Person: Beck, D.L.
Loading...
Email Address
Birth Date
Research Projects
Organizational Units
Job Title
Last Name
Beck
First Name
D.L.
Name
Beck, D.L.
11 results
Search Results
Now showing 1 - 10 of 11
- Técnicas para sincronizar floración de semilla hibrida de maíz(Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, 2004) Torres Flores, J.L.; Beck, D.L.; Carballo-Carballo, A.; Estrada Gómez, J.A.
Publication - Puma 1075 y Puma 1076, híbridos de maíz de temporal para los valles altos de México (2200 a 2600 msnm)(Sociedad Mexicana de Fitogenética, 2004) Tadeo Robledo, M.; Espinosa Calderón, A.; Martínez Mendoza, R.; Srinivasan, G.; Beck, D.L.; Lothrop, J.E.; Torres Flores, J.L.; Azpíroz Rivero, S.
Publication - H-153 maíz hibrido para riego en la zona de transición el bajio-valles altos(Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, 2002) Espinosa Calderón, A.; Tadeo Robledo, M.; Lothrop, J.E.; Beck, D.L.
Publication - Management of hybrid maize seed production(CIMMYT, 2002) Beck, D.L.Numerous types of both conventional (based only on inbred lines) and nonconventional (where at least one parent is not an inbred line) maize hybrids may be produced. Conventional hybrid types include single crosses, three way crosses and double crosses. Single cross hybrids are based on two parental inbred lines whereas three way crosses first require the production of a single cross hybrid followed by its use as a female parent crossed to a male inbred line. Double cross hybrids are the product of crossing two distinct single crosses. Single crosses are popular in the developed world because of their high yield performance and uniformity. However, they are expensive and difficult to produce as the female parent on which the hybrid seed is produced is typically a relatively low yielding inbred line. Three way and double cross hybrids overcome this difficulty as the female parent in these conventional hybrid types is a single-cross hybrid. Disadvantages of double cross hybrids is that they need seven separate production fields including four blocks to maintain and produce the inbred lines, two fields to produce the two single-cross hybrids, and finally a production field to form the double cross hybrid. At present, three way cross hybrids are the most common maize hybrids types grown in much of the developing world.
Publication - Selección recíproca recurrente en poblaciones de maíz de valles altos en suelos con alto y bajo contenido de nitrógeno, en México(Colegio de Postgraduados, 2004) Moreno-Pérez, E.C.; Beck, D.L.; Cervantes Santana, T.; Torres Flores, J.L.El objetivo de este trabajo fue evaluar los efectos de dos ciclos de selección recíproca recurrente realizados en las poblaciones 902 (A) y 903 (B) de maíz (Zea mays L.), de Valles Altos, México, provenientes del Centro Internacional de Mejoramiento de Maíz y Trigo (CIMMYT), en suelos con alto y bajo contenido de nitrógeno. Con los ciclos 0, 1 y 2 de selección en las poblaciones A y B se formaron nueve cruzas Ai ×Bj (i, j= ciclo 0, 1, 2). La generación F2 del ciclo i de la población A y del ciclo j de la población B, las cruzas Ai ×Bj y los testigos ACROSS96902, ACROSS96903, CMS929001, ASPROS721 y CMS939083, se evaluaron en suelos con alto y bajo contenido de nitrógeno en El Batán, México y en suelos con alto contenido de nitrógeno en Montecillo, México, en 2000 y 2001. El diseño experimental usado fue bloques completos al azar con tres repeticiones. El rendimiento de grano promedio de las cruzas Ai ×Bj (8.24 t ha−1 ) no fue estadísticamente diferente al de los testigos (8.45 t ha−1 ), y las poblaciones Bj fueron las de menor rendimiento (5.55 t ha−1). No hubo diferencias significativas entre genotipos de cada población. La ganancia en rendimiento de grano por ciclo de selección no fueron significativas y la heterosis respecto al progenitor medio tampoco lo fue.
