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23 p.-2 tab., Stem borers (Lepidoptera) are common cereal pests. In many parts of the world, the species Ostrinia nubilalis and Sesamia nonagrioides stand out as important insect pests of economically important crops such as maize. Their management relied mainly on transgenic host plant resistance over the last 25 years. Technologies based on the insecticidal properties of Bacillus thuringiensis-derived proteins allowed widespread pest population suppression, especially for O. nubilalis. However, the recent discovery of Bt resistance, which has revitalized interest in both pests’ biology and management, may jeopardize the effectiveness of such transgenic technologies. Historical information on O. nubilalis bionomy may need to be reassessed in light of changing climate conditions and changing agricultural practices, as well as increased production of alternate host crops across its distribution range. The current paper examines the bioecology and historical research that has been conducted to manage these two important maize-boring pests.

Higher hydroxycinnamate content makes maize tissues more recalcitrant to damage by insects, less digestible by ruminants, and less suitable for biofuel production. In a Genome Wide Association Analysis (GWAS) study carried out in a maize MAGIC population, we identified 24 SNPs associated with esterified cell wall-bound hydroxycinnamates, that represented 15 Quantitative Traic Loci (QTL). We identified new genomic regions associated to cell wall bound hydroxycinnamates in maize stover that could have an impact on their content across different genetic backgrounds. The high resolution QTL described in this study could be valuable for addressing positional mapping of genes involved in hydroxycinnamate biosynthesis and could uncover genes implicated in the esterification of hydroxycinnamic acids to the arabinoxylan chains that are poorly understood. However, we found that genetic correlation coefficients between hydroxycinnamate content and economical important traits such as saccharification efficiency, animal digestibility andi pest resistance were low to moderate, so modify specific hydroxycinnamates to indirectly improve cultivar performance will be unsuitable., This research has been developed in the frame of the “Agri-Food Research and Transfer Centre of the Water Campus (CITACA)” at the University of Vigo (Spain), which is economically supported by the Galician Government, and in the Mision ´ Biologica ´ de Galicia (CSIC). It was funded by the “Plan Estatal de Ciencia y Tecnología de Espana˜ ” (projects RTI2018–096776-B-C21, and RTI2018–096776-B-C22 cofinanced with European Union funds under the FEDER program). A. Lopez-Malvar ´ ’s scholarship for the PhD fulfilment has been granted by University of Vigo and by a contract charged to the project RTI2018–096776-B-C22. The funding body played no role in study design, data analysis and manuscript preparation.

Plant long-term response against chewing insects could become stronger than initial reactions and even turn into systemic. The objectives of the present study were 1) to evaluate whether the long-running attack to the stem by corn borers can improve the stem antibiotic properties; 2) to check whether hydroxycinnamic acids could be involved in this antibiotic response; 3) and to check whether elicitation by Sesamia nonagrioides Lef. (Lepidoptera: Noctuidae) regurgitant could activate long-term plant responses. In this sense, we observed that long-term feeding by S. nonagrioides larvae induced genotype-dependent changes in stem antibiosis and phenolic profiles, but the hydroxycinnamate content does not have a significant role in the systemic defense induced by the attack. In addition, response to long-term feeding by larvae could not be fully mimicked by elicitation using S. nonagrioides regurgitant alone. For the first time, it has been demonstrated that 'long-term' attack to the stem by corn borers can increase the stem antibiotic properties, and this has to be considered attending to breeding strategies.

Limited attention has been paid to maize (Zea mays L.) resistance induced by corn borer damage, although evidence shows that induced defenses have lower resource allocation costs than constitutive defenses. Maize responses to short- and long-term feeding by the Mediterranean corn borer (MCB, Sesamia nionagrioides) have been previously studied, but the suggested differences between responses could be due to experimental differences. Therefore, in the current study, a direct comparison between short- and long-term responses has been made. The objectives were (i) to determine changes in the level of antibiosis of the stems induced by feeding of S. nonagrioides larvae for 2days (short-term feeding) and 9days (long-term feeding), (ii) to characterize the metabolome of the stems’ short- and long-term responses to borer feeding, and (iii) to look for metabolic pathways that could modulate plant resistance to MCB. Defenses were progressively induced in the resistant inbred, and constitutive defenses were broken down in the susceptible inbred. Results suggest that the different resistance levels of the two inbreds to stem tunneling by MCB could depend on their ability to establish a systemic response. Based on these results, a high throughput look for specific metabolites implicated in systemic induced resistance to maize stem borers is recommended; the current focus on constitutive defense metabolites has not been successful in finding molecules that would be valuable tools for pest control. Agencia Estatal de Investigación | Ref. RTI2018-096776-B-C21 Agencia Estatal de Investigación | Ref. RTI2018-096776-B-C22

