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The Mexican Landraces: Description, Classification and Diversity
Abstract
The domestication of maize gave rise to a group of ancestral landraces that eventually diversified and adapted to a wide range
of climatic and geographic conditions. Although biologists do not always agree in the total number of landraces currently
existing in Mexico, there are at least 59 that can be clearly and consistently distinguished on the basis of biochemical and
morphological characteristics. Following a historical perspective, this chapter reviews our current knowledge of the phenotypic
and geographical distinctions among Mexican landraces, and illustrates their most recent classification. It also discusses
some of the opportunities that the genomic characterization of landrace germplasm could offer for the study of maize functional
diversity and molecular evolution.
... Considering that Mexico is the center of origin and one main center of diversity of maize, and further considering the cultural importance of maize, genetic variability in Mexico has been thoroughly studied since 1913 [23,24]. The concept of the racial complex for the classification of Mexican maize landraces was established in the early 1950s [25]. ...
... Later, using a comprehensive review of previous research [26], Mexican landraces were placed into three main groups: the first containing long and narrow ears that are found in northwestern Mexico and southwestern United States; another comprised of high elevation maize with conical ears; and the last group possessing maize with small and long ears typical from the lowlands from southern Mexico. This classification is accepted as correct by most researchers, but refinements and modifications have been suggested [23,24] (S1 Fig). Compared to the wealth of data available for Mexican landraces, landraces from the rest of Latin America have been very poorly characterized overall. ...
... Genetic diversity values, average number of alleles per locus, and unique alleles found between the three main groups and sub-groups identified by Structure and sub-structure analyses for the 194 maize populations are presented in Table 3. Overall genetic diversity for all 194 accessions was 0.62, all markers were polymorphic, and 291 alleles were detected for the 28 SSRs (ranging from 2-21 per locus with an average of 10.39). The largest number of unique alleles (24) per main group was obtained in the Andean maize (G3); other main clusters had 15 (G1) to 14 (G2) alleles. The highest diversity index was found within G1 (0.63) and the lowest within G3 (0.57). ...
This study describes the genetic diversity and population structure of 194 native maize populations from 23 countries of Latin America and the Caribbean. The germplasm, representing 131 distinct landraces, was genetically characterized as population bulks using 28 SSR markers. Three main groups of maize germplasm were identified. The first, the Mexico and Southern Andes group, highlights the Pre-Columbian and modern exchange of germplasm between North and South America. The second group, Mesoamerica lowland, supports the hypothesis that two separate human migration events could have contributed to Caribbean maize germplasm. The third, the Andean group, displayed early introduction of maize into the Andes, with little mixing since then, other than a regional interchange zone active in the past. Events and activities in the pre- and post-Columbian Americas including the development and expansion of pre-Columbian cultures and the arrival of Europeans to the Americas are discussed in relation to the history of maize migration from its point of domestication in Mesoamerica to South America and the Caribbean through sea and land routes.
... In Mexico, there are more than 59 races of maize (Zea mays L.), each associated with specific origins, distribution, and geographic regions [1]. These maize races present genetic diversity related to their biological and anthropocentric processes, their selection, their adaptation, and the cultivation of different niches and ecological biotypes in various socioeconomic conditions, which has generated a wide diversity of maize. ...
... Antibiosis: We used the growth rate (ri), as a parameter to determine the antibiosis on the population of T. merganser. ri was calculated with the following equation [61]: ri = [ln(N t /N 0 )] × (1/t) (1) where N t is the number of individuals at time t (surviving adult females plus the eggs laid at the end of the bioassay), N 0 is the number of individuals at time 0 (initial cohort = 10 adult females of T. merganser), and t is the number of days elapsed from the start to the end of the bioassay (equal to 3 days). Positive values of ri indicate a growing population, negative values indicate a declining population, and ri = 0 indicates a stable population [62]. ...
At least 59 maize races (Zea mays L.) have been registered in Mexico. The feeding damage caused by insects and mites to maize crops generates up to ~30% of maize yield losses. Spider mite-resistant plants are needed. The red spider mite, Tetranychus merganser Boudreaux (Acari: Tetranychidae), is distributed in the United States, China, Mexico, and Thailand. It is considered a potential pest in Mexican agriculture. The aim of this study was to evaluate the resistance mechanisms (antixenosis and antibiosis) of 11 native maize populations, representative of each race of maize grown in Tamaulipas, Mexico, to T. merganser under laboratory conditions. The aim was also to obtain
information on the chemical composition and some morphological characteristics of these maize races and to identify resistant maize races for incorporation into a breeding program. Antixenosis was assessed by non-preference for oviposition and feeding. Antibiosis was measured by growth rate (ri). The presence of secondary metabolites in the 11 maize races were different. In the 11 maize races, quantitative analysis of total phenol concentration, total flavonoid concentration, and antioxidant capacity were significantly different. The multivariate analysis of variance showed that there is
evidence of antixenosis noted by maize race differences in egg laying and percentage feeding damage but not of antibiosis noted by growth rate. Red spider mites laid significantly more eggs on the Celaya (24 h: 25.67 ± 17.04, 48 h: 42.67 ± 26.86, 72 h: 49.33 ± 28.54) race than on Raton (24 h: 7.00 ± 5.00, 48 h: 12.67 ± 8.02, 72 h: 14.67 ± 9.29) and Elotes Occidentales × Tuxpeño (24 h: 9.67 ± 5.85, 48 h: 15.33 ± 10.69, 72 h: 17.67 ± 10.97) races. However, the growth rate and mortality of T. merganser in the
11 corn races were similar. The Vandeño (24 h: 11.67 ± 2.89, 48 h: 27.67 ± 7.64, 72 h: 30.00 ± 18.03) and Tabloncillo × Tuxpeño (24 h: 18.33 ± 7.64, 48 h: 25.00 ± 8.66, 72 h: 25.00 ± 8.66) races were the most resistant to red spider mite damage, whereas the most susceptible race was Celaya (24 h: 26.67 ± 15.28, 48 h: 48.33 ± 29.30, 72 h: 65.00 ± 30.00). Further analysis by PCA at 24, 48, and 72 h found the Celaya race positively correlated to growth rate and oviposition of T. merganser and to a lesser extent
with the percentage of feeding damage, suggesting that the Celaya race was most susceptible to T. merganser. At 24 h, the Vandeño race was most resistant, given a negative correlation to growth rate and oviposition by T. merganser. The PCA at 48 and 72 h noted the Elotes Occidentales × Tuxpeño race was most resistant to red spider mite, with negative relationships to growth rate and oviposition and, to a lesser extent, to feeding damage. This resistance is due to the differences in both its morphological characteristics and the secondary metabolites present in their leaves.
... Our results indicate that domesticated landraces of maize productive enough to be a staple grain existed in Central America by 4,300 cal B.P. maize | teosinte | Central America | domestication | agriculture T he domestication and diversification of maize [Zea mays subspecies (ssp.) mays] during the past ∼9,000 y (1,2) has resulted in landraces with remarkable genetic and morphological diversity adapted to a range of geographic constraints and climatic conditions (3)(4)(5)(6)(7)(8)(9)(10)(11). Fifty-nine extant landraces of maize are documented in Mexico alone (11), and morphological variability exists elsewhere in North, Central, and South America (4)(5)(6)12). ...
... mays] during the past ∼9,000 y (1,2) has resulted in landraces with remarkable genetic and morphological diversity adapted to a range of geographic constraints and climatic conditions (3)(4)(5)(6)(7)(8)(9)(10)(11). Fifty-nine extant landraces of maize are documented in Mexico alone (11), and morphological variability exists elsewhere in North, Central, and South America (4)(5)(6)12). The known extant landraces represent only a fraction of the diversity that existed during the evolutionary history of this globally important domesticate; however, this diversity is presently threatened by the proliferation of genetically modified (GM) and improved hybrid varieties (13), as well as an associated loss of cultural knowledge and traditional farming practices (14). ...
Significance
Maize was initially domesticated in the Balsas region of Mexico ∼9,000 y ago, but it remains unclear when this globally important cultigen became a staple crop in the Americas. We demonstrate that highly productive maize varieties were present in Central America outside the natural distribution of ancestral teosinte populations [ Zea mays subspecies (ssp.) parviglumis ] by ∼4,340 calendar years B.P., and we hypothesize that reduced introgression with Z. mays ssp. parviglumis and Z. mays ssp. mexicana was instrumental in the development of more productive staple grain varieties.
... parviglumis Iltis & Doebley) in present-day Mexico (Matsuoka et al., 2002). Accordingly, Mexico has the greatest diversity of maize genetic resources, including dozens of maize landraces and hundreds of 'geographic populations' of several of maize's wild relatives, the annual and perennial Mexican teosintes (Fukunaga et al., 2005;Vigouroux et al., 2008;Vielle-Calzada & Padilla, 2009). The Mexican landraces were developed over millennia by farmers through continuous selection and adaptation to the tremendous variety of ecological, geographical, and cultural contexts in which maize is grown (Ortega-Paczka, 2003). ...
... Thus, ca. 60 major landraces and hundreds of local landrace variants are presently recognized for Mexico (Sanchez et al., 2000;Ortega-Paczka, 2003;Vielle-Calzada & Padilla, 2009), and Mexican maize production relies heavily on smallholder production of those landraces (Nadal, 2000). The Mexican teosintes include at least two perennial species [Zea diploperennis Iltis, Doebley & Guzmán, and Zea perennis (Hitchcock) Reeves & Mangelsdorf] and two sister subspecies of maize [Balsas teosinte, and Z. mays ssp. ...
