The Sechium P. Br. genus composed of 11 species, which originated from the mountainous regions of Mesoamerica, have been domesticated and diversified. These species are clustered in two large groups: the Mexican clade and the Central American clade. Morphological and molecular studies have shown that species of the Mexican clade are formed through interspecific hybridizations and genetic flow, with the exception of S. mexicanum, which is strongly linked to the genus Sicyos. The objective of this review was to analyze the phylogenetics of Sechium based on morphological and molecular studies, which contributed to taxonomic knowledge and utilization, thereby favoring its conservation and improvement. The Central American clade is well supported with molecular data, but not so with morphological data. The species in this clade were geographically isolated and endemic. S. edule and S. tacaco are exploited species in the agricultural and industrial sectors, and both have an extensive genetic and phenotypic diversity that has allowed them to diversify and expand into different ecological niches. Finally, the Central American species of Sechium thrive in adverse environments of temperatures of mesophyll forest and high relative humidity, with characteristics that can give resistance to frosts and phytopathogenic agents, as well as cultivated species of this genus.
Tomato (Solanum lycopersicum L.) is a vegetable with worldwide importance. Its wild or close related species are reservoirs of genes with potential use for the generation of varieties tolerant or resistant to specific biotic and abiotic factors. The objective was to determine the geographic distribution, ecological descriptors, and patterns of diversity and adaptation of 1296 accessions of native tomato from Mexico. An environmental information system was created with 21 climatic variables with a 1 km2 spatial resolution. Using multivariate techniques (Principal Component Analysis, PCA; Cluster Analysis, CA) and Geographic Information Systems (GIS), the most relevant variables for accession distribution were identified, as well as the groups formed according to the environmental similarity among these. PCA determined that with the first three PCs (Principal Components), it is possible to explain 84.1% of the total variation. The most relevant information corresponded to seasonal variables of temperature and precipitation. CA revealed five statistically significant clusters. Ecological descriptors were determined and described by classifying accessions in Physiographic Provinces. Temperate climates were the most frequent among tomato accessions. Finally, the potential distribution was determined with the Maxent model with 10 replicates by cross-validation, identifying areas with a high probability of tomato presence. These results constitute a reliable source of useful information for planning accession sites collection and identifying accessions that are vulnerable or susceptible to conservation programs.
El maíz (Zea mays L.) de México presenta amplia diversidad debido a que este país es considerado como centro de origen, domesticación y diversificación de esta especie, y si bien existen estudios al respecto, la gran abundancia de tipos hace pertinente profundizar en su análisis. El presente estudio tuvo como objetivo evaluar la diversidad genética inter e intra-poblacional de 25 poblaciones de razas de maíz con 10 marcadores SSR. La primera coordenada principal explicó 42.11 % y la segunda 18.18 % de la variación total. Se encontró un promedio de 2.6 alelos por locus y un valor de diversidad génica de 0.44. El estadístico FST (0.427) indicó una alta diferenciación genética entre las razas de maíz (Zea mays L.). Las razas Serrano de Jalisco y Tabloncillo mostraron los índices más altos de diversidad génica (0.53). La variación inter-poblacional fue del 43 %. Las razas destinadas para usos especiales y con distribución geográfica limitada, como Comiteco (0.33) y Chalqueño (0.30), presentaron los niveles más bajos de diversidad y a su vez exhibieron graves procesos de endogamia (FIT = 0.618) y deriva genética.
Objective: Determine current and potential distribution of S. tacaco in Costa Rica with seven Species Distribution Models (SDM), in order to optimize the management of S. tacaco genetic resources, aimed at identifying patterns of geographic distribution and possible climatic adaptations allowing to have perspectives on their conservation and genetic breeding. Design/Methodology/Approach: 21 points of occurrence together with 19 bioclimatic variables and altitude were used to evaluate seven machine learning models and an assembly of these. Open-source libraries running in Rstudio were used. Results: Distribution models were inferred by the variables bio1, bio2, bio3, bio4, bio12, bio13, bio14, bio18 y bio19. The generalized additive model obtained the highest values ??of area under the curve (0.96) and True skill statistic (0.90), however, the seven models tested and the assembly showed adequate performance (AUC> 0.5 and TSS> 0.4). Bioclimatic variables related to temperature were the ones with the greatest contribution to the models and the main limitations in the distribution of S. tacaco. Study limitations/implications: Possibly a greater number of occurrence points are required to evaluate distribution models. Findings/Conclusions. Areas with high potential distribution suitability for S. tacaco are found in central valleys of Costa Rica, covering regions of the provinces of Alajuela, Cartago, San José and Puntarenas. These areas can be sources of germplasm for future conservation and breeding studies.
