Dr. Byram will give an invited presentation on Tuesday, August 26, for the IUFRO-CTIA Main Conference.  The abstract of his presentation is provided below.

The Promise and Unresolved Challenges of Marker Assisted Breeding in Southern Pine Tree Breeding Programs

T. D. Byram[1] and N. C. Wheeler[2]

Molecular markers have revolutionized the science of genetics by directly revealing the variability present in the genetic code and giving clues to the underlying structure of economically important traits.  However, molecular techniques and especially forward selection through marker-assisted selection (MAS) has had little impact on applied southern pine tree breeding.  Most economically important traits are quantitative, under the control of a number of genes each with small effect.  Quantitative trait loci (QTLs) have been difficult to discover and then verify in existing populations.  The first generation of QTL experiments was pedigree specific, often revealing significant genotypic, environmental, and temporal interactions.  QTLs from these experiments were therefore of limited utility in population improvement programs.  Second-generation MAS tools, especially association genetics, holds more promise for population improvement, but will require extensive investments for allele discovery and validation in forest trees.   Biological limitations are far from the only problems.  When wood is a commodity, quality traits are of little economic importance and the only traits of interest in a breeding program are those that lower the cost of production, i.e. volume growth.  This is a composite characteristic that involves many poorly understood and complexly regulated traits. Even in the case of disease resistance genes, MAS may prove less than effective if gene-specific markers for functional variants of resistance alleles are unknown.

Despite these unresolved challenges, the southern pine tree breeding programs should be taking a number of steps to realize the promise of MAS.  First and foremost, pedigree verification and quality control should become a regular part of all our programs.  Measurements of genetic distance and variation should be obtained to inform population structure, guide gene conservation plans, and to direct possible infusions of new material.  Next, because of the long lead time needed and the fact that most existing programs will provide limited types of families with small numbers of seedlings, tree breeders must work more closely with molecular geneticists to design the specialized populations needed for future studies. Better statistical techniques must be developed and adopted by the tree breeding community.  Populations should be structured to rapidly fix QTLs of high breeding values in small sub-populations.  Finally, economic simulations should be developed and refined to provide a rigorous tool for thinking through MAS breeding plans and to identifying steps with the most economic impact.  Many of these needs are currently being addressed through the Conifer Translational Genomic Network which will be briefly described. 

---

[1] Director Western Gulf Forest Tree Improvement Program and Assistant Professor, Department of Ecosystem Science and Management, Texas A&M University, College Station TX

[2] Adjunct Professor, Dept. Forestry Environmental Science, NC State University, Raleigh, NC

Thomas D. Byram is the Director of the Western Gulf Forest Tree Improvement Program (WGFTIP) whose 13 members are collectively responsible for planting approximately 300 million pine trees annually in the states of Arkansas, Louisiana, Mississippi, Oklahoma and Texas.  The WGFTIP coordinates breeding and progeny testing activities and provides technical guidance to its members.  In addition, he is also responsible for the WGFTIP – Hardwood with six members committed to developing improved strains of hardwood trees for reforestation.  He also manages day to day operations of the Texas Forest Service Pine Tree Improvement Program, Urban Tree Improvement Program, and Hardwood Tree Improvement Program.  He is an Assistant Professor in the Department of Ecosystem Science and Management, Texas A&M University.  He received his B.A. in Biology from Hendrix College, Conway, AR in 1975.  He did his graduate work at Texas A&M University where he was awarded a M.S. in Forestry in 1978 and a Ph.D. in Molecular and Environmental Plant Sciences in 2000.  Prior to taking the role of WGFTIP Director in 2001 he was the WGFTIP Assistant Geneticist.