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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

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).

© 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 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.

© 2020 by the authors., In this review, we present a comprehensive revisit of past research and advances developed on the stay-green (SG) paradigm. The study aims to provide an application-focused review of the SG phenotypes as crop residuals for bioenergy. Little is known about the SG trait as a germplasm enhancer resource for energy storage as a system for alternative energy. Initially described as a single locus recessive trait, SG was shortly after reported as a quantitative trait governed by complex physiological and metabolic networks including chlorophyll efficiency, nitrogen contents, nutrient remobilization and source-sink balance. Together with the fact that phenotyping efforts have improved rapidly in the last decade, new approaches based on sensing technologies have had an impact in SG identification. Since SG is linked to delayed senescence, we present a review of the term senescence applied to crop residuals and bioenergy. Firstly, we discuss the idiosyncrasy of senescence. Secondly, we present biological processes that determine the fate of senescence. Thirdly, we present the genetics underlying SG for crop-trait improvement in different crops. Further, this review explores the potential uses of senescence for bioenergy crops. Finally, we discuss how high-throughput phenotyping methods assist new technologies such as genomic selection in a cost-efficient manner., Part of this research was funded by the Spanish Plan for Research and Development (AGL2016-77628-R) and the European Regional Development Fund (FEDER).

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).