Govindan Velu

Race non-specific resistance to rust diseases in CIMMYT spring wheats

Rust diseases continue to cause significant losses to wheat production worldwide. Although the life of effective race-specific resistance genes can be prolonged by using gene combinations, an alternative approach is to deploy varieties that posses adult plant resistance (APR) based on combinations of minor, slow rusting genes. When present alone, APR genes do not confer adequate resistance especially under high disease pressure; however, combinations of 4–5 such genes usually result in “near-immunity” or a high level of resistance. Although high diversity for APR occurs for all three rusts in improved germplasm, relatively few genes are characterized in detail. Breeding for APR to leaf rust and stripe rust in CIMMYT spring wheats was initiated in the early 1970s by crossing slow rusting parents that lacked effective race-specific resistance genes to prevalent pathogen populations and selecting plants in segregating populations under high disease pressure in field nurseries. Consequently most of the wheat germplasm distributed worldwide now possesses near-immunity or adequate levels of resistance. Some semidwarf wheats such as Kingbird, Pavon 76, Kiritati and Parula show high levels of APR to stem rust race Ug99 and its derivatives based on the Sr2-complex, or a combination of Sr2 with other uncharacterized slow rusting genes. These parents are being utilized in our crossing program and a Mexico-Kenya shuttle breeding scheme is used for selecting resistance to Ug99. High frequencies of lines with near-immunity to moderate levels of resistance are now emerging from these activities. After further yield trials and quality assessments these lines will be distributed internationally through the CIMMYT nursery system.

Harnessing Diversity in Wheat to Enhance Grain Yield, Climate Resilience, Disease and Insect Pest Resistance and Nutrition Through Conventional and Modern Breeding Approaches

Current trends in population growth and consumption patterns continue to increase the demand for wheat, a key cereal for global food security. Further, multiple abiotic challenges due to climate change and evolving pathogen and pests pose a major concern for increasing wheat production globally. Triticeae species comprising of primary, secondary, and tertiary gene pools represent a rich source of genetic diversity in wheat. The conventional breeding strategies of direct hybridization, backcrossing and selection have successfully introgressed a number of desirable traits associated with grain yield, adaptation to abiotic stresses, disease resistance, and bio-fortification of wheat varieties. However, it is time consuming to incorporate genes conferring tolerance/resistance to multiple stresses in a single wheat variety by conventional approaches due to limitations in screening methods and the lower probabilities of combining desirable alleles. Efforts on developing innovative breeding strategies, novel tools and utilizing genetic diversity for new genes/alleles are essential to improve productivity, reduce vulnerability to diseases and pests and enhance nutritional quality. New technologies of high-throughput phenotyping, genome sequencing and genomic selection are promising approaches to maximize progeny screening and selection to accelerate the genetic gains in breeding more productive varieties. Use of cisgenic techniques to transfer beneficial alleles and their combinations within related species also offer great promise especially to achieve durable rust resistance.

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

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.

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.

Phenotyping in Wheat Breeding

Approximately 25 % of global agricultural land is utilized for wheat cultivation, making wheat the largest food crop worldwide in terms of area. Wheat is the second most produced cereal crop after Maize with more than 650 million tons produced every year. Wheat productivity is increasing at less than 1 percent annually, while the annual productivity must increase at 2 % annually to meet the global demand. The potential of increasing arable land is limited; hence future increases in wheat production must be achieved by enhancing the productivity per unit area. Increasing grain yield, yield stability, resistance/tolerance to biotic and abiotic stresses, and end-use quality characteristics are among the most important wheat breeding goals.

Genetic impact of Rht dwarfing genes on grain micronutrients concentration in wheat.

Highlights • The Rht dwarfing genes decreased micronutrient concentrations, however, the magnitude depends on the genetic background.• There was a negative effect on kernel weight indicating that Rht genes increased the number of kernels per spike as well as kernels per unit area.• Highly significant positive correlation between the micronutrients; rate of reductions differs in different genetic background.

Variability in iron, zinc and phytic acid content in a worldwide collection of commercial durum wheat cultivars and the effect of reduced irrigation on these traits

Highlights • Malnutrition is a major challenge worldwide associated with diets rich in cereals.• Durum wheat is important source of calories and protein in developing countries.• A modified scale-down method to quantify phytate was validated.• 46 durum varieties were analyzed for Fe, Zn and phytate (bioavailability) content.• Variation was detected for Phy:Fe (12.1–29.6) and Phy:Zn (16.9–23.6) molar ratios.

