Stenocereus Stellatus Research Articles

Maintenance of Phenotypic and Genotypic Diversity in Managed Populations of Stenocereus Stellatus (Cactaceae) by Indigenous Peoples in Central Mexico

The columnar cactus Stenocereus stellatus is used in Central Mexico for its edible fruits which are harvested in wild, managed in situ and cultivated populations. Management in situ of wild populations is conducted by selectively sparing and enhancing the abundance of plants with desirable phenotypes when fields are cleared for agricultural use. Cultivation of desirable phenotypes is carried out by vegetative propagation in homegardens. Effects of human management on morphological and genetic variation of S. stellatus were analyzed by comparing morphological diversity indices (MD, based on Simpson’s index) and expected (He) heterozygosity indices from allozyme analysis, in wild, managed in situ, and cultivated populations from La Mixteca and the Tehuacan Valley regions. Morphological diversity was similar among regions, but populations from the wetter La Mixteca region averaged higher genetic variation (He = 0.279) than populations from Tehuacan (He = 0.265). On average, populations manipulated by people had higher levels of variation (MD = 0.479 ± 0.012, He = 0.289 in cultivated populations; MD = 0.461 ± 0.014, He = 0.270 in managed in situ populations) than wild populations (MD = 0.408 ± 0.017, He = 0.253), which is apparently due to a continual introduction and replacement of plant materials in the manipulated populations. The results illustrate that human management may not only maintain but also increase both morphological and genetic diversity of manipulated plant populations in relation to that existing in the wild. Managed in situ and cultivated populations of S. stellatus are important reservoirs of variation, and are crucial for the general maintenance of diversity in wild populations. These populations may play a principal role in designing strategies for the conservation of variation of this cactus.

Seed germination of wild and cultivated Stenocereus stellatus (Cactaceae) from the Tehuacán-Cuicatlán Valley, Central México

Germination rate and percentage, and seed weight were compared among wild and cultivated populations of the columnar cactus Stenocereus stellatus to analyse the effect of domestication on their seed behaviour and dormancy mechanisms. Experiments on germination capacity were tested on constant (25°C) and fluctuating temperature (20/35°C; 18/6 h) under white light and darkness, and adding five different concentrations of gibberellic acid (GA3) in darkness at 25 °C. Cultivated individuals had significantly heavier seeds (1·12±0·04 mg) than wild individuals (0·80±0·02 mg). Germination percentage in all populations was generally higher at constant temperature but cultivated plants had significantly higher seed germination than the wild ones in both temperature treatments. All seeds increased their germination percentage with storage age in both constant and fluctuating temperature. All seeds were positive photoblastic, and addition of GA3did not promote germination in darkness. The results suggest that human selection has favoured seedling vigour and a greater germination capacity in cultivated variants.

Reproductive biology and the process of domestication of the columnar cactus Stenocereus Stellatus in Central Mexico

Pollination biology, breeding system, and floral phenology of the columnar cactus Stenocereus stellatus were studied in wild, wild managed in situ and cultivated populations of central Mexico, in order to examine whether these aspects have been modified under domestication and whether they determine reproductive barriers between wild and manipulated individuals. Individuals of both wild and manipulated populations are self-incompatible, indicating that artificial selection has not modified the breeding system. Their pollination biology is also similar. Anthesis is mainly nocturnal, with a peak of nectar production between 0200 and 0400 when the stigma presents maximum turgidity. Nocturnal visitors are the effective pollinators. Nearly 75% of flowers exposed for nocturnal pollination set fruit, while none of the flowers exposed for diurnal pollination produced fruits. The bats Leptonycteris curasoae, L. nivalis, and Choeronycteris mexicana (Glossophaginae) are the most likely pollinators, and their time of foraging is synchronized with the time of nectar production and stigma receptivity in S. stellatus. Bats potentially move pollen over a considerable distance, so there is apparently no spatial isolation to prevent pollen exchange between wild and cultivated populations. Phenological studies showed that there are also no apparent temporal barriers. However, manual cross pollination failed between some domesticated and wild phenotypes, suggesting that gene flow between wild and cultivated populations might be limited by pollen incompatibility.

