can be seen from the literature — other isolating factors can play a role here. 4. In the subgenus Eupopulus a greater degree of heterosis can be obtained in the intrasectional hybrids between parents of distant provenances than in intersectional hybrids between sympatric parents. 5. In the subgenus Leuce the results are not as clear cut, since hybrids between the sections Albidao and Trepidae often show considerable heterosis in spite of the fact that the parents are sympatric. UTJECAJ RODITELJSKOG AFINITETA NA STUPANJ IIETEROZISA KOD HIBRIDA TOPOLA Zaključak 1. Na osnovi raspoloživih podataka teško je zasada utvrditi tačno određen odnos između roditeljskog srodstva i heterozisa potomstva. Međutim .izgleda da taj odnos nije u jednostavnoj ovisnosti o sistematskom položaju roditelja. 2. Unutar sistematske jedinice (vrsta ili skupina) izgleda da je heterozis između hibrida to veći što je veća heterogenost roditeljskih formi. 3. Ta heterogenost se može najbolje objasniti geografskom izolacijom roditeljskih staništa porijekla koja vjerojatno imaju različite ekološke prilike, a također — kao što je vidljivo iz literature — ovdje mogu igrati ulogu i različiti drugi izolirajući faktori. 4. Kod podroda Eupopulus veći stupanj heterozisa može se dobiti kod unutarskupinskih hibrida između roditelja udaljenih provenijencija, nego kod međuskupinskih hibrida između roditelja istog područja rasprostranjenja. 5. Kod podroda Leuce rezultati nisu tako jasni budući da hibridi između skupina Albidae i Trepidae često pokazuju heterozis usprkos činjenici da su im roditelji s istog područja rasprostranjenja. |