Maize [Zea mays L. ssp. mays (Poaceae)] was domesticated from Balsas teosinte (Zea mays ssp. parviglumis Iltis & Doebley) in present‐day Mexico. Fall armyworm, Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae), is among the most important pests of maize in Mexico and Central America. We compared the strength of plant defenses against fall armyworm between micro‐sympatric landrace maize and Balsas teosinte in the field and laboratory. The field comparison, conducted in Mexico, consisted of comparing the frequency of fall armyworm infestation between young maize and Balsas teosinte plants in dryland agricultural fields in which Balsas teosinte grew as a weed. The laboratory comparison contrasted the performance of fall armyworm larvae provided a diet of leaf tissue excised from maize or Balsas teosinte plants that were intact or had been primed by larval feeding. In the field, maize plants were more frequently infested with fall armyworm than Balsas teosinte plants: over 3 years and three fields, maize was infested at a ca. 1.8‐fold greater rate than Balsas teosinte. In the laboratory, larval growth, but not survivorship, was differently affected by feeding on maize vs. Balsas teosinte, and on primed vs. intact plants. Specifically, survivorship was ca. 98%, and did not differ between maize and Balsas teosinte, nor between primed and intact plants. Larvae grew less on intact vs. primed maize, and similarly on intact vs. primed Balsas teosinte; overall, growth was 1.2‐fold greater on maize compared to Balsas teosinte, and on primed compared to intact plants. Parallel observations showed that the differences in growth could not be attributed to the amount of leaf tissue consumed by larvae. We discuss our results in relation to differences in the strength of plant defenses between crops and their ancestors, the relevance of unmanaged Balsas teosinte introgression in the context of fall armyworm defenses in maize, and whether greater growth of larvae on primed vs. intact plants signifies herbivore offense.
... ). Accordingly, Mexico has the greatest diversity of maize genetic resources, including dozens of maize landraces and hundreds of 'geographic populations' of several of maize's wild relatives, the annual and perennial Mexican teosintes (Fukunaga et al., 2005; Vigouroux et al., 2008; Vielle-Calzada & Padilla, 2009). The Mexican landraces were developed over millennia by farmers through continuous selection and adaptation to the tremendous variety of ecological, geographical, and cultural contexts in which maize is grown (Ortega-Paczka, 2003). ...
... Thus, ca. 60 major landraces and hundreds of local landrace variants are presently recognized for Mexico (Sanchez et al., 2000; Ortega-Paczka, 2003; Vielle-Calzada & Padilla, 2009), and Mexican maize production relies heavily on smallholder production of those landraces (Nadal, 2000). The Mexican teosintes include at least two perennial species [Zea diploperennis Iltis, Doebley & Guzmán, and Zea perennis (Hitchcock) Reeves & Mangelsdorf] and two sister subspecies of maize [Balsas teosinte, and Z. mays ssp. ...
... Color has a positive significant impact on the acquirement of food as they show a significant role in desirability, marketing, and consumption of products. Maize grain naturally displays spectrum of kernel colors among the collections of landraces (Calzada and Padilla 2009). However, white and yellow color predominates over orange, blue, red, purple, brown, or black color among the Mexican genotypes (Trujillo et al. 2009). ...
Specialty corn has emerged as a preferred choice as food, feed, and various industrial products due to its diverse usage. Among the various types, sweet corn, popcorn, waxy corn, high amylose corn, high oil corn, colored corn, and baby corn are quite popular worldwide. Genes or QTLs governing these traits are now well documented. Introgression of such loci has led to the development of improved specialty corn cultivars worldwide. Information on markers has further helped in accelerating the breeding cycle through marker-assisted breeding. Crop biofortification has now regarded as a sustainable and cost-effective approach to alleviate malnutrition. Various genes are now available to enhance nutritional quality like provitamin-A, provitamin-E, lysine, and tryptophan in maize. These nutritional quality traits have been integrated into the genetic background of specialty corn cultivars. Here, we present the importance of each of the specialty corn, their genetics, and scope of enhancing the nutritional quality traits in the specialty corn background. Various challenges in popularization and adoption of the biofortified maize have also been discussed.
... Color has a positive significant impact on the acquirement of food as they show a significant role in desirability, marketing, and consumption of products. Maize grain naturally displays spectrum of kernel colors among the collections of landraces (Calzada and Padilla 2009). However, white and yellow color predominates over orange, blue, red, purple, brown, or black color among the Mexican genotypes (Trujillo et al. 2009). ...
Maize being versatile crop is known for its many uses. It has substantially contribution to food security in the poor country. In the recent past, deliberate attempts have been made to integrate trait-based genomic approaches to complement conventional plant breeding. However, the success of the genomics mainly based on phenotypic expression of a trait, hence phenotyping, is one of the key components of plant breeding including maize. Genetic dissection of key traits and its molecular mechanism involves extensive phenotyping of large set of population. Screening of such a huge population is with traditional methods, which is expensive and tedious and consumes a lot of time. In addition, plant phenotypes are the results of interaction between genotype × environment × management (G × E × M); thus, they are complex in nature. Recent developments in phenomics led to the improvement in phenotyping protocol that is more powerful than ever to dissect complex traits into easily scorable traits. In addition, this helps in uncovering underlying genetic mechanism for trait expression. This chapter aimed at describing phenotyping tools available for plant scientist to fast track their maize improvement in precise and robust manner for climate resilient agriculture.
... In México there are a broad diversity of maize, and at least 59 races have been described (Vielle-Calzada & Padilla, 2009), among them the 'Chalqueño' race, which has variations in grains colour such as white, yellow, blue, and red (Herrera-Cabrera et al., 2004), and predominates in the High Valleys of the Mexican Central Plateau for irrigation crops (Arellano-Vázquez et al., 2014). ...
Maize endosperm consists of about 70 % starch, which makes it an excellent substrate for fermentation. However, due to its low diastatic power, it is used in brewing as an adjunct, mainly. In order to include both red and blue maize as an enzyme source in the brewing process, the effect of temperature and time germination on the diastatic power of malts was studied. The research consisted in a completely randomized three-factor experimental design where the involved factors were colour of maize (blue and red), germination temperature (15, 20, and 25 °C), and germination time (3, 4, 5, 6, 7, 8, and 9 days). The response variables were germination percentage, acrospire length, malting yield, and diastatic power. Data was analysed through Analysis of variance and Comparison Multiple Tukey’s Test. Results showed that both temperature and germination time encouraged the acrospire length, which had a negative effect on malting yield. Regarding to diastatic power, it maintained an increase from third to seventh germination day, at the three tested temperatures. Additionally, as the germination temperature increased, the diastatic power also increased. The highest diastatic power for blue and red maize malts were 39 and 42 °L, respectively, and it was reached when these malts were germinated for 7 days at 25 °C. It was concluded that, by germinating both blue and red maize under the resulting optimum conditions, the obtained malts would be capable of converting their own starch.
... The greatest genetic diversity of the species is concentrated in the centers of the origin and diversification of maize, and this specie continues to evolve under domestication, commonly classified phenotypically in native populations, landraces, or races. These landraces and races are highly heterogeneous and phenotypically share common morpho-agronomic biochemical characteristics and are adapted to certain geographic regions (Vielle-Calzada and Padilla, 2009;Newton et al., 2010). The biochemical composition of the grain is the product of selection by farmers in their cultivation plots and storage places (Hoogendoom et al., 2018) to satisfy their family nutritional needs and of adaptation to agroecological crop conditions and is a research hotspot for the landraces of blue, red, yellow, purple and variegated grains as sources of secondary metabolites, minerals, protein and starch and their interaction with abiotic factors and crop conditions (Domínguez-Hernández et al., 2022). ...
The Mesoamerican region is center of origin, domestication, and diversification of maize. In this ecogeographic context, the objective was to evaluate the variation in the phenolic compounds, antioxidant activity and concentration of minerals in the grain of a population collection of yellow maize landraces from southeastern Mexico. During 2016, samples of landraces of yellow maize were collected and integrated into 32 populations and experimental varieties, which were planted in two locations in Oaxaca, Mexico, under a random block design. At harvest, a sample of grain was taken, which was grounded to evaluate the polyphenolic compound contents and antioxidant activity by UV-visible spectrophotometry, and macro-and microelement contents were determined using inductively coupled plasma-optical emission spectrometry. The effect of crop location was significantly greater than the effects of populations and location-population interaction on polyphenol contents and concentration of Ca, P, Mg, K, Na, S, Cu, Fe, Mn and Zn. In the Amatengo locality, a higher macroelement contents were recorded, and in the second locality, the concentration of microelements, polyphenols, and flavonoids contents were higher. The populations showed high variability, with significant interactions with crop location in bioactive compounds, antioxidant activity and Ca, Cu, Na, Mn and S contents.
... Within Mexico, topographic variation and cultural diversity combine to make the state of Oaxaca a major center of maize and Phaseolus diversity, with wild relatives of both crops present. Oaxacan farmers maintain 35 (59%) of the 59 maize races native to Mexico [15] (referred to as "landraces" in that reference) [16,17] in the form of hundreds of farmer-named varieties. Maize races are groupings first based on morphological, physiological, genetic, and other criteria [18]; varieties are subgroups within races, often identified with an area, that share distinguishing characteristics. ...
Crop diversity conservation in situ is an ecosystem service with benefits at household, community, and global scales. These include risk reduction and adaptation to changing physical and sociocultural environments—both important given the accelerating changes in climate, human migration, and the industrialization of agriculture. In situ conservation typically occurs as part of small-scale, traditionally based agriculture and can support cultural identity and values. Although decisions regarding crop diversity occur at the household level, few data detail the household context of in situ crop diversity management. Our research addressed this data gap for maize and Phaseolus bean in Oaxaca, Mexico, a major center of diversity for those crops. We defined diversity as farmer-named varieties and interviewed 400 farming households across eight communities in two contrasting socioecological regions. Our research asked, “In a major center of maize and Phaseolus diversity, what are the demographic, production, and consumption characteristics of the households that are stewarding this diversity?” We describe the context of conservation and its variation within and between communities and regions and significant associations between diversity and various independent variables, including direct maize consumption, region, and marketing of crops. These results provide a benchmark for communities to understand and strengthen their maize and bean systems in ways they value and for scientists to support those communities in dynamically stewarding locally and globally significant diversity.
... México, as the center of its origin, possesses a great maize diversity and a high number of landraces (native maize varieties) that are still cultivated, consumed and preserved as a part of culture and tradition (Vielle-Calzada and Padilla, 2009;Lopez-Martinez et al., 2009;Uriarte-Aceves et al., 2018). However, a considerable part of Mexican maize production also depends on commercial agriculture that plants high-yielding commercial hybrids developed by different seed companies, and this is widely evident in Sinaloa, the main maize producing Mexican State (SIAP-SAGARPA, 2020). ...
