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.

A Novel STS Marker for Polyphenol Oxidase Activity in Bread Wheat

Abstract: The enzyme activity of polyphenol oxidase (PPO) in grain has been related to undersirable brown discoloration of bread wheat (Triticum aestivum L.) based end-products, particularly for Asian noodles. Breeding wheat cultivars with low PPO activity is the best approach to reduce the undesirable darkening. Molecular markers could greatly improve selection efficiency in breeding programs. Based on the sequences of PPO genes (GenBank Accession Numbers AY596268, AY596269 and AY596270) conditioning PPO activity during kernel development, 28 pairs of primers were designed using the software ‘DNAMAN’. One of the markers from AY596268, designated as PPO18, can amplify a 685-bp and an 876-bp fragment in the cultivars with high and low PPO activity, respectively. The difference of 191-bp size was detected in the intron region of the PPO gene. The STS marker PPO18 was mapped to chromosome 2AL using a DH population derived from a cross Zhongyou 9507 · CA9632, a set of nulli-tetrasomic lines and ditelosomic line 2AS of Chinese Spring. QTL analysis indicated that the PPO gene co-segregated with the STS marker PPO18 and is closely linked to Xgwm312 and Xgwm294 on chromosome 2AL, explaining 28 – 43% of phenotypic variance for PPO activity across three environments. A total of 233 Chinese wheat cultivars and advanced lines were used to validate the correlation between the polymorphic fragments of PPO18 and grain PPO activity. The results showed that PPO18 is a co-dominant, efficient and reliable molecular marker for PPO activity and can be used in wheat breeding programs targeted for noodle quality improvement.

A consensus map for Ug99 stem rust resistance loci in wheat.

Abstract: Key message This consensus map of stem rust genes, QTLs, and molecular markers will facilitate the identi‑ fication of new resistance genes and provide a resource of information for development of new markers for breeding wheat varieties resistant to Ug99.

High yield potential, shuttle breeding, genetic diversity, and a new international wheat improvement strategy

Abstract: The main elements of the international wheat improvement program of the Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT), also known as the International Maize and Wheat Improvement Center, have been shuttle breeding at two contrasting locations in Mexico, wide adaptation, durable rust and Septoria resistances, international multisite testing, and the appropriate use of genetic variation to enhance yield gains of subsequently produced lines. Such an approach yielded successes known collectively as the Green Revolution. However, at the beginning of the 21st century, this “cultivar assembly line” approach needs fine tuning to address crop needs under increasingly adopted resource conserving practices, as well as those related to nutritional requirements of the end-users. International wheat improvement will therefore focus on the targeting of traits in respective mega-environments, and the use of participatory methods, especially in marginal environments. The main features of this wheat improvement strategy include the introduction of new and novel sources of genetic variation through wild species, landraces, and, potentially, the use of transgenes for intractable traits. This variation will be combined using international shuttle breeding, and increased breeding efficiency will be achieved through marker-aided methods, more targeted use of crop physiology, plant genetics, biostatistics, and bioinformatics. Likewise, CIMMYT will increase its focus on the needs of end-users by emphasizing regional efforts in participatory research and client-oriented plant breeding.

Genetic Diversity for Wheat Improvement as a Conduit to Food Security

Abstract: Genetic diversity is paramount for cultivated crops genetic improvement, and for wheat this resides in three gene pools of the Triticeae. In wheat, access to this diversity and its exploitation is based upon the genetic distance of the wild species relatives from the wheat genomes. For several decades, these wide crosses have been a reservoir of novel variation for wheat improvement. Among these, close relatives of the primary gene pool have been preferred since this ensures successful gene transfer as they permit homologous genetic exchanges to occur between related genomes, as exemplified by the A and D genome diploid progenitors. One strategy has been based upon first producing genetic stocks that capture the potential of the diploids via bridge crossing where the D genome synthetic hexaploid wheats (2n = 6x = 42, AABBDD) are exploited. The synthetics are products of crosses between elite durum wheat cultivars (Triticum turgidum) and various Aegilops tauschii accessions. Similarly, the diversity of the A and B genomes has also been assembled as AABBAA (T. turgidum/A genome diploids Triticum boeoticum, Triticum monococcum, Triticum urartu) and AABBBB (SS) (T. turgidum/Aegilops speltoides). The utilization of these useful diversity for various biotic/abiotic stresses including in the development of molecular tools for enhancing breeding efficiency has been in the forefront of wheat improvement over the past two decades. Additional strategy employed includes the direct crosses between parental diploids and recipient wheat cultivars extended to give even swifter products by top- or backcrossing the F1 combinations with either durum or bread wheats. Relatively less progress has been made in the use of genes from tertiary gene pool often involving “intergeneric crosses.” The potency of potentially useful diversity in tertiary gene pool warrants further exploitation of this resource. Presented here are major facets of intergeneric hybridization embracing a taxonomic consideration of genetic diversity within the Triticeae, the exploitation protocols, prebreeding strategies, and some of the outputs from distant hybridization with a major focus on wheat/alien chromosomal exchanges classed as “translocations” such as T1BL.1RS and to a lesser degree the T1AL.1RS Robertsonian translocations. This chapter also attempts to relate the exploitation of the Triticeae genetic diversity with wheat productivity as a means of addressing diverse stress constraints that if pursued will provide yield enhancing outputs necessary for overriding environmental limitations of climate change, unpredictable incidences of biotic stresses, and catalyzing gains for food security with wheat.