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Silverio García-Lara (2007)
Aunque en el mercado existe una amplia gama de variedades mejoradas, esta tecnología no está al alcance de muchos agricultores, porque muchas veces no es posible conseguirla en la zona objeto del presente estudio o porque su precio es muy elevado. Además, muchas de esas variedades no contienen todas las características que los agricultores del Estado de México requieren. Por tanto, en un ambiente de producción como el de esta zona del país, los maíces criollos locales, que han sido desarrollados durante varias generaciones, siguen siendo los más apropiados, por su adaptación y sus características de producción y consumo. Sin embargo, las variedades criollas, que han sido seleccionadas por los productores y los consumidores locales, pueden mejorarse con mayor rendimiento, tolerancia a la sequía, resistencia a las plagas postcosecha o mayor contenido de nutrientes. El objetivo del proyecto que aquí se describe es facilitar el mejoramiento del maíz criollo, capacitando a los productores, para que puedan participar en el proceso de mejoramiento de sus propios materiales, e incorporar las características que ellos necesitan por medio de cruzas con las variedades mejoradas.
Olaf Erenstein (1997)
La clave de la labranza de conservacion es el uso de los residuos como mantillo. Sin embargo, existe mucha confusion en relacion al termino labranza de conservacion, entre otras cosas por poner demasiado enfasis en la labranza. El laboreo es so1o uno de los factores que afecta la disponibilidad de los residuos en areas tropicales. Por ende, la conservacion de residuos parece un termino mas apropiado para estos ambientes. En Mexico la promocion de la labranza de conservacion hasta la fecha enfatizo la no- quema y la no-inVersion de suelo (el no barbechar). De hecho, estos dos factores son incompatibles con la conservacion de suficientes residuos para formar un mantillo efectivo. Sin embargo, hay que destacar que para llevar a cabo la conservacion de residuos es necesario ver todos sus usos en conjunto. O sea, no so1o la quema o el barbecho, sino tambien la extraccion productiva, el total de la incorporacion y el desgaste, ademas de la produccion de residuos. El conjunto de usos alternativos y la produccion se reune en el balance de residuos y este balance es particular para cada localidad.
Genomic prediction (GP) combines genomewide marker data with phenotypic data in a training population to predict the genomic estimated breeding values of untested individuals in a relevant testing population. Our objective was to evaluate the effects of population structure, genotype × trial, tester, and management interactions, and imputation methods on the accuracy of GP for grain yield in the CIMMYT’s African maize (Zea mays L.) program. The dataset included 2022 diverse breeding lines in 156 Stage 1 yield trials and 66,000 single-nucleotide polymorphism markers. The first two principal components from principal component analysis explained 10.5% of the variance in marker data. Based on marker data, five clusters were detected, but cluster of origin explained only 2% of the phenotypic variation. Prediction accuracy, assessed by cross validation, ranged from 0.20 to 0.36 within clusters and from 0.04 to 0.26 across clusters. Mean GP accuracy within clusters (0.27) outperformed pedigree-based prediction (0.03). Imputation methods did not strongly affect prediction accuracy. Testers and management had large effects. To achieve acceptable GP accuracy within such a diverse population, one can employ (i) a very large training population size, (ii) carefully planned and relevant testers, and (iii) common trial environments and management between the training and validation populations and related genetic materials.
В статье представлен обзор деятельности международных центров ИКАРДА и СИММИТ по улучшению сортов пшеницы в регионе Центральной Азии. В частности, описываются основные виды селекционной работы центров по созданию в регионе сортов с улучшенными хозяйственна-ценными свойствами -высокой урожайностью и устойчивостью к биотическим и абиотическим факторам и работы по интегрированной защите растений. Результаты такой деятельности способствуют подъему производства зерновых культур и всего сельского хозяйства в странах ЦА в целом.
Селекция Питомник Пшеница Сорт Международный Центр Интегрированная Защита AGRICULTURAL SCIENCES AND BIOTECHNOLOGY PUCCINIA SORGHI GENOMES MAIZE WHEAT INTEGRATED PROTECTION VARIETY CIENCIAS AGROPECUARIAS Y BIOTECNOLOGÍA
La production du maïs (zea mays) en afrique au sud du sahara est constamment menacée par l'apparution de multiple infections des feuilles par le streak, le mildiou, le brunissement des feuilles et moisissures. L'augmentation de la résistance a cette maladie peut apporter une importante composante de gestion intégrée de la peste (ipm). Dans cet article, l'approche de croisement assiste des marqueurs conventionels et moléculaires sont présentés et les stratégies d'amélioration de la résistance de la plante hote sont présentées. Les facteurs de résistances pyramidiques et quantitatives utilisant la technique de croisement moléculaires seront facilités à travers les efforts de recherches coopératives et l'adoption d'une approache expérimentale appropriée.