Publication - Inbred line evaluation nurseries and their role in maize breeding at CIMMYT(Consiglio per la Ricerca e la sperimentazione in Agricoltura, Unità di Ricerca per la Maiscoltura, 1999) Vasal, S.K.; Srinivasan, G.; Cordova, H.S.; Pandey, S.; Jeffers, D.P.; Bergvinson, D.J.; Beck, D.L.CIMMYT initiated its hybrid maize (Zea mays) research programme in 1985 in response to the growing needs of the national programmes for hybrid-oriented source germplasm. Since 1991 CIMMYT has released a total of 424 inbreds that are widely distributed and used by public and private sector researchers around the world. Inbred line evaluation nurseries are an important component of a hybrid research programme. At CIMMYT, inbreds are routinely evaluated for various biotic and abiotic stresses, their yield potential and other agronomic attributes. Several promising lines have been identified for specific stresses, although they were not selected during the development process which can be attributed to the genetic diversity of CIMMYT's source germplasm. Resistant/tolerant lines have been identified for abiotic stresses (drought, low-N use efficiency and acid soils). In addition, resistant lines have been identified for biotic stresses, including fusarium ear/stalk rot (Fusarium spp.), banded leaf and sheath blight (Rhizoctonia spp.), tar spot (Phyllachora maydis), grey leaf spot (Cercospora zeae-maydis), rust (Puccinia polysora), maize streak virus (MSV), fall armyworm (Spodoptera frugiperda), sugarcane borer (Diatraea saccharalis) and Striga. Lines with above average general combining ability and yield stability were identified. These lines are available for public use
Publication - Heterosis and combining ability of CIMMYT's tropical late white maize germplasm(Consiglio per la Ricerca e la sperimentazione in Agricoltura, Unità di Ricerca per la Maiscoltura, 1992) Vasal, S.K.; Srinivasan, G.; Beck, D.L.; Crossa, J.; Pandey, S.; De Leon, C.Seven tropically adepted, late maturity maize gene pools and populations (Populations 21, 22, 25, 29, 32 and 43, and Pool 24) developed and improved at CIMMYT were crossed in a 7 x 7 diallel mating system. The parent and 21 crosses were evaluated for graind yiedl, days to silk and plant height at five locations in México, and one each in Colombia and Thailand. The objectives of the study were to determine the heterosis and combining ability among these materials and to identify appropriate germplasm suitable for hybrid development work. The combined analysis of variance for all three traits measured showed no significant genotype x environment (G xE) interaction. Genotypes themselves showed significant differences for all three traits, as did their partitions into partents and crosses. General combining ability (GCA) was significant for all traits whereas specific combining ability (SCA) was not significant for any of the traits. Mean grain yeild for the trial was 6.98 t/ha. the highest yielding combination was Population 21 x Population 43 (7.83 t/ha) followed by crosses of Population 22 with Population 32 (dent x flint) yielded 7.36 t/ha while exhibiting the maximun high-parent heterosis (12.7%) for yield. Population 43 (La Posta) was the tallest and latest parent and produced high yields in crosses whit other populations. All crosses to Population 43 per se. Population 21 (0.24 t/ha), Population 22 (0.13 t/ha) and Population 43 (0.23 t/ha) possessed significant positive GCA for yield. Populations 21 and 43 also showed significant positive GCA for days to silk while only Population 43 showed positive GCA for plant height. Aignificant (P <0.05) positive SCA effects for yield were observed in two crosses involving Population 32 whit Population 22 and 29 (flint x dent). Based on our study the best choices for initianting hybrid work are Populations 21, 22, 29 and 43. Many of the Tuxpeño based populations are ideal candidates forinterpopulation improvement using Population 32 (ETO Blanco) as heterotic partner.
Publication - Heterosis and combining ability of CIMMYT's tropical early and intermediate maturity maize (Zea mays L.) germplasm(Consiglio per la Ricerca e la sperimentazione in Agricoltura, Unità di Ricerca per la Maiscoltura, 1990) Beck, D.L.; Vasal, S.K.; Crossa, J.A 10 parent diallel was formed to determine combining ability and heterotic patterns among CIMMYT'S tropically adapted, early and intermediate maturity maize (Zea mays L.) gene pools and populations. The parents and their crosses were avaluated for yeild (t/ha), plant and ear height (cm), and days to silk at five locations in México, and one each in Colombia, Ecuador, India and Thailand. The test for average heterosis, parents vs. crosses, was significant for graind yield, and plant and ear height in the combined analysis of variance. General combining ability (GCA) was significant for all traits. Specific combining anility (SCA) was significant anly for ear height. Although yield heterosis over the better parent was low in most crosses, moderate levels were observed in the Population 49 x Population 26 cross (9.6%). Population 26 also combined over the better parent. Pool 22 had the highest GCA effect for yield (0.37 t/ha), and was a parent in three of the five top yielding crosses. High yielding combinations included Pool 22 with Pool 20 (6.33 t/ha), Population 23 (6.24 t/ha), and Population 26 (6.23 t/ha). However, maximun heterosis over the better parent was only 3.2% in these crosses. The only cross wiht a significant positive SCA effect for yield was Population 23 x Pool 20 yielding 6.13 t/ha with 6.7% heterosis. Heterosis for plant and ear height, and days to silk were generally low. Based on our study, the best choices for initiating hybrid work among white grain materials are Population 23 and Pool 20, and among yellow grain materials Populations 26, Pool 21, and Pool 22.
Publication - Mejoramiento para aumentar la tolerancia a sequía y a deficiencia de nitrógeno en el maíz: de la teoría a la práctica(CIMMYT, 2012) Banziger, M.; Edmeades, G.O.; Beck, D.L.; Bellon, M.Este documento, dirigido inicialmente a los mejoradores de maíz en África al sur del Sahara, se basa en un método probado que fue elaborado en el CIMMYT con el fin de mejorar la tolerancia del maíz al estrés por sequía y por deficiencia de nitrógeno. La intención al elaborar este manual fue usarlo como complemento en un curso para mejoradores y agrónomos que ostenten, como mínimo, la licenciatura. Entre los temas tratados se incluyen los efectos que los déficits de agua y de nitrógeno tienen en la planta de maíz; los incrementos de rendimiento que se pueden lograr con la selección; los factores que afectan la intensidad de la sequía y de la deficiencia de N en el maíz; la elección de parcelas que sean adecuadas para realizar la evaluación inicial de la tolerancia a sequía y a deficiencia de N; el manejo que se les da a los ensayos de sequía y bajos niveles de N para lograr un estrés uniforme; el diseño de experimentos y planos de campo apropiados para los ensayos de estrés; la elección y el análisis de datos; y el uso de la evaluación inicial de la tolerancia a sequía y deficiencia de N en un programa fitogenético tradicional.
