Bernardo Ordás

Genetic variation and quantitative trait loci associated with developmental stability and the environmental correlation between traits in maize

There is limited experimental information about the genetic basis of micro-environmental variance (V(E)) (developmental stability) and environmental correlations. This study, by using a population of maize recombinant inbred lines (RIL) and simple sequence repeat (SSR) polymorphic markers, aims at the following: firstly, to quantify the genetic component of the V(E) or developmental stability for four traits in maize and the environmental correlation between these traits, and secondly, to identify quantitative trait loci (QTLs) that influence these quantities. We found that, when estimating variances and correlations and testing their homogeneity, estimates and tests are needed that are not highly dependent on normality assumptions. There was significant variation among the RILs in V(E) and in the environmental correlation for some of the traits, implying genetic heterogeneity in the V(E) and environmental correlations. The genetic coefficient of variation of the environmental variance (GCV(V(E))) was estimated to be 20%, which is lower than estimates obtained for other species. A few genomic regions involved in the stability of one trait or two traits were detected, and these did not have an important influence on the mean of the trait. One region that could be associated with the environmental correlations between traits was also detected.

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

BackgroundOstrinia nubilalis (ECB) and Sesamia nonagrioides (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.ResultsThree 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.ConclusionsOur 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.

Adaptation of super-sweet maize to cold conditions: mutant × genotype interaction.

SUMMARY Super-sweet maize (shrunken2, sh2) has a longer post-harvest life than standard sweetcorn (sugary1, su1), but is less well-adapted to cold conditions. The objective of the present work was to determine if the replacement of su1 by sh2 alters the combining abilities of sweetcorn inbreds for adaptation to early planting under cold conditions. Two diallel sets of su1 and sh2 near-isogenic inbred lines were evaluated in a cold chamber and by early field planting. For most of the traits related to adaptation, except silking date, there were significant mutantrgenotype interactions and the estimates of general combining ability (GCA) of each version of the same inbred were different, probably due to epistasis. Therefore, to widen the genetic base of the super-sweet germplasm for adaptation, conversion of the earliest su1 inbreds to sh2, ignoring other characteristics such as emergence or early vigour in early planting or cold tests, is proposed.

Relationship between time to flowering and stalk and ear damage by second generation corn borers

ABSTRACT In the Mediterranean area, the main corn borer species are Sesamia nonagrioides Lefebvre (Mediterranean corn borer) and Ostrinia nubilalis Hübner (European corn borer). In the overall context of integrated pest control, it is possible to reduce the effect of a pest without having a negative effect on the environment by varying the sowing date. Benefits are possible if the most susceptible stages of the crop no longer coincide with the peak of the pest. We used different cycles of selection (0, 6, 8, 10, and 12) of two populations (Purdue A and Purdue B) of maize selected for early flowering to get a more precise estimation of the relationship between maturity of plant tissues and corn borer damage. We found a relationship between the damage produced by corn borers and the number of days from flowering to infestation. We conclude that, after flowering, a later stage of plant development at the moment of the infestation by corn borers reduces the damage caused by the larvae. Based on our results, we recommend to plant as early as possible so the tissues would be as mature as possible at the moment of insect attack.

Genomic regions affecting fitness of the sweet corn mutant sugary1

This research was supported by the Spanish Plan I+D (AGL2007-64218/AGR and AGL2010-22254) and the Excma. Diputacion Provincial de Pontevedra. A. Djemel acknowledges his fellowship from the Spanish Council for Scientific Research (CSIC).

Biomass, sugar, and bioethanol potential of sweet corn

Sweet corn is a widely distributed crop that generates agricultural waste without significant commercial value. In this study, we show that sweet corn varieties produce large amounts of residual biomass (10 t ha−1) with high content of soluble sugars (25% of dry matter) in a short growing season (3 months). The potential ethanol production from structural and soluble sugars extracted from sweet corn stover reached up to 4400 l ha−1 in the most productive hybrids, 33% of which (1500 l ha−1) were obtained by direct fermentation of free sugars. We found wide genetic variation for biomass yield and soluble sugars content suggesting that those traits can be included as complementary traits in sweet corn breeding programs. Dual‐purpose sweet corn hybrids can have an added value for the farmers contributing to energy generation without affecting food supply or the environment.

