Netzahualcóyotl Mayek-Pérez

Genetic diversity analysis of common beans based on molecular markers

A core collection of the common bean (Phaseolus vulgaris L.), representing genetic diversity in the entire Mexican holding, is kept at the INIFAP (Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias, Mexico) Germplasm Bank. After evaluation, the genetic structure of this collection (200 accessions) was compared with that of landraces from the states of Oaxaca, Chiapas and Veracruz (10 genotypes from each), as well as a further 10 cultivars, by means of four amplified fragment length polymorphisms (AFLP) +3/+3 primer combinations and seven simple sequence repeats (SSR) loci, in order to define genetic diversity, variability and mutual relationships. Data underwent cluster (UPGMA) and molecular variance (AMOVA) analyses. AFLP analysis produced 530 bands (88.5% polymorphic) while SSR primers amplified 174 alleles, all polymorphic (8.2 alleles per locus). AFLP indicated that the highest genetic diversity was to be found in ten commercial-seed classes from two major groups of accessions from Central Mexico and Chiapas, which seems to be an important center of diversity in the south. A third group included genotypes from Nueva Granada, Mesoamerica, Jalisco and Durango races. Here, SSR analysis indicated a reduced number of shared haplotypes among accessions, whereas the highest genetic components of AMOVA variation were found within accessions. Genetic diversity observed in the common-bean core collection represents an important sample of the total Phaseolus genetic variability at the main Germplasm Bank of INIFAP. Molecular marker strategies could contribute to a better understanding of the genetic structure of the core collection as well as to its improvement and validation.

Genetic differentiation among Maconellicoccus hirsutus (Hemiptera: Pseudococcidae) populations living on different host plants.

ABSTRACT The pink hibiscus mealybug Maconellicoccus hirsutus (Green) is a dangerous pest that damages a wide variety of agricultural, horticultural, and forestry crops. Amplified fragment length polymorphism (AFLP) fingerprints were used to characterize the genetic variation of 11 M. hirsutus populations infesting three plant species in Nayarit, Mexico. Analysis was carried out using four primers combinations, producing 590 polymorphic bands. Cluster analysis, as well as bootstrap dendrogram and nonmetric multidimensional scaling analysis, grouped M. hirsutus populations according to their host plant. The estimated FST values indicated a high differentiation in M. hirsutus populations among the three host plant species. These results were also supported by a Bayesian analysis, which indicated a population clustering robustness according to their host plant. Genetic variation among populations is not caused by geographic distances, as shown by a Mantel test.

Bases bioquímicas de la tolerancia al estrés osmótico en hongos fitopatógenos: el caso de Macrophomina phaseolina (Tassi) Goid.

Fungus Macrophomina phaseolina (Tassi) Goid. is the causative agent of charcoal rot disease which causes significant yield losses in major crops such as maize, sorghum, soybean and common beans in Mexico. This fungus is a facultative parasite which shows broad ability to adapt itself to stressed environments where water deficits and/or high temperature stresses commonly occur. These environmental conditions are common for most cultivable lands throughout Mexico. Here we describe some basic facts related to the etiology and epidemiology of the fungus as well as to the importance of responses to stressed environments, particularly to water deficits, based on morphology and growth traits, as well as on physiology, biochemistry and pathogenicity of fungus M. phaseolina. To conclude, we show some perspectives related to future research into the genus, which emphasize the increasing need to improve the knowledge based on the application of both traditional and biotechnological tools in order to elucidate the mechanisms of resistance to environmental stress which can be extrapolated to other useful organisms to man.

Karyotype characterization of four Mexican species of Schoenoplectus (Cyperaceae) and first report of polyploid mixoploidy for the family

Karyomorphological analysis of four species of Schoenoplectus (Cyperaceae) from north-central Mexico were carried out. Chromosome numbers ranged from 2n = 38 to 2n = 84. New records of counting are given for Schoenoplectus acutus var. occidentalis (2n = 38 and 2n = 84) and S. americanus (2n = 66). Intra-individual variation in chromosome number is reported for the first time for S. acutus, with a rare polyploid mixoploidy with a prevalence of cells with 2n = 38 (36 small + 2 compound, larger chromosomes) and a few cells with 2n = 84 small, dot-shaped chromosomes, this being the first record of polyploid mixoploidy for Cyperaceae. Mean length of the diploid set ranged from 51.5 μm (S. tabernaemontani) to 79.5 μm (S. acutus). The lowest average chromosome length for the dot-shaped chromosomes was 0.69 μm (S. acutus) and the highest 1.62 μm (S. tabernaemontani); the pair of large chromosomes in S. acutus reached 3.17 μm. A low interchromosomal asymmetry index (A2), 0.11 to 0.14 was found, very similar among all the species except for S. acutus (A2 = 0.30). Absence of primary constrictions was confirmed. The most common mechanism of karyotype variation in the studied species is dysploidy, followed by polyploidy. A comparison of chromosome numbers between Schoenoplectus and the recently segregated Schoenoplectiella based on the literature reveals that Schoenoplectus has higher numbers (n = 18 to 64; 2n = 36 to 84) than Schoenoplectiella (n = 5 to 44; 2n = 18 to 76) as well as a higher prevalence of disploids.

