Wolfgang H. Pfeiffer

Bringing wild relatives back into the family: recovering genetic diversity in CIMMYT improved wheat germplasm

SummaryThe dangers of a narrow genetic base of the worlds major domesticated food crops have become a great global concern in recent decades. The efforts of the International Maize and Wheat Improvement Center (CIMMYT) to breed common wheat cultivars for resource poor farmers in the developing world (known as the Green Revolution wheats) has met with notable success in terms of improved yield, yield stability, increased disease resistance and utilization efficiency of agricultural inputs. However, much of the success was bought at the cost of an overall reduction in genetic diversity in the species; average Modified Rogers distances (MRD) within groups of germplasm fell from 0.64 in the landraces to a low of 0.58 in the improved lines in the 1980s. Recent efforts by CIMMYT breeders to expand the genetic base of common wheat has included the use of landraces, materials from other breeding programs, and synthetic wheats derived from wild species in the pedigrees of new advanced materials. The result, measured using SSR molecular markers, is a highly significant increase in the latent genetic diversity of recently developed CIMMYT breeding lines and cultivars compared to the original Green Revolution wheats (average MRD of the latest materials (0.63) is not significantly different from that of the landraces, as tested using confidence intervals). At the same time, yield and resistance to biotic and abiotic stresses, and end-use quality continue to increase, indicating that the Green Revolution continues to this day.

Global adaptation patterns of Australian and CIMMYT spring bread wheat

The International Adaptation Trial (IAT) is a special purpose nursery designed to investigate the genotype-by-environment interactions and worldwide adaptation for grain yield of Australian and CIMMYT spring bread wheat (Triticum aestivum L.) and durum wheat (T. turgidum L. var. durum). The IAT contains lines representing Australian and CIMMYT wheat breeding programs and was distributed to 91 countries between 2000 and 2004. Yield data of 41 reference lines from 106 trials were analysed. A multiplicative mixed model accounted for trial variance heterogeneity and inter-trial correlations characteristic of multi-environment trials. A factor analytic model explained 48% of the genetic variance for the reference lines. Pedigree information was then incorporated to partition the genetic line effects into additive and non-additive components. This model explained 67 and 56% of the additive by environment and non-additive by environment genetic variances, respectively. Australian and CIMMYT germplasm showed good adaptation to their respective target production environments. In general, Australian lines performed well in south and west Australia, South America, southern Africa, Iran and high latitude European and Canadian locations. CIMMYT lines performed well at CIMMYT’s key yield testing location in Mexico (CIANO), north-eastern Australia, the Indo-Gangetic plains, West Asia North Africa and locations in Europe and Canada. Maturity explained some of the global adaptation patterns. In general, southern Australian germplasm were later maturing than CIMMYT material. While CIANO continues to provide adapted lines to northern Australia, selecting for yield among later maturing CIMMYT material in CIANO may identify lines adapted to southern and western Australian environments.

Variation of the crossability of durum wheat with maize

With the aim of examining crossability of durum wheat with maize, two sets of durum wheat genotypes and a set of D-genome chromosome substitution lines of the durum wheat variety ‘Langdon’ were crossed with maize, and followed by 2,4-dichlorophenoxyacetic acid (2,4-D) treatment in detached-tiller culture. In crosses of 25 durum wheat genotypes (breeding lines) with maize, percent frequencies of embryo formation increased from 1.4% to 2.8% by adding silver nitrate to the detached-tiller culture solution. In crosses of 32 durum wheat genotypes (advanced lines and varieties) with maize using the silver nitrate addition, frequencies of embryo formation ranged from 0.0% to 15.8%; seven genotypes showing more than 6.0% embryo formation frequency were related in their pedigrees. In crosses of a set of chromosome substitution lines with maize, higher frequencies of embryo formation were obtained in substitution lines with chromosomes 1D, 3D, 4D and 7D. These results suggest that 1) adding silver nitrate to the 2,4-D treatment increases overall frequency of embryo formation but is not effective enough to induce the development of seeds and embryos from all durum wheat genotypes, and 2) some D-genome chromosomes substituted in a durum wheat genetic background may enhance crossability with maize in combination with homoeologous chromosomes of durum wheat.