Cellulosic ethanol derived from fast growing C4 grasses could become an alternative to finite fossil fuels. With the potential to generate a major source of lignocellulosic biomass, maize has gained importance as an outstanding model plant for studying the complex cell wall network and also to optimize crop breeding strategies in bioenergy grasses. A genome-wide association study (GWAS) was conducted using a subset of 408 Recombinant Inbred Lines (RILs) from a Multi-Parent Advanced Generation Intercross (MAGIC) Population in order to identify single nucleotide polymorphisms (SNPs) associated with yield and saccharification efficiency of maize stover. We identified 13 SNPs significantly associated with increased stover yield that corresponded to 13 QTL, and 2 SNPs significantly associated with improved saccharification efficiency, that could be clustered into 2 QTL. We have pointed out the most interesting SNPs to be implemented in breeding programs based on results from analyses of averaged and yearly data. Association mapping in this MAGIC population highlight genomic regions directly linked to traits that influence the final use of maize. Markers linked to these QTL could be used in genomic or marker-assisted selection programs to improve biomass quality for ethanol production. This study opens a possible optimisation path for improving the viability of second-generation biofuels., This research has been developed in the frame of the ‘Agri-Food Research and Transfer Centre of the Water Campus (CITACA) at the University of Vigo (Spain), which is economically supported by the Galician Government and in the MIsión Biológica de Galicia-CSIC. It was funded by the “Plan Estatal de Ciencia y Tecnología de España” (projects RTI2018–096776-B-C21, and RTI2018–096776-B-C22 co-fnanced with European Union funds under the FEDER program). A. López-Malvar’s scholarship for the PhD fulflment has been granted by University of Vigo and by a contract charged to the project RTI2018–096776-B-C22. R. Santiago’s postdoctoral contract “Ramón y Cajal” has been fnanced by the Ministry of Economy and Competiveness (Spain), Vigo University, and the European Social Fund. D. Figueroa-Garrido contract was funded by the project RTI2018–096776-B-C22. The funding body played no role in study design, data analysis, and manuscript preparation.

Forage feedstock is the greatest source of energy for livestock. Unfortunately, less than 50% of their fiber content is actually digested and assimilated by the ruminant animals. This recalcitrance is mainly due to the high concentration of plant cell wall material and to the limited digestion of the fiber by the microorganisms. A Genome-Wide Association Study (GWAS) was carried out in order to identify Single Nucleotide Polymorphisms (SNPs) associated with forage digestibility traits in a maize Multi-Parent Advanced Generation Intercross (MAGIC) population. We identified seven SNPs, corresponding to five Quantitative Trait Loci (QTL), associated to digestibility of the organic matter, 11 SNPs, clustered in eight QTLs, associated to Neutral Detergent Fiber (NDF) content and eight SNPs corresponding with four QTL associated with Acid Detergent Fiber (ADF). Candidate genes under the QTL for digestibility of the organic matter could be the ones involved in pectin degradation or phenylpropanoid pathway. Transcription factor genes were also proposed for the fiber QTL identified, in addition to genes induced by oxidative stress, or a gene involved in lignin modifications. Nevertheless, for the improvement of the traits under study, and based on the moderate heritability value and low percentage of the phenotypic variability explained by each QTL, a genomic selection strategy using markers evenly distributed across the whole genome is proposed., This research has been developed in the frame of the ‘Agri-Food Research and Transfer Centre of the Water Campus (CITACA) at the University of Vigo (Spain), which is economically supported by the Galician Government and in the Misión Biológica de Galicia-CSIC. It was funded by the “Plan Estatal de Ciencia y Tecnología de España” (projects RTI2018–096776-B-C21, RTI2018–096776-B-C22, and PID2019-108127RB-I00 co-financed with European Union funds under the FEDER program). A. López-Malvar’s scholarship for the PhD fulfilment has been granted by University of Vigo and by a contract charged to the project RTI2018–096776-B-C22.

