Quantitative trait loci in Two Soybean Recombinant Inbred Line Populations Segregating for Yield and Disease Resistance

Abstract

ments over several years which is expensive, time consuming, and labor intensive (Maughan et al., 1996). Molecular makers linked to quantitative trait loci (QTL) can assistComponents of yield are often identifiable which aid soybean [Glycine max (L.) Merr.] breeders to combine traits of low heritability, such as yield, with disease resistance. The objective of this the selection of yield (Fehr, 1987;Specht et al., 1999). study was to identify markers linked to yield QTL in two recombinantIn soybeans, the basis of yield improvement is unclear, inbred line (RIL) populations ['Essex' ϫ 'Forrest' (EϫF; n ϭ 100) but maturity and growth habit have major effects (Manand 'Flyer' ϫ 'Hartwig' (FϫH; n ϭ 94)] that also segregate for soybean sur et al., 1996;Orf et al., 1999;Specht et al., 1999). cyst nematode (SCN) resistance genes (rhg1 and Rhg4 ). Each popula-Resistance to disease is usually a strong component of tion was yield tested in four environments between 1996 and 1999. yield in disease infested environments (Njiti et al., 1998). The resistant parents produced lower yields. Heritability of yield Disease resistance in cultivars (particularly SCN resisacross four environments was 47% for EϫF and 57% for FϫH. Yield tance) has consistently been associated with a 1-2% was normally distributed in both populations. High yielding, SCN decrease in yield when disease was absent (Concibido resistant transgressive segregants were not observed. In the EϫF RIL et al., 1997). In addition, many SCN resistant cultivars population, 134 microsatellite markers were compared against yield by ANOVA and MAPMAKER QTL. Regions associated with yield appear to display poor combining ability during interwere identified by SATT294 on linkage group (LG.) C1 (P ϭ 0.006, crossing (Concibido et al., 1997). Sudden death syn-R 2 ϭ 10%), SATT440 on LG. I (P ϭ 0.007, R 2 ϭ 10%), and SATT337 drome (SDS) resistance has also been associated with on LG. K (P ϭ 0.004, R 2 ϭ 10%). Essex provided the beneficial allele low yield potential (Rupe et al., 1993). at SATT337. Mean yields among FϫH RILs were compared against Genetic maps have been useful for soybean genome 33 microsatellite markers from LG. K. In addition 136 markers from analysis. Maps have allowed the identification of many randomly selected LGs were compared with extreme phenotypes by economically important soybean genes conditioning bulk segregant analysis. Two regions on LG. K (20 cM apart) associquantitative trait loci (QTL), including those for disease ated with yield were identified by SATT326 (P ϭ 0.0004, R 2 ϭ 15%)

Unraveling the Complex Trait of Crop Yield With Quantitative Trait Loci Mapping in Brassica napus

“…In other words, QTL for yield may result from pleiotropic QTL: genomic regions that affect multiple traits by containing multiple, tightly linked, trait-specific genes or genes that affect multiple traits (Hall et al 2006). Most published fine-mapped QTL and the genes identified as affecting yield exhibit pleiotropic effects on at least one trait (Peng et al 1999;Brown 2002;Yuan et al 2002;Li et al 2004;Ashikari et al 2005;Waller et al 2005;Clark et al 2006;Tian et al 2006a;Cockram et al 2007) or multiple yieldassociated traits (Quarrie et al 2006;Xie et al 2006Xie et al , 2008Burstin et al 2007;Song et al 2007;Shomura et al 2008;Xue et al 2008). Even a short region with a confidence interval of 0.4 cM and a physical distance of 37.4 kb has revealed pleiotropic effects between seven QTL of different yield-associated traits and the QTL of grain yield in rice (Xie et al 2008).…”

“…Yield-related traits (such as biomass, harvest index, plant architecture, adaptation, resistance to biotic and abiotic constraints) may also indirectly affect yield by affecting the yield-component traits or by other, unknown mechanisms. Increasing evidence suggests that ''fine-mapped'' quantitative trait loci (QTL) or genes identified as affecting crop yield involve diverse pathways, such as seed number (Ashikari et al 2005;Tian et al 2006b;Burstin et al 2007;Xie et al 2008;Xing et al 2008;Xue et al 2008), seed weight (Ishimaru 2003;Song et al 2005;Shomura et al 2008;Wang et al 2008;Xie et al 2006Xie et al , 2008Xing et al 2008;Xue et al 2008), flowering time (Cockram et al 2007;Song et al 2007;Xie et al 2008;Xue et al 2008), plant height (Salamini 2003;Ashikari et al 2005;Xie et al 2008;Xue et al 2008), branching (Clark et al 2006;Burstin et al 2007;Xing et al 2008), biomass yield (Quarrie et al 2006;Burstin et al 2007), resistance and tolerance to biotic and abiotic stresses (Khush 2001;Brown 2002;Yuan et al 2002;Waller et al 2005;Zhang 2007;Warrington et al 2008), and root architecture (Hochholdinger et al 2008).…”

Separate loci underlie resistance to root infection and leaf scorch during soybean sudden death syndrome

“…The genetic material used in this study consisted of 92 FxH F 5 -derived recombinant inbred lines (RILs; Yuan et al 2002). The population was advanced from the the roots also appeared to be resistant to infection by F. virguliforme (Gibson et al, 1994;Wrather et al 1995;Njiti et al 1997;Mueller et al 2003).…”

“…Hartwig was strongly resistant to most HG Types of SCN (Anand 1992;Niblack et al 2003). Flyer was susceptible to most SCN HG Types and partially susceptible to SDS (McBlain et al 1990;Gibson et al 1994;Njiti et al 1997;Yuan et al 2002;Kazi 2005). Roots of Flyer did not appear to be resistant to infection by F. virguliforme ).…”

“…The confirmed QTL either mapped to a similar location in separate populations or were mapped for a second time in near isogeneic lines (NILs) derived from RILs segregating across regions that encompassed the QTL. The confirmed QTL include C2 (Hnetkovsky et al 1996;Njiti et al 1998;, one on D2 Farias-Neto et al 2007), three all on G (Prabhu et al 1999;Iqbal et al 2001;Njiti et al 2002), J (Sanitchon et al 2004Kassem et al 2006) and N (Njiti et al 2002;Hashmi 2004). The ExF QTL on F and I (Iqbal et al 2001) were not yet confirmed by association in a second population by late 2007.…”