Ordas et al. BMC Genomics 2010, 11:174 http://www.biomedcentral.com/1471-2164/11/174 involved in borer resistance, as, in general, different sub- sets of QTLs can segregate in different populations [11]. Significant variation for resistance to ECB and MCB was found in the European Union Maize Landrace Core collec- tion and some populations from Central and Eastern Spain seemed to be promising sources of resistance to maize stem borers, that is, those populations probably carry favourable alleles for ECB or MCB resistance [5,12,13]. Consequently, the use of mapping populations derived from these European materials could allow to widen the already known genomic regions for corn borer resistance. Additive effects have been consistently reported as more important than dominant effects for stalk tunnel- ling by MCB [14-16], while additive and dominant effects has been reported as important for MCB ear resistance and yield under infestation [17,18]. It is inter- esting to mention that stalk tunnel length, the character typically used to quantify corn borer damage, is nega- tively correlated with yield [19-21], although the genetic mechanism responsible of that relationship, whether pleitropy or repulsion linkage, is unknown. A population of recombinant inbred lines (RILs) is a useful tool for mapping QTLs for traits under additive control because RILs represent a permanent sample of progenies for eva- luations using replications in different environments. Most inbreds used in temperate zones derive from Corn Belt Dent varieties, but adapted flint lines derived from European populations are also widely used, parti- cularly, in Europe, northern areas of North America, and Japan [22-25]. A heterotic pattern widely used by western European breeders is Corn Belt Dent × Eur- opean Flint [23,26-28] using preferentially materials from the Still Stalk Synthetic because the Stiff Stalk Syn- thetic subgroup shows more heterosis with European Flint than other Corn Belt Dent subgroups [26]. A Page 2 of 10 population of RILs derived from two European flint lines will be used to address the objectives: (1) to esti- mate the genetic correlations between MCB resistance and agronomic traits; (2) to identify and characterize QTLs responsible for MCB resistance and agronomic traits within the European Flint group. Results EP42 had higher stalk tunnel length than EP39, while EP39 × EP42 had a value close to the mid-parent value (Table 1). In contrast to stem resistance, EP39 × EP42 had higher level of ear resistance than the most resis- tance parent. The average value of the RILs was close to the mid-parent value for several traits, either agronomic or related to resistance. Genetic variances in the RIL population were highly significant for all traits, while the genotype × environment interaction variances were highly significant for agronomic traits, but not for resis- tance traits, except for cob damage. Regarding the agronomic traits, a negative genetic cor- relation coefficient between flowering and yield was found among RILs, while a positive genetic correlation coefficient was found between flowering and grain humidity (Table 2). Regarding the relationship between agronomic and resistant traits, plant height and flower- ing had a positive and moderate genetic relationship with stalk tunnel length. The genetic map had a total length of 1791 cM and an average distance between loci of about 20 cM (Figure 1). In the RILs, three QTLs were detected for stalk tun- nel length at chromosomes 1, 3 and 8 (Figure 1; Table 3). Those QTLs explained 33% of the genetic variance, calculated with the whole data set, but this value was reduced to 7.5% when the cross validation method was used. The additive values for the QTLs varied between Table 1 Characteristics of EP39 and EP42, EP42 × EP39 and the RIL population developed from EP42 × EP39. Stalk tunnel length (cm) Relative stalk tunnel length Kernel damage (1-9 scale)a Shank damage (1-9 scale)a Cob damage (1-9 scale)a Anthesis (days) Silking (days) Plant height (cm) Grain humidity (%) Yield (t ha-1) EP39 19.9 ± 5.5 0.38 ± 0.11 6.67 ± 0.58 3.09 ± 0.37 5.33 ± 0.35 64.6 ± 7.4 67.3 ± 6.5 56.4 ± 4.0 18.9 ± 0.7 0.93 ± 0.25 Means EP42 54.9 ± 5.5 0.51 ± 0.11 6.82 ± 0.59 3.90 ± 0.37 7.37 ± 0.35 66.3 ± 7.4 67.6 ± 6.5 109.7 ± 4.0 15.5 ± 0.7 2.51 ± 0.25 F1 43.4 ± 4.0 0.32 ± 0.03 8.43 ± 0.16 5.97 ± 0.69 8.50 ± 0.10 59.2 ± 6.1 61.3 ± 5.7 132.5 ± 7.8 19.4 ± 0.3 6.67 ± 0.96 RILs 38.9 ± 4.0 0.42 ± 0.07 7.38 ± 0.12 4.05 ± 0.43 7.53 ± 0.21 66.8 ± 7.2 68.8 ± 6.3 93.7 ± 4.2 17.8 ± 0.3 1.80 ± 0.24  g2 39.3 ± 8.0** 0.098 ± 0.0557 0.55 ± 0.17** 0.632 ± 0.123** 7.88 ± 1.02** 9.05 ± 1.25** 121.2 ± 18.0** 0.82 ± 0.33** 0.37 ± 0.08** Variances  g2e 11.8 ± 6.6 1.23 ± 0.35** 2.31 ± 0.52** 26.5 ± 9.6** 1.59 ± 0.35** 0.26 ± 0.06** 0.080 ± 0.070 0.00 ± 0.00 1.148 ± 0.073** 2.68 ± 0.20** 0.041 ± 0.003** 1.217 ± 0.093**  e2 101.6 ± 6.3** 4.23 ± 0.26** 5.26 ± 0.32** 126.8 ± 7.9** 3.46 ± 0.21** 0.64 ± 0.04** 0.0016 ± 0.0006** 0.0013 ± 0.0007 0.01125 ± 0.0007** Estimates of means ± standard deviation, as well as of variance components were obtained for several agronomic and resistance traits after evaluation in two environments under artificial infestation with corn borer eggs a Kernel, Shank and cob damages were estimated on a 9 point scale (9 = without injury; 1 = wholly damaged) ** Variance component was significant at the 0.01 probability level