The cell wall putatively plays a role in host-plant resistance to phytopathogens. Here, we investigated which cell wall-bound phenolic compounds have determining roles in maize (Zea mays) resistance to attack by the Mediterranean corn borer Sesamia nonagrioides (Lefebvre). Diverse sets of maize genotypes having contrasting hydroxycinnamate contents and borer resistance levels were evaluated. The interdependent relationships among some cell wall-bound phenolic compounds, such as ferulic acid and its dimers, or p-coumaric acid and syringyl lignin subunits, were analyzed. Both p-coumaric acid and syringyl momoners showed significant negative correlations with damage, as assessed by tunnel lengths, caused by S. nonagrioides larvae. Thus, the use of cell wall-bound p-coumaric acid in pest-resistant crop breeding programs is advisable.

Food contamination with mycotoxins is a worldwide concern, because these toxins produced by several fungal species have detrimental effects on animal and/or human health. In maize, fumonisins are among the toxins with the highest threatening potential because they are mainly produced by Fusarium verticillioides, which is distributed worldwide. Plant breeding has emerged as an effective and environmentally safe method to reduce fumonisin levels in maize kernels, but although phenotypic selection has proved effective for improving resistance to fumonisin contamination, further resources should be mobilized to meet farmers’ needs. Selection based on molecular markers linked to quantitative trait loci (QTL) for resistance to fumonisin contamination or/and genotype values obtained using prediction models with markers distributed across the whole genome could speed up breeding progress. Therefore, in the current paper, previously identified genomic regions, genes, and/or pathways implicated in resistance to fumonisin accumulation will be reviewed. Studies done until now have provide many markers to be used by breeders, but to get further insight on plant mechanisms to defend against fungal infection and to limit fumonisin contamination, the genes behind those QTLs should be identified. Agencia Estatal de Investigación | Ref. RTI2018-096776-B-C21 Agencia Estatal de Investigación | Ref. RTI2018-096776-B-C22

[Background] Plant breeding has been proposed as one of the most effective and environmentally safe methods to control fungal infection and to reduce fumonisin accumulation. However, conventional breeding can be hampered by the complex genetic architecture of resistance to fumonisin accumulation and marker-assisted selection is proposed as an efficient alternative. In the current study, GWAS has been performed for the first time for detecting high-resolution QTL for resistance to fumonisin accumulation in maize kernels complementing published GWAS results for Fusarium ear rot., [Results] Thirty-nine SNPs significantly associated with resistance to fumonisin accumulation in maize kernels were found and clustered into 17 QTL. Novel QTLs for fumonisin content would be at bins 3.02, 5.02, 7.05 and 8.07. Genes with annotated functions probably implicated in resistance to pathogens based on previous studies have been highlighted., [Conclusions] Breeding approaches to fix favorable functional variants for genes implicated in maize immune response signaling may be especially useful to reduce kernel contamination with fumonisins without significantly interfering in mycelia development and growth and, consequently, in the beneficial endophytic behavior of Fusarium verticillioides., This research was funded by the Autonomous Government of Galicia, Spain (project IN607A/013), and by the “Secretaría de Estado de Investigación, Desarrollo e Innovación”, Spain, within the projects AGL2015–67313-C2–1-R and AGL2015–67313-C2–2-R, which were co-financed with European Social Funds. R. Santiago acknowledges postdoctoral contract “Ramón y Cajal” financed by the “Secretaría de Estado de Investigación, Desarrollo e Innovación” and co-financed by the “Universidad de Vigo”, Spain, and the European Social Funds.