The hydration kinetics of 26 commercial white maize hybrids/varieties were investigated, satisfactorily (r > 0.9; P < 0.01) described by the Peleg model and related to the physical, chemical and wet-milling properties of the maize hybrids. The Peleg constants K1 [0.142–0.294 h(g/100 g solids)⁻¹], K2 [0.030–0.037 (g/100 g solids)⁻¹] and equilibrium moisture content, ME, [41.76–47.83 g/100 g solids] showed genotypic differences. The distributions, associations and groupings of the maize hydration, physical, chemical and wet-milling properties were evaluated with Principal Component Analysis (PCA), Pearson's correlation coefficients and clustering analysis using Agglomerative Hierarchical Clustering (AHC). The Peleg K2 was influenced by the grain protein content and kernel density, and concomitantly impacted the starch yield. The ME also related to the starch yield, in addition to the starch recovery. The AHC analysis was extended to include 16 commercial yellow maize hybrids from our previous study. The groupings of the resulting 42 of the most widely grown maize hybrids/varieties in México confirmed the close association between maize water absorption, physical, chemical and wet-milling properties. The findings on the hydration kinetics, and the starch yield and recovery from wet-milling are of specific interests to the maize industry.
... Maize grain kernels display a great variety of colors, particularly in tropical maize landraces. 1,2 In the center of origin, the most common grain colors are white and yellow, but Mexican maize genotypes display many other colors such as green, orange, blue, red, purple, brown, or black. 3 Seed color is determined by the pigment content in three different cell layers: pericarp, aleurone, and endosperm. ...
Corn seeds contain natural pigments and antioxidants, such as the molecular variants of flavonoids and carotenoids. The aleurone and pericarp tissue from pigmented genotypes were extracted for metabolic fingerprinting and evaluated using UV-VIS and mass spectrometry (MS). MS ionomic fingerprints classified samples according to genetic background and kernel color. The MS/MS fragmentation pattern (daughter and neutral loss methods) allowed the tentative identification of 18 anthocyanins with glycosyl, malonyl and succinyl moieties, including 535 m/z for cyanidin-3-O-(6″-malonyl-glucoside) and 621 m/z for cyanidin-3-O-(3″,6″-dimalonyl-glucoside). We also detected 663 m/z for pelargonidin-3-O-(disuccinyl-glucoside) and 633 m/z for peonidin-3-O-(disuccinyl-glucoside). Cyanidin-based anthocyanins were the most abundant in dark purple colored kernels while pelargonidins predominated in the red-pink kernels of the “Elote occidental” landrace. Grains of “Conico negro” had a simultaneous pigmentation of aleurone and pericarp, while Vitamaize had purple pigmentation only in the aleurone layer. Most landraces had a white endosperm while Vitamaize had a yellow endosperm and a dark seed coat. We conclude that Vitamaize grains contain both carotenes and cyanidins and therefore it is proposed as a non-transgenic agronomically improved variety of tropical purple maize: a good source for organic superfoods.
... parviglumis Iltis & Doebley) (Van Heerwaarden et al., 2011). At least 59 maize races have been described in Mexico and related by origin and distribution to specific geographic regions (Vielle-Calzada & Padilla, 2009). ...
The objective of this work was to evaluate the genetic diversity of nine maize races (Zea mays ssp. mays) from Northwestern Mexico and one population of teosinte of the Balsas race (Zea mays ssp. parviglumis). A total of 649 alleles were identified, with an average of 20.9 alleles per locus using 31 microsatellite loci; 84.3% of them were polymorphic loci with a 0.49 expected heterozygosity. Graphic representation of principal coordinate analysis (PCoA) showed broad variation and population distribution. The highest probabilistic value obtained with the ∆K criterion confirmed the existence of five population groups clustered by the Bayesian model. This grouping coincided with the population distribution observed in the PCoA graph. Maize races examined retain broad genetic diversity among and within the evaluated populations.
... The domestication of maize occurred in southern Mexico about 9000 years ago and gave rise to a group of ancestral landraces adapted to diverse climatic and geographic conditions. Over time, maize spread throughout the continent and all over the world, as well as the utilization of maize silks for medicinal purposes (Kato-Yamakake, Mapes-Sánchez, Mera-Ovando, Serratos-Hernández, & Bye-Boettler, 2009;Vielle-Calzada & Padilla, 2009). Nowadays, maize silks are employed worldwide as an alternative natural-based treatment for various illnesses, standing out their use in Latin American and Asiatic countries (Hasanudin, Hashim, & Mustafa, 2012;Žilić, Janković, Basić, Vančetović, & Maksimović, 2016). ...
Maize silks are used worldwide as a natural-based treatment for various illnesses. The biological activity of maize silks is mainly attributed to their content of polysaccharides and polyphenols. Therefore, it is worthwhile the identification of maize varieties or races that accumulate large amounts of these compounds in their staminate flowers. In the present study, the compositional and antioxidant properties of silks from three maize races (Cónico, Gordo and Cristalino) natives to Mexico were investigated. In general, the content of phenolic compounds including flavonoids and anthocyanins as well as the antioxidant capacity of maize silks from the landrace Cónico were higher than values reported in silks of hybrid maize varieties. The presence of the flavonoid maysin was confirmed in the silks of the landrace Cónico but not in the other two races. Whereas, the largest amount of polysaccharides was observed in silks from the landrace Cristalino. © 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
... Considering that Mexico is the center of domestication of maize, and the cultural, economic, and academic importance of this species for the country (Vielle-Calzada & Padilla, 2009), the Mexican government, under the auspices of the CIBIOGEM (Inter-Secretarial Commission on Biosafety of Genetically Modified Organisms), is keen to support the in situ conservation of maize germplasm by encouraging small farmers to maintain the cultivation of traditional landraces and considering incentives which would benefit the farmers who preserve the most diverse genotypes, even though these are often not commercially viable materials. The main challenges to implementing a strategy of incentives are to: (1) implement a relatively simple experimental strategy that can be easily replicated in low-tech laboratories, but allows reliable sampling and genotyping of a maximum number of individuals while maintaining overall costs at a minimum, (2) obtain a realistic image of the existing diversity in the main regions of the country where landraces are routinely grown, and (3) identify within these samples the most uncommon or " rare " genotype combinations. ...
As maize was domesticated in Mexico around 9,000 years ago, local farmers have selected and maintained seed stocks with particular traits and adapted to local conditions. In the present day, many of these landraces are still cultivated; however, increased urbanization and migration from rural areas implies a risk that this invaluable maize germplasm may be lost. In order to implement an efficient mechanism of conservation in situ, the diversity of these landrace populations must be estimated. Development of a method to select the minimum number of samples that would include the maximum number of alleles and identify germplasm harboring rare combinations of particular alleles will also safeguard the efficient ex-situ conservation of this germplasm. To reach this goal, a strategy based on SSR analysis and a novel algorithm to define a minimum collection and rare genotypes using landrace populations from Puebla State, Mexico, was developed as a “proof of concept” for methodology that could be extended to all maize landrace populations in Mexico and eventually to other native crops. The SSR-based strategy using bulked DNA samples allows rapid processing of large numbers of samples and can be set up in most laboratories equipped for basic molecular biology. Therefore, continuous monitoring of landrace populations locally could easily be carried out. This methodology can now be applied to support incentives for small farmers for the in situ conservation of these traditional cultivars.
... Maize monoculture and the replacement of colored maize varieties by white maize as observed in our study have been identified elsewhere (Ortega-Paczka, 2003;Vielle-Calzada and Padilla, 2009). This tendency can be explained by the substitution of MS by SP in our study area. ...
... Different varieties of corn produce grains ranging in color from red to purple to blue and black. With 59-recorded varieties, Mexico has the largest diversity of corn varieties in the world (Vielle-Calzada & Padilla, 2009). Among these is blue corn, originally from Peru and cultivated by ancient civilizations such as the Inca, Maya, and Aztec. ...
Physicochemical and structural analyses were done of extruded snacks produced with two types of blue corn (hard and soft endosperm) combined with orange bagasse. Chemical composition, expansion index (EI), penetration force, water absorption index, and water solubility index values were calculated for all treatments. They were also analyzed with scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Addition of bagasse increased crude fiber content and hardness in the extrudates. It also lowered the EI, resulting in harder products with higher numbers of pores per area but of smaller sizes than in the extrudates without bagasse. Both the X-ray diffraction patterns and infrared spectra showed the starch to lose its semicrystalline structure due to mechanical shearing and high temperature. Orange bagasse was successfully incorporated into extrudated snacks made with blue corn of different endosperm hardnesses. Blue corn is a viable base for extruded snacks, and orange bagasse is a potential source of low cost, natural source fiber.
... Remnants associated with ancient human shelters in the Central Balsas Valley of Mexico indicate the use of primitive maize by pre-Hispanic communities around 8,700 YBP (30). Today, across rural Mexico, a great array of 59 maize landraces (MLRs) is harbored in living genetic libraries that were passed through generations by indigenous people in traditional agroecosystems (44). Genetic diversity and diverse ecological adaptations exist within and among MLR populations; each MLR has unique chemical and physical characteristics shaped over thousands of years by human preference for foods, feeds, and other uses (37,39). ...
Maize, the critical staple food for billions of people, was domesticated in Mexico about 9,000 YBP. Today, a great array of maize landraces (MLRs) across rural Mexico is harbored in a living library that has been passed among generations since before the establishment of the modern
state. MLRs have been selected over hundreds of generations by ethnic groups for adaptation to diverse environmental settings. The genetic diversity of MLRs in Mexico is an outstanding resource for development of maize cultivars with beneficial traits. Maize is frequently contaminated with
aflatoxins by Aspergillus flavus, and resistance to accumulation of these potent carcinogens has been sought for over three decades. However, MLRs from Mexico have not been evaluated as potential sources of resistance. Variation in susceptibility to both A. flavus reproduction
and aflatoxin contamination was evaluated on viable maize kernels in laboratory experiments that included 74 MLR accessions collected from 2006 to 2008 in the central west and northwest regions of Mexico. Resistant and susceptible MLR accessions were detected in both regions. The most resistant
accessions accumulated over 99 % less aflatoxin B1 than did the commercial hybrid control Pioneer P33B50. Accessions supporting lower aflatoxin accumulation also supported reduced A. flavus sporulation. Sporulation on the MLRs was positively correlated with aflatoxin accumulation
(R = 0.5336, P < 0.0001), suggesting that resistance to fungal reproduction is associated with MLR aflatoxin resistance. Results of the current study indicate that MLRs from Mexico are potentially important sources of aflatoxin resistance that may contribute to the breeding
of commercially acceptable and safe maize hybrids and/or open pollinated cultivars for human and animal consumption.
