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Senescence is a programmed process that involves the destruction of the photosynthesis apparatus and the relocation of nutrients to the grain. Identifying senescence-associated genes is essential to adapting varieties for the duration of the cultivation cycle. A genome-wide association study (GWAS) was performed using 400 inbred maize lines with 156,164 SNPs to study the genetic architecture of senescence-related traits and their relationship with agronomic traits. We estimated the timing of senescence to be 45 days after anthesis in the whole plant and specifically in the husks. A list of genes identified in a previous RNAseq experiment as involved in senescence (core senescence genes) was used to propose candidate genes in the vicinity of the significant SNPs. Forty-six QTLs of moderate to high effect were found for senescence traits, including specific QTLs for husk senescence. The allele that delayed senescence primarily increased grain yield and moisture. Seven and one significant SNPs were found in the coding and promoter regions of eight core senescence genes, respectively. These genes could be potential candidates for generating a new variation by genome editing for functional analysis and breeding purposes, particularly Zm00001d014796, which could be responsible for a QTL of senescence found in multiple studies. info:eu-repo/semantics/publishedVersion

Senescence is an important trait in maize (Zea mais L.), a key crop that provides nutrition values and a renewable source of bioenergy worldwide. Genome-wide association studies (GWAS) can be used to identify causative genetic variants that influence the major physiological measures of senescence, which is used by plants as a defense mechanism against abiotic and biotic stresses affecting its performance. We measured four physiological and two agronomic traits that affect senescence. Six hundred seventy-two recombinant inbred lines (RILs) were evaluated in two consecutive years. Thirty-six candidate genes were identified by genome-wide association study (GWAS), and 11 of them were supported by additional evidence for involvement in senescence-related processes including proteolysis, sugar transport, and sink activity. We identified a candidate gene, Zm00001d043586, significantly associated with chlorophyll, and independently studied its transcription expression in an independent panel. Our results showed that Zm00001d043586 affects chlorophyl rate degradation, a key determinant of senescence, at late plant development stages. These results contribute to better understand the genetic relationship of the important trait senescence with physiology related parameters in maize and provide new putative molecular markers that can be used in marker assisted selection for line development.

Stay-green (SG) is a term used to describe genotypes that have delayed leaf senescence as compared to reference genotypes. SG could be favorable for grain yield, silage yield and quality, double exploitation (grain for feed and stover for bioenergy), stress resistance, etc. However, some studies show contradictory results regarding the influence of senescence or SG in the uptake and remobilization of nutrients and the yield and moisture of stover and grain. This experiment is aimed to study the impact of senescence in grain and stover yield and moisture in inbred lines of maize and assess the potential of SG genotypes for double exploitation. We also study the influence of senescence in the uptake of N and remobilization of dry matter and N from stover to grain. We evaluated 16 maize inbred lines with contrasting expression of senescence in the field at two locations in Galicia in 2017. We confirmed that SG is functional, meaning that the SG genotypes maintained photosynthesis activity for a lengthy period. Coordinated with a delayed senescence, the grain filling of the SG genotypes was 9 days longer than NSG genotypes. SG genotypes took up more N after flowering, although the remobilization of N and, in general, of dry matter from stover to kernels was less efficient. However, the higher uptake compensated the poor remobilization, and the final effect of SG on the N content of the kernels was favorable. SG was also favorable for kernel weight and the kernels of SG genotypes were 20% heavier than for NSG. The stover yield was also higher in the SG genotypes, indicating a potential of SG for breeding for double purpose (grain for feed and stover for bioenergy)., This research was funded by a grant from the “Xunta de Galicia” (Project IN607D 2016/002).

Yellow maize (Zea mays L. var. indurata) is mainly produced in the Ecuadorian lowlands (less than 1,200 m a.s.l.), primarily for feed production. Although Ecuador has recently increased maize production, new genotypes are needed for self-sufficiency and in order to avoid costly imports. Maize is sown mostly from December to January during the rainy season. However, the irregularity of rainfall has become a constraint on production. "INIAP H-603 Superior" is a new single-cross maize hybrid developed for the Ecuadorian lowlands with improved yields, which could contribute to domestic food security. The new hybrid had an average yield of 8.48 t ha-1 with outstanding performance under the rainfall, sustained moisture, and irrigation conditions, outperforming the commercial hybrids INIAP H-602, DEKALB-7088 and INIAP H-553. Additionally, the new hybrid showed tolerance to the principal foliar diseases: leaf blight (Exserohilum turcicum), rust (Puccinia sorghi), and leaf spot (Curvularia lunata), as well as good adaptability and stability, with a regression coefficient (bi) of 0.98 when it was evaluated in 29 locations from 2010 to 2013. The greatest yield potential of the new hybrid (10.82 t ha-1) was obtained with irrigation during the dry season. RESUMEN El maíz amarillo duro (Zea mays L. var. indurata) es producido principalmente en las zonas bajas o costeras del Ecuador (menos de 1200 m s.n.m.) y está destinado mayoritariamente para la elaboración de alimento balanceado. A pesar de que la producción de este cereal en el Ecuador se ha incrementado en los últimos años, se requieren de nuevos genotipos que permitan la autosuficiencia y eviten importaciones de maíz. El cultivo de maíz es realizado principalmente en la época de lluvia, cuando las irregulares precipitaciones se convierten en las principales limitantes para la productividad del cultivo. "INIAP H-603 Superior" es un híbrido simple de maíz desarrollado para expresar su potencial bajo condiciones de riego, lluvia o humedad remanente. El nuevo híbrido obtuvo rendimientos promedios de 8.48 t ha-1, superando a los híbridos comerciales INIAP H-602, DEKALB-7088 e INIAP H-553 y mostró tolerancia a las principales enfermedades que afectaron al cultivo: lancha (Exserohilum turcicum), roya (Puccinia sorghi), y mancha por curvularia (Curvularia lunata); así como buena adaptabilidad y estabilidad de rendimiento, con un coeficiente de regresión (bi) de 0.98, basado en pruebas multi-ambiente en 29 localidades, realizadas del 2010 al 2013. El mayor potencial de rendimiento del nuevo híbrido (10.82 t ha-1) se obtuvo en la época seca bajo riego.

