Mapping the Diversity of Maize Races in Mexico

Traditional landraces of maize are cultivated throughout more than one-half of Mexico''s cropland. Efforts to organize in situ conservation of this important genetic resource have been limited by the lack of knowledge of regional diversity patterns. We used recent and historic collections of maize classified for race type to determine biogeographic regions and centers of landrace diversity. We also analyzed how diversity has changed over the last sixty years. Based on racial composition of maize we found that Mexico can be divided into 11 biogeographic regions. Six of these biogeographic regions are in the center and west of the country and contain more than 90% of the reported samples for 38 of the 47 races studied; these six regions are also the most diverse. We found no evidence of rapid overall decline in landrace diversity for this period. However, several races are now less frequently reported and two regions seem to support lower diversity than in previous collection periods. Our results are consistent with a previous hypothesis for diversification centers and for migration routes of original maize populations merging in western central Mexico. We provide maps of regional diversity patterns and landrace based biogeographic regions that may guide efforts to conserve maize genetic resources.     

Variation of Kernel Anthocyanin and Carotenoid Pigment Content in USA/Mexico Borderland Land Races of Maize

Variation of Kernel Anthocyanin and Carotenoid Pigment Content in USA/Mexico Borderland Land Races of Maize. Maize is the only major cereal crop that displays abundant variation for health-promoting carotenoid and anthocyanin pigments. Traditional farmers in the USA/Mexico Borderland region utilize many land race varieties with diverse kernel characteristics reflecting enculturated preferences, including color. Food prepared using these varieties may provide benefits to human health, but the kernel pigment content, and grain physical and compositional traits, have not been characterized. Seed from 48 diverse accessions representing 18 races of maize originating from the Borderland region were obtained from Native Seeds/SEARCH and planted in replicated nurseries at two locations (Ohio and Arizona) in 2008. We visually determined kernel color and quantified total carotenoid and anthocyanin pigment content of samples obtained from these nurseries using spectrophotometric analysis. Nonpigmented (white) followed by yellow kernel colors were most abundant. Populations with high carotenoid pigment content (i.e., above 40 μg/g) were not observed, whereas many accessions produced ears with mixtures of red, purple, and blue kernels containing anthocyanin pigments. A wide range in anthocyanin pigment content was observed across and within populations—some kernels displayed concentrations above 50 mg/100 g. Kernel hardness was determined visually, and protein and oil content were determined by near-infrared spectrometric analysis. Flinty (hard) followed by floury (soft) kernel types were most abundant. Carotenoid content was highest in orange- and yellow-colored pop-type kernels. Anthocyanin content was highest in blue- and purple-colored floury and flint-type kernels. Kernel weight, protein, oil, and carotenoid content were significantly affected by location. Preservation of culturally-adapted varieties with diverse kernel pigments is important not only because of their genetic diversity—they also may contribute to enhanced human health and nutrition.     

Morphological Comparison of Three Host Races of Meloidogyne javanica

A morphological and morphometric comparison using light microscopy and scanning electron microscopy was made of six populations of Meloidogyne javanica belonging to three host races (infective on pepper, peanut, or noninfective on both). The variability of certain morphological characters was studied within these populations, and the reliability of these taxonomic traits was evaluated for usefulness in species identification. The most useful diagnostic characters of M. javanica were head and stylet morphology of males and stylet morphology and perineal patterns of females. Males have an offset head region, usually lacking annulations, and a distinct, narrow head cap with slightly raised labial disc. The stylet has a cone markedly wider than the shaft at the junction and large, transversely ovoid knobs that are offset from the shaft. Females have a robust stylet with a dorsally curved cone and large, transversely ovoid knobs. Perineal patterns are oval to squarish in shape, usually with coarse, broken striae and with conspicuous lateral lines. The host races could not be differentiated on a morphological basis.     

