Miguel Salvador-Figueroa

Genetic Diversity of Jatropha curcas in Southern Mexico

The importance of the Euphorbiaceous plant Jatropha curcas L. lies in its high-quality seed oil, ideal for the manufacture of biodiesel. As a result, its extensive cultivation has already reached several million hectares in Asia, Africa and Latin America, and implies certain challenges since it is not yet a fully domesticated plant, and with limited information on the agronomic processes and selected varieties for its cultivation. In addition, little is known about the biology, ecology, genetic diversity and geographic origin of its populations. Despite the growing body of knowledge on J. curcas, there are only a few studies on phenotypic and genotypic diversity in populations of Mexico, from where it is probably native. The greatest extension of J. curcas sown in Mexico is located in the state of Chiapas, for that reason this chapter describes diversity of populations of this state and other sites in Southern Mexico. To broadly understand the diversity of populations, our group has used two types of markers: direct adaptive value characteristics, such as floral characters and fatty acids in the seed, and neutral molecular markers such as AFLP and microsatellites. The results of the chemical studies showed that the content of seed oil in accessions ranged from 8.02 % to 54.28 %, with the proportion of unsaturated fatty acids varying from 74.5 % to 83.7 %. A discriminant analysis separated populations according to their geographical origin, which was verified with a Mantel test. Using the Monmonier’s algorithm, two genetic barriers were identified between the populations. The results are discussed according to the putative evolutionary significance of the seeds fatty acid composition for this tropical species. Studies on floral anatomy confirmed a large variation among Mexican J. curcas and revealed the existence of plants exclusively with female inflorescences, which could be useful in the development of future plantations. Molecular studies showed that Mexican J. curcas is moderately structured in subpopulations, but with a high diversity within populations. A conglomerate analysis revealed the highest coefficient of dissimilarity based on accessions reported so far. The existence of genetic barriers isolating some populations was confirmed with molecular data. The results are discussed with reference to the possible ancestry of the populations. Finally, we highlight the relevance of some of our findings in the scientific and productive realms.

Reproductive biology of the biofuel plant Jatropha curcas in its center of origin

In this work, we studied the main characteristics of flowering, reproductive system and diversity of pollinators for the biofuel plant Jatropha curcas (L.) in a site of tropical southeastern Mexico, within its center of origin. The plants were monoecious with inflorescences of unisexual flowers. The male flowers produced from 3062–5016 pollen grains (266–647 per anther). The plants produced fruits with both geitonogamy and xenogamy, although insect pollination significantly increased the number and quality of fruits. A high diversity of flower visiting insects (36 species) was found, of which nine were classified as efficient pollinators. The native stingless bees Scaptotrigona mexicana (Guérin-Meneville) and Trigona (Tetragonisca) angustula (Latreille) were the most frequent visitors and their presence coincided with the hours when the stigma was receptive. It is noteworthy that the female flowers open before the male flowers, favoring xenogamy, which may explain the high genetic variability reported in J. curcas for this region of the world.

Sterility and Sexual Competitiveness of Tapachula-7 Anastrepha ludens Males Irradiated at Different Doses

A genetic sexing strain of Anastrepha ludens (Loew), Tapachula-7, was developed by the Mexican Program Against Fruit Flies to produce and release only males in programs where the sterile insect technique (SIT) is applied. Currently, breeding are found at a massive scale, and it is necessary to determine the optimum irradiation dose that releases sterile males with minimum damage to their sexual competitiveness. Under laboratory and field conditions, we evaluated the effects of gamma irradiation at doses of 0, 20, 40, 60 and 80 Gy on the sexual competitiveness of males, the induction of sterility in wild females and offspring survivorship. The results of the study indicate that irradiation doses have a significant effect on the sexual behavior of males. A reduction of mating capacity was inversely proportional to the irradiation dose of males. It is estimated that a dose of 60 Gy can induce more than 99% sterility in wild females. In all treatments, the degree of offspring fertility was correlated with the irradiation dose of the parents. In conclusion, the results of the study indicate that a dose of 60 Gy can be applied in sterile insect technique release programs. The application of this dose in the new genetic sexing strain of A. ludens is discussed.

