Drought stress and tropical maize: QTL-by-environment interactions and stability of QTLs across environments for yield components and secondary traits.
A recombinant inbred line (RIL) population was evaluated in seven field experiments representing four environments: water stress at flowering (WS) and well-watered (WW) conditions in Mexico and Zimbabwe. The QTLs were identified for each trait in each individual experiment (single-experiment analysis) as well as per environment, per water regime across locations and across all experiments (joint analyses). For the six target traits (male flowering, anthesis-to-silking interval, grain yield, kernel number, 100-kernel fresh weight and plant height) 81, 57, 51 and 34 QTLs were identified in the four step-wise analyses, respectively. Despite high values of heritability, the phenotypic variance explained by QTLs was reduced, indicating epistatic interactions. About 80, 60 and 6% of the QTLs did not present significant QTL-by-environment interactions (QTL x E) in the joint analyses per environment, per water regime and across all experiments. The expression of QTLs was quite stable across years at a given location and across locations under the same water regime. However, the stability of QTLs decreased drastically when data were combined across water regimes, reflecting a different genetic basis of the target traits in the drought and well-watered trials. Several clusters of QTLs for different traits were identified by the joint analyses of the WW (chromosomes 1 and 8) and WS (chromosomes 1, 3 and 5) treatments and across water regimes (chromosome 1). Those regions are clear targets for future marker-assisted breeding, and our results confirm that the best approach to breeding for drought tolerance includes selection under water stress.
Messmer
Rainer
R
ETH Zurich, Institute of Plant Sciences, 8092 Zurich, Switzerland. rainer.messmer@ipw.agrl.ethz.ch
Fracheboud
Yvan
Y
Bänziger
Marianne
M
Vargas
Mateo
M
Stamp
Peter
P
Ribaut
Jean-Marcel
JM
D002874:Chromosome Mapping; D055864:Droughts; D004843:Epistasis, Genetic; D018745:Genome, Plant / Q000235:genetics; D007178:Inbreeding; D008126:Lod Score; D010641:Phenotype; D040641:Quantitative Trait Loci / Q000235:genetics*; D019655:Quantitative Trait, Heritable; D012044:Regression Analysis; D013312:Stress, Physiological / Q000235:genetics*; D014329:Tropical Climate; D003313:Zea mays / Q000235:genetics* / Q000254:growth & development*