... There are several types of pigmented genotypes, with colors such as white, yellow, violet, red, black, and blue. Mexico has the largest diversity of genetic resources in the world with about 59 different landraces [1]. ...
Se presenta la evaluación de los procesos de elaboracion de tortilla, nixtamalización y extrusión, sobre los niveles de fitoquímicos (compuesto fenólicos totales, ácido ferúlico, antocianinas) y propiedades nutracéuticas de maíces criollos pigmentados mexicanos.
Como materiales de estudio se utilizaron maíces criollos pigmentados (Azul y Rojo) de la región de Sinaloa, México y como control maíces comerciales (Blanco y Amarillo). Se produjeron harinas instantáneas aptas para la elaboración de tortillas. Para la obtención de harinas de maíz se utilizaron dos procesos: (1) Nixtamalización: como medio de cocción se empleó una disolución de hidróxido de calcio de 5.4 g/L (relacioón maíz / medio de cocción de !:3), temperatura de nixtamalización 85°C, tiempo de nixtamalización 31 min y reposo de 8.1 h; el nixtamal se lavó tres veces con agua potable, se secó (55°C/12 h) y se molturó hasta pasar por malla 80 (0.180 mm). (2) Extrusión: se utilizó un extrusor de tornillo simple alimentado con maíz fragmentado (1.2 mm), mezclado con cal (2.1 g cal / kg maíz), acondicionado a 28% de humedad. Temperatura de extrusión 85°C y velocidad de tornillo de 240 rpm. Los extrudidos se secaron con ventilador doméstico (25°C/ 12 h) y molturaron hasta pasar por malla 80 (0.180 mm). La harinas de maíz, nixtamlizado y extrudido, se utilizaron para la preparación de tortillas.
Las tortillas preparadas con harinas de maíces extrudidos, al compararse con grano crudo, retuvieron mayor (p<0.05) porcentaje de compuestos fenólicos totales (76-94% vs 51-76%) y ácido ferúlico total (58-97% vs 20-56%) que las tortillas elaboradas con harins de maíces nixtamalizadas.
La mayor parte de los compuestos fenólicos (>80%) en el grano de maíz crudo y sus tortillas se encuentran en forma ligada. Del 97 al 99% del ácido ferúlico total, asociado a granos crudos, se encuentra en forma ligada.
Ambos procesos de elaboración de tortillas, nixtamalización y extrusión, disminuyeron el contenido de antocianinas en 55.3 % y 57.3%, respectivamente.
En maíz crudo los fitoquímicos ligados contribuyeron con la mayor parte (68.4-92.2%) de la actividad antioxidante total. El proceso de transformación de maíz crudo en tortilla, vía nixtamalización, produjo una disminución de las actividades antioxidantes de fitoquímicos libres (17-56%) y ligados (38-66%) y total (16-52%) de los maíces comerciales y criollos.
Las tortillas preparadas por los procesos de nixtamalización y extrusión retuvieron 43.8-83.6% y 75.2-93.2% de la actividad antioxidante, respectivamente. Las tortillas elaboradas con harinas de maíz Azul nixtamalizado y extrudido retuvieron los mayores (p>0.05) porcentajes de actividad antioxidante total, 83.6 % y 93.2%, respectivamente; y de ácido ferúlico total, 56% cuando se nixtamalizó y 97% cuando se aplicó extrusión.
La transformación de maíz crudo en tortillas a través de la nixtamalización, ocasionó una disminución (p<0.05) en el contenido de fibra dietaria insoluble (FDI) (13.1-19.4%) y un incremento en los niveles de fibra dietaria soluble (FDS) (18.5-19.2%). El proceso de elaboración de tortillas, vía extrusión, causó un incremento en los niveles de FDI (3.0-27-9%), FDS (58.8-75%) y fibra dietaria total (FDT) (8.8-31.3%).
Para todos los maíces, comerciales y criollos, las tortillas elaboradas por el proceso de extrusión tuvieron el mayor (p<0.05) contenido de FDT que sus correspondientes tortillas preparadas por nixtamalización (12.3-13.7% vs 9.9-11.4%).
Las tortillas preparadas por extrusión, consideradas productos integrales, presentaron, en su fracción de fitoquímicos ligados, mayor (p<0.05) contenido de compuestos fenólicos, actividad antioxidante y ácido ferúlico que su misma fracción en tortillas preparadas por nixtamalización; sin embargo, el mayor efecto citotóxico en células Caco-2 lo presentaron fitoquímicos ligados en tortillas elaboradas por nixtamalización.
El proceso de nixtamalización tracidional ocasiona la liberación, de la pared celular, de compuestos potencialmente biaoactivos, aún no identificados con actividad anticarcinogénica, o que pueden actuar sinergísticamente con diferentes compuestos disponibles en el grano de maíz.
... Within Mexico alone landraces encounter extremely diverse environments in terms of mean annual temperature (from 12uC to 29.1uC) and precipitation (from 400 to 3555 mm) [17]. The diversity of growing conditions and cultural preferences in Mexico has led to extensive differentiation of maize races [18,19]. Four of these landraces—Arrocillo Amarillo, Palomero Toluqueñ o, Chapalote, and Nal-Tel—are believed to be among the most ancient landraces of maize [20,21] and likely represent early adaptations during the diffusion of maize from its center of origin. ...
The species Zea mays includes both domesticated maize (ssp. mays) and its closest wild relatives known as the teosintes. While genetic and archaeological studies have provided a well-established history of Z. mays evolution, there is currently minimal description of its current and past distribution. Here, we implemented species distribution modeling using paleoclimatic models of the last interglacial (LI; ∼135,000 BP) and the last glacial maximum (LGM; ∼21,000 BP) to hindcast the distribution of Zea mays subspecies over time and to revisit current knowledge of its phylogeography and evolutionary history.
Using a large occurrence data set and the distribution modeling MaxEnt algorithm, we obtained robust present and past species distributions of the two widely distributed teosinte subspecies (ssps. parviglumis and mexicana) revealing almost perfect complementarity, stable through time, of their occupied distributions. We also investigated the present distributions of primitive maize landraces, which overlapped but were broader than those of the teosintes. Our data reinforced the idea that little historical gene flow has occurred between teosinte subspecies, but maize has served as a genetic bridge between them. We observed an expansion of teosinte habitat from the LI, consistent with population genetic data. Finally, we identified locations potentially serving as refugia for the teosintes throughout epochs of climate change and sites that should be targeted in future collections.
The restricted and highly contrasting ecological niches of the wild teosintes differ substantially from domesticated maize. Variables determining the distributions of these taxa can inform future considerations of local adaptation and the impacts of climate change. Our assessment of the changing distributions of Zea mays taxa over time offers a unique glimpse into the history of maize, highlighting a strategy for the study of domestication that may prove useful for other species.
... There are several types of pigmented genotypes, with colors such as white, yellow, violet, red, black, and blue. Mexico has the largest diversity of genetic resources in the world with about 59 different landraces [1]. Currently, pigmented maize has received increased attention from a nutraceutical perspective owing to its potential health benefit. ...
The effects of traditional nixtamalization and extrusion cooking on total phenolics, ferulic acid, anthocyanins and Oxygen Radical Absorbance Capacity (ORAC) of Mexican pigmented (blue and red) and commercial (white and yellow) maize processed into tortillas were investigated. Tortillas prepared from extruded flours retained between 76.2–93.9% and 58–96.7% of total phenolics and total ferulic acid (TFA) respectively, compared to 50.5–75.7% and 19.6–55.8% assayed in traditional tortillas. Approximately 97–99% of TFA in raw kernels and their tortillas was in its bound form. The retention of TFA in traditional tortillas was significantly lower compared to tortillas from extruded flours. Traditional tortillas contained more free ferulic acid compared to tortillas produced from extruded flours indicating that the first process liberated bound ferulic acid with cell walls more efficiently. Blue maize lost more than 55% of the anthocyanins when processed into extruded or traditional tortillas. Approximately 68–92% of the ORAC associated with raw kernels or their tortillas was due to bound compounds. Traditional and extruded tortillas lost 16.4–52.4% and 6.8–24.8%, respectively, of the total ORAC associated with raw grains. Results clearly indicate that the proposed lime-cooking extrusion strategy was instrumental in retaining higher levels of phytochemicals, particularly ferulic acid, and antioxidants in all tortillas.
... There are several types of pigmented genotypes, with colors such as white, yellow, violet, red, black, and blue. Mexico has the largest diversity of genetic resources in the world with about 59 different landraces [1]. Currently, pigmented maize has received increased attention from a nutraceutical perspective owing to its potential health benefit. ...
The lime-cooking extrusion represents an alternative technology for manufacturing pre-gelatinized flours for tortillas with the advantages of saving energy and generation of null effluents. The phytochemical profiles (total phenolics, anthocyanins) and antioxidant activity of four different types of whole pigmented Mexican maize [white (WM), yellow (YM), red (RM), blue maize (BM)] processed into tortillas were studied. The lime-cooking extrusion process caused a significant decrease (p < 0.05) in total phenolics and antioxidant capacity when compared to raw kernels. Most of the total phenols assayed in raw grains (76.1-84.4 %) were bound. Tortillas from extruded maize flours retained 76.4-87.5 % of total phenolics originally found in raw grains. The BM had the highest anthocyanin content (27.52 mg cyanidin 3-glucoside/100 g DW). The WM, YM, RM and NWM contained 3.3, 3.4, 2.9, and 2.2 %, respectively, of the amount of anthocyanins found in BM. The BM lost 53.5 % of total anthocyanins when processed into extruded tortillas. Approximately 64.7 to 74.5 % of bound phytochemicals from raw kernels were the primary contributors to the ORAC values. Extruded tortillas retained amongst 87.2 to 90.7 % of total hydrophilic antioxidant activity when compared to raw kernels. Compared to the data reported by other authors using the conventional process, the lime-cooking extrusion process allowed the retention of more phenolics and antioxidant compounds in all tortillas.