The ability to stay-green (SG) in later stages of the crop cycle is a valuable trait for plants cultivated in standard or stressful environments. Few QTLs studies for SG have been conducted in temperate maize, apart from some experiments carried out with Chinese lines. The aim of our study was to identify QTLs related to SG in temperate maize using PHG39, an important SG line in private breeding. We developed two large F2 mapping populations by crossing PHG39 to the no stay-green (NSG) lines B73 (Corn Belt Dent) and EA1070 (European flint). Samples of individuals of the extreme tails (high and low) of the populations for visual score were genotyped. We found an association between markers and SG in three regions at bins 1.04–1.09, 5.02 and 10.04–10.06. The association was strong for some markers in chromosome 1, for example, for bnlg1556 the frequency of the SG allele was 0.75 and 0.34 in the high and the low tail, respectively. Furthermore, for this marker the homozygote’s with the SG allele had 4 times more chlorophyll than the homozygote’s with the NSG allele 2 months after flowering. Some alleles most likely conferred SG because they increased the maximum chlorophyll content at flowering while other alleles did by diminishing the rate of senescence. The SG conferred by some alleles could be functional as some favourable alleles for SG were also favourable for kernel weight. Regardless of the physiological basis of the SG, the significant markers detected could be useful for marker assisted selection., Part of thesis submitted by M Kante in partial fulfilment of requirements for a MS degree from the International Centre for Advanced Mediterranean Agronomic Studies (CIHEAM). Research supported by the Spanish National Plan for Research and Development (project code AGL2010-22254/C02-00 and AGL2013-48852-C3-1-R). M Kante acknowledges a Grant from the West Africa Agricultural Productivity Program (WAAPP) and B Ordás a “Ramon y Cajal” contract from the Ministry of Economy and Competitiveness of Spain.

[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.

The use of plant biomass is a sustainable alternative to the reduction of CO2 emissions. Agricultural residues are interesting bioenergy feedstocks because they do not compete with food and add extra value to the crop, which might help to manage these residues in many regions. Breeding crops for dual production of food and bioenergy has been reported previously, but the ideal plant features are different when lignocellulosic residues are burnt for heat or electricity, or fermented for biofuel production. Stover moisture is one of the most important traits in the management of agricultural waste for bioenergy production which can be modified by genetic improvement. A delayed leaf senescence or the stay-green characteristic contributes to higher grain and biomass yield in standard, low nutrient, and drought-prone environments. In addition, the stay-green trait could be favorable for the development of dual purpose varieties because this trait could be associated with a reduction in biomass losses and lodging. On the other hand, the stay-green trait could be detrimental for the management of agricultural waste if it is associated with higher stover moisture at harvest, although this hypothesis has been insufficiently tested. In this paper, a review of traits relevant to the development of dual purpose varieties is presented with particular emphasis on stover moisture and stay-green, because less attention has been paid to these important traits in the literature. The possibility of developing new varieties for combined production is discussed from a breeding perspective., We thank A. Ordás for his valuable comments and suggestions. Marlon Caicedo recognizes a grant from Scholarship Program of the Instituto Nacional de Investigaciones Agropecuarias (INIAP) of Ecuador, Jaime Barros gratefully acknowledges a grant from University of Santiago de Compostela (Spain), and Bernardo Ordás “Ramon y Cajal” contract from the Ministry of Economy and Competitiveness of Spain. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).

The pedigree method of breeding with visual selection for plant and/or ear appearance has been traditionally used in maize (Zea mays L.) breeding. We evaluated 121 F2:3 families for plant and ear appearance as well as for several objectively measured traits and estimated the heritability of the traits and the genetic correlations between them. Heritability was greater than zero for most traits and the genetic correlation between the intuitive selection indexes and several of the objective traits were moderate or even high. Based on these results we predicted that selection based on intuitive selection indices would improve several characteristics of the inbred lines simultaneously. To confirm this we developed 20 inbred lines using pedigree selection with visual per se selection (VPSS) and 20 inbred lines without selection. The selected inbreds had a higher average value than the unselected lines for several traits across different environments; for example, the selected lines were 17 cm taller and yielded 0.3 Mg ha−1 more than the unselected inbreds. Furthermore, testcrosses of the selected lines were, on average, taller and yielded about 0.5 Mg ha−1 more than testcrosses of the unselected lines. We conclude that, under certain conditions, VPSS can achieve a high effectiveness improving both the performance of the lines and the yield of their hybrids, Research supported by Spain’s National Plan for Research and Development (Project Cod AGL2010-22254-C02-01)., MICINN