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Maize (Zea mays L.) landraces are useful materials that can introduce new diversity into breeding programs, but they will need to be selected to maximize their agronomic performance. The objective of this study was to use molecular markers to investigate the changes in the genetic diversity and structure over the cycles of a maize breeding program that combined intra- and interpopulation recurrent selection for grain yield in two broad-based Spanish maize composites. Using 76 polymorphic simple sequence repeat (SSR) markers and two flowering time related indels, this study looked at 10 populations derived from a breeding program designed to exploit the heterotic pattern northern Spain × southern Spain. Agronomic evaluations demonstrated that the selection effectively increased the yield of the composites and their crosses, but, as the molecular data from this study show, the improvement was at the expense of some variability. The genetic distance between populations increased with selection, which is accordant with the increment of heterosis found in the agronomic evaluation. The changes observed were consistent with a model in which genetic drift is the main force, although selection could also play a role in the changes observed in EPS7 and EPS13. Allele frequencies changed significantly for one marker during intrapopulation selection and three markers under interpopulation selection, pointing to regions 3.04, 7.03, 9.01, and 9.03 as quantitative trait loci (QTL) related to grain yield., The authors thank S.J. Miller for editing the manuscript. Research was supported by the Spanish Plan of Research and Development (AGL2010-22254-C02-01). M.C. Romay acknowledges a fellowship from the Ministry of Education and Science of Spain., MICINN, MEC

5 Pags., 3 Tabls., Selection for reduced stalk tunnel length by the Mediterranean corn borer (MCB) (Sesamia nonagrioides Lef.) while maintaining yield under infestation has already been evaluated. Significant reductions for tunnel length were reported, but yield showed a nonsignificant tendency to decrease with selection that could be due to increased inbreeding or significant genetic correlation between yield and resistance. Simultaneously, the presence of major quantitative trait loci (QTL) for resistance in chromosome 4 has been suggested. In the present study, we investigated the genetic relationship between yield and stalk tunneling resistance by conducting one generation of selection each for yield alone, resistance alone, and yield and resistance combined in a broad-based population. In addition, we tested the effectiveness of marker-assisted selection at two markers on chromosome 4 for reducing tunnels by MCB. Evaluations were made for 2 yr at two locations under MCB infestation. Unfavorable genetic correlation between stalk tunnel length and yield has been confirmed and could prevent detection of major QTL for tunnel length by using selection mapping. Markers phi076 and umc1329 could be linked to QTL for plant height but are not useful markers for reducing tunnel length and hence damage caused by borers. Finally, results advise against selection for reduced tunnel length by MCB or any index involving yield and tunnel length., Research supported by the Plan Nacional I+D+I (AGL2009-09611) and the “Deputación Provincial de Pontevedra.” M.C. Romay and J Peña-Asín acknowledge their fellowships from the Ministry of Education and Science of Spain.

White maize (Zea mays L.) is preferred for human consumption, but little is known about the genetic regulation of flour quality, and the potential value of genotypes adapted to temperate areas has not been reported. The objectives of this work were to assess the potential value of flint white maize inbreds from northwestern Spain and to determine the genetic effects of quality. A diallel among flint and dent white inbred lines was evaluated in northwestern Spain, and generation mean analyses were performed for three crosses representing flint by flint, dent by dent, and flint by dent combinations. Dent × dent hybrids had low density. Considering grain yield and density together, the best hybrids were EP64 × K301, EP71 × K301, and EC22 × Mo20W, which had poor milling test values, and high proportions of whole kernels. Considering the relative importance of nonadditive genetic effects, the final goal of breeding programs should be to obtain hybrids. Both additive and nonadditive genetic effects have to be taken into account to improve any of these traits in the flint genetic background. Moreover, it will be difficult to improve kernel density and proportion of whole kernels in any genetic background., Research supported by the European Commission and Ministry of Science and Technology of Spain (Project code 1FD1997-2352-C02-01), the INIA (Project code RF2007-00007-C05), and the Excma. Diputación Provincial de Pontevedra, Spain., UE, MCYT, INIA, Diputación Provincial de Pontevedra

Low spring temperatures are one of the main limiting factors for maize (Zea mays L.) growth along the European Atlantic coast. Several breeding programs have been performed to obtain cold-tolerant maize genotypes, but the few cold-tolerant inbreds and hybrids available need further improvements for cold tolerance and agronomic performance. The objective of this study was to identify cold-tolerant maize populations with favorable alleles to improve cold tolerance and agronomic performance in early sowing of two cold-tolerant hybrids. The parental inbred lines of two cold-tolerant hybrids were crossed to nine cold-tolerant populations. Tests were performed in a cold chamber and in the field for 2 yr at two locations. The populations Rojo de Tolosa and Puenteareas were the most promising sources of new favorable alleles for transferring cold tolerance to the hybrids EP80 × F7 and EP80 × Z78007, respectively. The populations Puenteareas and Silver King were the most outstanding donors to improve the agronomic performance of EP80 × F7 and EP80 × Z78007, respectively. Some improved versions of the cold-tolerant inbred parents could be developed from crosses between F7 or Z78007 and Puenteareas; alternatively, Rojo de Tolosa or Silver King could be used as donors of favorable alleles, but the simultaneous improvement of yield and cold tolerance is not straightforward., Research was supported by the National Plan for Research and Development of Spain (AGF01-3946 and AGF2004-06776), the Autonomous Government of Galicia (PGIDIT04RAG403006PR and PGIDIT02PXIC40301PN) and Excma. Diputación Provincial de Pontevedra. V.M. Rodríguez acknowledges a fellowship from the Ministry of Science and Technology from Spain., MCYT, Xunta de Galicia, Diputación Provincial de Pontevedra

Early planting can contribute to increased grain yield of maize (Zea mays L.), but it requires cold tolerance. A limited number of cold-tolerant maize genotypes have been reported. The objectives of this study were to test a new strategy to improve cold tolerance in maize searching for broad x narrow genetic combinations that may be useful as base populations for breeding programs, to compare genotype performance under cold-controlled and field conditions, and to establish the major genetic effects involved in crosses between cold-tolerant inbred lines and populations. Nine cold-tolerant populations were crossed to five inbred lines and evaluated in a cold chamber and in the field. Most inbred line x population crosses performed better than populations per se or hybrids used as checks, both in the cold chamber and in the field, suggesting that broad x narrow genetic combination could be a suitable start point for further breeding programs for cold tolerance. The crosses between the inbred line EP80 and northwestern Spanish populations are the most promising base germplasm. In particular, EP80 x Puenteareas showed the greatest yield and good performance at the first stages of development under cold conditions. In addition, EP80 and Puenteareas showed favorable general combining ability for most traits. Early vigor rating would be the most suitable trait to select maize genotypes with superior cold tolerance during emergence and postemergence stages, because it was the only trait for which differences among genotypes were observed in both the cold chamber and the field. Although evaluation under controlled conditions is essential to test cold tolerance, field evaluations are complementary because no association was found between traits evaluated in both conditions.