... Palomero Toluqueño is a landrace of the Central and Northern Highlands Group characterized by short plants with frequent tassel branches, small conically shaped ears, a weakly developed root system, and pubescent leaf sheaths often pigmented by anthocyanins. It is one of several ancient landraces that are believed to have spread from the Pacific Coast to Northern areas of Mexico, contributing to the emergence of popcorn elite cultivars in the USA [15]. ...
In-depth sequencing analysis has not been able to determine the overall complexity of transcriptional activity of a plant organ or tissue sample. In some cases, deep parallel sequencing of Expressed Sequence Tags (ESTs), although not yet optimized for the sequencing of cDNAs, has represented an efficient procedure for validating gene prediction and estimating overall gene coverage. This approach could be very valuable for complex plant genomes. In addition, little emphasis has been given to efforts aiming at an estimation of the overall transcriptional universe found in a multicellular organism at a specific developmental stage.
To explore, in depth, the transcriptional diversity in an ancient maize landrace, we developed a protocol to optimize the sequencing of cDNAs and performed 4 consecutive GS20-454 pyrosequencing runs of a cDNA library obtained from 2 week-old Palomero Toluqueño maize plants. The protocol reported here allowed obtaining over 90% of informative sequences. These GS20-454 runs generated over 1.5 Million reads, representing the largest amount of sequences reported from a single plant cDNA library. A collection of 367,391 quality-filtered reads (30.09 Mb) from a single run was sufficient to identify transcripts corresponding to 34% of public maize ESTs databases; total sequences generated after 4 filtered runs increased this coverage to 50%. Comparisons of all 1.5 Million reads to the Maize Assembled Genomic Islands (MAGIs) provided evidence for the transcriptional activity of 11% of MAGIs. We estimate that 5.67% (86,069 sequences) do not align with public ESTs or annotated genes, potentially representing new maize transcripts. Following the assembly of 74.4% of the reads in 65,493 contigs, real-time PCR of selected genes confirmed a predicted correlation between the abundance of GS20-454 sequences and corresponding levels of gene expression.
A protocol was developed that significantly increases the number, length and quality of cDNA reads using massive 454 parallel sequencing. We show that recurrent 454 pyrosequencing of a single cDNA sample is necessary to attain a thorough representation of the transcriptional universe present in maize, that can also be used to estimate transcript abundance of specific genes. This data suggests that the molecular and functional diversity contained in the vast native landraces remains to be explored, and that large-scale transcriptional sequencing of a presumed ancestor of the modern maize varieties represents a valuable approach to characterize the functional diversity of maize for future agricultural and evolutionary studies.
The Vitamaize project developed new lines of pigmented corn with better yields. The new lines were generated through a backcrossing process of CIMMYT elite lines (CMLs) with a pigmented aleurone landrace as a tester parent. The project produced new pigmented lines named ‘Vitamaize lines’ (VMLs). A new open-pollination variety (OPV), E3E4, was developed from the VMLs for food production. The development of these new lines generated a new question: Is the introgression of alleles for a pigmented aleurone phenotype accompanied by metabolism differences? To answer this question, a series of experiments were performed.
In the first experiment, landraces were compared with Vitamaize lines and E3E4 to find differences in the metabolism in grains of different colors. The second experiment was a comparative analysis between Vitamaize lines and their parental CMLs. This experiment’s objective was to test whether the introgression of genes for a blue phenotype produced modifications in the metabolism. The third experiment consisted of eliminating the environmental variation from the previous experiment. The latter was executed by comparing differently pigmented grains from the same ear. Those ears came from a cross between CMLs and their pigmented offspring, the VMLs. The metabolic research started with analyses by direct-infusion mass spectrometry (DIMS), including fragmentation techniques for metabolite identification. Besides, this thesis includes biochemical studies such as the carotenoid profile, the total quantity of anthocyanins, and the evaluation of the protein quality trait (QPM) through the quantification of lysine and tryptophan.
E3E4 and the VMLs showed differences in the profiles of soluble amino acids, hexoses, phenolamides, and anthocyanins compared to pigmented landraces. The wide diversity of grain coloration was due to two or more pigmented tissues in the same seed, such as the pericarp and the endosperm tissues, respectively. The following experiments evaluated if other changes occurred when introducing the anthocyanin accumulation trait. Some metabolites, such as hexoses and trigonelline, increased in the pigmented versions. However, this did not happen with all pigmented grains. Besides, the VMLs did not inherit the QPM trait. Therefore, there was no metabolic difference due to the introgression of anthocyanin expressing genes, although it happened via the visual selection of the pigmented grains. Even the converted lines from QPM CMLs lost that trait. In conclusion, the metabolic differences are caused by all introgressed genes and not only by those responsible for expressing the accumulation of anthocyanins. Finally, Vitamaize should be used as a fortified food for rural populations that grow corn for self-consumption.
El maíz (Zea mays L.) de origen tropical y subtropical de México es un reservorio de alelos útiles y diferentes a los existentes en razas de valles altos de México, que ayudaría a enfrentar distintos factores adversos y a contribuir a incrementar su adaptabilidad. El objetivo del presente estudio fue identificar la variabilidad morfológica existente entre poblaciones de maíz exóticas, adaptadas y sin adaptación previa a valles altos, y entre algunas de sus cruzas interraciales. El material genético evaluado estuvo integrado por nueve poblaciones originales de maíz exótico y sus ciclos avanzados de selección en valles altos, ocho cruzas simples, dos cruzas dobles, una cruza triple, las generaciones avanzadas de las cruzas y cuatro testigos locales. Las evaluaciones se realizaron en tres ambientes, mediante un diseño de bloques completos al azar con tres repeticiones; la unidad experimental consistió de dos surcos de 6 m de longitud, separados a 0.80 m y con una distancia entre plantas de 0.5 m. Se registraron 28 caracteres cualitativos y cuantitativos. Mediante análisis de componentes principales, agrupamiento jerárquico, análisis discriminante y comparación de medias con la prueba de Tukey se identificaron seis grupos contrastantes. Las variables de estructura morfológica, precocidad de planta y características de mazorca explicaron la variabilidad y agrupación de los genotipos. Las poblaciones exóticas originales fueron de mayor altura, más tardías y disminuyeron su rendimiento en mazorca. En contraste, las poblaciones seleccionadas para adaptación a valles altos mostraron mayor rendimiento en mazorca, menos días a floración, menor altura de planta, más ramas primarias de espiga y mazorcas cónicas. Estos atributos podrían incorporarse en programas de mejoramiento de maíz para valles altos de México o combinarse con el germoplasma local para mejorar su adaptabilidad y su heterosis.
Tropical and subtropical maize (Zea mays L.) native from Mexico is an important source of useful alleles that could be different to those of the germplasm from the mexican high valleys, and that would help avoiding the effects of adverse factors and contributing to increase their adaptability. The aim of this study was to identify the morphological variation between adapted and non-adapted exotic maize populations to high valleys and some of their interracial crosses. The germplasm evaluated was nine original populations of exotic maize and their advanced selection cycles in high valleys, eight single crosses, two double crosses, one triple cross, the advanced generations of the crosses and four local checks. The evaluations were done in three environments under a randomized complete block design with three replicates; the experimental plot had two rows of 6 m, separated to 0.80 m and with 0.5 m between plants. Twenty-eight qualitative and quantitative characters were recorded. Principal component analysis, hierarchical grouping, discriminant analysis and the Tukey's mean comparison allowed to identify six contrasting groups. Traits of morphological structure, plant earliness and ear characteristics explained the variability and clustering of the genotypes. The original exotic populations increased in height, were late-flowering and decreased their ear yield. In contrast, the selected populations showed higher ear yields, fewer days to flowering, lower plant height, more primary tassel branches and conical ears. These attributes could be incorporated into maize breeding programs for mexican high valleys or combined with the local germplasm to improve their adaptability and heterosis.
Maize is a highly relevant source of diverse phytochemicals. While these active compounds with nutraceutical and defensive properties, and their germplasm sources have been elucidated for maize, especially those related to phenolic compounds, some compounds such as hydroxycinnamic acid amides (HCAAs) are poorly studied. In this investigation, the distribution of HCAAs was investigated in 32 Mexican landraces to provide an estimation of the range of variability of HCAA content in maize kernel. Kernel tissues were analysed to localize and quantify these compounds. The variation in HCAAs was also analysed in relation of its eco-geographical origin, distribution and as taxonomic marker. The major compounds determined were diferuloyl putrescine, feruloyl putrescine and cinnamoyl putrescine. Ranges of concentration were detected from 428 to 2336 μg/g for diferuloyl putrescine meanwhile feruloyl putrescine and cinnamoyl putrescine were quantified from 6 to 85 μg/g. A significant correlation (r² = 0.603, p = 0.018) was found between the maximum altitude of origin of the landrace and the concentration of diferuloyl putrescine in the external grain tissues. This relationship suggests that the maize with high HCAAs content were selected in low altitudes environments under natural selection pressure. Maize landraces are proposed as sources of HCAAs for diverse purposes.
The diversity of maize (Zea mays L.) in Mexico is wide and there is still a need to carry out works that allow to discern the variation within and between racial groups and establish collections of racial reference for their understanding. The morphological diversity of representative populations of 10 mexican maize races was assessed. In the spring-summer cycle of 2010, experiments were established with 88 representative accessions of Bofo, Celaya, Coscomatepec, Dulce de Jalisco, Elotes Occidentales, Mushito, Palomero de Jalisco, Serrano de Jalisco, Tablilla de Ocho, and Zamorano Amarillo races, in the localities of Roque, Guanajuato and Ciudad Guzmán, Jalisco, under an experimental design of incomplete blocks, 30 morphological characters were measured. The analysis of variance indicated significant differences among the accessions for all the characters (variables). The repeatability analysis showed that 16 characters had a coefficient ≥ 3.0, these were the least affected by the environment. In the analysis of main components and conglomerates, variation within and between races was observed, with a continuous dispersion, but which allowed the identification of four racial complexes. Group I was made up of accessions mainly from Bofo, Celaya II, Dulce de Jalisco III and Elotes Occidentales IV, the remaining races are mostly added in group II as subgroups. This study confirmed clustering of accessions in well-defined races and represented in germplasm banks. It is necessary to conduct deeper studies in races with few accessions to achieve a better racial definition.