Classification of cacao beans (Theobroma cacao L.) of southern Mexico based on chemometric analysis with multivariate approach

Abstract The aim of this study was to group samples of cacao collected in Southern of Mexico. For this, several physical bean variables (weight, length, width and bean circumference), chemical (moisture, ash, fat, protein, fatty acids) in addition to polyphenol content and antioxidant capacity (ABTS method) were measured. Forty-five cacao samples derived from plants with Criollo phenotype, and a control sample of T. bicolor was included. All variables were analyzed by multivariate analysis (principal component analysis—PCA, k-means and discriminant analysis—DA). The four physical bean traits were not useful when incorporated into the analysis altogether with the chemical variables and led to wrong grouping, and the PCA did not separate T. bicolor of the cocoa samples, so they were discarded for further analysis. Among chemical variables, those that contributed most to the variance and explained the total variance (PCA) were palmitoleic, palmitic, oleic and stearic fatty acids, as well as moisture content and polyphenol content. All samples were classified into seven homogeneous groups. The geographical origin of the samples did not correlate with chemometric grouping, which shows little influence of microclimates, the possible dispersion of highly related materials or individuals adapted to the microenvironmental conditions of the region. Multivariate analysis allowed the grouping of individuals of cacao based on six chemical characteristics of the beans.

Genetic identification of Theobroma cacao L. trees with high Criollo ancestry in Soconusco, Chiapas, Mexico.

Criollo-type cacao trees are an important pool of genes with potential to be used in cacao breeding and selection programs. For that reason, we assessed the diversity and population structure of Criollo-type trees (108 cultivars with Criollo phenotypic characteristics and 10 Criollo references) using 12 simple sequence repeat (SSR) markers. Cultivars were selected from 7 demes in the Soconusco region of southern Mexico. SSRs amplified 74 alleles with an average of 3.6 alleles per population. The overall populations showed an average observed heterozygosity of 0.28, indicating heterozygote deficiency (average fixation index F = 0.50). However, moderate allelic diversity was found within populations (Shannon index for all populations I = 0.97). Bayesian method analysis determined 2 genetic clusters (K = 2) within individuals. In concordance, an assignment test grouped 37 multilocus genotypes (including 10 references) into a first cluster (Criollo), 54 into a second (presumably Amelonado), and 27 admixed individuals unassigned at the 90% threshold likely corresponding to the Trinitario genotype. This classification was supported by the principal coordinate analysis and analysis of molecular variance, which showed 12% of variation among populations (FST = 0.123, P < 0.0001). Sampled demes sites (1- 7) in the Soconusco region did not show any evidence of clustering by geographic location, and this was supported by the Mantel test (Rxy = 0.54, P = 0.120). Individuals with high Criollo lineage planted in Soconusco farms could be an important reservoir of genes for future breeding programs searching for fine, taste, flavor, and aroma cocoa.

Sex expression and floral diversity in Jatropha curcas: a population study in its center of origin

Sex expression and floral morphology studies are central to understand breeding behavior and to define the productive potential of plant genotypes. In particular, the new bioenergy crop Jatropha curcas L. has been classified as a monoecious species. Nonetheless, there is no information about its reproductive diversity in the Mesoamerican region, which is considered its center of origin and diversification. Thus, we determined sex expression and floral morphology in J. curcas populations from southern Mexico and Guatemala. Our results showed that most of J. curcas specimens had typical inflorescences with separate sexes (monoecious); meanwhile, the rest were atypical (gynoecious, androecious, andromonoecious, androgynomonoecious). The most important variables to group these populations, based on a discriminant analysis, were: male flower diameter, female petal length and male nectary length. From southern Mexico “Guerrero” was the most diverse population, and “Centro” had the highest variability among the populations from Chiapas. A cluster analysis showed that the accessions from southern Mexico were grouped without showing any correlation with the geographical origin, while those accessions with atypical sexuality were grouped together. To answer the question of how informative are floral morphological traits compared to molecular markers, we perform a Mantel correlation test between the distance matrix generated in this study and the genetic distance matrix (AFLP) previously reported for the same accessions. We found significant correlation between data at the level of accessions. Our results contribute to design genetic improvement programs by using sexually and morphologically contrasting plants from the center of origin.

Unique haplotypes of cacao trees as revealed by trnH-psbA chloroplast DNA

Cacao trees have been cultivated in Mesoamerica for at least 4,000 years. In this study, we analyzed sequence variation in the chloroplast DNA trnH-psbA intergenic spacer from 28 cacao trees from different farms in the Soconusco region in southern Mexico. Genetic relationships were established by two analysis approaches based on geographic origin (five populations) and genetic origin (based on a previous study). We identified six polymorphic sites, including five insertion/deletion (indels) types and one transversion. The overall nucleotide diversity was low for both approaches (geographic = 0.0032 and genetic = 0.0038). Conversely, we obtained moderate to high haplotype diversity (0.66 and 0.80) with 10 and 12 haplotypes, respectively. The common haplotype (H1) for both networks included cacao trees from all geographic locations (geographic approach) and four genetic groups (genetic approach). This common haplotype (ancient) derived a set of intermediate haplotypes and singletons interconnected by one or two mutational steps, which suggested directional selection and event purification from the expansion of narrow populations. Cacao trees from Soconusco region were grouped into one cluster without any evidence of subclustering based on AMOVA (FST = 0) and SAMOVA (FST = 0.04393) results. One population (Mazatán) showed a high haplotype frequency; thus, this population could be considered an important reservoir of genetic material. The indels located in the trnH-psbA intergenic spacer of cacao trees could be useful as markers for the development of DNA barcoding.

