-Selection for reduced stalk tunnel length by the Mediterranean corn borer (MCB, 12 Sesamia nonagrioides Lef.), while maintaining yield under infestation, has already been evaluated. 13Significant reductions for tunnel length were reported, but yield showed a non significant 14 tendency to decrease with selection that could be due to increased inbreeding or significant 15 genetic correlation between yield and resistance. Simultaneously, the presence of major QTLs for 16 resistance in chromosome 4 has been suggested. In the present study, we investigated the genetic 17 relationship between yield and stalk tunneling resistance by conducting one generation of 18 selection each for yield alone, resistance alone, and yield and resistance combined in a broad-

Molecular changes during intra and inter recurrent selection of two populations of maize: one adapted and one non adapted to the selection environment

In Europe a heterotic pattern commonly used in maize breeding is "American Dent× European Flint". Maize breeding programs generally use only a small portion of the useful genetic variability present in the local open-pollinated varieties which, otherwise, have a poor performance that hampers their use. Two maize composites, EZS33 formed by open-pollinated flint varieties from dry or Mediterranean Spain, and EZS34 from USA dent populations, were developed in Zaragoza (Spain). Both were subjected to three cycles of full-sib reciprocal recurrent selection (RRS) for yield. The objective of our study was to evaluate after three cycles of selection the effect of RRS. The selection significantly increased yield in the population crosses (3.0% per cycle) and in the crosses of the populations with testers of different origin. The correlated responses for the population crosses in other agronomic traits like flowering and early vigor were in the desired direction, but plant height was reduced. We propose that stover yield or related traits could be included in selection programs as selection criteria to prevent their decline. The adapted population increased the frequency of favorable alleles for yield, but the inbreeding depression counteracted their effect on the mean. RRS had a positive effect on other traits. According to our data, RRS can be useful to develop improved populations from which it would be possible to develop lines with improved both specific and general combining ability with different heterotic groups. We conclude that the heterotic pattern "Mediterranean Spain x US Dent" is potentially very useful for maize breeding for adaptation to Mediterranean conditions and an interesting source of cultivars for low-input agriculture.

One of the most important stress factors in maize (Zea mays L.) fields is weed competition, which reduces the crop yield. Weeds chiefly interfere with maize and establish considerable competition for light, water and nutrients. To avoid these harmful effects, there are different agronomic measures and factors among which, the most relevant are the interactions between crop and weed, weed management practices and type of germplasm. This study attempts to evaluate maize germplasm for tolerance to weed competition in order to achieve competitive ability and suitability for farming. Ten genotypes of maize, classified into two groups, i.e. improved populations and traditional cultivars, were grown under four types of weed management practices (mechanical harrowing control, chemical control, combination of harrowing and chemical control and untreated control as check) for three years (from 2009 to 2011) in Zaragoza (Spain). We found that the effect of weed management practices was not significantly different, whereas the genotype effect was highly significant, with genotype EZS34 (mean yield of 7.7 Mg ha -1 ) showing the highest yield. Other traits, such as earliness, displayed a good behaviour under weed competition. On the other hand, harrowing management proved to be the most effective method of weed control although it did not show a significant response. The best results are associated with some maize genotypes that have a specific adaptation to local conditions, according to their genetic background.