A worldwide maize panel revealed new genetic variation for cold tolerance

A large association panel of 836 maize inbreds revealed a broader genetic diversity of cold tolerance, as predominantly favorable QTL with small effects were identified, indicating that genomic selection is the most promising option for breeding maize for cold tolerance. Maize (Zea mays L.) has limited cold tolerance, and breeding for cold tolerance is a noteworthy bottleneck for reaching the high potential of maize production in temperate areas. In this study, we evaluate a large panel of 836 maize inbred lines to detect genetic loci and candidate genes for cold tolerance at the germination and seedling stages. Genetic variation for cold tolerance was larger than in previous reports with moderately high heritability for most traits. We identified 187 significant single-nucleotide polymorphisms (SNPs) that were integrated into 159 quantitative trait loci (QTL) for emergence and traits related to early growth. Most of the QTL have small effects and are specific for each environment, with the majority found under control conditions. Favorable alleles are more frequent in 120 inbreds including all germplasm groups, but mainly from Minnesota and Spain. Therefore, there is a large, potentially novel, genetic variability in the germplasm groups represented by these inbred lines. Most of the candidate genes are involved in metabolic processes and intracellular membrane-bounded organelles. We expect that further evaluations of germplasm with broader genetic diversity could identify additional favorable alleles for cold tolerance. However, it is not likely that further studies will find favorable alleles with large effects for improving cold tolerance in maize.

Dissecting the genetics of cold tolerance in a multiparental maize population

We identify the largest amount of QTLs for cold tolerance in maize; mainly associated with photosynthetic efficiency, which opens new possibilities for genomic selection for cold tolerance in maize. Breeding for cold tolerance in maize is an important objective in temperate areas. The objective was to carry out a highly efficient study of quantitative trait loci (QTLs) for cold tolerance in maize. We evaluated 406 recombinant inbred lines from a multi-parent advanced generation intercross (MAGIC) population in a growth chamber under cold and control conditions, and in the field at early and normal sowing. We recorded cold tolerance-related traits, including the number of days from sowing to emergence, chlorophyll content and maximum quantum efficiency of photosystem II (F_v/F_m). Association mapping was based on genotyping with near one million single nucleotide polymorphism (SNP) markers. We found 858 SNPs significantly associated with all traits, most of them under cold conditions and early sowing. Most QTLs were associated with chlorophyll and F_v/F_m. Many candidate genes coincided between the current research and previous reports. These results suggest that (1) the MAGIC population is an efficient tool for identifying QTLs for cold tolerance; (2) most QTLs for cold tolerance were associated with F_v/F_m; (3) most of these QTLs were located in specific genomic regions, particularly bin 10.04; (4) the current study allows genetically improving cold tolerance with genome-wide selection.