Uso combinado de radiación UV-C y biorecubrimiento de quitosán con aceites esenciales para el control de hongos en papaya Maradol

Anthracnose and soft rot cause deterioration of quality as well as large losses during post-harvest handling of papaya fruits. The single strategies for disease control is little efficient. We analyzed the effect of to integrate control strategies on the incidence of disease caused by the inoculation of spores of the fungi Colletotrichum gloeosporioides (Penz.) and Rhizopus stolonifer (Ehrenb.) into papaya (Carica papaya L.) ‘Maradol’. The following treatments were evaluated: a combination of the use of composite films made with chitosan (15 g L-1) enriched with clove, thyme and / or lime essential oils, (EO) (5 or 10 mL L-1 of each EO) and three irradiation UV-C doses (0.97 kJ·m-2, 2 kJ·m-2 y 2.88 kJ·m-2), applied at 12, 24, and 48 h post-inoculation of phytopathogens spores. The treatment where combined coating with 10 mL L-1 of clove EO and 10 mL L-1 of thyme EO and a UV-C irradiation at dose of 2.88 kJ m-2 (B1T92) applied at 24 h postinoculation was able to maintain the disease incidence lower than 25% (for both fungi) during nine days of storage at tropical room conditions (28 ± 3 °C and 80% RH). The same treatment reduced the specific rate of the disease, with values of 0.549 and 0.029 d-1 for C. gloeosporoides and R. stolonifer, respectively. Other treatments (B2T62, B1T34, B1T34, and B1T94) had antifungal activity (mean values of incidence of 35% throughout storage) for R. stolonifer. These results demonstrate that the synergistic effect of the use of biofilms enriched with EO and UV-C irradiation controls the development of fungi causing anthracnose and soft rot in Maradol papaya fruits.

Use of starter culture of native lactic acid bacteria for producing an artisanal Mexican cheese safe and sensory acceptable

ABSTRACT Unpasteurized artisanal cheeses are a source of pathogens for humans. We isolated lactic acid bacteria (LAB) from raw milk and from cheeses made with raw milk, and formulate starter cultures for producing an artisanal Mexican cheese known as ‘Queso Bola de Ocosingo’. We evaluated six combinations of strains as starter culture-treatments. The proximate composition of the cheeses, the sensorial evaluation, and the microbiological safety of cheeses made with pasteurized milk was evaluated. The use of starter culture helped to maintain the pathogen microbial total count of pasteurized cheese below the standard limit maximums. The sensory judges did not find differences among the cheese elaborated with unpasteurized milk and that elaborated with pasteurized milk and the starter culture added. The starter culture formulated with LAB derived from unpasteurized cheese can be used for producing ‘Bola de Ocosingo’ cheese which is sensory acceptable and microbiological safe.

Association Between SSR Molecular Markers and Chemical and Sensory Traits of Cacao Samples Using Multiple Regression Analysis

The sensory properties of cacao beans are linked to the chemical composition of the seeds, and both characteristics are the partial results of its allelic composition. Therefore, it is useful to search for molecular markers associated with these traits. We perform multiple regression analysis to associate previously generated data of alleles generated with 12 SSR (of cultivated cacao trees) with data obtained from chemical and sensory characterization (of beans) of plants grown in the southern region from Mexico. When the association was significant, the mathematical models for predictive purposes were proposed. All phenotypic traits evaluated showed equations with setting values R2 > 0.5. All chemical characters tested have a significant association with at least two alleles (P < 0.05). In addition, the fat content was associated with six molecular markers (mTcCIR03209, mTcCIR12188, mTcCIR19286, mTcCIR07150, mTcCIR19310). The most common allele was mTcCIR12188, which was associated with the contents of eicosanoic acid, moisture, fat and total polyphenols content. The mTcCIR28362 allele is associated with sensory characters bitterness, musty odor, and roasted odor. These alleles could be useful as molecular markers of chemical and sensory characteristics of cacao samples.