Is the basal area of maize internodes involved in borer resistance?

<p>Abstract</p> <p>Background</p> <p>To elucidate the role of the length of the internode basal ring (LIBR) in resistance to the Mediterranean corn borer (MCB), we carried out a divergent selection program to modify the LIBR using two maize synthetic varieties (EPS20 and EPS21), each with a different genetic background. We investigated the biochemical mechanisms underlying the relationship between the LIBR and borer resistance. Selection to lengthen or shorten the LIBR was achieved for each synthetic variety. The resulting plants were analyzed to determine their LIBR response, growth, yield, and borer resistance.</p> <p>Results</p> <p>In the synthetic variety EPS20 (Reid germplasm), reduction of the LIBR improved resistance against the MCB. The LIBR selection was also effective in the synthetic variety EPS21 (non-Reid germplasm), although there was no relationship detected between the LIBR and MCB resistance. The LIBR did not show correlations with agronomic traits such as plant height and yield. Compared with upper sections, the internode basal ring area contained lower concentrations of cell wall components such as acid detergent fiber (ADF), acid detergent lignin (ADL), and diferulates. In addition, some residual 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3-(4H)-one (DIMBOA), a natural antibiotic compound, was detected in the basal area at 30 days after silking.</p> <p>Conclusion</p> <p>We analyzed maize selections to determine whether the basal area of maize internodes is involved in borer resistance. The structural reinforcement of the cell walls was the most significant trait in the relationship between the LIBR and borer resistance. Lower contents of ADF and ADL in the rind of the basal section facilitated the entry of larvae in this area in both synthetic varieties, while lower concentrations of diferulates in the pith basal section of EPS20 facilitated larval feeding inside the stem. The higher concentrations of DIMBOA may have contributed to the lack of correlation between the LIBR and borer resistance in EPS21. This novel trait could be useful in maize breeding programs to improve borer resistance.</p

QTL mapping for Mediterranean corn borer resistance in European flint germplasm using recombinant inbred lines

<p>Abstract</p> <p>Background</p> <p><it>Ostrinia nubilalis </it>(ECB) and <it>Sesamia nonagrioides </it>(MCB) are two maize stem borers which cause important losses in temperate maize production, but QTL analyses for corn borer resistance were mostly restricted to ECB resistance and maize materials genetically related (mapping populations derived from B73). Therefore, the objective of this work was to identify and characterize QTLs for MCB resistance and agronomic traits in a RILs population derived from European flint inbreds.</p> <p>Results</p> <p>Three QTLs were detected for stalk tunnel length at bins 1.02, 3.05 and 8.05 which explained 7.5% of the RILs genotypic variance. The QTL at bin 3.05 was co-located to a QTL related to plant height and grain humidity and the QTL at bin 8.05 was located near a QTL related to yield.</p> <p>Conclusions</p> <p>Our results, when compared with results from other authors, suggest the presence of genes involved in cell wall biosynthesis or fortification with effects on resistance to different corn borer species and digestibility for dairy cattle. Particularly, we proposed five candidate genes related to cell wall characteristics which could explain the QTL for stalk tunnelling in the region 3.05. However, the small proportion of genotypic variance explained by the QTLs suggest that there are also many other genes of small effect regulating MCB resistance and we conclude that MAS seems not promising for this trait. Two QTLs detected for stalk tunnelling overlap with QTLs for agronomic traits, indicating the presence of pleitropism or linkage between genes affecting resistance and agronomic traits.</p

Defensive changes in maize leaves induced by feeding of Mediterranean corn borer larvae

[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.Peer reviewe

Combining abilities in maize for the length of the internode basal ring, the entry point of the Mediterranean corn borer larvae

