Ordas et al. BMC Genomics 2010, 11:174 http://www.biomedcentral.com/1471-2164/11/174 to QTLs for stalk strength or cell wall compounds detected in other experiments, suggesting that genes involved in the synthesis of cell wall compounds in maize could be good candidate genes for resistance to corn borers. Thus, Flint-Garcia et al. [42] detected only one QTL for stalk strength in common across four populations which is approximately located in bin 3.05. Regarding cell wall main components, QTLs for neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL) and hemicellulose were detected in bins 1.01/1.02, 3.05/3.06 and 8.03/8.04 [43-47]. In addition, Barriere et al. [43] found cell wall-bound phe- nolic compounds (p-coumaric acid, esterified ferulic acid, etc) to be associated to the three genomic regions, particularly to bin 1.01/1.02. Silage corn digestibility for dairy cattle is related to cell wall characteristics [48] and therefore probably related to maize resistance to corn borers too. Thus, QTLs for silage corn digestibility were also detected in bins 1.01/1.02 and 3.05/3.06 [43,49]. Furthermore, out of the five expression QTL (eQTL) hotspots for silage corn digestibility detected by Shi et al. [50], the two main ones were in bins 8.03 and 3.05. The eQTL hotspot on bin 3.05 was co-localized with a QTL for cell wall digestibility, concluding the authors that the gene underlying QTL and eQTL are identical. In the region of bin 3.05 approximately 1000 protein- coding genes of rice and sorghum aligned to maize gen- ome http://www.plantgdb.org/ZmGDB/DisplayGeneAnn. php?ds=&q=. For that reason, the isogenization-assisted by molecular markers - of the QTL could narrow its interval and facilitate the clonation of genes. However, we propose some candidate genes according to the hypothesis that genes involved in cell wall biosynthesis or fortification confer also resistance to corn borers. Candidate genes for stem tunnelling were selected from the gene expression data repertory of cell wall biosynth- esis and assembly in maize contained in MAIZEWALL http://www.polebio.scsv.ups-tlse.fr/MAIZEWALL/index. html, the genes located in those QTL regions. We have found in the region 3.05 three genes from the phenyhl- propanoid pathway which is the pathway that controls the biosynthesis of monolignols, the monomers of lig- nins [51]. These genes are: a peroxidase (GRMZM2G103342, ctg126, AC211202: 70944-73152, http://www.maizesequence.org/Zea_mays2/geneview? db=core;gene=GRMZM2G103342), a laccase (GRMZM2G072780, ctg137, AC207620: 82019-85418, http://www.maizesequence.org/Zea_mays2/geneview? db=core;gene=GRMZM2G072780), and a p-coumarate- 3-hydroxylase (C3H) (GRMZM2G138074, ctg138, AC200558: 57765-60725, http://www.maizesequence. org/Zea_mays2/geneview?db=core;gen- e=GRMZM2G138074). In addition to the MAIZEWALL repertory of genes, we also searched in MaizeGDB for Page 6 of 10 genes related to cell wall biosynthesis located at the QTLs’ regions. In bin 3.05 lies a gene that codifies for the sucrose phosphate synthase 2 enzyme (ctg 131, between position 152605600 and 152708500, http:// www.maizegdb.org/cgi-bin/displaylocusrecord.cgi? id=96665) which is involved in cellulose biosynthesis [52]. The lax midrib1 gene which affects the midrib portion of the leaf [53] is also in the region (ctg 132, between position 161945000 and 163130800, http:// www.maizegdb.org/cgi-bin/displaylocusrecord.cgi? id=12405). Inbred lines of maize with lax midribs have lower levels of fiber, lignin and xylose and are more digestible than ‘normal’ inbreds [54]. The five genes at bin 3.05 constitute possible candidate genes for resis- tance to stalk tunneling that could be validated by an association study [55]. For stalk tunnel length the proportion of genotypic variance explained by the QTLs following cross valida- tion in our experiment was similar to that found by Papst et al. [34] and Ordas et al. [10]. Given the low number of detected QTL and the small proportion of genotypic variance explained, it is likely that the trait be regulated by many QTL of small effect. Therefore, according to different QTL experiments, for resistance to corn borer tunnelling the theoretical expectation of the efficacy of MAS for increasing resistance to corn borers is low and it can be concluded that MAS seems not promising. However, the genomic regions related to resistance to corn borer detected in this and others QTL experiments are useful as start points for fine map- ping in order to address, in the future, the cloning of genes related to resistance. Regarding the utility of the QTLs for maize breeding, we evaluated a sample of 118 of the RILs crossed to a tester (A641) in two different sowing dates in the same location and year (data not shown), and no QTLs for resistance were found in the testcross population. We found, consistently with a previous experiment with MCB [10], that MCB produce higher tunnels length than ECB [7,9,35]. In both experiments with MCB we found less QTLs for stalk tunnelling, 3 and 2 respectively, than the average number of QTLs reported for ECB stalk tunneling that ranged from six to nine [7,8,33-35]. As argued by Ordas et al. [10], it is possible that, due to the aggressiveness of the insect, most geno- types seem to be susceptible, although some of them carry a low level of resistance. This is in agreement with the phenotypic performance of the two parents and the segregation among RILs. Regarding the agronomic traits, the major QTL for flowering time detected at bin 8.05 is located within a consensus region of major effect [56] with at least two different QTLs: vgt1, recently cloned by Salvi et al. [57] and vgt2 [58]. The confidence interval of this QTL for