Traditional Maize Storage Methods of Mayan Farmers in Yucatan, Mexico: Implications for Seed Selection and Crop Diversity

For small-scale farmers who maintain genetically diverse crop populations, aspects of the storage of their seeds and harvest may be just as important for successful farming as those related to productivity. The community of Yaxcaba, Yucatan, Mexico was studied to understand how the conditions under which Maya farmers store their maize harvests influence their seed selection practices and the diversity of maize varieties grown. Most farmers select their maize seed based primarily on ear characteristics and secondarily on grain characters. Farmers incorporate storability concerns by selecting for an archetypal healthy ear and by conducting selection in several steps between harvest and planting of the subsequent crop generation. Most farmers store their maize harvest in the husk, initially in the field and then in rustic granaries constructed of logs and palm thatch, in which farmers conserve separately their different seed lots. All local landrace populations show morphological adaptation (principally husk characteristics) for local storage conditions, indicating that storability has been an important selection pressure on traditional maize. Storability also appears to be a key factor working against the straightforward adoption of improved maize seed in Yaxcaba. Local farmers value many qualities of improved maize varieties, but their principal complaint is that improved maize cannot be conserved reliably under local storage conditions. Nearly all farmers who utilize improved seed stock in Yaxcaba grow locally adapted or ‘creolized’ versions of improved varieties, displaying characteristics of local maize landraces that facilitate their storage.     

Estimation of Morphological Marker Diversity

A genetic statistical method for estimation of intraspecific diversity of cultivated plants with respect to morphological genes is proposed. The method may be used for estimation of probability distributions of morphological (marker) mutations with respect to the frequencies of their expression and for prediction of experimental parameter such as the total number of markers, the scale (duration) of the experiment that is necessary for detection of a given proportion of the total marker diversity of the species, etc. The method was tested on tomato Lycopersicon esculentumMill. using data from the SolGenes Internet databank.     

福建山樱花形态多样性分化的研究

以闽、赣、粤、台4省13个种群292份福建山樱花种质为分析材料,对16个形态性状进行聚类分析和主成分分析。结果表明:福建山樱花不同个体间各性状均有明显差异,变异系数较大,优株选择潜力很大。系统聚类分析可将292份参试材料划分为2个表征群4个亚表征群,除重瓣型福建山樱花外,单瓣型福建山樱花的形态特征在种群间总体上无明显的分化规律,不同种群的个体交叉聚在同一个表征群内,但在同一亚表征群内,同一种群的多数个体常能聚在一起,表明种群之间在形态上发生了一定程度的分化,只是这种分化还不能清楚地区分不同的种群。主成分分析结果表明叶形、叶尖、叶缘、分枝能力、60 d苗高、花色和花形是造成福建山樱花形态分化的主要因素。     

Morphological Integration and the Interpretation of Fossil Hominin Diversity

The fossil record of primate and human evolution cannot provide accurate estimates of within species variation and integration. This means that we cannot directly observe how patterns of integration have evolved over time in this lineage. And yet, our interpretations of fossil diversity are awash with assumptions about variation patterning in precisely these fossil taxa. Most commonly, researchers rely on extant models of variation for interpreting past diversity, by assuming equality of variation (and occasionally covariation) among extant and fossil populations. Yet one of the things we know from studies of integration in primates is that patterns of morphological covariation can differ among even closely related taxa, indicating that they have diverged over evolutionary time, either in response to selection or as the result of neutral evolution. At the same time, overall patterns of integration remain remarkably similar, meaning that in many respects they are highly conserved evolutionarily. Taken together, these seemingly contradictory observations offer an important conceptual framework for interpreting patterns that we observe in the fossil past. This framework dictates that while we can use patterns of covariation in extant taxa as proxies for extinct diversity, and indeed their conserved nature makes them superior to approaches that rely on variation alone, we also need to account for the fact that such patterns change over time, and incorporate that into our models. Here I provide examples using covariation patterns estimated from modern humans and African great apes to demonstrate the extent to which divergence in covariance structure might affect our interpretations of hominin diversity.

Some Physiological and Morphological Responses in Flooded Maize

After flooding of maize seedlings for fourteen days, their stomata were closed, and total nucleic acid was accumulated in subwater knots before adventitious roots appeared. Aerenchyma were developed and some physiological and morphological changes were induced in fourweek old Zea mays L. seedlings. It aeems possible that the maize seedlings had adapted to the flood circumstances by forming adventitious roots on submerged knots of the stems, which was not only thick and white but also with no root hairs and grew upwards.     

