Hans J. Braun

Prediction of genetic values of quantitative traits in plant breeding using pedigree and molecular markers

The availability of dense molecular markers has made possible the use of genomic selection (GS) for plant breeding. However, the evaluation of models for GS in real plant populations is very limited. This article evaluates the performance of parametric and semiparametric models for GS using wheat (Triticum aestivum L.) and maize (Zea mays) data in which different traits were measured in several environmental conditions. The findings, based on extensive cross-validations, indicate that models including marker information had higher predictive ability than pedigree-based models. In the wheat data set, and relative to a pedigree model, gains in predictive ability due to inclusion of markers ranged from 7.7 to 35.7%. Correlation between observed and predictive values in the maize data set achieved values up to 0.79. Estimates of marker effects were different across environmental conditions, indicating that genotype × environment interaction is an important component of genetic variability. These results indicate that GS in plant breeding can be an effective strategy for selecting among lines whose phenotypes have yet to be observed.

Research investment implications of shifts in the global geography of wheat stripe rust

Breeding new crop varieties with resistance to the biotic stresses that undermine crop yields is tantamount to increasing the amount and quality of biological capital in agriculture. However, the success of genes that confer resistance to pests induces a co-evolutionary response that depreciates the biological capital embodied in the crop, as pests evolve the capacity to overcome the crops new defences. Thus, simply maintaining this biological capital, and the beneficial production and economic outcomes it bestows, requires continual reinvestment in new crop defences. Here we use observed and modelled data on stripe rust occurrence to gauge changes in the geographic spread of the disease over recent decades. We document a significant increase in the spread of stripe rust since 1960, with 88% of the worlds wheat production now susceptible to infection. Using a probabilistic Monte Carlo simulation model we estimate that 5.47 million tonnes of wheat are lost to the pathogen each year, equivalent to a loss of US

Variation in zinc efficiency among and within Aegilops species

979 million per year. Comparing the cost of developing stripe-rust-resistant varieties of wheat with the cost of stripe-rust-induced yield losses, we estimate that a sustained annual research investment of at least US

Genetic yield gains in CIMMYT’s international elite Spring Wheat yield trials by modeling the Genotype X environment interaction

32 million into stripe rust resistance is economically justified.

CIMMYT Series on Carbohydrates, Wheat, Grains, and Health: Carbohydrates, Grains, and Wheat in Nutrition and Health: An Overview. Part I. Role of Carbohydrates in Health1,2

