PIMIENTA, EULOGIO*, ALEJANDRO MUņOZ, AND MARTIN HUERTA. Departamento de Ecologia, Universidad de Guadalajara, Guadalajara,Jalisco. Mexico. Carretera Internacional Km 15.5,C.P. 45110. - Adaptations to aridity of pitayo (Stenocereus queretaroensis, Cactaceae).
Pitayos ('<'I'>'Stenocereus'<'/I'>' spp.) are columnar cacti
that produces edible fruit 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. The main
objective of this work is to relate seasonal aspects of vegetative and
reproductive growth, CO'<'SUB'>'2'<'/SUB'>' uptake, and
carbohydrates resources to abiotic components of the environment.
Flower and fruit production occur during the dry season in theand this
century 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 reduce competitive sink effects, regulating assimilate
partition to different organs, which may allow '<'I'>'Stenocereus
queretaroensis'<'/I'>' to adapt to water limited environments.
Reserve carbohydrates (starch, mucilage) accumulate early summer just
after reproductive growth and in the early winter just after stem
extension. Reducing sugar increase during the middle of the summer
before stem extension. The low rates of growth and photosynthesis for
'<'I'>'S. queretaroensis'<'/I'>' are associated with low
tissue levels of nitrogen, chlorophyll and some micronutrients (Fe,
Mn). Low levels of gibberellic acid may also contribute of its slow
growth rate. It does not respond morhologicallly to irrigation during
the dry period, indicating a low plasticity for growth. Although
'<'I'>'S. queretaroensis'<'/I'>' 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
partition.
Key words: Adaptation,aridity,cacti,carbohydrates,growth,photosynthesis