Morphological variation and the process of domestication of Stenocereus stellatus (Cactaceae) in Central Mexico

Morphological variation was analyzed in wild, managed in situ, and cultivated populations of the columnar cactus Stenocereus stellatus in central Mexico. The purpose was to evaluate whether morphological divergence between manipulated and wild populations has resulted from domestication processes. Variation of 23 morphological characters was analyzed among 324 individuals from 19 populations of the Tehuacán Valley and La Mixteca Baja. Multivariate statistical analyses were used to group individuals and populations according to their morphological similarity. Individuals grouped according to the way of management and fruit characteristics were the most relevant for grouping. Within each region, sweet fruits with pulp colors other than red were more frequent in cultivated populations, where fruits were also larger, contained more and bigger seeds, and had thinner peel and fewer spines than fruits from wild individuals. Phenotypes common in managed in situ and cultivated populations generally occur in the wild but in lower frequencies. Artificial selection has thus operated by enhancing and maintaining desirable rare phenotypes in managed in situ and cultivated populations, causing divergent patterns of morphological variation from wild populations. Cultivation has caused the strongest level of divergence, but divergence has also been significant with management of wild populations in situ.

Germinación y supervivencia de cinco especies de cactáceas del Valle de Tehuacán: implicaciones para su conservación

Se analizaron experimentalmente las condiciones de germinación y establecimiento de cinco especies de cactáceas del Valle de Zapotitlán Salinas (Puebla) susceptibles de ser cultivadas y comercializadas como ornamentales por campesinos de la región. Las especies estudiadas fueron Cephalocereus chrysacanthus, Cephalocereus hoppenstedtii, Ferocactus latispinus, Stenocereus stellatus y Wilcoxia viperina, todas endémicas de México y cuyos individuos juveniles son usados como plantas de ornato. Con el fin de diseñar una alternativa para el manejo conservacionista de estas especies, el objetivo del trabajo fue evaluar si los requerimientos para el establecimiento pueden cubrirse con prácticas de cultivo simples que estén dentro de las posibilidades económicas y tecnológicas de los campesinos del área.

Ethnobotany and domestication in Xoconochtli,Stenocereus stellatus (Cactaceae), in the Tehuacán Valley and La Mixteca Baja, México

Ethnobotanical information is presented on use, management, folk nomenclature and classification of the “xoconochtli” (Stenocereus stellatus) as well as on the role of this plant in subsistence of the Nahua, Mixtec and Popoloca peoples from the Tehuacan Valley and La Mixteca Baja in Central Mexico. Among all three groups, S. stellatus was used for various purposes but mainly for its edible fruits. Different variants of this species were distinguished, named and classified by indigenous people according to characteristics of the fruit; particularly size, color and flavor of the pulp, spininess and thickness of the peel. Wild plants characteristically had small red sour fruits with many spines and thick peel, while individuals selected for cultivation usually differed in one or more of these characters. Three general forms of interaction between people and this species were found: 1) gathering of useful products from the wild; 2) management of wild populations in situ which involves the sparing and enhancing of individuals with more desirable characteristics and the removal of others during clearance of the land for agriculture; and 3) cultivation, mainly in home gardens, by propagation of vegetative parts from desirable individuals. Fruit yields per individual and per population were measured and compared in wild, managed in situ and cultivated populations from the Tehuacan Valley and La Mixteca Baja. Wild and cultivated individuals from La Mixteca Baja yielded more than wild and cultivated individuals from the Tehuacan Valley. Within each region, fruit yields were similar in wild and managed in situ populations but significantly larger in cultivated populations. Forms of management of this plant species are discussed in terms of availability of products and demand for them in the local economy.