DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 1-2/1966 str. 107 <-- 107 --> PDF |
THE OCCURRENCE AND MEANING OF HETEROSIS IN HYBRIDS WITHIN AND BETWEEN SPECIES« (Introductory paper) by MIRKO VIĐAKOVIC Forestry Faculty, Zagreb and Institute for Conifers, Jastrebarsko, Yugoslavia. INTRODUCTION Much has been written about the concept of heterosis, and there are various opinions about it, but we believe that in a general way everybody agree if we say that by heterosis we mean the phenomenon occurring when the hybrid is more productive than either of its parents. The location of the test is important to the evaluation of this effect. Duffiel d and Snyde r (15) discussed this matter and stated that it is possible to obtain different results, depending on whether the hybrid is tested in the area of occurrence of one or the other parent or in an intermediate area. As an example, the authors mentioned the hybrid Pinus monticola x (P. monticola x P. strobus), A similar situation is encountered in the hybrid Pinus contorta var. latifolia x P. banksiana (42,45). Wrigh t reported in his exhaustive work on hybridization between and within species that it is well known that the phenomenon of heterosis may be evident in one place and not in another (61). Paule y (40), on the other hand, assumed that often what is understood by the phenomenon of heterosis in Fi in the poplar hybrids is in fact a favourable action of the daylength and not the effect of heterosis. Such interpretation was given by Rohme d e r and Schönbach (48), as well as by other authors. From this it follows — as stated by Duffield and Snyder — that when determining heterosis it is necessary to indicate the origin of the parents and the locality where the hybrids where tested. Besides, in forest tree species it may happen that one hybrid does not show vigor in its early development, while in the later stages of development it exhibits a vigorous growth. This is the case in the hybrid between Pinus ponderosa and P. engelmannii (13). From the standpoint of forestry the phenomenon of hybrid vigour is significant even if it does not fulfill the strict sense of the heterosis concept, if the hybrid shows a combination of a satisfactory growth rate and other qualities such as resistance to diseases or extreme climatic conditions, or at least grows better on a certain site than either parent. * The author wishes to express his thanks to Professor Howard B. Kriebel who has read and corrected the manuscript. 105 |