RESUMO

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.

RESUMO

ABSTRACT 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.

RESUMEN México es el centro de origen del chayote (Sechium edule Jacq. Sw), una planta importante en la alimentación humana y en la farmacéutica. El objetivo de este estudio fue determinar la distribución potencial de S. edule domesticado en México utilizando siete algoritmos de distribución de especies, con el fin de gestionar eficientemente los recursos de S. edule y ayudar a su conservación mediante la identificación de patrones de distribución geográfica. Por otra parte, las zonas de alta idoneidad pueden ser utilizadas para la producción de semilla mejorada a un menor costo. Se utilizaron 162 puntos de ocurrencia de la GBIF y nueve capas en formato ráster para evaluar siete algoritmos de modelos de distribución de especies. Para evaluar la confiabilidad y el rendimiento de los modelos se utilizaron los estadísticos Área bajo la curva y el verdadero estadístico de habilidad. Los tipos de clima predominantes fueron Cwb (33,3 %) y Aw (17,9 %); los tipos de suelo predominantes fueron leptosol (33,3 %) y phaozem (16,7 %). Los siete modelos mostraron áreas de alta idoneidad (> 0,75) para los estados de Chiapas, Guerrero, Oaxaca, Veracruz, Tabasco, Puebla e Hidalgo. Los valores de AUC para los siete modelos fueron > 0,8 y su rendimiento fue adecuado (0,4> TSS <0,7). Se encontró que el análisis de árboles de clasificación fue el mejor algoritmo medido por AUC (0,90), sin embargo, los siete modelos fueron adecuados para explicar la distribución de S. edule en México. La adaptabilidad climática de S. edule también le permite distribuirse hacia la Península de Yucatán y occidente de México. La distribución de S. edule en México, según los algoritmos estudiados, se limita a la precipitación total anual y la estacionalidad de la temperatura.

RESUMO

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.