Using Amplified Fragment Length Polymorphisms (AFLP) to Study Genetic Variability in Several Freshwater Rotifer Species

We have used amplified fragment length polymorphisms (AFLP) to investigate the potential of this technique as a tool to measure genetic variability in eight species of freshwater rotifers: Brachionus calyciflorus, Lecane bulla, L. luna, L. quadridentata, Plationus patulus, Philodina acuticornis odiosa, Rotaria neptunia, and R. rotatoria. We used nine combinations of oligonucleotides. We observed a total of 806 amplified bands, 798 polymorphic and 8 monomorphic. The data were analyzed using cluster analysis with UPGMA, first within each set of oligonucleotide combination and finally using all nine combinations. Our best dendrogram clearly separated monogononts from digononts, and grouped the species of monogononts in the two genera. However, it grouped R. neptunia with P. acuticornis odiosa rather than with R. rotatoria. These results are discussed in view of recent works in the literature measuring genetic variability and discussing the phylogeny of the Rotifera.

CARACTERIZACIÓN MORFOLÓGICA DE GERMOPLASMA DE GUAYABOS DE MÉXICO: IMPLICACIONES EN SU CONSERVACIÓN Y MEJORAMIENTO GENÉTICO

Guavas (Psidium guajava L.) growing throughout Mexico show broad morphologic and productive variation due the crop is commonly sexual-propagated. The characterization of genetic diversity of Mexican guava germplasm will allow identify potential parents for genetic improvement as well as the production of new clonal cultivars. In this work 88 guava accessions [87 belong to P. guajava and one from P. friedrichsthalianum (Berg.) Niedz] growing in Huanusco, Zacatecas Mexico were characterized on the basis of 50 morphologic descriptors. The 95% of germplasm shows ovoid or round fruit shape; 92% fruits with beige or white mesocarp and 87.5% has yellow fruits. Fruits with these traits are locally named as ‘China’ or ‘Media China’ and they are preferred for fresh use. Seven quantitative traits were those that better described the morphologic variability of germplasm: two from trees (stem thickness and leaf length) and five from fruits (polar and equatorial diameter; sepal size; calyx cavity diameter; and total solid soluble content). Three accessions (numbers 68, 52, and 49) outstand due their high values of tree growth under field conditions although showing small fruit sizes while other five accessions (numbers 79, 57, 60, 78, and 56) exhibited small tree sizes but high values for fruit, sepals and calyx cavity, and total solid soluble contents.

Climatic adaptation and ecological descriptors of wild beans from Mexico

Abstract Despite its economic, social, biological, and cultural importance, wild forms of the genus Phaseolus are not well represented in germplasm banks, and they are at great risk due to changes in land use as well as climate change. To improve our understanding of the potential geographical distribution of wild beans (Phaseolus spp.) from Mexico and support in situ and ex situ conservation programs, we determined the climatic adaptation ranges of 29 species and two subspecies of Phaseolus collected throughout Mexico. Based on five biotic and 117 abiotic variables obtained from different databases—WorldClim, Global‐Aridity, and Global‐PET—we performed principal component and cluster analyses. Germplasm was distributed among 12 climatic types from a possible 28. The general climatic ranges were as follows: 8–3,083 m above sea level; 12.07–26.96°C annual mean temperature; 10.33–202.68 mm annual precipitation; 9.33–16.56 W/m2 of net radiation; 11.68–14.23 hr photoperiod; 0.06–1.57 aridity index; and 10–1,728 mm/month of annual potential evapotranspiration. Most descriptive variables (25) clustered species into two groups: One included germplasm from semihot climates, and the other included germplasm from temperate climates. Species clustering showed 45% to 54% coincidence with species previously grouped using molecular data. The species P. filiformis, P. purpusii, and P. maculatus were found at low‐humidity locations; these species could be used to improve our understanding of the extreme aridity adaptation mechanisms used by wild beans to avoid or tolerate climate change as well as to introgress favorable alleles into new cultivars adapted to hot, dry environments.

MORPHOLOGICAL AND GENETIC ANALYSIS OF Triplaris guayaquilensis Wedd (POLYGONACEAE): ONE NATIVE TREE OF ECUADOR

In this paper, we assessed six native populations (55 trees) of Triplaris guayaquilensis Wedd (Fernan Sanchez), one of the major forest species from Ecuador, using morphological and AFLP (Amplified Fragment Length Polymorphisms) data. The populations were collected through two macro-sites (Central coastals: Quevedo, Ventanas, la Guayas; Andean surroundings: la Mana, Patricia Pilar, Pichincha). The populations showed the following traits: straight shaft (66 %); round, irregular top shape (50 %); and branch insertion angle 0° - 30° (86 %). Four qualitative (straight shape, type of leaf edge, leaf width and leaf pubescence) and four quantitative (commercial tree height, basal area, commercial volume and total volume) traits were the most explicative traits present after Principal Component Analysis (PCA). PCA separated populations into two groups: one group included populations from Central Coastals which showed morphological traits highly and positively correlated with wood production, and the other group included populations with lower tree growth from the Andean surroundings. Populations from Central Coastals showed the highest values of genetic diversity indexes, AFLP markers separated populations based on the macro site of origin. For K= 2 Bayesian analysis separated FS populations into two groups; two populations from Central Coastals region and the other four the Andean surroundings region (3) and 1 from Central Coastals (La Guayas). For greater K values, the genetic fragmentation of populations by origins was evident since for K = 5 four groups were performed: one including populations from Quevedo and Ventanas and other from La Guayas (Coastals), the third group included trees from La Mana and Pichincha and the fourth, from Patricia Pilar (Andean surroundings). Results suggested the constant and effective genetic recombination or the genetic flow among and within Fernan Sanchez populations with a clear tendency towards genetic differentiation.