Genetic effects on fitness of the mutant sugary1 in wild-type maize

SUMMARY Knowing the genetic regulation of fitness is crucial for using mutants in breeding programmes, particularly when the mutant is deleterious in some genetic backgrounds, as it happens with the sweet corn mutant sugary1 (su1 )i n maize (Zea mays L.). The fitness and genetic effects of maize mutant su1 were monitored through five successive selfing generations in two separated mean-generation designs. The first involved two inbreds with similar genetic backgrounds, while unrelated inbreds were used for the second design. Parents, F1s, F2s, and backcrosses were crossed to P39 as the donor of su1 and the 12 crosses were successively self-pollinated for 5 years. The su1 frequency decreased linearly across selfing generations in both designs. Additive effects were significant for su1 seed viability. However, dominance effects were of higher magnitude than additive effects, even though the dominance effects were not significant. Genetic effects depended on genotypes and environments. Therefore, the fitness of su1 is under genetic control, with significant additive effects due to minor contributions of multiple genes. The fitness of su1 is strongly affected by maize genotypic background and environment. It is hypothesized that genotypes could have evolutionary potential for modulating the fitness of single mutations.

Redefining Agricultural Residues as Bioenergy Feedstocks

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.

Molecular changes during intra and inter recurrent selection of two populations of maize: one adapted and one non adapted to the selection environment

In several reciprocal recurrent selection (RRS) programs heterosis and favorable characteristics are achieved by means of one adapted and one non adapted population. We evaluated with molecular markers, an intrapopulation selection followed by RRS of one Spanish population adapted to Mediterranean Spain and one US Corn Belt population non adapted to Spanish conditions. Results from other authors suggest that during recurrent selection, non adapted populations have higher loss of variability, genetic differentiation and lower effective population size than expected according to the number of families selected each generation. This could be due to natural selection which is not under the breeder’s control and is expected to mainly act on non adapted populations. The number of markers with convergent allelic change was similar to the number of markers with divergent allelic change which explains the lack of genetic differentiation and the failure to increase heterosis during RRS because the effects of both types of changes compensate. It seems that the predominant mode of gene action depends on the particular germplasm involved in the RRS. By evaluating the allelic changes during selection, we identified four regions (2.04, 4.06, 6.03, 9.02) that significantly changed during selection in our selection experiment and that have been associated to selection in other selection experiments and to multiple traits in QTL experiments.

Corn borer (Lepidoptera: Noctuidae and Crambidae) resistance of main races of maize from North America.

Abstract Resistance to corn borers, Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) and Sesamia nonagrioides (Lefebvre) (Lepidoptera: Noctuidae) in maize, Zea mays L., populations is partial, and more resistant populations are needed. The objective of this research was to compare resistance to corn borers of the main maize races from North America. Twenty open-pollinated maize populations belonging to the races Southern Dent, Corn Belt Dent, and Northern Flint, and three check populations, were evaluated under artificial infestation with S. nonagrioides and O. nubilalis. None of the populations had complete resistance. Northern Flint had the lowest yield under corn borer infestation, whereas Southern Dent had the highest yield but also the largest damage. Corn Belt Dent had a shorter growing cycle and similar yield of infected plants than Southern Dent. The checks had intermediate yield and resistance and were not significantly different from Corn Belt Dent for any trait. The Southern Dent populations Tennessee Red Cob and White Dent (PI221885 and PI311232) could be used as sources of tolerance to corn borers, although they are not expected to provide great gains compared with the levels of tolerance already present in some Corn Belt Dent and European Flint populations and would require adaptation to short growing cycle. The Corn Belt Dent synthetic BS17 had the highest yield and general agronomic performance under corn borer infestation, along with Rustler and Silver King, and the European Flint composite EPS13.