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Botaniska Notiser 1946, Häfte 2. Lund
Progeny of triploid Betula verrucosa Erh.
By Helge Johnsson.
Forest Tree Breeding Institute, Ekebo, Källstorp, Sweden.
In an earlier paper (Johnsson, 1944) the writer has described t wo
spontaneous triploids of Betald verrucosa Erh. Another triploid
verrucosa birch has been reported by Löve (1944). All three triploids have
been found to possess extremely great sterility after open pollination.
The results obtained from crossing experiments with two triploid
verrucosa birches will be submitted below. One of them is the
pre-viouslv described tree from Kode in Bohuslän. The other has its station
at Vänjasjön in Darlecarlia. This tree was discovered by dr. Hugo
Ågren of Gävle, and the writer is indebted to him for information
about it as well as material from it. Besides the two autotriploid
B. verrucosa individuals, the experiments embrace diploid B. verrucosa,
B. pubescens (a tetraploid species) as well as a 42-chromosomal
indi-vidual that in all probability represents an F, of B.
pubescensY,verru-cosa (Johnsson, 1944). The crosses were carried out according to the
method described by the writer (Johnsson, 1945).
The extent of the crosses can be seen from Table 1, which also
shows Iheir fertility. In view of the fact that in ordinary varietv crosses
wilhin B. verrucosa as well as B. pubescens and with the crossing
tech-nique employed the percentage of fruits with embryos usuallv averages
about 50 and often ainounts to over 80, it is clear that the fertility of
the triploids is greatly reduced in all cross combinations as well as
after open pollination. In a couple of the present crosses, however. the
fertility is rather high. Thus, the cross 44—1, triploid VänjanXtriploid
Kode, showed 12.45 °/o of fruits with embryos and the cross 45–1(),
triploid VänjanX diploid (21—16), gåve a corresponding figure of
21.80 °/o. Ön the basis of the experimental results hitherto attained it
cannot be decided whether there is any fertility difference between
triploidX triploid and triploidX diploid B. verrucosa. The fertility of
crosses between triploid B. verrucosaXB. pubescens seems, however,
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