DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 1-2/1966 str. 129 <-- 129 --> PDF |
between the hybrids and their parents being the result of age, and that the same trees after several years may present a different picture as regards the occurence of heterosis. A review of the hybrids presented in Table 1 according to their taxonomic groupings (after Dode 1905) permits to draw the following conclusions. I. Subgenus Leuce I. 1. Section Albidae — no data. 2. Section Albidae x Section Trepidae. The natural hybrid P. x canescens Sm. displays according to the general belief a heterosis with respect to both its parents. Satisfactory results were obtained from the crosses P. alba x P. tremula and the reciprocal, however, some authors criticize the view that these results indicate heterosis. 3. Section Trepidae The crossing of P. tremula with P. tremuloides and reciprocally is considered very promising with respect to the heterosis of growth and resistance to some diseases (e.g. Venturia tremulae Aderh.) Several breeders seek heterosis, with partial success, in the hybrids between the various different provenances of P. tremula. 71. Subgenus Eupopulus 1. Section Aigeiros. Hybrids carrying the general name of Euroamerican poplars originated from the cross between P. nigra and P. deltoides. Many of them show heterosis with respect to their parents. 2. Section Aigeiros x Section Tacamahaca. The hybrids P. pyramidalis x P. simonii, P. angulata x P. berolinensis and P. deltoides x P. trichocarpa gave good results as regards frost resistance and fast growth. 3. Section Tacamahaca x Section Aigeiros. Particularly the hybrids P. maximowiczii x P. pyramidalis, P. maximowiczii x P. nigra, P. simonii x P. pyramidalis as regards their luxurious growth, and P. suaveolens x P. pyramidalis as regards frost resistance, need to be mentioned. 4. Section Tacamahaca. The most successful and heterotic hybrids come from the breeding work done by Schreiner and Stout (P. maximowiczii x P. berolinensis, P. maximowiczii x P. trichocarpa). This same maternal tree yilds good results in crosses with P. laurifolia. There are many more successful hybrids within this section. This short review of the data presented in Table 1 should be supplemented with information about hybrids which do not show heterosis. Data on this subject are incomplete since the authors often publish only those results of their works which have yielded successful cultivars. However, as an example, some of the respective data are presented in Table 2. The crosses between P. maximowiczii and P. berolinensis mentioned in Table 2 were made in Körnik in 1950 and 1954, but gave poor results from the economic standpoint, whereas similar crosses made by Schreiner and Stout have produced some very valuable cultivars that are characterized by heterosis with respect to the both parents. It is also interesting that the hybrid P. angulata x P. laurifolia has produced no heterotic individuals, whereas the |