Fifteen accessions of Aegilops tauschii (DD), 10 of Ae. speltoides (SS) and 8 of the tetraploid Aegilops species sharing the U genome were used to study the influence of varied zinc (Zn) supply on development of Zn-deficiency symptoms, and on shoot dry weight and Zn concentration. Plants were grown in a Zn-deficient calcareous soil under greenhouse conditions with (+Zn = 5 mg kg—1 soil) and without (—Zn) Zn supply. Four accessions of wild tetraploid wheat, Triticum turgidum var. dicoccoides (BBAA), a group known for its high sensitivity to Zn-deficiency, were used in the experiments for comparison. As expected, the accessions of wild T. turgidum var. dicoccoides showed the highest sensitivity to Zn deficiency, and had more severe leaf symptoms of Zn deficiency (whitish-brown necrotic patches). Among the Aegilops species, leaf symptoms of Zn deficiency were, in general, more distinct in Ae. tauschii (DD) and least in Ae. speltoides (SS). Zinc efficiency, expressed as the percentage of shoot dry weight produced under conditions of Zn deficiency compared to Zn supply, averaged, 15% for T. turgidum, 32% for Ae. tauschii, 52% for Ae. speltoides and 61% for the tetraploid Aegilops species carrying the U genome. Differences in Zn efficiency among and within Aegilops species and T. turgidum were significantly correlated with the Zn amount per shoot, but not with the Zn amount per unit dry weight of shoots. The results show that Aegilops species can be exploited as an important genetic source for Zn efficiency genes, particularly Ae. speltoides var. ligustica (SS) and Ae. triuncialis (UUCC). Transfer of these genes to cultivated modern wheat may bring about a greater variation in Zn efficiency in wheat, and facilitate production of Zn-efficient modern wheat cultivars for Zn-deficient soil conditions. Reaktion verschiedener Aegilops-Arten auf Zinkmangel Zinkmangelsymptome, Spross-Trockengewicht und die Zn-Konzentration im Spross wurde an 15 Aegilops tauschii (DD Genom), 10 Ae. speltoides (SS Genom) und 8 tetraploiden Aegilops-Herkunften untersucht. Die Pflanzen wurden in einem kalkhaltigen Boden mit Zn-Mangel im Gewachshaus angezogen. Die Versuchsvarianten waren keine Zn-Dungung (—Zn) und 5 mg Zn kg—1 Boden (+Zn). Als Vergleich wurden 4 tetraploide Wildherkunfte von Triticum turgidum var. dicoccoides (BBAA) berucksichtigt, da sie Zn-Mangel gegenuber sehr anfallig sind. Wie erwartet, erwiesen sich die T. turgidum var. dicoccoides Wildherkunfte als am anfalligsten und ihre Blatter hatten die ausgepragtesten Zn-Mangelsymptome (weiss-braune nekrotische Flecken). Ein Vergleich zwischen den Aegilopsarten zeigte, dass im allgemeinen die Zn-Mangelsymptome auf den Blattern bei Ae. tauschii (DD) am starksten und bei Ae. speltoides (SS) am wenigsten ausgepragt waren. Die Zn-Effizienz, ausgedruckt als Prozentsatz des Spross-Trockengewichts unter Zn-Mangel relativ zum Spross-Trockengewicht unter Zugabe von Zn, war im Durchschnitt 15% fur T. turgidum, 32% fur Ae. tauschii, 52% fur Ae. speltoides und 61% fur die tetraploiden Aegilopsarten mit U Genom. Die Unterschiede in der Zn-Effizienz sowohl zwischen als auch innerhalb der Aegilopsarten waren signifikant mit der Gesamtmenge Zn pro Spross korreliert, nicht jedoch mit der Menge Zn pro Einheit Spross-Trockengewicht. Die Ergebnisse zeigen, das Aegilopsarten eine wichtige Quelle fur Gene zur Verbesserung der Zn-Effizienz in Weizen sein konnen, insbesondere Ae. speltoides var. ligustica (SS) und Ae. triuncialis (UUCC). Die Ubertragung dieser Gene konnte die Zuchtung von Zn-effizienten Sorten fur Zn-Mangelstandorte ermoglichen.

Strategic crossing of biomass and harvest index—source and sink—achieves genetic gains in wheat

We calculated the annual genetic gains for grain yield (GY) of wheat (Triticum aestivum L.) achieved over 8 yr of international Elite Spring Wheat Yield Trials (ESWYT), from 2006–2007 (27th ESWYT) to 2014–2015 (34th ESWYT). In total, 426 locations were classified within three main megaenvironments (MEs): ME1 (optimally irrigated environments), ME4 (drought-stressed environments), and ME5 (heat-stressed environments). By fitting a factor analytical structure for modeling the genotype × environment (G × E) interaction, we measured GY gains relative to the widely grown cultivar Attila (GYA) and to the local checks (GYLC). Genetic gains for GYA and GYLC across locations were 1.67 and 0.53% (90.1 and 28.7 kg ha–1 yr–1), respectively. In ME1, genetic gains were 1.63 and 0.72% (102.7 and 46.65 kg ha–1 yr–1) for GYA and GYLC, respectively. In ME4, genetic gains were 2.7 and 0.41% (88 and 15.45 kg ha–1 yr–1) for GYA and GYLC, respectively. In ME5, genetic gains were 0.31 and 1.0% (11.28 and 36.6 kg ha–1 yr–1) for GYA and GYLC, respectively. The high GYA in ME1 and ME4 can be partially attributed to yellow rust races that affect Attila. When G × E interactions were not modeled, genetic gains were lower. Analyses showed that CIMMYT’s location at Ciudad Obregon, Mexico, is highly correlated with locations in other countries in ME1. Lines that were top performers in more than one ME and more than one country were identified. CIMMYT’s breeding program continues to deliver improved and widely adapted germplasm for target environments.

