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.

Photosynthetic contribution of the ear to grain filling in wheat: a comparison of different methodologies for evaluation

Abstract: The culm (particularly the flag leaf) and the ear are believed to play a major role in providing assimilates for grain filling in wheat. However, the results obtained in the past varied depending on the methodology applied. Three different methodologies were compared that aimed to assess the relative contribution of the culm (photosynthetic organs below the ear) and the ear to grain filling. The first two consisted of applications of photosynthesis inhibition treatments, including the use of the herbicide DCMU and organ shading. The third was a non-intrusive method that compared the carbon isotope composition (δ(13)C) of mature kernels with the δ(13)C of the water-soluble fraction of the peduncle, awns and glumes. Several advanced CIMMYT lines were tested under good agronomic conditions. The δ(13)C approach assigned a higher photosynthetic contribution to the ear than to the culm. However, some methodological considerations should be taken into account when applying the δ(13)C approach, particularly the sampling method used, in order to prevent post-harvest respiration. The shading approach assigned a similar contribution to the ear as to the culm. The DCMU approach assigned a greater role to the culm but herbicide application to the culm affected the ear, thus biasing the final grain weight. Moreover DCMU and shading approaches may cause compensatory effects which overestimated the contribution of unaffected organs. This study may help to develop precise phenotyping tools to identify physiological traits such as ear photosynthesis that could contribute towards increasing grain yield.

Cloning of seed dormancy genes (TaSdr) associated with tolerance to pre-harvest sprouting in common wheat and development of a functional marker

Abstract: After cloning and mapping of wheat TaSdr genes, both the functional markers for TaSdr - B1 and TaVp - 1B were validated, and the distribution of allelic variations at TaSdr - B1 locus in the wheat cultivars from 19 countries was characterized. Seed dormancy is a major factor associated with pre-harvest sprouting (PHS) in common wheat (Triticum aestivum L.). Wheat TaSdr genes, orthologs of OsSdr4 conferring seed dormancy in rice, were cloned by a comparative genomics approach. They were located on homoeologous group 2 chromosomes, and designated as TaSdr-A1, TaSdr-B1 and TaSdr-D1, respectively. Sequence analysis of TaSdr-B1 revealed a SNP at the position -11 upstream of the initiation codon, with bases A and G in cultivars with low and high germination indices (GI), respectively. A cleaved amplified polymorphism sequence marker Sdr2B was developed based on the SNP, and subsequently functional analysis of TaSdr-B1 was conducted by association and linkage mapping. A QTL for GI co-segregating with Sdr2B explained 6.4, 7.8 and 8.7 % of the phenotypic variances in a RIL population derived from Yangxiaomai/Zhongyou 9507 grown in Shijiazhuang, Beijing and the averaged data from those environments, respectively. Two sets of Chinese wheat cultivars were used for association mapping, and results indicated that TaSdr-B1 was significantly associated with GI. Analysis of the allelic distribution at the TaSdr-B1 locus showed that the frequencies of TaSdr-B1a associated with a lower GI were high in cultivars from Japan, Australia, Argentina, and the Middle and Lower Yangtze Valley Winter Wheat Region and Southwest Winter Wheat Region in China. This study provides not only a reliable functional marker for molecular-assisted selection of PHS in wheat breeding programs, but also gives novel information for a comprehensive understanding of seed dormancy.

Long-term yield sustainability and financial returns from grain legume-maize intercrops on a sandy soil in subhumid north central zimbabwe

Abstract: SUMMARY To measure the yield and financial returns from five grain legume–maize intercrop combinations over 12 years of cropping, a field experiment was conducted on a loamy sand soil in the subhumid unimodal rainfall environment of Domboshava in north-central Zimbabwe. Inputs and management followed smallholder practice, including partial grazing of crop residues and a zero mineral fertilizer treatment. The intercropped legumes grew moderately well most years. Cowpea averaged the highest grain yield (0.244 t ha −1 ) and haulm yield (1.54 t ha −1 ) over the 12 years, followed by pigeonpea and sugar bean. Intercropped pigeonpea yield was the least variable of the legumes over the years. Maize grain yield was highly variable across years with or without fertilizer and was reduced in years of low (533 mm) and high (1313 mm) rainfall. The pigeonpea–maize intercrop grown without fertilizer produced 0.11 t ha −1 (6.25 %) more maize grain yield per year than sole crop maize, in addition to pigeonpea grain and haulms. Intercropped cowpea (which yielded more than double the above-ground non-grain biomass of pigeonpea) had less effect on maize grain yield. There was no trend to greater benefits from the legumes on maize yield after more years of intercropping. Net present values of annual margins accumulated over the 12 years for sole maize with fertilizer (US$1719 ha−1) and without fertilizer (US$935 ha−1) were higher than the fertilized and unfertilized intercropping options (US$1017 and US$745 ha −1 ). Pigeonpea or cowpea– unfertilized maize generated more financial returns than the other intercrops, but the low yields and high labour costs for the legumes made the intercrops financially unattractive. We conclude that regularly intercropped pigeonpea or cowpea can to a small extent help to maintain maize yield when maize is grown without mineral fertilizer on sandy soils in sub humid zones of Zimbabwe, and simultaneously provide some nutritious food, but that financial considerations will encourage smallholder farmers to persist with growing low input sole crop maize.

Are synthetic hexaploids a means of increasing grain element concentrations in wheat

Abstract: Element concentration in wheat grains is an important objective of plant breeding programs. For this purpose, synthetic hexaploid lines (Triticum durum ×Aegilops tauschii) have been identified as potential sources of high element concentration in grains. However, it is not known if these lines reach higher element concentrations in grains as the consequence of a dilution effect due to lower grain yield. In addition, most of the studies carried out with these lines did not evaluate above-ground element uptake. The objective of this study was to improve understanding of grain element concentrations as a function of grain yield, element uptake and biomass and element partitioning to grains in synthetic and conventional cultivars of wheat. One experiment with two standard sowing dates was carried out under field conditions. Biomass, grain yield, and macronutrient(Ca, Mg, K, P and S) and micronutrient (Cu,Fe, Mn and Zn) concentrations in grains and vegetative tissues were measured in two cultivars and one synthetic (chosen from ten lines). The synthetic showed higher element concentration in grains, e.g. between 25 and 30% for Fe, Mn and Zn across sowing dates, than cultivars while grain yield was similar or lower, depending on the sowing date. On the contrary, the synthetic showed lower concentration of Cain grains. This line showed also higher uptake of Fe, Mn, K and P than cultivars. The superior grain element concentration of the synthetic line was not only due to a dilution effect but also to a higher uptake efficiency. Therefore, synthetics would bea valuable source of germplasm for increasing element grain concentration, at least in this case for Fe, Mn, K and P.