Quantitative trait loci for early plant vigour of maize grown in chilly environments

Maize (Zea mays L.) is particularly sensitive to chilling in the early growth stages. The objective of this study was to determine quantitative trait loci (QTL) for early plant vigour of maize grown under cool and moderately warm conditions in Central Europe. A population of 720 doubled haploid (DH) lines was derived from a cross between two dent inbred lines contrasting in early vigour and were genotyped with 188 SSR markers. The DH lines per se and their testcrosses with a flint line were evaluated in field experiments across 11 environments in 2001 and 2002. Plants were harvested after six to eight leaves had been fully developed to assess fresh matter yield as a criterion of early vigour. Seven QTL were detected for line performance and ten QTL for testcross performance, explaining 64 and 49% of the genetic variance. Six out of seven QTL detected in the lines per se were also significant in their testcrosses. Significant QTL x environment interaction was observed, but no relationship existed between the size of the QTL effects and the mean temperature in the individual environment. The correlation between fresh matter yield and days to silking was non-significant, indicating that differences in early plant vigour were not simply caused by maturity differences. For three additional chilling-related traits, leaf chlorosis, leaf purpling, and frost damage seven, six, and five QTL were detected, respectively. Three QTL for leaf chlorosis, two for leaf purpling, and two for frost damage co-localized with QTL for fresh matter yield. Results are considered as a reliable basis for further genetic, molecular, and physiological investigations.