Maize is the highest produced cereal worldwide. There is an increased interest in maize product consumption as a gluten-free alternative and its bioactive compounds content. Maize is mainly processed by wet-milling, dry-milling, or nixtamalization, and additional processing happens during meal preparation. Maize processing can generate several food ingredients such as starch, sweeteners, oil, and flours (whole, nixtamalized, or germinated). The maize kernel contains a high amount of carbohydrates, and a good amount of proteins and bioactive compounds. However, maize genotype and processing methods influence the chemical composition. Thus, this review aims to discuss the current information for maize processing, product development, and the nutritional content and health benefits.
Maize (Zea mays subspecies mays) has been culturally and economically a very important crop since it was domesticated from its wild relatives, the teosintes (both the lowlands teosinte, Zea mays subspecies parviglumis and the highlands teosisnte, Zea mays subspecies mexicana) in Mexico. In this chapter, we review molecular studies analyzing different aspects of the genetic resources, domestication, phylogeography, and other aspects of the evolution of maize and teosintes, including niche modeling. The genetic studies range from isoenzymes to single nucleotide polymorphisms and other genomic and transcriptomic studies. Both cultivated maize and wild teosintes have high levels of genetic variation and signals of strong local adaptation. Currently, the most accepted hypothesis on maize origin indicates that domestication occurred 9000 years ago in a single event in southern Mexico from the lowland subspecies, Z. m. parviglumis. According to these ideas, later maize spread into higher elevations through adaptive introgression with highland teosintes, Z. m. mexicana. But these ideas are still open to discussion, as better data are needed. Since the origin of maize, there has been strong ongoing artificial selection that has allowed maize to diversify and spread globally and to highly new environments. This intensive selection in maize has left strong molecular signals of selection on a variety of genes that go from domesticated genes to improvement genes. To help respond to climate and global changes, it will be important to determine genes of agronomic importance for tolerance (weather, plagues) and improvement (increase in productivity) to cope with these changes.
Maize (Zea mays L.) is the most domesticated plant in the world. Among the largest diversity of genetic resources of Mexican maize, pigmented genotypes, as purple, red, and blue are the most common. Of the total number of races (landraces) currently existing in Mexico, there are at least 59 that are clearly and consistently distinguishable on the basis of biochemical and morphological characteristics. Pigmented maize has received increased attention from a nutraceutical perspective owing to its potential health benefits. Phytochemicals such as phenolics, anthocyanins, among others have been previously reported on several genotypes. The term nixtamalization refers to the alkaline cooking process of converting maize into foods such as tortillas and snack foods (maize chips, tortillas chips, and tacos). This chapter reviews our current knowledge about the effect of nixtamalization process on the level of total phenolics, anthocyanins and antioxidant activity of nixtamalized products (masa, nixtamal, tortillas, chips) produced from pigmented maize genotypes.
Most research studies in food science have been focused in the field of dietary polyphenols or phenolic compounds, but there is an important part of polyphenols not extracted with organic solvents and the reports are few of those compounds. Pigmented maize (mainly blue and red) have presented significant anthocyanins content and antioxidant capacity; however, the studies about phytochemical content of pigmented maize in Mexico and their biological effects are limited. The aim of this study was to evaluate the antioxidant capacity of extractable and non-extractable polyphenols of blue and red maize. Total polyphenols was determined, as the sum of the polyphenols present in methanol: acetone: water extracts (extractable polyphenols), condensed tannins and hydrolysable polyphenols (non-extractable polyphenols) in the corresponding residues of maize samples. The non- extractable polyphenols content was higher than extractable polyphenols. It was estimated that high percentage of phenolics could be more bio-accessible in the large intestine. In general, blue and red maize presented an antioxidant capacity (FRAP and ABTS assays). These results are important for the use of maize-based foods, industrial and pharmaceutical products.
White, blue, red and purple corns (Zea mays L.) were lime-cooked to obtain masa for tortillas. The total phenolics and anthocyanins content, antioxidant activity expressed as total reducing power (TRP), peroxyl radical bleaching (PRAC), total antioxidant activity (TAA) and quinone reductase (QR) induction in the murine hepatoma (Hepa 1 c1c7 cell line) as a biological marker for phase II detoxification enzymes were investigated. Among the extracts prepared from raw corn varieties the highest concentration of total phenolics, anthocyanins, antioxidant index and induction of QR-inducing activity were found in the Veracruz 42 (Ver 42) genotype. The nixtamalization process (masa) reduced total phenolics, anthocyanins and antioxidant activities and the ability for QR induction when was compared to raw grain. Processing masa into tortillas also negatively affected total phenolics, anthocyanin concentration, antioxidant activities, and QR induction in the colored corn varieties. The blue variety and its corresponding masa and tortillas did not induce QR. Ver 42 genotype and their products (masa and tortilla) showed the greatest antioxidant activity and capacity to induce QR.
On-farm conservation is recognized as a key component of a comprehensive strategy to conserve crop genetic resources. A fundamental problem faced by any on-farm conservation project is the identification of crop populations on which efforts should be focused. This paper describes a method to identify a subset of landraces for further conservation efforts from a larger collection representing the diversity found in the Central Valleys of Oaxaca, Mexico. Mexico is a center of origin and diversity for maize (Zea mays L.). The 17 landraces selected from an initial collection of 152 satisfy two criteria. First, they represent the diversity present in the larger collection. Second, they appear to serve the interests of farmers in the region. Data for applying the method were elicited through participatory as well as conventional techniques. They incorporate the complementary perspectives of both men and women members of farm households, and of plant breeders and social scientists.
To date, mobile Mu transposons and their autonomous regulator MuDR have been found only in the two known Mutator lines of maize and their immediate descendants. To gain insight into the origin, organization, and regulation of Mutator elements, we surveyed exotic maize and related species for cross-hybridization to MuDR. Some accessions of the mexican land race Zapalote chico contain one to several copies of full-length, unmethylated, and transcriptionally active MuDR-like elements plus non-autonomous Mu elements. The sequenced 5.0-kb MuDR-Zc element is 94.6% identical to MuDR, with only 20 amino acid changes in the 93-kD predicted protein encoded by mudrA and ten amino acid changes in the 23-kD predicted protein of mudrB. The terminal inverted repeat (TIR) A of MuDR-Zc is identical to standard MuDR; TIRB is 11.2% divergent from TIRA. In Zapalote chico, mudrA transcripts are very rare, while mudrB transcripts are as abundant as in Mutator lines with a few copies of MuDR. Zapalote chico lines with MuDR-like elements can trans-activate reporter alleles in inactive Mutator backgrounds; they match the characteristic increased forward mutation frequency of standard Mutator lines, but only after outcrossing to another line. Zapalote chico accessions that lack MuDR-like elements and the single copy MuDR a1-mum2 line produce few mutations. New mutants recovered from Zapalote chico are somatically stable.
We measured sequence diversity in 21 loci distributed along chromosome 1 of maize (Zea mays ssp. mays L.). For each locus, we sequenced a common sample of 25 individuals representing 16 exotic landraces and nine U.S. inbred lines. The data indicated that maize has an average of one single nucleotide polymorphism (SNP) every 104 bp between two randomly sampled sequences, a level of diversity higher than that of either humans or Drosophila melanogaster. A comparison of genetic diversity between the landrace and inbred samples showed that inbreds retained 77% of the level of diversity of landraces, on average. In addition, Tajima's D values suggest that the frequency distribution of polymorphisms in inbreds was skewed toward fewer rare variants. Tests for selection were applied to all loci, and deviations from neutrality were detected in three loci. Sequence diversity was heterogeneous among loci, but there was no pattern of diversity along the genetic map of chromosome 1. Nonetheless, diversity was correlated (r = 0.65) with sequence-based estimates of the recombination rate. Recombination in our sample was sufficient to break down linkage disequilibrium among SNPs. Intragenic linkage disequilibrium declines within 100-200 bp on average, suggesting that genome-wide surveys for association analyses require SNPs every 100-200 bp.
Association studies based on linkage disequilibrium (LD) can provide high resolution for identifying genes that may contribute to phenotypic variation. We report patterns of local and genome-wide LD in 102 maize inbred lines representing much of the worldwide genetic diversity used in maize breeding, and address its implications for association studies in maize. In a survey of six genes, we found that intragenic LD generally declined rapidly with distance (r(2) < 0.1 within 1500 bp), but rates of decline were highly variable among genes. This rapid decline probably reflects large effective population sizes in maize during its evolution and high levels of recombination within genes. A set of 47 simple sequence repeat (SSR) loci showed stronger evidence of genome-wide LD than did single-nucleotide polymorphisms (SNPs) in candidate genes. LD was greatly reduced but not eliminated by grouping lines into three empirically determined subpopulations. SSR data also supplied evidence that divergent artificial selection on flowering time may have played a role in generating population structure. Provided the effects of population structure are effectively controlled, this research suggests that association studies show great promise for identifying the genetic basis of important traits in maize with very high resolution.
There exists extraordinary morphological and genetic diversity among the maize landraces that have been developed by pre-Columbian cultivators. To explain this high level of diversity in maize, several authors have proposed that maize landraces were the products of multiple independent domestications from their wild relative (teosinte). We present phylogenetic analyses based on 264 individual plants, each genotyped at 99 microsatellites, that challenge the multiple-origins hypothesis. Instead, our results indicate that all maize arose from a single domestication in southern Mexico about 9,000 years ago. Our analyses also indicate that the oldest surviving maize types are those of the Mexican highlands with maize spreading from this region over the Americas along two major paths. Our phylogenetic work is consistent with a model based on the archaeological record suggesting that maize diversified in the highlands of Mexico before spreading to the lowlands. We also found only modest evidence for postdomestication gene flow from teosinte into maize.
