International Maize and Wheat Improvement Center

About: International Maize and Wheat Improvement Center is a nonprofit organization based out in Texcoco, Mexico. It is known for research contribution in the topics: Population & Agriculture. The organization has 1976 authors who have published 4799 publications receiving 218390 citations.

Interactions between markers can be caused by the dominance effect of quantitative trait loci.

Abstract: F2 populations are commonly used in genetic studies of animals and plants. For simplicity, most quantitative trait locus or loci (QTL) mapping methods have been developed on the basis of populations having two distinct genotypes at each polymorphic marker or gene locus. In this study, we demonstrate that dominance can cause the interactions between markers and propose an inclusive linear model that includes marker variables and marker interactions so as to completely control both additive and dominance effects of QTL. The proposed linear model is the theoretical basis for inclusive composite-interval QTL mapping (ICIM) for F2 populations, which consists of two steps: first, the best regression model is selected by stepwise regression, which approximately identifies markers and marker interactions explaining both additive and dominance variations; second, the interval mapping approach is applied to the phenotypic values adjusted by the regression model selected in the first step. Due to the limited mapping population size, the large number of variables, and multicollinearity between variables, coefficients in the inclusive linear model cannot be accurately determined in the first step. Interval mapping is necessary in the second step to fine tune the QTL to their true positions. The efficiency of including marker interactions in mapping additive and dominance QTL was demonstrated by extensive simulations using three QTL distribution models with two population sizes and an actual rice F2 population.

Genetic Gains for Grain Yield in CIMMYT Spring Bread Wheat across International Environments

Abstract: The Global Wheat Program of the International Maize and Wheat Improvement Center (CIMMYT) develops and distributes improved germplasm targeted toward various wheat growing regions of developing world. The objective of our study was to quantify the genetic yield gains in CIMMYT’s spring bread wheat (Triticum aestivum L.) in the Elite Spring Wheat Yield Trial (ESWYT) distributed over the past 15 yr (1995–2009) as determined by the performance of entries across 919 environments in 69 countries. To determine the annual genetic gains, differences in mean yields of the fi ve highest yielding entries from mean trial yield and mean yield of the widely grown international check ‘Attila’ were regressed over 15 yr of ESWYT testing. Across locations in all countries, mean yields of the fi ve highest yielding entries showed an annual gain of 27.8 kg ha −1 (0.65%) compared to Attila. Annual yield gains in megaenvironment 1 (ME1) (optimally irrigated), ME2 (high rainfall), Egypt, India, and Pakistan were 27.4 (0.55%), 21.4 (0.62%), 111.6 (1.13%), 32.5 (0.83%), and 18.5 kg ha −1 (0.5%), respectively. These results demonstrate continuous genetic yield gains in the elite spring bread wheat lines developed and distributed by CIMMYT and the positive outcomes achieved through breeding and the international exchange of elite spring wheat germplasm that have benefi ted national programs throughout the world.

Conservation agriculture, increased organic carbon in the top-soil macro-aggregates and reduced soil CO2 emissions

Abstract: Conservation agriculture, the combination of minimal soil movement (zero or reduced tillage), crop residue retention and crop rotation, might have the potential to increase soil organic C content and reduce emissions of CO2. Three management factors were analyzed: (1) tillage (zero tillage (ZT) or conventional tillage (CT)), (2) crop rotation (wheat monoculture (W), maize monoculture (M) and maize-wheat rotation (R)), and (3) residue management (with (+r), or without (−r) crop residues). Samples were taken from the 0–5 and 5–10 cm soil layers and separated in micro-aggregates (< 0.25 mm), small macro-aggregates (0.25 to 1 mm) and large macro-aggregates (1 to 8 mm). The carbon content of each aggregate fraction was determined. Zero tillage combined with crop rotation and crop residues retention resulted in a higher proportion of macro-aggregates. In the 0–5 cm layer, plots with a crop rotation and monoculture of maize and wheat in ZT+r had the greatest proportion of large stable macro-aggregates (40%) and highest mean weighted diameter (MWD) (1.7 mm). The plots with CT had the largest proportion of micro-aggregates (27%). In the 5–10 cm layer, plots with residue retention in both CT and ZT (maize 1 mm and wheat 1.5 mm) or with monoculture of wheat in plots under ZT without residues (1.4 mm) had the greatest MWD. The 0–10 cm soil layer had a greater proportion of small macroaggregates compared to large macro-aggregates and micro-aggregates. In the 0–10 cm layer of soil with residues retention and maize or wheat, the greatest C content was found in the small and large macro-aggregates. The small macro-aggregates contributed most C to the organic C of the sample. For soil cultivated with maize, the CT treatments had significantly higher CO2 emissions than the ZT treatments. For soil cultivated with wheat, CTR-r had significantly higher CO2 emissions than all other treatments. Reduction in soil disturbance combined with residue retention increased the C retained in the small and large macro-aggregates of the top soil due to greater aggregate stability and reduced the emissions of CO2 compared with conventional tillage without residues retention and maize monoculture (a cultivation system normally used in the central highlands of Mexico).

Occurrence and direct control potential of parasitoids and predators of the fall armyworm (Lepidoptera: Noctuidae) on maize in the subtropical lowlands of Mexico

Abstract: 1 Native natural enemies have the potential to control fall armyworm Spodoptera frugiperda (Smith) in tropical maize grown in Mexico, where this insect pest causes severe economic losses to farmers. It has been proposed that enhancing herbivore-induced volatile emissions in maize plants may help to increase the effectiveness of natural enemies, which use these volatiles to locate their prey. This will only be of immediate benefit to farmers if the activity of the natural enemies results in a direct reduction in herbivory. Here we report on field surveys for the most common natural enemies in a tropical maize-growing region in Mexico and the potential effects of these enemies on herbivory by fall armyworm. 2 Caterpillars were collected in maize fields near Poza Rica in the state of Veracruz during January and February 1999, 2000 and 2001. Plants were either naturally infested by S. frugiperda, or artificially infested with laboratory-reared larvae. Ten species of parasitoids emerged from the collected larvae and eight species of predators that are known to feed on larvae and eggs were observed on the plants. Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae) was the dominant parasitoid species, in 1999 and 2001. 3 Of the nine larval parasitoids collected, six (all solitary) are known to reduce herbivory, whereas one causes the host to eat more (for two species this is not known). This implies that enhancing the effectiveness of solitary endoparasitoids may benefit subsistence farmers in developing countries by immediately reducing herbivory. The overall benefit for the plant resulting from parasitoid activity also has important implications for the evolutionary role of parasitoids in contributing to selection pressures that shape indirect defences in plants.