Dynamic Management of Maize Landraces in Central Mexico

Conservationists of crop genetic resources have feared that in situ conservation was not viable for agriculture precisely because of changes resulting from introduction of new varieties of existing crops, new crops, and new farm practices. In addition, conservation within farming systems necessarily implies a constantly changing crop population resulting from the processes of crop evolution. Even though in situ conservation of crop genetic resources is now generally understood to be dynamic, there are few examples of how evolution takes place in farmers fields. This study describes several changes in maize landraces in four communities along an altitude transect in Central Mexico (1200 to 2400 masl). While true modern varieties have not been widely adopted in the study region, farmer management results in numerous changes in maize landrace populations. Five types of dynamic management were observed: (1) purposeful hybridization between traditional and modern maize types, (2) possible creation of a new maize landrace by directional selection of the progeny of hybridization between two traditional landraces, (3) displacement of a local landrace by the introduction of a modern variety and a non-local landrace, (4) maintenance of stable populations of a locally dominant landrace, and (5) market-driven selection for a minor variety. We concur that in situ conservation of crops must be conceived as an open process where the objective is not to maintain historic varieties or static genetic conditions. Rather, in situ conservation of crops is totally in the hands of the farmer, although interventions may be designed to influence farmers’ management of agrobiodiversity.     

Genetic Analysis of the Morphological Differences between Maize and Teosinte

Molecular marker loci were used to investigate the inheritance of morphological traits that distinguish maize (Zea mays ssp. mays) from a closely related wild relative, teosinte (Z. mays ssp. mexicana). Regression and interval mapping analyses gave largely congruent results concerning the numbers of loci controlling the morphological traits and the magnitudes of their effects; however, interval mapping tended to give larger estimates for the magnitudes of the effects of the morphological trait loci. This tendency was exaggerated for traits that were non-normally distributed. Variation for most inflorescence traits is controlled by one or two regions of the genome with large effects plus several other regions with relatively small effects. As such, the data are congruent with a mode of inheritance for most traits involving one or two major loci plus several minor loci. Regions of the genome with large effects on one trait consistently had smaller effects on several other traits, possibly as a result of pleiotropy. Most of the variation for the dramatic differences in inflorescence morphology between maize and teosinte is explained by five restricted regions of the genome. One of these regions encompasses a previously described gene, tb1 (teosinte branched), and the effects of this region on inflorescence architecture are similar to the known effects of tb1. Implications of this work for the genetic basis of morphological evolution in plants are discussed.     

Phylogenetic Composition of Angiosperm Diversity in the Cloud Forests of Mexico

Several members of the most ancient living lineages of flowering plants (angiosperms) inhabit humid, woody, mostly tropical habitats. Here we assess whether one of these forest types, the cloud forests of Mexico (CFM), contain a relatively higher proportion of phylogenetically early-diverging angiosperm lineages. The CFM houses an extraordinary plant species diversity, including members of earliest-diverging angiosperm lineages. The phylogenetic composition of CFM angiosperm diversity was evaluated through the relative representation of orders and families with respect to the global flora, and the predominance of phylogenetically early- or late-diverging lineages. Goodness-of-fit tests indicated significant differences in the proportional local and global representation of angiosperm clades. The net difference between the percentage represented by each order and family in the CFM and the global flora allowed identification of clades that are overrepresented and underrepresented in the CFM. Early-diverging angiosperm orders and families were found to be neither over- nor underrepresented in the CFM. A slight predominance of late-diverging phylogenetic levels among overrepresented clades, however, was encountered in the CFM. The resulting pattern suggests that cloud forests provide habitats where the most ancient angiosperm lineages have survived in the face of accumulating species diversity belonging to phylogenetically late-diverging lineages.     

山东大豆种质资源形态多样性分析

通过对山东省205份大豆种质资源的形态多样性分析,结果表明主茎节数的形态多样性指数最高,为1．96;花色的遗传多样性指数最低,为0．63。总体上是数量性状形态多样性指数大于质量性状。通过主成分分析,第一主成分的方差贡献率为36．49％,第二主成分的方差贡献率为13,24％;基于形态性状的聚类分析把205份材料聚为3类,其中第1类149份材料,品种生育日数较短,株高低,主茎节数和分枝数均少于其他2类。第2类54份材料,品种生育日数稍长,单株荚数、单株粒数较多,株高较高,百粒重较小。第3类仅2份材料,分别来自第Ⅳ生态区和第Ⅴ生态区。这2个品种生育期较长,株高较高。百粒重较大。     

Isozyme Diversity in Indian Primitive Maize Landraces

Polymorphism for peroxidase, esterase and acid phosphatase Isozymes in pollen grains of major Indian maize land races known as ‘Sikkim primitives’ were studied and compared with primitive races of maize of Mexican origin and five species of teosinte, Coix lacryma-jobi, Chionachne koenigii and Sorghum bicolor. The isozyme patterns and the resulting dendrograms revealed similarities in primitive Indian maize landraces from Northeastern Himalayan region and Nal-Tel an ancient indigenous race of Mexico. Further, the Asiatic taxa of Maydeae, C. lacryma-jobi and Ch. koenigii differed widely from each other and also from the Zea spp. Presence of greater diversity among the Indian maize collections was also evident from the present analysis.     