CIMMYT Series on Carbohydrates, Wheat, Grains, and Health: Wheat-Based Foods: Their Global and Regional Importance in the Food Supply, Nutrition, and Health1,2

To address many current claims that disparage and discourage the ingestion of carbohydrates (CHOs), wheat, and cereal grains, even whole grains, as well as to celebrate the versatility, nutritional and health benefits, and contribution of these foods to the world food supply, we felt compelled to defend their role in the diet and write this series of reviews. Where data exist, cereal grains and wheat as a source of CHOs and other important nutrients will be the focus. CHO-rich staple foods, including those from a wide array of whole and refined grains, are inexpensive sources of energy, protein, and other nutrients. Grain-based staple ingredients have been incorporated into an enormous variety of foods, becoming cultural icons and national dishes that are accepted by populations around the world and adapted to specific agricultural necessities and cultural preferences. Dietary guidance by health promotion bodies around the world recommends that 45–65% of total calories be from CHOs and reinforces the mess...

CIMMYT Series on Carbohydrates, Wheat, Grains, and Health: Carbohydrates, Grains, and Wheat in Nutrition and Health: An Overview. Part II. Grain Terminology and Nutritional Contributions1,2

To accelerate genetic gains in breeding, physiological trait (PT) characterization of candidate parents can help make more strategic crosses, increasing the probability of accumulating favorable alleles compared to crossing relatively uncharacterized lines. In this study, crosses were designed to complement “source” with “sink” traits, where at least one parent was selected for favorable expression of biomass and/or radiation use efficiency—source—and the other for sink-related traits like harvest-index, kernel weight and grains per spike. Female parents were selected from among genetic resources—including landraces and products of wide-crossing (i.e. synthetic wheat)—that had been evaluated in Mexico at high yield potential or under heat stress, while elite lines were used as males. Progeny of crosses were advanced to the F4 generation within Mexico, and F4-derived F5 and F6 generations were yield tested to populate four international nurseries, targeted to high yield environments (2nd and 3rd WYCYT) for yield potential, and heat stressed environments (2nd and 4th SATYN) for climate resilience, respectively. Each nursery was grown as multi-location yield trials. Genetic gains were achieved in both temperate and hot environments, with most new PT-derived lines expressing superior yield and biomass compared to local checks at almost all international sites. Furthermore, the tendency across all four nurseries indicated either the superiority of the best new PT lines compared with the CIMMYT elite checks, or the superiority of all new PT lines as a group compared with all checks, and in some cases, both. Results support—in a realistic breeding context—the hypothesis that yield and radiation use efficiency can be increased by improving source:sink balance, and validate the feasibility of incorporating exotic germplasm into mainstream breeding efforts to accelerate genetic gains for yield potential and climate resilience.

Occurrence of wheat blast in Bangladesh and its implications for South Asian wheat production

Meeting the growing demand for food over the next 20–30 years will be challenging, mainly because the fastest population growth is occurring in already highly populated developing countries and because producing cereal crops (the main source of nutrients in these countries) requires that serious production constraints, due mainly to the effects of climate change, be overcome. Wheat supplies the most calories and proteins to the global population in the form of diverse wheat-based foods. Wheat-based foods are staples that are major sources of micronutrients that are fundamental for normal development, as well as metabolic and cognitive functioning, from childhood to adulthood. Furthermore, whole grain, wheat-based foods have potential additional health benefits because they contribute fiber and bioactive compounds that can help reduce the risk of chronic conditions, such as cardiovascular disease, type 2 diabetes, and other chronic conditions. In this article, we describe common wheat-based foods consumed ...

CIMMYT Series on Carbohydrates, Wheat, Grains, and Health: Carbohydrates, Grains, and Wheat in Nutrition and Health: Their Relation to Digestion, Digestive Disorders, Blood Glucose, and Inflammation1,2

To address many current claims that disparage and discourage the ingestion of carbohydrates (CHOs), wheat, and cereal grains, as well as to celebrate the versatility, nutritional and health benefits, and contribution of these foods to the world food supply, we felt compelled to defend their role in the diet and write a series of reviews. Where data exist, cereal grains and wheat as a source of CHOs and other important nutrients are the focus. In this second review, grain- and wheat-based staples are shown to be important contributors of CHOs (including cereal fiber), as well as necessary proteins, vitamins, and minerals, as part of a balanced diet for most healthy individuals. The terminology associated with grains and whole grains and their processing also is discussed and defined. Dietary fiber and resistant starch are defined, and a whole grain food characterization is provided. Clear delineation of terms is critical because they differ from country to country and are a source of consumer confusion in ...