Characterization of grain protein content gene ( GPC - B1 ) introgression lines and its potential use in breeding for enhanced grain zinc and iron concentration in spring wheat

At least two billion people around the world suffer from micronutrient deficiency, or hidden hunger, which is characterized by iron-deficiency anemia, vitamin A and zinc deficiency. As a key staple food crop, wheat provides 20% of the world’s dietary energy and protein, therefore wheat is an ideal vehicle for biofortification. Developing biofortified wheat varieties with genetically enhanced levels of grain zinc (Zn) and iron (Fe) concentrations, and protein content provides a cost-effective and sustainable solution to the resource-poor wheat consumers. Large genetic variation for Fe and Zn were found in the primitive and wild relatives of wheat, the potential high Zn and Fe containing genetic resources were used as progenitors to breed high-yielding biofortified wheat varieties with 30–40% higher Zn content. Grain protein content (GPC) determines processing and end-use quality of wheat for making diverse food products. The GPC-B1 allele from Triticum turgidum L. var. dicoccoides have been well characterized for the increase in GPC and the associated pleiotropic effect on grain Zn and Fe concentrations in wheat. In this study effect of GPC-B1 allele on grain Zn and Fe concentrations in wheat were measured in different genetic backgrounds and two different agronomic management practices (with- and without foliar Zn fertilization). Six pairs of near-isogenic lines differing for GPC-B1 gene evaluated at CIMMYT, Mexico showed that GPC-B1 influenced marginal increase for grain Zn, Fe concentrations, grain protein content and slight reduction in kernel weight and grain yield. However, the magnitude of GPC and grain Zn and Fe reductions varied depending on the genetic background. Introgression of GPC-B1 functional allele in combination with normal or delayed maturity alleles in the CIMMYT elite wheat germplasm has the potential to improve GPC and grain Zn and Fe concentrations without the negative effect on grain yield due to early senescence and accelerated maturity.

Genetic dissection of grain zinc concentration in spring wheat for mainstreaming biofortification in CIMMYT wheat breeding

Wheat is an important staple that acts as a primary source of dietary energy, protein, and essential micronutrients such as iron (Fe) and zinc (Zn) for the world’s population. Approximately two billion people suffer from micronutrient deficiency, thus breeders have crossed high Zn progenitors such as synthetic hexaploid wheat, T. dicoccum, T. spelta, and landraces to generate wheat varieties with competitive yield and enhanced grain Zn that are being adopted by farmers in South Asia. Here we report a genome-wide association study (GWAS) using the wheat Illumina iSelect 90 K Infinitum SNP array to characterize grain Zn concentrations in 330 bread wheat lines. Grain Zn phenotype of this HarvestPlus Association Mapping (HPAM) panel was evaluated across a range of environments in India and Mexico. GWAS analysis revealed 39 marker-trait associations for grain Zn. Two larger effect QTL regions were found on chromosomes 2 and 7. Candidate genes (among them zinc finger motif of transcription-factors and metal-ion binding genes) were associated with the QTL. The linked markers and associated candidate genes identified in this study are being validated in new biparental mapping populations for marker-assisted breeding.

Genetic Gains for Grain Yield in CIMMYT’s Semi-Arid Wheat Yield Trials Grown in Suboptimal Environments

Wheat (Triticum aestivum L.) is a major staple food crop grown worldwide on >220 million ha. Climate change is regarded to have severe effect on wheat yields, and unpredictable drought stress is one of the most important factors. Breeding can significantly contribute to the mitigation of climate change effects on production by developing drought-tolerant wheat germplasm. The objective of our study was to determine the annual genetic gain for grain yield (GY) of the internationally distributed Semi-Arid Wheat Yield Trials, grown during 2002–2003 to 2013–2014 and developed by the Bread Wheat Breeding program at the CIMMYT. We analyzed data from 740 locations across 66 countries, which were classified in low-yielding (LYE) and medium-yielding (MYE) environments according to a cluster analysis. The rate of GY increase (GYC) was estimated relative to four drought-tolerant wheat lines used as constant checks. Our results estimate that the rate of GYC in LYE was 1.8% (38.13 kg ha−1 yr−1), whereas in MYE, it was 1.41% (57.71 kg ha−1 yr−1). The increase in GYC across environments was 1.6% (48.06 kg ha−1 yr−1). The pedigrees of the highest yielding lines through the coefficient of parentage analysis indicated the utilization of three primary sources—‘Pastor’, ‘Baviacora 92’, and synthetic hexaploid derivatives—to develop drought-tolerant, high and stably performing wheat lines. We conclude that CIMMYT’s wheat breeding program continues to deliver adapted germplasm for suboptimal conditions of diverse wheat growing regions worldwide.