Vegetative, reproductive, and physiological Adaptations to aridity of pitayo (Stenocereus queretaroensis, Cactaceae)

Abstract

Pitayos fStenocereus spp.) are columnar cacti that produce attractive edible fruits under both wild and cultivated conditions. Until recently the study of pitayos has been relatively neglected even though they have been a crucial staple for the inhabitants of subtropical semiarid lands of Mexico since ancient times and this century have become an important fruit crop there. The main objective of this review is to relate seasonal aspects of vegetative and reproductive growth, CO2 uptake, and carbohydrate resources to abiotic components of the environment. Flower and fruit production occur during the dry season in the late winter and spring, roots grow during the summer wet season, and stem elongation commences in the autumn at the beginning of the dry season. Vegetative growth thus does not coincide with reproductive growth, as it does for other fruit crops in temperate and tropical regions. The time offset of vegetative and reproductive activities reduces competitive sink effects, regulating assimilate partitioning to different organs, which may allow Stenocereus queretaroensis to adapt to water-limited environments. Reserve carbohydrates (starch, mucilage) accumulate in the early summer just after reproductive growth and in the early winter just after stem extension. Reducing sugars increase during the middle of the summer before stem elongation begins. The low rates of growth and of photosynthesis for S. queretaroensis are associated with low tissue levels of nitrogen, chlorophyll, and some micronutrients (Fe, Mn). Low levels of gibberellic acid may also contribute to its low growth rate. It does not respond morphologically to irrigation during the dry period, indicating a low plasticity for growth. Although S. queretaroensis is cultivated, its physiological and phenological activities closely resemble those of wild CAM species and other wild perennial plants, reflecting its rather recent domestication and the fact that selections were based mainly on fruit quality and adaptation to aridity rather than biomass productivity.