Genomic selection (GS) as a promising molecular breeding strategy has been widely implemented and evaluated for plant breeding, because it has remarkable superiority in enhancing genetic gain, reducing breeding time and expenditure, and accelerating the breeding process. In this study the factors affecting prediction accuracy (rMG) in GS were evaluated systematically, using six agronomic traits (plant height, ear height, ear length, ear diameter, grain yield per plant and hundred-kernel weight) evaluated in one natural and two biparental populations. The factors examined included marker density, population size, heritability, statistical model, population relationships and the ratio of population size between the training and testing sets, the last being revealed by resampling individuals in different proportions from a population. Prediction accuracy continuously increased as marker density and population size increased and was positively correlated with heritability; rMG showed a slight gain when the training set increased to three times as large as the testing set. Low predictive performance between unrelated populations could be attributed to different allele frequencies, and predictive ability and prediction accuracy could be improved by including more related lines in the training population. Among the seven statistical models examined, including ridge regression best linear unbiased prediction (RR-BLUP), genomic BLUP (GBLUP), BayesA, BayesB, BayesC, Bayesian least absolute shrinkage and selection operator (Bayesian LASSO), and reproducing kernel Hilbert space (RKHS), the RKHS and additive-dominance model (Add + Dom model) showed credible ability for capturing non-additive effects, particularly for complex traits with low heritability. Empirical evidence generated in this study for GS-relevant factors will help plant breeders to develop GS-assisted breeding strategies for more efficient development of varieties.
Mainassara Zaman-Allah Omar Vergara Diaz Jose Luis Araus Pablo J. Zarco-Tejada Alberto Hornero Cosmos Magorokosho Biswanath Das Amsal Tarekegne Jill Cairns Prasanna Boddupalli Michael Olsen Peter Craufurd (2015)
Recent developments in unmanned aerial platforms (UAP) have provided research opportunities in assessing land allocation and crop physiological traits, including response to abiotic and biotic stresses. UAP-based remote sensing can be used to rapidly and cost-effectively phenotype large numbers of plots and field trials in a dynamic way using time series. This is anticipated to have tremendous implications for progress in crop genetic improvement. Results: We present the use of a UAP equipped with sensors for multispectral imaging in spatial field variability assessment and phenotyping for low-nitrogen (low-N) stress tolerance in maize. Multispectral aerial images were used to (1) characterize experimental fields for spatial soil-nitrogen variability and (2) derive indices for crop performance under low-N stress. Overall, results showed that the aerial platform enables to effectively characterize spatial field variation and assess crop performance under low-N stress. The Normalized Difference Vegetation Index (NDVI) data derived from spectral imaging presented a strong correlation with ground-measured NDVI, crop senescence index and grain yield. Conclusion: This work suggests that the aerial sensing platform designed for phenotyping studies has the potential to effectively assist in crop genetic improvement against abiotic stresses like low-N provided that sensors have enough resolution for plot level data collection. Limitations and future potential uses are also discussed.
Conservation agriculture (CA) based on the principles of minimum soil disturbance, crop residue retention, and crop rotation has been the focus of intensive research in recent years. A study was carried out to determine the effects of tillage and fertilizer on the population densities of plant-parasitic nematodes in maize. Three tillage regimes, (i) basin planting, (ii) rip line seeding, and (iii) conventional tillage, were combined with four fertilizer regimes: (i) no-fertilizer, (ii) low fertilizer rate, (iii) medium fertilizer rate, and (iv) high fertilizer rate. The experiment was arranged as a split plot in randomized complete block design, replicated three times with tillage as the main plot factor and fertilizer as the sub-plot factor. The study was conducted on fine-textured Cambisol soils at Chinhoyi University of Technology farm, Zimbabwe, over two cropping seasons between December 2014 and April 2016. Eight plant-parasitic nematode genera were observed belonging to five groups based on their feed in sites: (i) sedentary endoparasites (Meloidogyne and Rotylenchulus), (ii) migratory endoparasites (Pratylenchus), (iii) semi-endoparasites (Scutelonema and Helicotylenchus), (iv) ectoparasites (Xiphinema and Trichodorus), and (v) algal, lichen or moss feeders (Tylenchus). In both cropping seasons, semi-endoparasitic nematodes were double under rip line seeding and triple under basin planting compared to conventional tillage. Basin planting had higher plant-parasitic nematode richness than rip line seeding. Nematode densities did not have a measurable effect on maize grain yield. Maize grain yield was higher in rip line seeding (37%) and planting basins (52%) than conventional tillage during 2014/15 cropping season. On the other hand, during 2015/16 cropping season, maize grain yield was 78% and 113% higher in rip line seeding and basin planting, respectively, compared to conventional tillage. The results show that under the environmental and edaphic conditions of this specific study site, semi-endoparasitic ematodes were higher under rip line seeding and basin planting compared to conventional tillage. The authors conclude that (i) plant-parasitic nematode genera exhibited differential responses to different tillage systems but were not affected by fertilizer application, and (ii) in the present study, maize grain yield response under different tillage and fertilizer regimes was overall not related to nematode population density and composition.