Reaching out to Farmers with High Zinc Wheat Varieties through Public-Private Partnerships – An Experience from Eastern-Gangetic Plains of India

The main objective of the HarvestPlus led wheat biofortification breeding program at the International Maize and Wheat Improvement Center (CIMMYT) and its national program partners in South Asia is to develop and disseminate competitive wheat varieties with high grain zinc (Zn) and other essential agronomic features. The emphasis of this program is to introduce novel sources of genetic diversity from wild species and landraces, into the adapted wheat background. This variation is being exploited through limited backcross approach with shuttle breeding at two contrasting locations in Mexico, which resulted in widely adapted, durable rust and foliar disease resistant, high Zn wheat varieties. The new wheat varieties developed by CIMMYT in HarvestPlus project are 20-40% superior in grain Zn concentration and are agronomically at par or superior to the popular wheat cultivars of South Asia. The biofortification breeding program of CIMMYT utilizes new wheat varieties from the core-breeding program as background parents that are higher yielding, resistant to rusts, heat tolerant, wateruse efficient and 5-10% higher yielding than main varieties grown at present. The biofortified high Zn wheat varieties with 20 to 40% (8-12 mg/kg) Zn superiority and grain yield potential at par or superior to the popular wheat varieties are being adopted by small-holder farmers in South Asia. Through Public-private partnerships (PPP) more than 50,000 farmers and 250,000 household members expected to benefit from the Zn-biofortified wheat varieties in South Asia by the 2015-2016 wheat seasons.

Crossability of tetraploid and hexaploid wheats with ryes for primary triticale production

SummaryCrossability of wheat and rye was investigated during thirteen crop cycles in two contrasting locations to 1) evaluate tetraploid and hexaploid wheat parents in crosses with rye, 2) identify genotypes with high crossability and 3) assess the impact of environment on seed development. The majority of the tetraploid wheats crossed with rye had seed set around 20%, but very low embryo viability. Several wheat genotypes with seed set above 50% were identified. The hexaploid wheats crossed with rye showed poor seed set, but plant recovery was relatively high. The majority of the hexaploid wheats with highest seed set (20–30%) were from China. The results suggest differences in crossability between the rye populations, and wheat species by rye interactions. The crossability of the tetraploid and hexaploid wheats was affected by climate in the two locations.

Triticale: Potential and Research Status of a Man-Made Cereal Crop

Triticale (Tcl) improvement concentrates on generating various crop and utilization options. These are associated with crop adaptive patterns, economic comparative advantages, issues of environmental sustainability, as well as issues of consumption, marketing, and end uses. By focusing on Tcl’s comparative advantages over other crops regarding these options, CIMMYT has shifted its Tcl breeding objectives. International yield data and past experience indicate high genetic progress in Tcl grain yield under marginal and high production conditions (> 1.5%/year). Since grain yield in marginal environments reflects the genotypic response to the total environment, progress has to be associated with advances for all biotic and abiotic factors involved. Under near optimal conditions, comparison in maximum yield trials at Cd. Obregon over three location years of Tcls developed in the 1980s and 1990s reveals overall yield progress to be at +17% due to increases in harvest index (+16%), grain biomass production rate (+21%), grains/m2 (+17%), spikes/m2 (+12%), and test weight (+12%) and a decrease in height (-11%). Genetic variabilities for these traits suggest that gains in genetic grain yield potential can be maintained in the future. High rates of progress in germplasm developed from crosses involving interspecific Tcl x wheat, spring x winter Tcl, and 2D(2R) x complete R type suggest that these gene pools are promising sources with which to achieve future genetic gains. The shift in breeding emphasis to complete R genome and 6D(6A) types in the 1980s was accompanied by improved test weights, but negative effects on baking quality. Subsequent research with wheat-Tcl grain and flour blends on milling and baking properties suggested blends for commercial use. In 1990, specialized requirements and markets for products for human consumption, feed grain, and growing interest in forage and dual purpose triticales were prompted by end-use oriented and expanded breeding objectives. By 1994, germplasm products for the range of utilizations are available. Current quality improvement hinges on introgressing high-molecular-weight glutenin subunits, particularly allelic variants at loci Glu-D1, Glu-B1 and Glu-Al. Spectacular increases in SDS sedimentation in 1D(1A), 1D(1B), and 1Rs.1Dl Tcls that carry D genome non-enzymatic storage proteins suggest a future breakthrough in improving Tel’s industrial quality, while additional gains can be expected from exploiting gliadins and secalins.