Publication - Genetic change in farmer-recycled maize seed: a review of the evidence(CIMMYT, 1999) Morris, M.L.; Risopoulos, J.; Beck, D.L.This paper summarizes what is known about farm-level maize seed management practices and reviews the theoretical and empirical evidence regarding the relationship between farmers’ seed recycling practices and the genetic composition (and agronomic performance) of maize cultivars. The focus is on farmers in developing countries, many of whom do not replace their seed annually with newly purchased commercial seed but rely instead on recycled seed saved from their own harvest or obtained from other farmers. Why is it important to know about the genetic composition of maize plants found in farmers’ fields? Although there are many possible reasons, for research organizations such as CIMMYT that carry out plant breeding activities one of the most important is to be able to calculate the value of improved germplasm. Modern varieties of maize (MVs) have been a major source of productivity growth in the past and are likely to be and increasingly important source in the future. In order to calculate the economic value of MVs (which is needed to determine the optimal level of investment in maize breeding research), it is necessary to estimate the productivity gains associated with adoption of improved germplasm. These productivity gains cannot be estimated unless it is possible to identify unequivocally the materials growing in farmers’ fields. Many empirical studies make clear that maize farmers in developing countries frequently save seed from their own production to replant the following season. By far the most common seed selection practice is post-harvest selection. Although there are a number of obvious advantages associated with selecting kernels from harvested ears, the practice does not always result in the production of genetically pure seed. Largely for this reason, recycling is often associated with changes in the genetic composition of maize cultivars. What happens, genetically speaking, when farmers save maize seed from their own harvest and replant it the following cropping cycle? Based on what is known about the reproductive biology of maize, as well as farmers’ varietal management practices and seed selection strategies, there are strong reasons to expect that the genetic composition of farmer-maintained cultivars will change over time. Seven potential sources of genetic change in recycled maize can be distinguished: (1) farmers’ seed selection practices, (2) unintentional seed mixing, (3) contamination, (4) genetic drift, (5) mutation, (6) natural selection, and (7) segregation. Each of these is discussed, and published studies are reviewed to determine whether theoretical predictions about the amount of genetic change attributable to each source are supported by empirical evidence. Our review of the literature suggests that landraces, improved open-pollinated varieties (OPVs) and hybrids all undergo changes in genetic composition as a result of seed recycling. The sources of these changes vary in importance by type of material. In landraces and improved OPVs, genetic changes result from a combination of intentional and unintentional selection pressure. Landraces and OPVs evolve not only because farmers deliberately select for desired characteristics, but also because of environmental influences, iv accidental cross-pollination, random mutation, and gene segregation. Since both types of selection pressure are highly variable, it is difficult to generalize about the rate of genetic change; depending on the circumstances, the genotype of a landrace or improved OPV can change significantly from one generation of plants to the next, or it can remain essentially unchanged across many generations of plants. In hybrids, by far the most important source of genetic changes is segregation — random recombination of alleles that occurs when seed is recycled. Key results of a simulation exercise designed to show the likely effects of inbreeding in maize hybrids appear to be supported by findings published in the empirical literature on seed recycling: When maize hybrids are recycled, yield usually decreases significantly from the F1 to the F2 generation. Yield tends to stabilize in subsequent generations, however, and may eventually begin to increase again if farmers are exerting selection pressure. When maize hybrids are recycled, the size of the yield decrease observed between the F1 and F2 generations depends in large part on the level of inbreeding of the original parents. Generally speaking, the greater the degree of inbreeding in the parents, the greater the degree of heterosis in the F1 generation, and the greater the yield decline observed between the F1 and F2 generations. This relationship may be confounded by environmental factors, however. The degree of inbreeding of the parents affects not only the size of the expected yield decrease but also its variability. The greater the level of heterozygosity in F1 plants, the greater the variability in inbreeding depression expected in F2 and F3 plants. Whether or not advanced-generation hybrids outyield landraces and improved OPVs depends on the original difference in yield and on the magnitude of the decline in yield caused by recycling. In some instances, recycled hybrids continue to outyield the other types of materials, which explains why hybrid recycling may make sense. Recycling of hybrids may have little effect on qualitative traits such as kernel size and shape, grain texture, and pounding quality. The finding that seed recycling often leads to significant genetic changes in farmermaintained cultivars suggests that there may be a need to reassess the categories traditionally used to classify maize varieties (e.g., landraces, improved OPVs, hybrids). In addition, the rapid rate of genetic change observed to take place in farmers’ fields has important implications for research impacts assessment studies. Practical guidelines for use in estimating the returns to maize breeding research are presented in the appendix.
Publication