QTL Associated with Maize Kernel Traits among Illinois High Oil × B73 Backcross-Derived Lines By J.J. Wassom, J.C. Wong, and T.R. Rocheford University of Illinois, Department of Crop Sciences

Illinois High Oil Maize Recurrent selection for oil in Illinois High Oil (IHO) since –4.7% of kernel weight at start. –19.3% of kernel weight at cycle 90.

IHO

Practical Advantages of Grain from High-oil Maize Livestock feeding value is improved. –More calories. –Improved amino acid balance. Improved oil quality. –Oleic acid tends to increase with higher oil. a mono-unsaturated fatty acid. Oil: one factor in overall improvement.

Selection for Oil Ample genetic variation for oil. High-oil maize typically has: –Small kernels. –Large embryo and small endosperm. –Reduced starch and increased protein. Heritable, but high-oil hybrids yield less. –About 8% less for the current market leader.

Kernel oil, protein, and starch interact Most stored lipids of the maize kernel accumulate in the scutellum of the embryo. High oil maize typically has: –Large embryo and small endosperm. –Small kernels. –Reduced starch and increased protein.

Kernel size of IHO and ILO

Previous Kernel QTL Studies IHO × ILO markers for oil, protein, and starch (Berke and Rocheford, 1995). But this population is not representative of modern hybrids.

Objectives in This Study In a population more relevant to practical hybrids: –Analyze variation for kernel traits. –Develop a molecular map. –Identify QTL for kernel oil, protein, starch, and related traits and determine their effects in genetic models. –Identify QTL with potential in MAS.

Materials and Methods 150 backcross1-derived S1 lines (BC 1 S 1 ). High oil donor: IHO cycle 90. –One plant. Recurrent parent: B73. –Historically important BSS inbred line. Testcrosses (TC) with Mo17. –Historically important Lancaster inbred line.

Materials and Methods Field trials at Urbana, IL. BC 1 S 1 : 1993, 1994, 1996, 2000, and TC:1995 and Kernel oil, starch, and protein each year. Fatty acids in BC 1 S 1 in 1993 and 1994.

Materials and Methods Linkage map: –110 markers, 38 RFLP and 72 SSR. –Total length = 1486 cM. –Average distance between markers = 14.9 cM. Composite interval mapping. –LOD 2.5 for detection. –Models developed with genome-wide  = –Additive and additive × additive effects.

Materials and Methods Heritability: h 2 =  2 g / (  2 /re +  2 ge /e +  2 g ). –(Hallauer and Miranda, 1981) Adjusted R 2 : R 2 adj = R 2 – [z/(n-z-1)](1-R 2 ). R 2 = coefficient of determination z = number of QTL and interaction terms n = number of individuals Q 2 = R 2 adj /h 2 –(Utz et al., 2000)

Kernel traits among BC 1 :S 1 families Oil, mg g -1 Prot, mg g -1 Star, mg g -1 K wt, mg IHO174 ± ± ± ± 37.8 B73 48 ± ± ± ± 32.5 BC 1 :S 1 70 ± ± ± ± 2.6 Range 48 ± ± ± ± 533 h 2,%

Correlations in BC 1 S 1 s Oil Protein Starch Oleic 0.35** Protein 0.51** Starch– 0.75**– 0.76** Kernel Wt– 0.26**– 0.17** 0.40**

Kernel traits and grain yield of Testcrosses Oil, mg g -1 Prot, mg g -1 Star, mg g -1 Yield, kg ha -1 TC 52 ± ± ± ± 131 Check 55 ± ± ± ± 1120 H 2,%

Correlations in Testcrosses OilProteinStarch Protein 0.34** Starch –0.65**–0.78** Yield –0.26*–0.55** 0.54**

QTL regression model for oil in BC 1 :S 1 s Chrom/positionLODEffectPart. R 2, % 3/ ** 5.0 5/ ** 4.4 6/ **36.7 7/ / **13.2 3/14 × 7/ R 2 adj = 46.9 R 2 /h 2 = 54.2

Summary of Models in BC 1 S 1 s Trait H 2 %QTL nR 2 adj %R 2 /H 2 % Oil Oleic Protein Starch Kernel Wt

QTL regression model for oil in TCs Chrom/positionLODEffectPart. R 2, % 1/ – / ** 5.7 6/ **18.4 R 2 adj = 17.5 R 2 /h 2 = 19.1

Summary of models in TC Trait H 2,%QTL, nR 2 adj,%R 2 /H 2,% Oil Protein Starch Grain Yield

QTL for kernel oil detected at LOD 2.5. Detected in BC1:S1 Detected in TC B73 favors oil IHO90 favors oil

Chromosome 6 with oil, oleic acid, protein, and starch QTL in BC 1 S 1 highlighted. QTL LOD Trait Favorable Allele Oleic IHO Oleic IHO Starch B Oil IHO Protein IHO Protein IHO90 Oil Oleic acid B73 Protein Starch IHO90

Intervals affecting multiple traits Many QTL are clustered within intervals (  22 cM) affecting multiple traits. Direction of the QTL effects on different traits often follow expectations based on trait correlations.

Intervals associated with common effects on oil, protein, starch, and grain yield are highlighted. Letters at the left indicate the associated trait. S O Y S P S S S S S S P P P P P O O O O O O Y Y S S S S S P P P P P

Chromosome 6: All QTL with LOD > 2.5. Common QTL intervals are shown as rectangles. QTL outside common intervals are shown as triangles. Interval LOD Generation Trait Favorable Allele 8 to TC Starch B73 8 to TC Protein IHO90 8 to BC 1 S 1 Oleic IHO90 50 to BC 1 S 1 Oleic IHO90 50 to BC 1 S 1 Starch B73 50 to BC 1 S 1 Oil IHO90 50 to BC 1 S 1 Protein IHO TC Oil IHO BC 1 S 1 Protein IHO90

Summary QTL were detected for all traits. Models in BC 1 S 1 s explained: – 47% of the phenotypic and 54% of the genotypic variation for oil. –51% of the phenotypic and 60% of the genotypic variation for oleic acid.

Summary One QTL on chromosome 6L in BC 1 S 1 explained: –37% of the phenotypic variation for oil. A nearby QTL on 6L explained: –24% of the phenotypic variation for oleic acid. Markers flanking these QTL show promise for MAS of high-oil, high-oleic lines. Many QTL for different kernel traits are clustered within common chromosome regions.

Marker Assisted Selection Separate oil from yield. Molecular markers identify high oil genomic regions. Directly select for markers. –Modify recurrent parent for oil-related genes only.

Introgression of minimal chromosomal segments, especially on chromosome 6L, from a high-oil donor into conventional breeding lines may enhance the development of agronomically desirable and productive high-oil breeding lines and hybrids.

Acknowledgements Funded by a grant from the Illinois-Missouri Biotechnology Alliance with matching support from Monsanto Company. Lab members, past and present. –Jeremy Johnson –Joe King –Venu Mikkillineni –Chandra Paul Fatty acid measurement. –Jan Hazebroek and associates at Pioneer Hi-Bred International