Elevational gradients have been highly useful for understanding the underlying forces driving variation in plant traits and plant-insect herbivore interactions. A widely held view from these studies has been that greater herbivory under warmer and less variable climatic conditions found at low elevations has resulted in stronger herbivore selection on plant defences. However, this prediction has been called into question by conflicting empirical evidence, which could be explained by a number of causes such as an incomplete assessment of defensive strategies (ignoring other axes of defence such as defence inducibility) or unaccounted variation in abiotic factors along elevational clines. We conducted a greenhouse experiment testing for inter-specific variation in constitutive leaf chemical defences (phenolic compounds) and their inducibility in response to feeding by gypsy moth larvae (Lymantria dispar L., Lepidoptera) using saplings of 18 oak (Quercus, Fagaceae) species. These species vary in their elevational distribution and together span >2400 m in elevation, therefore allowing us to test for among-species elevational clines in defences based on the elevational range of each species. In addition, we further tested for elevational gradients in the correlated expression of constitutive defences and their inducibility and for associations between defences and climatic factors potentially underlying elevational gradients in defences. Our results showed that oak species with high elevational ranges exhibited a greater inducibility of phenolic compounds (hydrolysable tannins), but this gradient was not accounted for by climatic predictors. In contrast, constitutive defences and the correlated expression of constitutive phenolics and their inducibility did not exhibit elevational clines. Overall, this study builds towards a more robust and integrative understanding of how multivariate plant defensive phenotypes vary along ecological gradients and their underlying abiotic drivers.

The genetic basis of commercial maize (Zea mays L.) is quite narrow. The incorporation of exotic germplasm, i.e. all germplasm that does not have immediate usefulness without selection for adaptation, is a way of enhancing the genetic basis of the material that a breeder can use. The populations of maize ‘Purdue Synthetic A o2’ (Purdue A) and ‘Purdue Synthetic B o2’ (Purdue B) were subjected to 18 cycles of recurrent mas selection for early flowering in Northwestern Spain. To evaluate the efficiency of selection, the original populations, the cycles of selection 6, 12, and 18, and five hybrid checks were evaluated in four environments in Spain. Both populations responded positively to selection for earlier female flowering with linear regression being highly significant. The change in the number of days from planting to silking was similar in both populations (1.01 days to silking/cycle of selection). Plant height, kernel moisture at harvest, and yield decreased significantly in both populations. Selection for early silking was efficient and resulted on similar decreases of kernel moisture in both populations, but yield and biomass decreased strongly. Therefore, although we must pay careful attention to agronomical important traits, these early o2 populations can be incorporated to a breeding program under short season conditions., This work was supported by the Spanish Plan for Research and Development (project codes AGL2007- 64218/AGR, AGL2010-22254-C02-01, AGL2013-48852-C3- 1-R, and AGL2016-77628-R), and FEDER funds. Bernardo Ordás wishes to acknowledge his grant from the ‘‘Ramón y Cajal’’ program of the Spanish Ministry of Economy and Competitiveness

8 páginas, 6 figuras y 1 tabla., Alternative approaches to linkage and association mapping using inbred panels may allow further insights into loci involved in resistance to Fusarium ear rot and lead to the discovery of suitable markers for breeding programs. Here, the suitability of a maize multiparent advanced generation intercross population for detecting quantitative trait loci (QTLs) associated with Fusarium ear rot resistance was evaluated and found to be valuable in uncovering genomic regions containing resistance-associated loci in temperate materials. In total, 13 putative minor QTLs were located over all of the chromosomes, except chromosome 5, and frequencies of favorable alleles for resistance to Fusarium ear rot were, in general, high. These findings corroborated the quantitative characteristic of resistance to Fusarium ear rot in which many loci have small additive effects. Present and previous results indicate that crucial regions such as 210 to 220 Mb in chromosome 3 and 166 to 173 Mb in chromosome 7 (B73-RefGen-v2) contain QTLs for Fusarium ear rot resistance and fumonisin content., This research was funded by the “Plan Estatal de Ciencia y Tecnologia de España” within the projects AGL2015-67313-C2-1-R and AGL2015-67313-C2-2-R, which were co-financed with European Union funds under the FEDER program, and the project IN607A/013 funded by the Autonomous Government of Galicia, Spain. R. Santiago acknowledges postdoctoral contract “Ramón y Cajal” financed by the Ministry of Economy and Competiveness (Spain), Vigo University, and the European Social Fund.

