W. Wen, T. Guo, V.H. Chavez T., J. Yan, S. Taba CIMMYT The strategy and potential utilization of temperate germplasm for tropical germplasm improvement—a case study of maize (Zea Mays L.) W. Wen, T. Guo, V.H. Chavez T., J. Yan, S. Taba CIMMYT

Heterotic groups A, B, C, D…… X B C X D Heterosis exploitation Organization of germplasm in genetically divergent heterotic groups is beneficial for a systematic and optimum exploitation of heterosis (Melchinger 1999). Well-developed heterotic patterns of mature breeding programs are artificial constructs created by breeders and enhanced by the process of breeding hybrids (Tracy and Chandler 2006)

CML: CIMMYT Maize Lines ,Tropical GEM: US Germplasm Enhancement of Maize (GEM) lines, Temperate

The CMLs originated from 35 mostly broad-based populations and pools with mixed origins, which are carefully selected inbred lines with good general combining ability (GCA) and a significant number of value-adding traits such as drought tolerance, nitrogen (N) use efficiency, acid soil tolerance, resistance to disease and insect pests (www.cimmyt.org). To date, the total number of CMLs held in trust in CIMMYT genebank is 530.

The Germplasm Enhancement of Maize project (GEM) is a cooperative effort of the United States Department of Agriculture’s Agricultural Research Service (USDA-ARS), land-grant universities, private industry, international, and non-governmental organizations. The objective is widening the germplasm base of commercial hybrid corn in the United States through introduction and incorporation of novel and useful germplasm gathered from around the globe (http://www.public.iastate.edu/~usda-gem/)

Features of CMLs The lack of structure within CMMYT lines and lower genetic distance between current heterotic groups due to the mixed genetic constitution of CIMMYT germplasm used to extract the inbred lines.

Why use temperate germplasm? Some favorable alleles may be unique to temperate germplasm, for instance, the allele of the gene encoding β-carotene hydroxylase (crtRB1), associated with β-carotene concentration and conversion in maize kernels, which was detected most recently (Yan et al. 2010) Some GEM lines performed well in tropical and subtropical areas. There should be favorably unique alleles or genomic regions in temperate germplasm that can be helpful in tropical maize improvement as well as utilization of tropical lines in temperate areas.

Traditional MAS Including two steps: identifying QTL and then estimating their effects. Weakness of QTL identification methods: Biparental populations, not representative, do not have the same level of allelic diversity and phase as the breeding program as a whole Costly Additional effort is needed to validate the mapping results Biased estimation

Genomic selection Genomic selection which involves calculating breeding values for all markers and utilizes all markers in selection without testing them for their significance may dramatically change the role of phenotyping especially with the rapid development of high through-put genotyping platform (Jannink et al. 2010) Heffner et al. 2009

Objectives to detect the potential of utilizing temperate germplasm in tropical maize breeding to construct a simple model using information of phenotypic values and molecular markers to predict single crosses (hybrid) performance to compare the efficiency of hybrid performance prediction by using random markers and selective markers with association analysis

Material Summary Heterotic Pattern Number Description CML A 48 Dent kernel B 38 Flint kernel A/B 8 Dent/Flint kernel GEM SS 35 Stiff stalk NSS 19 Non-stiff stalk Total 148 F1 654 F1: CML (A) X GEM (SS), CML (B) X GEM (NSS)

CML GEM F1

Phenotyping F1/TL F1/AF Inbreds/TL Inbreds/AF Trait Range Mean DA (day) 76-103 92.11 ±4.66 60-82 71.44 ±4.04 80-103 92.01 ±4.13 61.67-82 71.31 ±3.71 DS (day) 76-106 93.09 ±4.82 61-82 71.01 ±3.74 80-106 92.98 ±4.30 61-80 70.92 ±3.46 PH (cm) 125-275 209.12 ±21.48 140-285 228.38 ±18.25 155-250 209.91 ±17.30 183.33-261.25 228.29 ±14.21 EH (cm) 50-170 112.1 ±18.68 77.5-175 122.76 ±17.82 70-150 112.6 ±15.43 85-165 122.33 ±14.36 EW (kg) 0.12-2.23 0.87 ±0.37 0.1-2.78 0.85 ±0.46 0.13-1.77 0.92 ±0.34 0.21-2.78 0.95 ±0.49 EWP (kg) 0.04-0.84 0.27 ±0.09 0.13-1.42 0.43 ±0.14 0.13-0.84 0.28 ±0.08 0.21-0.83 0.43 ±0.09

SNPs used for genotyping Chromosome No. of SNPs 1 217 2 132 3 140 4 134 5 154 6 98 7 77 8 115 9 96 10 83 Unknown 20 Total 1,266

The frequency of the same specific allele of each SNP in GEM lines, CMLs and all 148 lines.

Principal component analysis (PCA) of 148 maize inbred lines based on 1266 SNPs

Principal component analysis (PCA) of 654 maize F1 lines based on 872 SNPs

Prediction of hybrid performance Training sample set: n=430 Testing sample set: n=215

Prediction of hybrid performance Marker type A: marker selection referring to association results from inbreds, and starting from the marker with highest significance. Marker type B: marker selection referring to association results from F1s, and starting from the marker with highest significance. Marker type C: markers selected randomly from the genome-covering 1,266 SNPs

Implication and discussion Utilizing temperate lines in tropical breeding program In this study, unique alleles harbored within the temperate lines imply the utilization of temperate lines in tropical breeding program and the potential of mutual improvement Clear heterotic patterns of the GEM lines can broaden the genetic divergence between heterotic groups within CMLs

The potential and strategy of genomic selection in maize breeding The high prediction accuracy indicates the potential and efficiency of genomic selection based on our model, for predicting hybrid performance. Replacing a larger number of genome-covering markers with a smaller number of trait-associated markers may be more effective because the latter produces less noise

PPB in Oaxaca Project Trails of landrace collections, hybrids, CIMMYT gene pools Seed production of hybrids and inter-varietal hybrids in Central Valley of Oaxaca Seed processing and Declared seeds for distribution Low cost seed bags: 500-600 pesos for 20kg. Good yield and plant performance of some gene pools: potential useful gene flow into the local maize production communities

PPB in Valle Central, Oaxaca

End. Thank you very much.