Maize was domesticated from teosinte, a wild grass, by ∼ 6300 years ago in Mexico. After initial domestication, early farmers
continued to select for advantageous morphological and biochemical traits in this important crop. However, the timing and
sequence of character selection are, thus far, known only for morphological features discernible in corn cobs. We have analyzed
three genes involved in the control of plant architecture, storage protein synthesis, and starch production from archaeological
maize samples from Mexico and the southwestern United States. The results reveal that the alleles typical of contemporary
maize were present in Mexican maize by 4400 years ago. However, as recently as 2000 years ago, allelic selection at one of
the genes may not yet have been complete.
To conserve the long-term selection potential of maize, it is necessary to investigate past and present evolutionary processes that have shaped quantitative trait variation. Understanding the dynamics of quantitative trait evolution is crucial to future crop breeding. We characterized population differentiation of maize landraces from the State of Oaxaca, Mexico for quantitative traits and molecular markers. Qst values were much higher than Fst values obtained for molecular markers. While low values of Fst (0.011 within-village and 0.003 among-villages) suggest that considerable gene flow occurred among the studied populations, high levels of population differentiation for quantitative traits were observed (ie an among-village Qst value of 0.535 for kernel weight). Our results suggest that although quantitative traits appear to be under strong divergent selection, a considerable amount of gene flow occurs among populations. Furthermore, we characterized nonproportional changes in the G matrix structure both within and among villages that are consequences of farmer selection. As a consequence of these differences in the G matrix structure, the response to multivariate selection will be different from one population to another. Large changes in the G matrix structure could indicate that farmers select for genes of major and pleiotropic effect. Farmers' decision and selection strategies have a great impact on phenotypic diversification in maize landraces.
Assessing the impact of farmer management of maize landraces in the Central Valleys of Oaxaca, Mexico is crucial to an understanding of maize evolution, as it was first domesticated there. In this paper, we report on the impact of traditional farmer management of maize populations in this region in structuring molecular diversity and on the population dynamics of maize landraces. These populations, from a sample of local landraces cultivated by farmers in six villages, show little among-population differentiation (Fst=0.011). Most surprisingly, there is no isolation by distance and small among-village differentiation (Fst=0.003). For an outbreeding plant such as maize, one would expect populations to fit Hardy-Weinberg equilibrium, but significant homozygote excess (Fis=0.13) was found. This homozygote excess shows remarkable interpopulation and interlocus differences. We show that this pattern is related to variation in the mean anthesis-silking interval as well as to the flowering range or heterogeneity in flowering of a given population. A short anthesis-silking interval and high level of heterogeneity in flowering precocity will favor assortative mating. This leads to a locus-dependent population substructure giving an unusual case of Wahlund effect and inbreeding while high levels of seed exchange among farmers prevent population differentiation at both village and regional levels.
Domestication promotes rapid phenotypic evolution through artificial selection. We investigated the genetic history by which
the wild grass teosinte (Zea mays ssp. parviglumis) was domesticated into modern maize (Z. mays ssp. mays). Analysis of single-nucleotide polymorphisms in 774 genes indicates that 2 to 4% of these genes experienced artificial selection.
The remaining genes retain evidence of a population bottleneck associated with domestication. Candidate selected genes with
putative function in plant growth are clustered near quantitative trait loci that contribute to phenotypic differences between
maize and teosinte. If we assume that our sample of genes is representative, ∼1200 genes throughout the maize genome have
been affected by artificial selection.
We report a whole-genome comparison of gene content in allelic BAC contigs from two maize inbred lines. Genic content polymorphisms involve as many as 10,000 sequences and are mainly generated by DNA insertions. The termini of eight of the nine genic insertions that we analyzed shared the structural hallmarks of helitron rolling-circle transposons. DNA segments defined by helitron termini contained multiple gene-derived fragments and had a structure typical of nonautonomous helitron-like transposons. Closely related insertions were found in multiple genomic locations. Some of these produced transcripts containing segments of different genes, supporting the idea that these transposition events have a role in exon shuffling and the evolution of new proteins. We identified putative autonomous helitron elements and found evidence for their transcription. Helitrons in maize seem to continually produce new nonautonomous elements responsible for the duplicative insertion of gene segments into new locations and for the unprecedented genic diversity. The maize genome is in constant flux, as transposable elements continue to change both the genic and nongenic fractions of the genome, profoundly affecting genetic diversity.
Maize (Zea mays subsp mays) was domesticated from teosinte (Z. mays subsp parviglumis) through a single domestication event in southern Mexico between 6000 and 9000 years ago. This domestication event resulted in the original maize landrace varieties, which were spread throughout the Americas by Native Americans and adapted to a wide range of environmental conditions. Starting with landraces, 20th century plant breeders selected inbred lines of maize for use in hybrid maize production. Both domestication and crop improvement involved selection of specific alleles at genes controlling key morphological and agronomic traits, resulting in reduced genetic diversity relative to unselected genes. Here, we sequenced 1095 maize genes from a sample of 14 inbred lines and chose 35 genes with zero sequence diversity as potential targets of selection. These 35 genes were then sequenced in a sample of diverse maize landraces and teosintes and tested for selection. Using two statistical tests, we identified eight candidate genes. Extended gene sequencing of these eight candidate loci confirmed that six were selected throughout the gene, and the remaining two exhibited evidence of selection in the 3' portion of each gene. The selected genes have functions consistent with agronomic selection for nutritional quality, maturity, and productivity. Our large-scale screen for artificial selection allows identification of genes of potential agronomic importance even when gene function and the phenotype of interest are unknown.
Association mapping, a high-resolution method for mapping quantitative trait loci based on linkage disequilibrium, holds great promise for the dissection of complex genetic traits. The recent assembly and characterization of maize association mapping panels, development of improved statistical methods, and successful association of candidate genes have begun to realize the power of candidate-gene association mapping. Although the complexity of the maize genome poses several significant challenges to the application of association mapping, the ongoing genome sequencing project will ultimately allow for a thorough genome-wide examination of nucleotide polymorphism-trait association.
To examine the questions of whether the additive and dominance effects present for morphological characters in racial crosses are of sufficient consistency and magnitude to allow such genetic effects to be used for racial classification, we used a diallel experiment among the 25 well-defined Mexican races of maize, which include the ancestral stocks of most commercial and genetic maize types. With such an experiment, genetic effects and genotype by environmental interactions for one or more characters can be used to measure genetic and adaptational or environmental similarity. We used average parental effects (general combining abilities), specific effects, and genotype by environmental effects of 21 characters from the diallel (grown at three locations) to group the Mexican races of maize. The groupings based upon average genetic effects and upon genotype by environmental interactions are more satisfactory than groupings based upon specific effects. The standard errors for genetic distances based upon specific (largely dominance) effects seem to be too high for practical use. Principal components analyses of the same data suggest a similar conclusion.-The groupings based upon average genetic effects are in general agreement with previous studies, with the exception of Maíz Dulce, which is grouped with the Cónicos, rather than being isolated from the other Mexican races of maize.
Artificial selection results in phenotypic evolution. Maize (Zea mays L. ssp. mays) was domesticated from its wild progenitor teosinte (Zea mays subspecies parviglumis) through a single domestication event in southern Mexico between 6000 and 9000 years ago. This domestication event resulted in the original maize landrace varieties. The landraces provided the genetic material for modern plant breeders to select improved varieties and inbred lines by enhancing traits controlling agricultural productivity and performance. Artificial selection during domestication and crop improvement involved selection of specific alleles at genes controlling key morphological and agronomic traits, resulting in reduced genetic diversity relative to unselected genes.
This review is a summary of research on the identification and characterization by population genetics approaches of genes affected by artificial selection in maize.
Analysis of DNA sequence diversity at a large number of genes in a sample of teosintes and maize inbred lines indicated that approx. 2 % of maize genes exhibit evidence of artificial selection. The remaining genes give evidence of a population bottleneck associated with domestication and crop improvement. In a second study to efficiently identify selected genes, the genes with zero sequence diversity in maize inbreds were chosen as potential targets of selection and sequenced in diverse maize landraces and teosintes, resulting in about half of candidate genes exhibiting evidence for artificial selection. Extended gene sequencing demonstrated a low false-positive rate in the approach. The selected genes have functions consistent with agronomic selection for plant growth, nutritional quality and maturity. Large-scale screening for artificial selection allows identification of genes of potential agronomic importance even when gene function and the phenotype of interest are unknown. These approaches should also be applicable to other domesticated species if specific demographic conditions during domestication exist.
The report of a haplotype map for the selfing plant Arabidopsis thaliana has uncovered numerous major-effect polymorphisms and rapid linkage disequilibrium decay. This work lays the foundation for genome-wide association studies at near-gene-level resolution in a model organism possessing substantial functional diversity and extensive community resources.
The discovery of transgenic products in maize (Zea mays) landraces planted by small-scale Mexican farmers (Quist and Chapela, 2001, 2002; Christou, 2002; Editorial Note, 2002) raised questions about how the commercial introduction of transgenic maize varieties might affect the traditional agricultural systems of small-scale farmers. A key concern is whether their introduction will have a deleterious effect on the diversity of maize landraces that these farmers maintain.
Antecedentes L a diversidad de poblaciones de maíz que cultivan los cam-pesinos de muchas comunidades rurales es asombrosa. Cuando se exponen en forma conjunta las muestras reu-nidas de muchos vecinos en una parcela demostrativa, hasta a los miem-bros de la comunidad les llama la atención. El interés por la diversidad de maíz viene desde los tiempos prehispá-nicos, como se refleja en las leyendas sobre el origen de la planta y en los códices. Durante la Colonia y el siglo XIX hay referencias aisladas al tema. Pero sólo hasta el siglo XX se empiezan a estudiar y colectar en forma sis-temática poblaciones locales nativas de maíz* y se publican las magníficas monografías de Chávez (1913) y Anderson (1946). * Para referirme a lo que popularmente se conoce como "variedades criollas" usaré aquí el término "población local nativa" de maíz. El término "variedad" es, en botánica, una categoría taxonómica diferente a la que se da al término en el lenguaje común. Cuando se menciona una "variedad criolla", no queda claro si se refiere a una población de maíz mantenida por un agricultor (que a menudo es diferente a las de sus vecinos) o a todas las poblaciones parecidas de una región. El término "criollo" se relaciona históricamente con los descendientes de españoles nacidos en América, sentido que no corresponde al de las poblaciones de maíz mantenidas por los agricultores, aunque el Diccionario de la Lengua Española de la Real Academia admite una acepción aplicable: "Autóctono, propio, distintivo de un país hispanoamericano." Población local —según el "Glosario de recursos naturales" de Gutiérrez et al. (1983, p. 234)— es: "Grupo de individuos de la misma especie que se desarrollan lo bastante cer-ca unos de otros para efectuar cruzas de hibridación e intercambiar genes." Esta es la idea que se quiere expresar. Un agricultor puede tener dos o más poblaciones de maíz que siembra en forma contigua, por lo que podría argüirse que se trata de una sola población local, pero la selección de semillas puede mantener hasta cierto grado su separación. El término "nativa" se usa para diferenciar las poblaciones tradicionales de aquellas mantenidas por los agricultores pero generadas a partir de híbridos y va-riedades mejoradas.