4 páginas y 3 tablas, Two decades of investigations on maize resistance to Mediterranean corn borer (Sesamia nonagrioides Lefebvre; MCB) have shown that breeding for increased resistance to stem tunnelling by MCB often resulted in reduced yield because significant genetic correlation between both traits exists in some backgrounds. Unlike phenotypic selection, marker-assisted selection (MAS) could differentiate markers linked only to one trait from those linked simultaneously to yield potential and susceptibility to the pest. In the current study, the suitability of MAS for improving resistance to stem tunnelling without adverse effects on yield has been tested. The unfavourable genetic relationship between yield potential and susceptibility could be overcome using MAS. Gains obtained using MAS were weak, because genetic variance explained by the quantitative trait loci (QTL) was low but results encourage us to persevere in using marker information for simultaneous improvement of resistance and yield especially if genome-wide approaches are applied. Approaches to detect QTL are widely used, but studies on the suitability of markers linked to QTL for performing MAS have been mostly neglected., This research was supported by the National Plan for Research and Development of Spain (AGL2015-67313-C2-1-R), and co-financed by the European Social Fund

Biogeographical factors and phylogenetic history are key determinants of inter-specific variation in plant defences. However, few studies have conducted broad-scale geographical comparisons of plant defences while controlling for phylogenetic relationships, and, in doing so, none have separated constitutive from induced defences. This gap has limited our understanding of how historical or large-scale processes mediate biogeographical patterns in plant defences since these may be contingent upon shared evolutionary history and phylogenetic constraints. We conducted a phylogenetically-controlled experiment testing for differences in constitutive leaf chemical defences and their inducibility between Palearctic and Nearctic oak species (Quercus, total 18 species). We induced defences in one-year old plants by inflicting damage by gypsy moth larvae (Lymantria dispar), estimated the amount of leaf area consumed, and quantified various groups of phenolic compounds. There was no detectable phylogenetic signal for constitutive or induced levels of most defensive traits except for constitutive condensed tannins, as well as no phylogenetic signal in leaf herbivory. We did, however, find marked differences in defence levels between oak species from each region: Palearctic species had higher levels of constitutive condensed tannins, but less constitutive lignins and less constitutive and induced hydrolysable tannins compared with Nearctic species. Additionally, Palearctic species had lower levels of leaf damage compared with Nearctic species. These differences in leaf damage, lignins and hydrolysable (but not condensed) tannins were lost after accounting for phylogeny, suggesting that geographical structuring of phylogenetic relationships mediated biogeographical differences in defences and herbivore resistance. Together, these findings suggest that historical processes and large-scale drivers have shaped differences in allocation to constitutive defences (and in turn resistance) between Palearctic and Nearctic oaks. Moreover, although evidence of phylogenetic conservatism in the studied traits is rather weak, shared evolutionary history appears to mediate some of these biogeographical patterns in allocation to chemical defences.

The estimate of worldwide annual yield loss in maize due to pests ranges from 7 to 20%. Insects are among the most important pests of maize at all stages of development, from germination to grain filling, and can even be the main spoilers of grains in storage facilities. Each particular insect species shows preference for attacking a specific maize tissue, although other tissues are also susceptible to attack. Insect control has been achieved by diverse approaches, such as the use of insecticides, the modification of cultural practices, the use of biological methods involving parasitoids and sex pheromone-based mate-finding disruption, and the use of resistant cultivars based on monogenic or polygenic resistance. This chapter addresses the current knowledge about genomic regions and genes responsible for maize resistance to insect attack. The information on quantitative trait loci (QTL) and genes involved in resistance has been divided into six sections: (1) soil insects, (2) leaf feeders, (3) stem borers, (4) ear borers, (5) granary pests, and (6) relationships between maize genomics for resistance to insect and agronomical performance.

The objective of this study was to investigate the stability, across well-differentiated environments, of genetic control of maize resistance to Fusarium graminearum and Fusarium verticillioides ear rots and mycotoxin contamination, found in genotypes of diverse origin and adapted to different environments. This knowledge will help to design the most appropriate breeding programme to reduce mycotoxin content across a wide range of environments. Although maize genetics involved in resistance to ear rots and mycotoxin contamination greatly depended on the environment, additive and dominance effects were the predominant genetic effects in most environments. The stability across environments for resistance to ear rots and deoxynivalenol and fumonisin contamination was low, and recommended target areas of breeding programmes for either Fusarium species are different based on the different nature of genetic effect × environment interactions for each species. In general, the classification of inbreds and hybrids according to their resistance levels was similar across environments, suggesting that the same sources of resistance could be suitable for different environments, and breeding for resistance to one species would affect resistance to the other one., This research was supported by the National Plan for Research and Development of Spain (AGL2009-12770). R.S. acknowledges postdoctoral contracts ‘Isidro Parga Pondal’ supported by the Autonomous Government of Galicia and the European Social Fund and ‘Ramón y Cajal’ supported by the Ministry of Economy and Competitiveness of Spain. Funding for the Canadian part of this project was in part by an AAFC partnership with the Canadian Field Crop Research Alliance (CFCRA) though AAFC's Developing Innovative Agri-Products Initiative of the Growing Canadian Agri-Innovations Program., Ministerio de Economía y Competitividad (España, Xunta de Galicia, Agriculture and Agri-Food Canada

