Posts Tagged ‘landraces’

Maize landraces and adaptation to climate change in Mexico

Posted by Carelia Juarez on , in Journal Articles

Published in Journal of Crop Improvement  28 (4) : 484-501, 2014

Hellin, J.Bellon, M.R.Hearne, S. 

Mexico is the primary center of origin and diversity for maize (Zea mays L.). Farmers grow the crop largely under rain-fed conditions. Mexico is at considerable risk from climate change because of predicted rising temperatures, declining rainfall, and an increase in extreme weather events. Small-scale maize farmers are particularly vulnerable because of their geographical location as well as their limited adaptive capacity. Recommended climate change adaptation strategies include farmers’ increased use of heat and drought stress-tolerant maize. Farmer adoption of improved germplasm has been disappointing because of inefficient seed input chains and farmers’ preference for landraces for culinary, agronomic, and cultural reasons. Scientists have tended to overlook the fact that maize landraces have a critical role to play in climate change adaptation. Landraces may already exist that are appropriate for predicted climates. Furthermore, within the primary gene pool of maize and its wild relatives there exists unexploited genetic diversity for novel traits and alleles that can be used for breeding new high yielding and stress-tolerant cultivars. The breeding component of adaptation strategies should focus more on improving farmers’ landraces. The desired result would be a segmented maize seed sector characterized by both (improved) landraces and improved maize varieties. The public and private sector could continue to provide farmers with improved maize varieties and different actors, including farmers themselves, would generate seed of improved landraces for sale and/or exchange.

Microsatellite marker-based diversity and population genetic analysis of selected lowland and mid-altitude maize landrace accessions of India

Posted by Carelia Juarez on , in Journal Articles

Published in Journal of Plant Biochemistry and Biotechnology, 2012

Samanthi K. Wasala and B. M. Prasanna

Maize (Zea mays L.) harbours significant genetic diversity not only in its centre of origin (Mexico) but also in several countries worldwide, including India, in the form of landraces. In this study, DNA fingerprinting of 48 landrace accessions from diverse regions of India was undertaken using 42 fluorescent dye-labeled Simple Sequence Repeat (SSR) markers, followed by allele resolution using DNA sequencer and analysis of molecular diversity within and among these landraces. The study revealed a large number of alleles (550), with high mean number of alleles per locus (13.1), and Polymorphism Information Content (PIC) of 0.60, reflecting the level of diversity in the landrace accessions. Besides identification of 174 unique alleles in 44 accessions, six highly frequent SSR alleles were detected at six loci (phi014, phi090, phi112, umc1367, phi062 and umc1266) with individual frequencies greater than 0.75, indicating that chromosomal regions harboring these SSR alleles are not selectively neutral. F statistics revealed very high genetic differentiation, population subdivision and varying levels of inbreeding in the landraces. Analysis of Molecular Variance showed that 63 % of the total variation in the accessions could be attributed to within-population diversity, and 37 % represented between population diversity. Cluster analysis of SSR data using Nei’s genetic distance and UPGMA revealed considerable genetic diversity in these populations, although no clear separation of accessions was observed based on their geographic origin.

 

