Tl. Wang et al., GROWTH-PERFORMANCE OF HYBRID FAMILIES BY CROSSING SELFED LINES OF BETULA-PENDULA ROTH, Theoretical and Applied Genetics, 92(3-4), 1996, pp. 471-476
Hybrid breeding is an effective approach in many agricultural crops. I
n allogamous tree species severe inbreeding depression and long reprod
uctive cycles generally prohibit its use. However, three generations o
f selfing in silver birch (Betula pendula Roth) were obtained by forci
ng trees to flowering under greenhouse conditions. Hybrids were produc
ed by crossing first-, second- and third-generation selfed lines. The
effects of different levels of parental inbreeding on the growth perfo
rmance of hybrid families were observed in a 9-year-old field progeny
test. Also, provenance crosses were carried out between selfed lines f
rom different parts of Finland and several other European countries. O
bservations of growth performance of the provenance hybrids were made
in the same trial. The results indicated that the mean stem volumes we
re significantly different between classes of parental inbreeding coef
ficients (F-p) (P<0.0001), and were positively correlated with F-p (r=
0.9106, P<0.05). Within-family variation of the hybrid families decrea
sed with an increase of F-p. The performance of the provenance crosses
between parents at a relatively close distance did not depart signifi
cantly from the standard controls. However, when the cross distance wa
s extended far to the south, hybrids grew faster, indicating either hi
gher heterozygosity or an extended growth period.