Plants defend themselves against herbivores by activating a plethora of genetic and biochemical mechanisms aimed at reducing plant damage and insect survival. The short-term plant response to insect attack is well understood, but less is known about the maintenance of this response over time. We performed transcriptomic and metabolomics analyses in order to identify genes and metabolites involved in the long-term response of maize to attack by the corn borer Sesamina nonagrioides. To determine the role of elicitors present in caterpillar secretions, we also evaluated the response of maize stem challenged with insect regurgitates. The integrative analysis of the omics results revealed that the long-term response in maize is characterized by repression of the primary metabolism and a strong redox response, mainly mediated by germin-like proteins to produce anti-nutritive and toxic compounds that reduce insect viability, and with the glutathione–ascorbate cycle being crucial to minimize the adverse effects of reactive oxygen species (ROS) on the plant. Our results suggest that different defense mechanisms are involved in the long-term response compared to those reported during the early response. We also observed a marginal effect of the caterpillar regurgitates on the long-term defensive response.

[Background] Sesamia nonagrioides Lefebvere (Mediterranean corn borer, MCB) is the main pest of maize in the Mediterranean area. QTL for MCB stalk tunneling and grain yield under high MCB infestation had been located at bin 8.03–8.05 (4–21 cM and 10–30 cM respectively) in a previous analysis of the EP42 x EP39 RILs mapping population. The objective of the present work was to study with higher resolution those QTL, and validating and estimating with higher precision their locations and effects. To achieve this objective, we developed a set of 38 heterogeneous inbred families (HIFs) which were near-homozygous in the genome, except in the region under study. The HIFs were evaluated in multiple environments under artificial infestation with MCB and genotyped with SNPs., [Results] The QTL for grain yield under high infestation was confirmed with higher precision and improved reliability at 112.6–116.9 Mb. On the contrary, the location of the QTL for stalk tunneling was not validated probably due to the fixation of some genomic regions during the development of the HIFs. Our study confirmed that the co-localization of the QTL for stalk tunneling and grain yield in the previous study was due to linked genes, not to pleiotropic effects. So, the QTL for grain yield can be used for improving grain yield without undesirable effect on stalk tunneling., [Conclusions] The HIF analysis is useful for validating QTL and for conducting deeper studies in traits related to corn borer resistance., This research was funded by the Plan Estatal de Ciencia y Tecnologia de España within the projects AGL2012–33415 and AGL2015–67313-C2–1-R, both of which were co-financed with European Union funds under the FEDER program.

[Background] Plants can respond to insect attack via defense mechanisms that reduce insect performance. In this study, we examined the effects of several treatments applied to two maize genotypes (one resistant, one susceptible) on the subsequent growth and survival of Sesamia nonagrioides Lef. (Mediterranean corn borer, MCB) larvae. The treatments were infestation with MCB larvae, application of MCB regurgitant upon wounding, wounding alone, or exposure to methyl jasmonate, and they were applied at the V6–V8 stage of maize development. We also monitored changes in the concentrations of compounds known to be involved in constitutive resistance, such as cell wall-bound hydroxycinnamates and benzoxazinoids., [Results] In both maize genotypes, the leaves of plants pre-infested with MCB larvae were less suitable for larval development than those from untreated plants. Application of MCB regurgitant upon wounding, and wounding itself, resulted in leaf tissues becoming less suitable for larval growth than those of pre-infested plants, suggesting that there could be herbivore-associated effector molecules that suppress some wounding responses. A single application of MCB regurgitant did not seem to mimic feeding by MCB larvae, although the results suggested that regurgitant deposited during feeding may have enhanced ferulates and diferulates synthesis in infested vs. control plants. Jasmonic acid may play a role in mediating the maize response to MCB attack, but it did not trigger hydroxycinnamate accumulation in the leaves to a level comparable to that induced by larval leaf feeding. The EP39 maize genotype showed an increase in leaf cell wall strength by increasing hemicellulose cross-linking in response to MCB attack, while induced defenses in the EP42 plants appeared to reflect a broader array of resistance mechanisms., [Conclusions] The results indicated that leaf feeding by MCB larvae can increase leaf antibiosis against MCB in two maize genotypes with contrasting levels of resistance against this borer. Also, the larval regurgitant played a positive role in eliciting a defense response. We determined the effects of the plant response on larval growth, and detected defense compounds related to borer resistance., This research was supported by the National Plan for Research and Development of Spain (AGL2012-33415, AGL2015-67313-C2-1-R, and AGL2015-67313-C2-2-R) co-financed by the European Social Fund (FEDER). R. Santiago acknowledges postdoctoral contract “Ramón y Cajal” financed by the Ministry of Economy and Competitiveness (Spain), Vigo University, and the European Social Fund.