Length of the internode basal ring (LIBR) in maize is a morphological character that has been associated with resistance to Mediterranean corn borer (MCB), Sesamia nonagrioides Lef. The present study is the first research to evaluate the usefulness of this trait in breeding programmes. Six maize hybrids, from a complete diallel set of four inbred lines (two resistant and two susceptible to MCB), were evaluated under early and late sowing conditions at three locations in northwestern Spain. General and specific combining ability (GCA and SCA, respectively) for LIBR were estimated, and LIBR correlations with grain yield and other important agronomic traits were evaluated. Hybrid by environment interactions were not significant for LIBR and the sums of squares partitioning indicated a greater GCA effect (95%), suggesting that this trait is stable and shows important additive effects for this set of hybrids. Correlation coefficients not only indicate that selection for increasing LIBR could enhance grain yield and other related plant traits (height and silking) but also an increase in the MCB susceptibility. Based on the limited number genotypes evaluated, LIBR could be modified by selection; however, if LIBR is used as an indirect selection criterion to improve MCB resistance, then some negative effects on yield may be expected.MICINNEuropean Social FundThis research was supported by the National Plan for Research and Development of Spain (Proje cts Cod. AGL2006-13140, AGL 2009-09611). J. Barros acknowledges a grant from the Ministry of Science and Innovation (Spain). R. Santiago acknowledges a postdoctoral contract “Juan de la Cierva” partially financed by the European Social Fund.Peer Reviewe

Genome-wide association analysis for fumonisin content in maize kernels

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.Xunta de Galicia | Ref. IN607A/013Ministerio de Economía | Ref. AGL2015–67313-C2–1-RMinisterio de Economía | Ref. AGL2015–67313-C2–2-

Combining abilities for maize stem antibiosis, yield loss and yield under infestation and no infestation with pink stem borer

The pink stem borer (Sesamia nonagrioides Lef.) is the main pest of maize (Zea mays L.) in northwestern Spain. Little is known about combining ability for antibiosis and tolerance to this pest. Therefore, the objectives of this work were to estimate general combining ability (GCA), specific combining ability (SCA), and reciprocal effects for stem damage traits, yield, and yield loss by a complete diallel of 10 inbreds and to determine the most useful trait for evaluating the level of defense to pink stem borer. The diallel design was evaluated for 2 yr for stem damage traits, yield loss, and for yield under two conditions, infestation with Sesamia nonagrioides and non infestation. For all stem damage traits, GCA was significant, while SCA and reciprocal effects were not significant. This indicated that, for this set of inbreds, only additive effects were important for stem antibiosis. GCA and SCA effects were significant, in at least one trial, for yield under both infestation conditions and for yield loss. Reciprocal effects were significant for yield of infested and non infested plants in 1995. The lack of concordance among lines that exhibited the most favorable GCA effects for stem antibiosis, yield loss, and yield under infested conditions and the low correlation coefficient between SCA effects for yield under infested and non infested conditions showed that yield under infested conditions is the best trait for evaluating the level of defense against pink stem borer attack.Research supported by the Committee for Science and Technology of Spain (project AGF92-0161) and by the Department of Education of the Autonomus Government of Galicia (project XUGA 40301B95).MCYTXunta de GaliciaN

Mapping of resistance to corn borers in a MAGIC population of maize

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 colocalization 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. Keywords: Maize, Mediterranean corn borer, Sesamia nonagrioides, Resistance, Mapping with multi-parent advanced generation InterCrosses (MAGIC) populations, Quantitative trait loci (QTL), Genome wide association analysis (GWAS)Xunta de Galicia | Ref. IN607A/013Ministerio de Economía | Ref. AGL2015-67313Ministerio de Economía | Ref. AGL2012-3341

Variability and mechanisms of drought tolerance in maize populations from Honduras

Maize breeding for drought tolerance requires searching mechanisms and sources of drought tolerance. We assessed drought tolerance at juvenile stages of development in a collection of open-pollinated maize populations from a dry area of Honduras. Eighteen Honduran populations were evaluated for the response of morphological, physiological and photosynthetic traits to increasing levels of water stress during germination, seedling and early growth. Water stress was imposed by using solutions of polyethylene glycol6000. The population Natual Olote Gordo faced drought by increasing root elongation; the population Langueño was able to maintain natural photosynthetic traits under drought conditions at a reasonable level; Capulin was drought tolerant at germination and early growth, and Maicito Montecristo maintained root biomass at seedling and early growth stages. At early growth, Castaño Sur, Maicito Montecristo, Negrito, Sangre de Cristo, and Tuy showed diminished conductance while there was no significantreduction in Langueño. Considering photosynthetic performance, the response to drought can be classifiedas resistance (Langueño) or tolerance (Capulín). Therefore, diverse mechanisms of drought adaptation are displayed by these populations depending on the feature measured and the stage of development. Different adaptive traits to drought at early stages of development could be combined by crossing the appropriate populations