Sechium edule (Jacq.) Sw. (Cucurbitaceae) is a species native to Mexico and Central America. The collection, characterization, and evaluation of accessions maintained in genebanks is essential for the conservation of this species. However, there are no specific varietal descriptors that differ from those used in a phenetic approach and are adapted to international registration guidelines to help distinguish, improve, cluster, and protect intraspecific variants of common use and those obtained by breeding. Therefore, 65 morphological descriptors (qualitative and quantitative) were evaluated in 133 accessions obtained from Mexico, Guatemala, and Costa Rica located in the National Germplasm Bank of S. edule in Mexico. These characteristics were observed to be phenetically stable for five generations under the same agroclimatic conditions. In addition, an analysis of amplified fragment length polymorphism (AFLP) was applied to 133 samples from a set of 245 accessions. According to the multivariate analysis, 26 of the 65 descriptors evaluated (qualitative and quantitative) enabled differentiation of varieties of S. edule. The AFLP analysis showed a high level of polymorphism and genetic distance between cultivated accessions and their corresponding wild ancestor. The variations in S. edule suggest that the morphological characteristics have differentiated from an essentially derived initial edible variety (ancestral original variety), but unlike other cucurbits, there is no evidence of the ancestral edible for Sechium since the seed is unorthodox and there are no relicts.
Mexico is the centre of origin of the chayote (Sechium edule (Jacq.) Sw), an important plant in human consumption and in pharmaceuticals. The objective of this study was to determine the potential distribution of domesticated S. edule in Mexico using seven species distribution algorithms, to efficiently manage S. edule resources and help its conservation by identifying patterns of geographic distribution. Otherwise, areas of high suitability can be used to produce improved seed at a lower cost. 162 GBIF occurrence points and nine layers in raster format were used to evaluate seven algorithms of species distribution models. To evaluate the reliability and performance of the models, the statistics Area Under the Curve (AUC) and true skill statistic was used. Predominant climate types were Cwb (33.3 %) and Aw (17.9 %); predominant soil types were leptosol (33.3 %) and phaozem (16.7 %). The seven models showed areas of high suitability (> 0.75) in Chiapas, Guerrero, Oaxaca, Veracruz, Tabasco, Puebla and Hidalgo states. AUC values for the seven models were > 0.8 and their performance was adequate (0.4 > TSS < 0.7). Classification tree analysis was found to be the best algorithm measured by AUC (0.90); however, the seven models were adequate to explain S. edule distribution in Mexico. S. edule climatic adaptability also allows to be distributed towards the Yucatan Peninsula and western Mexico. The distribution of S. edule in Mexico, according to the studied algorithms, is limited to total annual precipitation and temperature seasonality.
Species distribution models identify regions with ideal environmental characteristics for the establishment and proliferation of species. The chayote is a crop that originated and domesticated in Mexico; however, it is cultivated in different parts of the world due to its nutritional and pharmaceutical importance. The objective of this research was to locate the potential distribution of S. edule in Japan supported on seven machine learning models, to also determine which bioclimatic variables influence its distribution, and which are the most suitable regions for its establishment. Thirty-one occurrence points, elevation, and the bioclimatic variables bio1, bio3, bio4, bio7, bio8, bio12, bio14, bio15, and bio17 were used to infer the models. Hundred percent of the occurrence points coincided with the Cfa climate distributed in Acrisol (60.9%), Andosol (17.4%), Cambisol (13%), Fluvisol (4.35%), and Gleysol (4.35%) soil. The Maxent model reported the highest AUC value (0.93), while the GLM obtained the best TSS value (0.84); the SVM model reported the largest suitability area ≥ 0.5 with 100,394.4 km2. Temperature-related variables were the major contributors to the models and the ones explaining the distribution limits of S. edule in Japan. The coastal eastern prefectures of Kantō, Chūbu, Kinki, Chūgoku, Kyūshū, and Shikoku regions showed a suitability ≥ 0.5.
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