Fusarium ear rot is a common disease of maize that affects food and feed quality globally. Resistance to the disease is highly quantitative, and maize breeders have difficulty incorporating polygenic resistance alleles from unadapted donor sources into elite breeding populations without having a negative impact on agronomic performance. Identification of specific allele variants contributing to improved resistance may be useful to breeders by allowing selection of resistance alleles in coupling phase linkage with favorable agronomic characteristics. We report the results of a genome-wide association study to detect allele variants associated with increased resistance to Fusarium ear rot in a maize core diversity panel of 267 inbred lines evaluated in two sets of environments. We performed association tests with 47,445 singlenucleotide polymorphisms (SNPs) while controlling for background genomic relationships with a mixed model and identified three marker loci significantly associated with disease resistance in at least one subset of environments. Each associated SNP locus had relatively small additive effects on disease resistance (±1.1% on a 0-100% scale), but nevertheless were associated with 3 to 12% of the genotypic variation within or across environment subsets. Two of three identified SNPs colocalized with genes that have been implicated with programmed cell death. An analysis of associated allele frequencies within the major maize subpopulations revealed enrichment for resistance alleles in the tropical/subtropical and popcorn subpopulations compared with other temperate breeding pools. © 2013 Zila et al., This research was supported by the National Science Foundation (projects DBI-0321467, IOS- 0820619 and IOS-0604923), USDA-ARS, the National Plan for Research and Development of Spain (AGL2009-12770), and the Excma. Diputación Provincial de Pontevedra. USDA-ARS supported the graduate fellowship of C.T. Zila. R. Santiago acknowledges postdoctoral contract “Isidro Parga Pondal” supported by the Autonomous Government of Galicia and the European Social Fund., National Science Foundation, USDA-ARS, MICINN, Excma. Diputación Provincial de Pontevedra, Autonomous Government of Galicia, European Social Fund

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.

21 Pag., 2 Tabl. The definitive version is available at www.springerlink.com, Mediterranean corn borer (MCB) (Sesamia nonagrioides Lef) and European corn borer (ECB) (Ostrinia nubilalis Hbn) are the most important biotic stresses of maize in Europe. The first selection program to improve stalk resistance to MCB was carried out in the maize population EPS12. It has shown that selection was effective to improve stalk resistance to MCB and ECB, while yield was not significantly diminished. The objective of this research was to determine if correlated changes in EPS12 occurred due to selection for resistance to MCB. Cycles of selection per se and testcrosses to three testers were evaluated under MCB and ECB artificial infestation at two different Spanish locations during 2 years. Selection has significantly reduced cob damage, days to silking, plant and ear height, and 100-kernel weight; meanwhile early vigor was increased. These changes could rather be a consequence of unconscious selection and/or the genetic correlation of these traits with resistance than a consequence of genetic drift., Research supported by the Plan Nacional I+D+I (AGL2003-00961 and AGL2006-1314). G. Sandoya acknowledges a fellowship from the Ministry of the Education and Science that allowed him to carry out this study; part of this study is a thesis by the senior author for the Ph.D. degree.