To determine the relationships and genetic diversity among the Mexican races of maize, 209 accessions representing 59 races were analyzed for 21 enzyme systems encoded by 37 loci; 154 out of the 209 accessions were grown in multiple locations and seasons in Mexico and 47 morphological characters were measured. A very high level of variation among and within the Mexican races was found. However, more than 65% of the alleles found in the accessions studied are rare, occurring at frequencies below 0.01. In addition, some populations have low levels of genetic diversity and have values of genetic differentiation similar to selflng crops. Most of the accessions with low values of genetic diversity are specialty varieties.
The wild ancestry of maize has long been a puzzle. Maize shows extraordinary phenotypic and genetic di-versity with no obvious morphological similarity to any of its wild relatives. Beadle's teosinte hypothesis, which regards teosinte as the sole wild ancestor of maize, has become widely accepted as the most probable model of maize evolution based on taxonomic, genetic, and other types of evidence. Molecular studies have refined the teosinte hypothesis by identifying a particular form of teosinte, Zea mays ssp. parviglumis, as the direct ancestor of maize. Maize and teosinte therefore provide a typical case in which modern molecular ge-netic analyses, in the absence of obvious morphological similarity, have been critical for distinguishing the exact ancestor of a crop from other close wild relatives. Furthermore, a recent microsatellite-based study shows that all extant pre-Columbian maize landraces arose from Z. mays ssp. parviglumis roughly 9,000 years ago through a single domestication event in the central Balsas River drainage (southern Mexico). That model, showing that maize is a domesticated form of Z. mays ssp. parviglumis, provides a logical, practical frame-work for investigations of the genetic mechanisms that drove maize domestication and diversification. This points up the importance of knowing exact origins in studies that use crops and their wild relatives as models. An overview of the progress in genetic and evolutionary studies is presented herein to clarify the identity of the wild progenitor of maize. Implications of recent findings on the origin of maize diversity are discussed.
Using principal component and cluster analyses of 20 ear characters for 219 Latin American races and subraces of maize, 14 groups of races are delimited. The relationships among these groups are indicated, and some subdivisions of the 14 racial groups are described. Only two of the 14 groups of races have been widely used in breeding; several groups have only been
slightly studied and a number of their component races verge upon extinction. There is a very small, but perhaps highly significant,
amount of overlap between the groups to which the Mexican and indigenous South American races belong.
Como parte del proceso de revisión de la obra Razas de Maíz en México de Wellhausen et al., el presente estudio se diseñó con la finalidad de mejorar la clasificación de las razas Mexicanas de maíz. Las interrelaciones se examinaron usando taxonomía numérica de caracteres morfológicos y las clasificaciones se compararon con estudios previos. Se estudiar 49 razas Mexicanas, representadas por 148 colectas típicas, las cuales fueron sembradas en varios ambientes en México de 1982 a 1984. Se midieron un total de 47 caracteres en forma directa; para los análisis de taxonomía numérica, los caracteres se eligieron en base al criterio de Goodman y Paterniani, o sea, todos aquellos caracteres con(Formula presented.). Las clasificaciones obtenidas en el presente estudio concuerdan, en lo general, con estudios previos basados en taxonomía convencional y taxonomía numérica. Adicionalmente, las razas no bien definidas y variantes recientemente descubiertas pueden ahora asignarse a grupos bien definidos.
Thesis (Ph. D.)--University of Wisconsin-Madison, 1986. Includes bibliographical references. Photocopy.
Although allelic sequences can vary extensively, it is generally assumed that each gene in one individual will have an allelic counterpart in another individual of the same species. We report here that this assumption does not hold true in maize. We have sequenced over 100 kb from the bz genomic region of two different maize lines and have found dramatic differences between them. First, the retrotransposon clusters, which comprise most of the repetitive DNA in maize, differ markedly in make-up and location relative to the genes in the bz region. Second, and more importantly, the genes themselves differ between the two lines, demonstrating that genetic microcolinearity can be violated within the same species. Our finding has bearing on the underlying genetic basis of hybrid vigor in maize, and possibly other organisms, and on the measurement of genetic distances.
Maize and its closest wild relatives, the teosintes, differ strikingly in the morphology of their female inflorescences or ears. Despite their divergent morphologies, several studies indicate that some varieties of teosinte are cytologically indistinguishable from maize and capable of forming fully fertile hybrids with maize. Molecular analyses identified one form of teosinte (Zea mays ssp. parviglumis) as the progenitor of maize. Analyses of the inheritance of the morphological traits that distinguish maize and teosinte indicates that they are under the control of multiple genes and exhibit quantitative inheritance. Nevertheless, these analyses have also identified a few loci of large effect that appear to represent key innovations during maize domestication. Remaining challenges are to identify additional major and minor effect genes, the polymorphisms within these genes that control the phenotypes, and how the combination of the individual and epistatic effects of these genes transformed teosinte into maize.
Different maize inbred lines are polymorphic for the presence or absence of genic sequences at various allelic chromosomal locations. In the bz genomic region, located in 9S, sequences homologous to four different genes from rice and Arabidopsis are present in line McC but absent from line B73. It is shown here that this apparent intraspecific violation of genetic colinearity arises from the movement of genes or gene fragments by Helitrons, a recently discovered class of eukaryotic transposons. Two Helitrons, HelA and HelB, account for all of the genic differences distinguishing the two bz locus haplotypes. HelA is 5.9 kb long and contains sequences for three of the four genes found only in the McC bz genomic region. A nearly identical copy of HelA was isolated from a 5S chromosomal location in B73. Both the 9S and 5S sites appear to be polymorphic in maize, suggesting that these Helitrons have been active recently. Helitrons lack the strong predictive terminal features of other transposons, so the definition of their ends is greatly facilitated by the identification of their vacant sites in Helitron-minus lines. The ends of the 2.7-kb HelB Helitron were discerned from a comparison of the McC haplotype sequence with that of yet a third line, Mo17, because the HelB vacant site is deleted in B73. Maize Helitrons resemble rice Pack-MULEs in their ability to capture genes or gene fragments from several loci and move them around the genome, features that confer on them a potential role in gene evolution.
• genome variability
• Helitrons
• bz locus
• corn
• polymorphisms
Over the past 10,000 years, man has used the rich genetic diversity of the maize genome as the raw material for domestication and subsequent crop improvement. Recent research efforts have made tremendous strides toward characterizing this diversity: structural diversity appears to be largely mediated by helitron transposable elements, patterns of diversity are yielding insights into the number and type of genes involved in maize domestication and improvement, and functional diversity experiments are leading to allele mining for future crop improvement. The development of genome sequence and germplasm resources are likely to further accelerate this progress.
Nuestro maíz, treinta monografías populares
- B G Bonfil
La agricultura en la Península de Yucatá n. In: Xolocotzia: Obras de Efrain Herná ndez Xolocotzi. Tomo 1. Revista de Geografía Agríola
- X E Herná
Maíces de México Panamá y Colombia (según las colec-ciones de N. S. Bukasov) In: Las plantas cultivadas de México, Guatemala y Colombia
- N N Kuslehov
Cultivo del Maíz. Imprenta y Fototipia de la Secretaria de Fomento
- E Chá
Estudio morfológico de cinco razas de maiz de la Sierra Madre Occidental de México: implicaciones filogenéticas y fitogeográ ficas
- X E Herná
- F Alanís
- X.E. Hernández
Constitución cromosómica de las razas de maiz. Su significado en la interpretación de relaciones entre las razas y variedades en las Américas
- B Mcclintock
- Y T A Kato
- A Z Blumenshein
Estado actual de lose studios sobre maíces nativos de México
- Ortega Paczka
- R Sá Nchez
- J J Castillo Gonzá Lez
- J M Herná Ndez Casillas
Reestudio de las razas mexicanas de maíz. Informe anual. Campo agr
- R Ortega Paczka
Bancos Genéticos: Un recurso mundial
- D L Plucknett
- J T Williams
- N J H Smith
- N M Anishetty
Razas de Maíz en México. Su origen, características y distribución
- E J Wellhausen
- L M Roberts
- E Hernández-Xoconostle
- P C Mangelsdorf
México and Central America as the principal centre of origin of cultivated plants of the new world
- N I Vavilov
- N.I. Vavilov
Genetic association mapping and genome organization of maize
- J Yu
- E S Buckler
- J. Yu
Variedades y razas mexicanas de maíz y su evaluación en cruzamientos con lineas de climas templado como material de partida para fitomejoramiento. Abbreviated Spanish Translation of PhD thesis. N. I. Vavilov National Institute of Plants
- R Ortega Paczka
La agricultura en la Península de Yucatá n
- X E Herná Ndez
Gemomic screening for artificial selection during domestication and improvement in maize
- M Yamasaki
- S I Wright
- M D Mcmullen
Maize Breeding and Genetics
- B D Walden
- B.D. Walden
Intraspecific violation of genetic colinearity and its implications in maize
- H Fu
- H K Dooner
Distance analysis in biology
- M M Goodman
- M.M. Goodman
Transcriptionally active
- N M L Gutiérrez
- C A Warren
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- V Walbot
y Colombia (según las colec-ciones de N. S. Bukasov). In: Las plantas cultivadas de México, Guatemala y Colombia
- N N Kuslehov