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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.

© The Author(s)., [Background]: Corn borers constitute an important pest of maize around the world; in particular Sesamia nonagrioides Lefèbvre, named Mediterranean corn borer (MCB), causes important losses in Southern Europe. Methods of selection can be combined with transgenic approaches to increase the efficiency and durability of the resistance to corn borers. Previous studies of the genetic factors involved in resistance to MCB have been carried out using bi-parental populations that have low resolution or using association inbred panels that have a low power to detect rare alleles. We developed a Multi-parent Advanced Generation InterCrosses (MAGIC) population to map with high resolution the genetic determinants of resistance to MCB., [Results]: We detected multiple single nucleotide polymorphisms (SNPs) of low effect associated with resistance to stalk tunneling by MCB. We dissected a wide region related to stalk tunneling in multiple studies into three smaller regions (at ~ 150, ~ 155, and ~ 165 Mb in chromosome 6) that closely overlap with regions associated with cell wall composition. We also detected regions associated with kernel resistance and agronomic traits, although the co-localization of significant regions between traits was very low. This indicates that it is possible the concurrent improvement of resistance and agronomic traits., [Conclusions]: We developed a mapping population which allowed a finer dissection of the genetics of maize resistance to corn borers and a solid nomination of candidate genes based on functional information. The population, given its large variability, was also adequate to map multiple traits and study the relationship between them., This research was funded by the Plan Estatal de Ciencia y Tecnología of Spain within the projects AGL2012–33415 and AGL2015–67313-C2–1 / 2-R, both of 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. The funding bodies played no role in the design of the study and collection, analysis, and interpretation of data and writing the manuscript. JCJG is grateful to the National Institute of Forestry, Agriculture and Livestock Research (INIFAP) and the National Council for Science and Technology (CONACYT) in Mexico for the fellowship that supported his Ph.D. research. BO and RS wishes to acknowledge their fellowships from the “Ramón y Cajal” program of the Spanish Ministry of Economy and Competitiveness.

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

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 pink stem borer (Sesamia nonagrioides Lef.) is the main corn (Zea mays L.) pest in the Mediterranean area. Although, screening for resistance to this pest has been successful, the level of resistance shown by the most resistant varieties is not high. The objectives of the present work were: (i) the evaluation for pink stem borer resistance of the nontested inbred lines, field and popcorn materials, from the collection maintained at the Mision Biologica de Galicia and (ii) the study of the performance, under pink stem borer infestation, of inbreds selected for resistance to pink stem borer in hybrid combination. Forty four inbred lines nontested yet for resistant to pink stem borer along with five inbred lines previously reported as resistant to stem and ear attack, were evaluated in 2002 and 2003. In adjacent experiments, hybrids EP79× W552, EP77× B93, and A661× EP42 were tested along with a resistant hybrid, MEB531-Bt, and a susceptible hybrid, INRA 260. New sources of resistance to pink stem borer have been detected among inbred lines improving the level of resistance presented by previously tested inbreds. Some of these lines were successfully developed by pedigree selection for resistance to pink stem borer.

The pink stem borer (Sesamia nonagrioides Lefèvbre) is the most important pest of maize (Zea mays L.) throughout the Mediterranean area. The maize composite EPS12 has been chosen as the base population for a breeding program based on its resistance to pink stem borer, with the main selection criterion being resistance to stem tunneling. Yield was taken as a secondary selection criterion to avoid any unwanted negatively correlated response on this character. The aims of investigation were: (1) to monitor the effects of selection for resistance to pink stem borer on allele frequency at 70 simple sequence repeat (SSR) markers and their impact on the genetic structure of EPS12 and (2) to identify loci at which allelic frequencies changed significantly due to directional selection. Genetic diversity was reduced during the selection process (as expected since random genetic drift as well as selection could reduce genetic variability), but not significantly so. Although the loss of genetic variation was generally consistent with that expected in a model in which random genetic drift acts alone on neutral alleles, the changes observed in the frequency of five alleles were significantly greater than expected. Further, the linear trend of the departure from the random genetic drift model was significant for some allelic versions of two SSR markers, umc1329 and phi076; directional selection was therefore acting on these loci. The significant effect of directional selection on those markers suggests the presence of quantitative trait loci (QTLs) for tunnel length and/or for yield under artificial infestation with Sesamia nonagrioides on the long arm of chromosome 4., This research supported by the National Plan of Research and Development of Spain (AGL2003-0961). R. Tarrío received support from contract DoctorI3P from the National Plan of Research and Development of Spain. This study was possible thanks to the invaluable laboratory work of Ana Carballeda, Begoña Giménez, and Elisa Santiago., MCYT

[Background] Corn borers are the primary maize pest; their feeding on the pith results in stem damage and yield losses. In this study, we performed a genome-wide association study (GWAS) to identify SNPs associated with resistance to Mediterranean corn borer in a maize diversity panel using a set of more than 240,000 SNPs., [Results] Twenty five SNPs were significantly associated with three resistance traits: 10 were significantly associated with tunnel length, 4 with stem damage, and 11 with kernel resistance. Allelic variation at each significant SNP was associated with from 6 to 9% of the phenotypic variance. A set of genes containing or physically close to these SNPs are proposed as candidate genes for borer resistance, supported by their involvement in plant defense-related mechanisms in previously published evidence. The linkage disequilibrium decayed (r2, [Conclusions] Most of the candidate genes found in this study are part of signaling pathways, others act as regulator of expression under biotic stress condition, and a few genes are encoding enzymes with antibiotic effect against insects such as the cystatin1 gene and the defensin proteins. These findings contribute to the understanding the complex relationship between plant-insect interactions., This work was supported by the National Plan for Research and Development of Spain (projects AGL2012-33415). L.F. Samayoa acknowledges a contract JAE-Predoc from the Spanish Council for Scientific Research (CSIC).