The Angoumois grain moth, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae), is found worldwide and infests maize grains in the field and during storage. Transgenic maize resistant to kernel attack by S. cerealella has been developed, but could pose a nutritional risk to humans and livestock. Therefore, alternative sources of resistance posing no threat to consumption should be identified. In this study, our main objectives were to assess genetic variability for kernel damage by S. cerealella under natural infestation and to determine genetic and environmental factors contributing to genotype, year, and genotype*year variability. Factorial regression was performed to obtain a biological explanation for the number of kernels damaged per ear. Seventy-seven Spanish maize landraces along with six hybrid checks were evaluated in 2004, 2005, and 2006. There was variability for kernel damage by natural infestation of S. cerealella among the landraces: popcorn landraces were among the least damaged, whereas hybrid checks were among the most susceptible genotypes. Plant characteristics associated with ear appearance could be the main stimulatory factors for oviposition and feeding of S. cerealella moths, followed by husk coverage of the ear. It was confirmed that temperature is the main environmental factor affecting S. cerealella development. Genotypes sensitive to infestation by S. cerealella were more negatively affected by higher temperatures than the least attractive genotypes, and lower temperatures reduced the number of kernels damaged on the most susceptible genotypes more than on the least susceptible., Research was supported by project RF03-007-C31 and the Excma. Diputación Provincial de Pontevedra. M.C. Romay acknowledges a fellowship from the Ministry of Education and Science of Spain., MEC, Diputación Provincial de Pontevedra

Recurrent selection has been reported as successful for improving maize resistance against corn borers. This study was conducted to determine if phenolics concentration in maize changes during recurrent selection to improve stalk resistance to the Mediterranean corn borer. Three cycles of selection [EPS12(S)C0, ESP12(S)C2, and EPS12(S)C3] from the maize synthetic population EPS12 and test crosses to inbred lines A639, B93, and EP42 were field grown and artificially infested with Mediterranean corn borer larvae, and the pith tissues were sampled for biochemical analyses. Two major simple phenolic acids [p-coumaric (p-CA) and trans-ferulic (E-FA) acids] were identified in free and cell-wall fractions, whereas four isomers of diferulic acid (DFA) (8−5′l, 5−5′, 8−o−4′, and 8−5′ benzofuran form) were present in the cell-wall bound fraction. The selection cycles EPS12(S)C0 and EPS12(S)C3 showed less damage and higher cell wall phenolics concentrations than the cycle EPS12(S)C2. In addition, higher concentrations of total DFAs were associated with shorter tunnel length and lower numbers of larvae per stem. The current study shows new and concrete evidence that the cell-wall bound phenolics could have a determinative role in the resistance to the Mediterranean corn borer, although future development of recurrent and divergent selection cycles will clarify this point.

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

B73 and Mo17 represent the main families of elite maize (Zea mays L.) inbred lines. B73 and Mo17 significantly differed in their proportion of germination under low-temperature conditions, and the IBM population derived from the cross B73 x Mo17 provides breeders a great opportunity for locating quantitative trait loci (QTLs) for cold tolerance in elite maize germplasm, the objective of this study. Under low-temperature conditions, the recombinant inbred lines significantly differed for all traits except vigor. No QTLs were detected at optimal conditions, but two QTLs involved in leaf color at low temperature were located in the short arm of chromosome 3 and the long arm of chromosome 6. The final fit for QTLs detected in our study explained 14.2% of phenotypic variance and 28.2% of genetic variance. However, in cross-validation analysis, QTLs detected in chromosomes 3 and 6 were detected in only 12.3% and 25.7% of all cross-validation runs, respectively, and explained 3.7% of the genetic variance. Although Mo17 could bring some favorable alleles, marker-assisted selection is not advisable because differences between allelic variants are small and explain a low proportion of genotypic variance. The locus luteus11 is proposed as a candidate gene for the QTL located in chromosome 6, while the QTL located in chromosome 3 probably corresponds to an unknown gene., We thank the Maize Genetic Cooperation Stock Center for germplasm and the Maize Genetics and Genomics Database for genotyping data. Research was supported by the National Plan for Research and Development AGL2004-06776), the Autonomous Government of Galicia (PGIDIT04RAG403006PR), and the Excelentísima Diputación Provincial de Pontevedra. V. M. Rodríguez acknowledges his fellowship from the Ministry of Science and Technology from Spain., MCYT, Diputación 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.