Genetic Gain and Gene Diversity of
Seed Orchard Crops
Kyu-Suk Kang
Department of Forest Genetics and Plant Physiology
Umeå
Doctoral thesis
Swedish University of Agricultural Sciences
Umeå, Sweden 2001
Acta Universitatis Agriculturae Sueciae
Silvestria 187
Opponent : Professor Yousry A. El-Kassaby
Department of Forest Sciences
Faculty of Forestry
University of British Columbia
Canada
Supervisor : Professor Dag Lindgren
Department of Forest Genetics and Plant Physiology
Faculty of Forestry
Swedish University of Agricultural Sciences (SLU)
Sweden
Examination committees :
Prof. Arnulf Merker, Department of Crop Science
SLU-Alnarp, Sweden
Prof. Per-Christer Odén, Forest Seed Science
Department of Silviculture, SLU-Umeå, Sweden
Dr. Jan Nygren, Seed orchard manager
Svenska Skogsplantor AB
Piparböle 50, 905 91 Umeå, Sweden
ISSN 1401-6230
ISBN 91-576-6071-9
Copyright © 2001 Kyu-Suk Kang, Umeå
Printed by SLU, Grafiska Enheten, Umeå, Sweden, 2001
Abstract
Kang, K.S. 2001. Genetic gain and gene diversity of seed orchard crops.
Doctor’s dissertation. ISSN 1401-6230, ISBN 91-576-6071-9
Seed orchards are the major tool for deploying the improvement generated by
breeding programs and assuring the consistent supply of genetically improved
seed. Attainment of genetic gain and monitoring of gene diversity through
selection and breeding were studied considering the factors: selection intensity;
genetic value; coancestry; fertility variation; and pollen contamination. The
optimum goal of a seed orchard is achieved when the orchard population is under
an idealized situation, i.e., panmixis, equal gamete contributions from all parental
genotypes, non-relatedness and no pollen contamination. In practice, however,
due to relatedness among parents, variation in clonal fertility and ramet number,
and gene migration from outside, the realized genetic gain and gene diversity
deviate from the expectation. In the present study, the genetic value of seed
orchard crops (genetic gain, G) could be increased by selective harvest, genetic
thinning and/or both. Status number (Ns) was used to monitor the loss of gene
diversity in the process of forest tree domestication, and calculated to be
reasonably high in most seed orchards. Fertility of parents was estimated based
on the assessment of flowering or seed production, which was shown to be under
strong genetic control. Variation in fertility among orchard parents was a general
feature and reduced the predicted gene diversity of the orchard crop. Fertility
variation among parents could be described by the sibling coefficient ( ). was
estimated to be 2 (CV= 100% for fertility). In calculating , it was possible to
consider, besides fertility variation, the phenotypic correlation between maternal
and paternal fertilities, and pollen contamination. Status number was increased by
controlling parental fertility, e.g., equal seed harvest, mixing seed in equal
proportions and balancing parental contribution. By equalizing female fertility
among over-represented parents, it was possible to effect a favorable tradeoff
between gene diversity and seed production. If the status number of orchard crop
is not large enough, loss of gene diversity, random drift in gene frequency and
potential inbreeding problems could occur in subsequent generations. Genetic
loss or erosion did not seem to be alarming during the domestication of forest
trees, because a large number of parents are commonly used in first-generation
seed orchards. An understanding of reproductive processes and monitoring of the
impacts of the management practices are essential to maximize genetic gain and
to maintain sustainable gene diversity in seed orchard programs.
Key words: status number, effective population size, group coancestry,
inbreeding, fertility variation, ramet variation, gene migration, sibling coefficient
Author’s permanent address: Kyu-Suk Kang, Tree Breeding Department, Korea
Forest Research Institute, 44-3 Omokchun, Kwonsun, Suwon, Kyonggi, 441-350,
Republic of Korea (kyu-suk.kang@genfys.slu.se; kang_kyu_suk@hotmail.com).
To my parents and
my family!
Contents
Introduction …………………………………………………….. 8
Overview of seed orchards……………………………………… 8
Genetic gain ……………………………………………………. 15
Gene diversity and group coancestry …………………………... 17
Objectives ……………………………………………………… 18
Materials and methods .….……………………………………. 20
Flowering and ramet data .……………………………………... 20
Theoretical methods …………………………………………… 21
Summarized results and discussion ………………………… 26
Genetic gain ……………………………………………………. 26
Gene diversity (status number) ………………………………… 32
Interpretation of status number ………………………………… 49
Gene diversity and heterozygosity …………………………….. 51
Selfing and inbreeding .………………………………………… 54
Concluding remarks…………………………………………… 59
Future perspectives related to this thesis ………………….. 61
References ……………………………………………………… 63
Acknowledgements …………………………………………… 75
Appendix (Papers I–XI)……………………………………… 77
Appendix
List of original papers included
Papers I-XI
The present thesis is based on the following articles that will be referred to in the
text by their respective Roman numerals.
I.
K.S. Kang, D. Lindgren and T.J. Mullin. 2001. Prediction of genetic gain
and gene diversity in seed orchard crops under alternative management
strategies. Theoretical and Applied Genetics 000: 000-000 (in press).
II.
Kang, K.S. and Lindgren, D. 1998. Fertility variation and its effect on the
relatedness of seeds in Pinus densiflora, Pinus thunbergii and Pinus
koraiensis clonal seed orchards. Silvae Genetica 47(4): 196-201.
III.
Kang, K.S. and Lindgren, D. 1999. Fertility variation among clones of
Korean pine (Pinus koraiensis S. et Z.) and its implications on seed
orchard management. Forest Genetics 6(3): 191-200.
IV.
Adolfo D. Bila, Kyu-Suk Kang, Anni M. Harju and Dag Lindgren. 2001.
Fertility variation in forest tree populations. (submitted manuscript to
Forestry)
V.
Kang, K.S. 2000. Clonal and annual variation of flower production and
composition of gamete gene pool in a clonal seed orchard of Pinus
densiflora. Canadian Journal of Forest Research 30(8): 1275-1280.
VI.
Kang, K.S. 2001. Correlated fertility between genders and its effect on the
effective population size of gamete gene pool in monoecious species.
(manuscript)
VII. K.S. Kang, A.M. Harju, D. Lindgren, T. Nikkanen, C. Almqvist, and G.U.
Suh. 2001. Variation in effective number of clones in seed orchards. New
Forests 21(1): 17-33.
VIII. Kang, K.S., Bila, A.D., Lindgren, D. and Choi, W.Y. 2001. Predicted drop
in gene diversity over generations in the population where the fertility
varies among individuals. (submitted manuscript to Silvae Genetica)
IX.
Kang, K.S., Lai, H.-L. and Lindgren, D. 2001. Using single family in
reforestation: gene diversity concerns. (manuscript)
X.
K.S. Kang, E.D. Kjær and D. Lindgren. 2001. Balancing gene diversity
(status number) and seed production in Corylus avelana L. collections
from native Danish populations. (manuscript)
XI.
Kang, K.S. and Lindgren, D. 2001. Relatedness, flowering and their effects
on gene diversity of seeds in a Pinus thunbergii clonal seed orchard in
Korea. (manuscript)
Publications I, II, III, V and VII are reproduced with the kind permission of
journal publishers.