燕麦种质资源形态学性状的遗传多样性

【目的】燕麦种质资源遗传多样性研究不仅有助于种质资源的收集和评价,而且对燕麦生产和育种具有重要指导意义。【方法】研究对260份燕麦种质资源的20个形态学性状多样性、变异及聚类进行分析,评价其形态学性状的遗传变异水平,明确燕麦种质资源的性状特点与遗传多样性,以期为燕麦种质创新和品种改良提供依据。【结果】260份燕麦种质资源形态学性状间存在广泛的遗传多样性,质量性状的遗传多样性指数以粒色最大(1.53),芒色最小(0.76);12个数量性状呈正态分布,数量性状的遗传多样性指数以千粒重最大(2.03),有效分蘖数最小(1.22),变异系数最大的是有效分蘖数(89.02%),最小的是株高(11.19%)。根据燕麦品种(系)间各性状的遗传差异,聚类分析将供试的260份燕麦种质资源分为6类,其中种质群Ⅰ包括42份材料,可作为种用型育种目标的亲本材料;种质群Ⅱ包括31份材料,可作为选育高产饲草品种的亲本材料;种质群Ⅳ包括41份材料,可作为选育大粒专用型品种的育种材料;种质群Ⅴ包括46份材料,可作为燕麦矮化的亲本材料;而种质群Ⅲ包括46份材料,种质群Ⅵ包括54份材料,这两类种质群材料的综合性状表现不突...     

Dispersal of Transgenes through Maize Seed Systems in Mexico

Objectives

Current models of transgene dispersal focus on gene flow via pollen while neglecting seed, a vital vehicle for gene flow in centers of crop origin and diversity. We analyze the dispersal of maize transgenes via seeds in Mexico, the crop''s cradle.

Methods

We use immunoassays (ELISA) to screen for the activity of recombinant proteins in a nationwide sample of farmer seed stocks. We estimate critical parameters of seed population dynamics using household survey data and combine these estimates with analytical results to examine presumed sources and mechanisms of dispersal.

Results

Recombinant proteins Cry1Ab/Ac and CP4/EPSPS were found in 3.1% and 1.8% of samples, respectively. They are most abundant in southeast Mexico but also present in the west-central region. Diffusion of seed and grain imported from the United States might explain the frequency and distribution of transgenes in west-central Mexico but not in the southeast.

Conclusions

Understanding the potential for transgene survival and dispersal should help design methods to regulate the diffusion of germplasm into local seed stocks. Further research is needed on the interactions between formal and informal seed systems and grain markets in centers of crop origin and diversification.     

Morphological and Genetic Diversity of Temperate Phages in Clostridium difficile

Eight temperate phages were characterized after mitomycin C induction of six Clostridium difficile isolates corresponding to six distinct PCR ribotypes. The hypervirulent C. difficile strain responsible for a multi-institutional outbreak (NAP1/027 or QCD-32g58) was among these prophage-containing strains. Observation of the crude lysates by transmission electron microscopy (TEM) revealed the presence of three phages with isometric capsids and long contractile tails (Myoviridae family), as well as five phages with long noncontractile tails (Siphoviridae family). TEM analyses also revealed the presence of a significant number of phage tail-like particles in all the lysates. Southern hybridization experiments with restricted prophage DNA showed that C. difficile phages belonging to the family Myoviridae are highly similar and most likely related to previously described prophages C2, C5, and CD119. On the other hand, members of the Siphoviridae phage family are more genetically divergent, suggesting that they originated from distantly related ancestors. Our data thus suggest that there are at least three genetically distinct groups of temperate phages in C. difficile; one group is composed of highly related myophages, and the other two groups are composed of more genetically heterogeneous siphophages. Finally, no gene homologous to genes encoding C. difficile toxins or toxin regulators could be identified in the genomes of these phages using DNA hybridization. Interestingly, each unique phage restriction profile correlated with a specific C. difficile PCR ribotype.     

Specialized Predation Drives Aberrant Morphological Integration and Diversity in the Earliest Ants

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