Maize grown in North America is often subjected to chilling temperatures at planting time, leading to disruption of seedling development. Laboratory protocols (cold germination, thermogradient plate germination and coleoptyle growth) were performed on 95 inbred lines in 1999 and 2000. Results from these tests were compared with field emergence data obtained from the same seed lots in Michigan and Illinois over two planting dates each year. In 1999 and 2000, cold germination had the highest correlation with early field emergence (r=0.78*** and 0.68***, respectively). Coleoptyle growth (r1999=0.51* and r2000=0.51**) and thermogradient plate germination (r1999=-0.63* and r2000=-0.48**) were also correlated with field emergence. Stepwise regression analyses indicated that the combination of cold germination and thermogradient plate germination was the best predictor of field emergence (r1999=0.64** and r2000=0.70***) when inbred lines are planted into cold, wet soils.A BC1F2 population (self-pollinated progeny of BC1 individuals) with 147 families was created from the cross of two inbred lines, 1111 (cold tolerant) and 2222 (cold susceptible). A linkage map was constructed with 89 SSR markers spanning 1570 cM and encompassing the 10 maize chromosomes with an average marker spacing of 30 cM. By means of interval mapping, a total of 21 QTLs, accounting for 8 to 76% of the variability, were identified and mapped. Eight QTLs controlled coleoptyle length, six QTLs controlled germination under cold temperatures and seven QTLs were associated with field emergence under cold soils. Most of these QTLs were clustered in three linkage groups and were consistently associated with field emergence and either coleoptyle growth or cold germination.Genetic variation exists for some of the major physiological processes or developmental stages that are affected by suboptimal temperatures. Thus, specific physiological processes or developmental stages that are affected during growth at suboptimal temperatures were identified. These traits should be useful to phenotypically characterize large populations for their ability to germinate, grow and develop at chilling temperatures. The cold germination test, the thermogradient plate and coleoptyle growth at chilling temperatures represent inexpensive, reliable, repeatable and easy-to-standardize methods to search for genetic variability for chilling tolerance during germination and early growth stages in corn. Moreover, these protocols have proven successful in the identification of superior donors for cold tolerant traits.
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