International Collaboration on Wheat Improvement

To paraphrase Cox (1991), all polyploid wheat grown today outside of what was the ancient Mesopotamian Fertile Crescent is there due to germplasm exchange and introductions resulting in the most widely and diversely grown crop. Around 6000 years ago, the Neolithic Dispersal of wheat began the development of a staple-food producing sedentary culture and economy in the Middle East, North Africa, Asia, and ultimately Europe (Harlan, 1987). During the Middle Ages (ca 1500 AD), wheat spread to the New World and Southern Africa, and in 1790 it was introduced to Australia. Mennonites emigrating from the Crimea to Kansas in 1873 carried seed of the landrace “Turkey Red”, the progenitor of the contemporary hard red winter wheats of the North American Great Plains (Smale and McBride, 1996). Though the Fertile Crescent served as the nucleus from where wheat radiated, traditional and modern breeders from all wheat growing areas of the world have made important contributions to gennplasm improvement. Peterson and Busch (1995), Smale and McBride (1996) and Rajaram and Ceccarelli (1998) have listed landraces and cultivars from more than twenty countries, which have made a major impact on global wheat improvement and production. Clearly, wheat today is the result of a truly international effort, for which we have all benefited.

Establishment of a Network for Genetic Resources

Systematic germplasm creation and deployment is the basis for the establishment of the ITA’s first ‘Co-operative Network’. Membership of the network will normally require an active contribution by an individual or organisation in the development of germplasm resources. Membership will also be afforded to organisations with a mandate for the development of regionally adapted germplasm. The germplasm centre at CIMMYT is willing to take a leadership role in the documentation, maintenance and distribution of newly developed germplasm. Germplasm will be freely interchanged among members of the co-operative, and all materials held in the CIMMYT collection will be available on request. The management committee will be subject to election by participating members of the co-operative during a meeting to be held at each International Triticale Symposium. The management committee is responsible for approving and amending membership lists and for co-ordinating various aspects of germplasm research. The genetic resources will initially include primary triticales, selected progenies from primary (or amphihaploid) times primary or secondary triticale crosses, standard wheats and ryes for triticale production or standard triticales with special attributes (eg. good GCA, disease resistance, spontaneous doubling genes for haploid producing systems, good green/albino ratio for anther culture derived regenerants, male sterility for germplasm deployment and recurrent selection, etc.). The network objectives, methodologies (strategies for germplasm production and evaluation/deployment), data and communication bases and contributions of the authors are presented along with membership and nomination lists for completion by intending participants.

CHARACTERIZATION OF LAMB-2, A NEW TRITICALE VARIETY FOR THE HIGHLY VARIABLE MOISTURE SITUATION OF CENTRAL MEXICO

The highly variable rainfall patterns in the eastern part of transversal volcanic zone in the Central Highlands of Mexico are reflected in the grain yields of small cereals grown there. Such situations demand germplasm that combines low moisture-efficiency with high moisture- and input-responsiveness to exploit the changing environmental yield potentials.