Diversity in global maize germplasm: Characterization and utilization

Posted by Carelia Juarez on , in Journal Articles

Published in Journal of Biosciences  37 (5) : 843-855, 2012

B.M. Prasanna

Maize (Zea mays L.) is not only of worldwide importance as a food, feed and as a source of diverse industrially important products, but is also a model genetic organism with immense genetic diversity. Although it was first domesticated in Mexico, maize landraces are widely found across the continents. Several studies in Mexico and other countries highlighted the genetic variability in the maize germplasm. Applications of molecular markers, particularly in the last two decades, have led to new insights into the patterns of genetic diversity in maize globally, including landraces as well as wild relatives (especially teosintes) in Latin America, helping in tracking the migration routes of maize from the centers of origin, and understanding the fate of genetic diversity during maize domestication. The genome sequencing of B73 (a highly popular US Corn Belt inbred) and Palomero (a popcorn landrace in Mexico) in the recent years are important landmarks in maize research, with significant implications to our understanding of the maize genome organization and evolution. Next-generation sequencing and high-throughput genotyping platforms promise to further revolutionize our understanding of genetic diversity and for designing strategies to utilize the genomic information for maize improvement. However, the major limiting factor to exploit the genetic diversity in crops like maize is no longer genotyping, but high-throughput and precision phenotyping. There is an urgent need to establish a global phenotyping network for comprehensive and efficient characterization of maize germplasm for an array of target traits, particularly for biotic and abiotic stress tolerance and nutritional quality. ‘Seeds of Discovery’ (SeeD), a novel initiative by CIMMYT with financial support from the Mexican Government for generating international public goods, has initiated intensive exploration of phenotypic and molecular diversity of maize germplasm conserved in the CIMMYT Gene Bank; this is expected to aid in effective identification and use of novel alleles and haplotypes for maize improvement. Multi-institutional efforts are required at the global level to systematically explore the maize germplasm to diversify the genetic base of elite breeding materials, create novel varieties and counter the effects of global climate changes.

 

Assessing the vulnerability of traditional maize seed systems in Mexico to climate change

Posted by Carelia Juarez on , in Journal Articles

Published in Proceedings of the National Academy of Sciences  108 (33): 13432-13437, 2012

Mauricio R. Bellon, David Hodson and Jon Hellin

Climate change is predicted to have major impacts on small-scale farmers in Mexico whose livelihoods depend on rain-fed maize. We examined the capacity of traditional maize seed systems to provide these farmers with appropriate genetic material under predicted agro-ecological conditions associated with climate change. We studied the structure and spatial scope of seed systems of 20 communities in four transects across an altitudinal gradient from 10–2,980 m above sea level in five states of eastern Mexico. Results indicate that 90% of all of the seed lots are obtained within 10 km of a community and 87% within an altitudinal range of ±50 m but with variation across four agro-climate environments: wet lowland, dry lowland, wet upper midlatitude, and highlands. Climate models suggest a drying and warming trend for the entire study area during the main maize season, leading to substantial shifts in the spatial distribution patterns of agro-climate environments. For all communities except those in the highlands, predicted future maize environments already are represented within the 10-km radial zones, indicating that in the future farmers will have easy access to adapted planting material. Farmers in the highlands are the most vulnerable and probably will need to acquire seed from outside their traditional geographical ranges. This change in seed sources probably will entail important information costs and the development of new seed and associated social networks, including improved linkages between traditional and formal seed systems and more effective and efficient seed-supply chains. The study has implications for analogous areas elsewhere in Mexico and around the world.

Grain and Tortilla Quality in Landraces and Improved Maize Grown in the Highlands of Mexico

Posted by Carelia Juarez on , in Journal Articles

Published in  Plant Foods for Human Nutrition 66(2): 203-208, 2011

Grain and Tortilla Quality in Landraces and Improved Maize Grown in the Highlands of Mexico

Gricelda Vázquez-Carrillo, Silverio García-Lara, Yolanda Salinas-Moreno, David J. Bergvinson and Natalia Palacios-Rojas

The maize produced in the highlands of Mexico (>2,400 masl) is generally not accepted by the flour and masa and tortilla industry. The objective of this work was to evaluate the grain quality and tortilla properties of maize landraces commonly grown in the highlands of Mexico and compare them with improved germplasm (hybrids). Germplasm analysis included 11 landraces, 32 white hybrids, and six yellow hybrids. Grain quality was analyzed for a range of physical and chemical factors, as well as for alkaline cooking quality. Landrace grains tended to be heterogeneous in terms of size, hardness and color. All landraces had soft-intermediate grains with an average flotation index (FI) of 61%. In contrast, hybrid grains were homogenous in size and color, and harder than landrace grains, with a FI of 38%. Protein, free sugars, oil and phenolic content in landraces were higher than in the hybrids. Significant correlations were found between phenolic content and tortilla color (r = −0.60; p < 0.001). Three landraces were identified as appropriate for the masa and tortilla industry, while all the hybrids evaluated fulfilled the requirements of this industry.

