marker-assisted selection in wheat

Chapter 15 – Marker-assisted selection in forestry species 293Keegstra, 2005).Lignin biosynthesis is well understoodat the molecular level in plants (reviewedby Boerjan, Ralph and Baucher, 2003 andPeter and Neale, 2004) and is of particularinterest in forest trees as removal of ligninfor paper-making has major economic andenvironmental costs. In some cases, geneticmodification of lignin structure has beenshown to improve delignification in pulpand paper-making (Jouanin and Goujon,2004), and down regulation of ligninpathway enzymes has also been shown toincrease cellulose content (Hu et al., 1999).Gymnosperms and angiosperms share acommon set of enzymes that are responsiblefor the formation of guaiacyl lignin,while angiosperms have evolved at least twoenzymes that catalyse the production ofsyringyl lignin. Association studies are nowbeing carried out in loblolly to examine theadaptive significance of sequence variationin monolignol biosynthetic genes (Peterand Neale, 2004) and other genes controllingwood properties (Brown et al.,2004). Similar research (Table 3) aimed atidentifying genes controlling wood formationis being undertaken in Douglas fir(Krutovsky et al., 2005), maritime pine (Potet al., 2004), radiata pine (S.G. Southertonand G.F. Moran, personal communication),spruce (MacKay et al., 2005) and eucalypts(Moran et al., 2002).The availability of genes linked to arange of other traits in model plants opensup new areas of investigation in associationgenetics. For example, associationstudies are in progress to identify genescontrolling pathogen resistance (Ersoz etal., 2004; MacKay et al., 2005), droughttolerance (Ersoz et al., 2004), cold tolerance(Krutovsky et al., 2005) and budset (Paoli and Morgante, 2005) (Table 3).Further opportunities exist for associationstudies aimed at identifying SNPs linked toimportant traits. Flowering is particularlywell understood at the molecular level (Zikand Irish, 2003), and increasing numbersof genes controlling flowering have beencloned in angiosperm tree species includingeucalypts (Southerton et al., 1998; Watsonand Brill, 2004), silver birch (Elo et al.,2001), poplar (Rottmann et al., 2000) andgymnosperm tree species including spruce(Tandre et al., 1995; Rutledge et al.,1998)and pines (Mouradov et al., 1998, 1999).Another important technologicaladvance that is making large-scale associationstudies possible is the recentdevelopment of rapid, high-throughputTable 3Association studies in progress for forest tree speciesSpecies Trait ReferenceEucalyptus nitens Wood properties Moran et al., 2002; Thumma et al., 2005Populus Wood properties MacKay et al., 2005Disease resistance MacKay et al., 2005Picea glauca Wood properties MacKay et al., 2005Disease resistance MacKay et al., 2005Picea abies Bud set Paoli and Morgante, 2005Pseudotsuga menziesii Wood properties Krutovsky et al., 2005;Cold hardiness Krutovsky et al., 2005;Pinus radiata Wood properties Southerton and Moran unpub. dataPinus taeda Wood properties Peter and Neale, 2004; Brown et al., 2004Disease resistance Ersoz et al., 2004Drought tolerance Ersoz et al., 2004Pinus pinaster Wood properties Pot et al., 2004