For efficient production of doubled haploid (DH) lines in maize, maternal haploid inducer lines with high haploid induction rate (HIR) and good adaptation to the target environments is an important requirement. In this study, we present second-generation Tropically Adapted Inducer Lines (2GTAILs), developed using marker assisted selection (MAS) for qhir1, a QTL with a significant positive effect on HIR from the crosses between elite tropical maize inbreds and first generation Tropically Adapted Inducers Lines (TAILs). Evaluation of 2GTAILs for HIR and agronomic performance in the tropical and subtropical environments indicated superior performance of 2GTAILs over the TAILs for both HIR and agronomic performance, including plant vigor, delayed flowering, grain yield, and resistance to ear rots. One of the new inducers 2GTAIL006 showed an average HIR of 13.1% which is 48.9% higher than the average HIR of the TAILs. Several other 2GTAILs also showed higher HIR compared to the TAILs. While employing MAS for qhir1 QTL, we observed significant influence of the non-inducer parent on the positive effect of qhir1 QTL on HIR. The non-inducer parents that resulted in highest mean HIR in the early generation qhir1+ families also gave rise to highest numbers of candidate inducers, some of which showed transgressive segregation for HIR. The mean HIR of early generation qhir1+ families involving different non-inducer parents can potentially indicate recipient non-inducer parents that can result in progenies with high HIR. Our study also indicated that the HIR associated traits (endosperm abortion rate, embryo abortion rate, and proportion of haploid plants among the inducer plants) can be used to differentiate inducers vs. non-inducers but are not suitable for differentiating inducers with varying levels of haploid induction rates. We propose here an efficient methodology for developing haploid inducer lines combining MAS for qhir1 with HIR associated traits.
Haploidy Quantitative Trait Loci Maize Phenotypic variation Doubled Haploids Maternal Haploid Inducers Marker-Assisted Selection Phenotyping MAIZE HAPLOIDY ARTIFICIAL SELECTION CIENCIAS AGROPECUARIAS Y BIOTECNOLOGÍA
Mixed crop-livestock farming systems prevail in Mexico - typically rain-fed and smallholder systems based on maize and ruminants and spanning diverse agro-ecologies. Maize grain is the key Mexican staple produced for home consumption and the market. Maize crop residues (stover) are an important by-product, primarily for feed use, often through in situ stubble grazing and/or as ex situ forage. This paper explores maize stover use along the agro-ecological gradient and the potential trade-offs, particularly the widespread use of maize stover as feed against its potential use as mulch (soil cover) to manage soil health within the context of conservation agriculture. The paper builds on three case study areas in Mexico in contrasting agro-ecologies: (semi-)arid, temperate highland and tropical sub-humid. Data were obtained through expert consultation and semi-structured farmer group/community surveys. Although in situ grazing is found in all three study sites, it represented the bulk of stover use in only one site (70% of stover in the sub-humid tropics), with ex situ feed dominating in the other two sites (>80%). Maize stover commercialization is limited and mainly restricted to households with no livestock and often within the local context. Farmers are generally hesitant to adopt conservation agricultural practices that require the retention of stover as mulch, as this competes with their livestock feed needs and purchased feed is expensive. To reduce trade-offs, a portfolio of options could be adapted to these mixed systems, including partial residue retention, cover and feed crops and sustainable intensification. Promising but yet to be explored, are investments in the genetic improvement of maize stover feed quality.