Assessment of high molecular weight glutenin sub-units and baking quality related traits in some of the Iranian bread wheat (Triticum aestivum L.) landraces

Posted by on , in Journal Articles

Published in Crop Breeding Journal 1(1): 29-40, 2011

Assessment of high molecular weight glutenin sub-units and baking quality related traits in some of the Iranian bread wheat (Triticum aestivum L.) landraces

M. Esmaeilzadeh Moghaddam, M. R. Jalal Kamali, S. Kazemi, A. Amini, R. Bozorgipour, G. Najafian and N. Baghaei

High molecular weight (HMW) glutenin sub-units and baking quality related traits were studied in 49 Iranian wheat landraces. The protein content ranged from 11.2% to 13.55%, and SDS sedimentation volume varied between 40 and 60 milliliters. High Molecular weight glutenin electrophoresis profiles revealed that at the Glu-A1 locus, the frequency of null allele was higher than sub-units 1 and 2*. Allelic variation for Glu-B1 locus was also considerable as sub-units of 7, 7+8, 6+8, 14+15, 7+9, 17+18, 13+16 and 20 were observed. The highest and lowest frequencies of Glu-B1 belonged to sub-units 7+8 (56%), and 13+16 (2%), respectively. For Glu-D1, 2+12 sub-units (74%) were of higher frequency in comparison with 5+10 sub-units (14%). At this locus, the rare 2***+12′ sub-units with frequency of 2% were also observed. Scoring of germplasm based on electrophoresis patterns using Payne method showed that the scores varied from 4 to 8. Based on this scoring, three landraces were ranked as superior. Cluster analysis based on electrophoresis patterns and Jaccard similarity criteria divided the landraces into three groups. Forty landraces with cv. Chamran, as check, were grouped in the first cluster. There was no similarity between grouping pattern based on HMW glutenin sub-units and quality related traits. Considering high variation observed for quality related traits and HMW glutenin sub-units, it can be concluded that these landraces are potential sources of desirable quality traits to be used in bread wheat breeding programs to improve bread- baking quality.

 

Phenotyping approaches for physiological breeding and gene discovery in wheat

Posted by on , in Journal Articles

Published in Annals of Applied Biology 155: 309-320

Phenotyping approaches for physiological breeding and gene discovery in wheat

Reynolds, M.; Manes, Y.; Izanloo, A.; Langridge, P.

Conceptual models of drought-adaptive traits have been used in breeding to accumulate complementary physiological traits (PT) in selected progeny, resulting in distribution of advanced lines to rain-fed environments worldwide by the International Maize and Wheat Improvement Center (CIMMYT). Key steps in PT breeding at CIMMYT include characterisation of crossing block lines for stress adaptive mechanisms, strategic crossing among parents that encompass as many target traits as possible and early generation selection (EGS) of bulks for canopy temperature (CT). The approach has been successful using both elite × elite crosses as well as three way crosses involving stress adapted landraces. Other EGS techniques that are amenable to high throughput include measurement of spectral reflectance indices and stomatal aperture-related traits. Their genetic- and cost-effectiveness are supported by realisation of genetic yield gains in response to trait selection, and by economic analysis, respectively. Continual reselection within restricted gene pools is likely to lead to diminishing returns, however, exotic parents can be used to introduce new allelic diversity. Examples include landraces from the primary gene pool, and products of inter-specific hybridisation with the secondary gene pool consisting of closely related wheat genomes. Both approaches have been successful in introducing stress-adaptive traits. The main problem with knowing which genetic resource to use in wide-crossing is the uncertainty with which phenotypic expression can be extrapolated from one genome/genepool to another because of their unimproved or undomesticated genetic backgrounds. Nonetheless, their PT expression can be measured and used as a basis for investing in crossing or wide crossing. Discovering the genetic basis of PT is highly complex because putative QTLs may interact with environment and genetic background, including genes of major effect. Detection of QTLs was improved in mapping populations where flowering time was controlled, while new mapping populations have been designed by screening potential parents that do not contrast in the Rht, Ppd and Vrn alleles. Association genetics mapping is another approach that can be employed for gene discovery using exclusively agronomically improved material, thereby minimising the probability of identifying yield QTLs whose alleles have been already improved by conventional breeding.