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.

Awns reduce grain number to increase grain size and harvestable yield in irrigated and rainfed spring wheat

Abstract: Genotypic variation in ear morphology is linked to differences in photosynthetic potential to influence grain yield in winter cereals. Awns contribute to photosynthesis, particularly under water-limited conditions when canopy assimilation is restricted. We assessed performance of up to 45 backcross-derived, awned–awnletted NILs representing four diverse genetic backgrounds in 25 irrigated or rainfed, and droughted environments in Australia and Mexico. Mean environment grain yields were wide-ranging (1.38–7.93 t ha−1) with vegetative and maturity biomass, plant height, anthesis date, spike number, and harvest index all similar (P >0.05) for awned and awnletted NILs. Overall, grain yields of awned–awnletted sister-NILs were equivalent, irrespective of yield potential and genetic background. Awnletted wheats produced significantly more grains per unit area (+4%) and per spike (+5%) reflecting more fertile spikelets and grains in tertiary florets. Increases in grain number were compensated for by significant reductions in grain size (–5%) and increased frequency (+0.8%) of small, shrivelled grains (‘screenings’) to reduce seed-lot quality of awnletted NILs. Post-anthesis canopies of awnletted NILs were marginally warmer over all environments (+0.27 °C) but were not different and were sometimes cooler than awned NILs at cooler air temperatures. Awns develop early and represented up to 40% of total spikelet biomass prior to ear emergence. We hypothesize that the allocation of assimilate to large and rapidly developing awns decreases spikelet number and floret fertility to reduce grain number, particularly in distal florets. Individual grain size is increased to reduce screenings and to increase test weight and milling quality, particularly in droughted environments. Despite the average reduction in grain size, awnless lines could be identified that combined higher grain yield with larger grain size, increased grain protein concentration, and reduced screenings.

Optimal Design of Preliminary Yield Trials with Genome-Wide Markers

Abstract: Previous research on genomic selection (GS) has focused on predicting unphenotyped lines. Genomic selection can also improve the accuracy of phenotyped lines at low heritability, e.g., in a preliminary yield trial (PYT). Our �耀 rst objective was to estimate this effect within a biparental family, using multilocation yield data for barley (Hordeum vulgare L.) and maize (Zea mays L.). We found that accuracy increased with training population size and was higher with an unbalanced design spread across multiple locations than when testing all entries in one location. The latter phenomenon illustrates that when seed is limited, genome-wide markers enable broader sampling from the target population of environments. Our second objective was to explore the optimum allocation of resources at a �耀 xed budget. When PYT selections are advanced for further testing, we propose a new metric for optimizing genetic gain: R max , the expected maximum genotypic value of the selections. For budgets up to 250 yield plot equivalents per family, the optimal design did not involve genotyping more progeny than were phenotyped, even when the cost of creating and genotyping each line was only 0.25 the cost of one yield plot unit (YPU). At a genotyping cost of 0.25 YPU, GS offered up to a 5% increase in genetic gain compared with phenotypic selection. To increase genetic gains further, the training population must be expanded beyond the full-sib family under selection, using close relatives of the parents as a source of prediction accuracy.

Sampling Strategies for Conserving Maize Diversity When Forming Core Subsets Using Genetic Markers

Abstract: Core subsets can be formed on the basis of molecular markers and different sampling strategies. This research used genetic markers on three maize data sets for studying 24 stratified sampling strategies to investigate which strategy conserved the most diversity in the core subset as compared with the original sample. The strategies were formed by combining three factors: (i) two clustering methods (UPGMA and Ward), based on (ii) two initial genetic distance measures, and using (iii) six allocation criteria [two based on the size of the cluster and four based on maximizing distances in the core (the D method) used with four diversity indices]. The objectives were (i) to study the influence of these factors and their interaction on the diversity of the core subsets and (ii) to compare the 24 stratified sampling strategies with the M strategy implemented in the MSTRAT algorithm. Success of each strategy was measured on the basis of maximizing genetic distances (Modified Roger and Cavalli-Sforza and Edwards distances) and genetic diversity indices (Shannon index, proportion of heterozygous loci, and number of effective alleles) in each core. Twenty independent stratified random samples were obtained for each strategy using a sampling intensity of 20% of the collection. For the three data sets, the UPGMA with D allocation methods produced core subsets with significantly more diversity than the other methods and were better than the M strategy for maximizing genetic distance. For most of the diversity indices, the M strategy outperformed the D method.

Refined mapping of the Pierce’s disease resistance locus, PdR1, and Sex on an extended genetic map of Vitis rupestris × V. arizonica

Abstract: A framework genetic map based on genomic DNA-derived SSR, EST-derived SSR, EST-STS and EST-RFLP markers was developed using 181 genotypes generated from D8909-15 (female) × F8909-17 (male), the ‘9621’ population. Both parents are half siblings with a common female parent, Vitis rupestris ‘A. de Serres’, and different male parents (forms of V. arizonica). A total of 542 markers were tested, and 237 of them were polymorphic for the female and male parents. The female map was developed with 159 mapped markers covering 865.0 cM with an average marker distance of 5.4 cM in 18 linkage groups. The male map was constructed with 158 mapped molecular markers covering 1055.0 cM with an average distance of 6.7 cM in 19 linkage groups. The consensus ‘9621’ map covered 1154.0 cM with 210 mapped molecular markers in 19 linkage groups, with average distance of 5.5 cM. Ninety-four of the 210 markers on the consensus map were new. The ‘Sex’ expression locus segregated as single major gene was mapped to linkage group 2 on the consensus and the male map. PdR1, a major gene for resistance to Pierce’s disease, caused by the bacterium Xylella fastidiosa, was mapped to the linkage group 14 between markers VMCNg3h8 and VVIN64, located 4.3 and 2.7 cM away from PdR1, respectively. Differences in segregation distortion of markers were also compared between parents, and three clusters of skewed markers were observed on linkage groups 6, 7 and 14.

Reduced and zero-tillage options for establishment of wheat after rice in South Asia

Abstract: One of the major constraints to higher production of wheat on the 12 million hectares of rice-wheat grown in the Indo-Gangetic flood plains of South Asia is late planting and resultant poor plant stands. Late planting results in a linear decline in yield potential equivalent to 1–1.5% loss ha-1 d-1 when planting occurs after November. Late harvest of the previous rice crop or long turnaround time from rice harvest to wheat planting are two major causes of late wheat planting. Reduced or zero-tillage options are proving effective in overcoming late planting and poor plant stands in the rice-wheat systems of Asia. This paper presents data on zero-tillage systems, ranging from surface seeding to planting with four-wheel tractor seed drills, resulting in higher yields at lower costs and savings in fuel use and tractor wear and tear. Reduced tillage systems include ‘data-using’ drills that combine land preparation and seeding in one operation. Both two and four-wheel tractors have been used to achieve good results. This paper concludes that conventional tillage systems can be replaced by more economic reduced tillage options. However, it is important with reduced tillage that soil moisture at seeding is maintained at a high enough level to keep soil strength low, as occurs in tilled soils. Some longer term research is needed to determine medium term positive or negative effects of reduced tillage on sustaining wheat yields.