RELATIONSHIP BETWEEN STORAGE CARBOHYDRATES, REDUCING SUGARS, GROWTH AND PHENOLOGY OF QUERÉTARO PITAYO [Stenocereus queretaroensis (Weber) Buxbaum]

Abstract

Pitayo [Stenocereus queretaroensis (Weber) Buxbaum] is a valuable fruit crop for the subtropical semiarid lands of México, mainly because their tolerance to drought. Recent works on pitayo had generated information related to mechanisms and strategies for drought tolerance; however, these studies did not consider the role of both reserve carbohydrates and soluble carbohydrates on the mechanism
and strategies for this tolerance. In this work we examined the seasonal variation on carbohydrates, and its relation with both the vegetative and reproductive development and with the climatic conditions. The greatest rate of primary stem growth occurred at the end of the Fall, and it did not coincide with flower and fruit development. The reserve carbohydrates, starch and mucilage, reached their highest content in stems of S. queretaroensis at the middle of the Summer (67 to 265 µmol of glucose eq. g^-1 and 0.035 to 0.22 g g^-1, respectively); thereafter it decreased. Conversely, reducing sugars remained low in the stems of S. queretaroensis (0.015 to 0.033 mg g^-1) during the early Summer, showing a remarkably increase (0.025 to 0.132 mg g^-1) from August to October. During the Autumn, the storage of reserve carbohydrates in the stems showed a reduction, which coincided with an the increase in stem growth; and it increased at the time when stem growth ceased at the beginning of the Winter. The patterns of seasonal variation on both reserve carbohydrates and reducing sugars recorded in pitayo stems revealed a close relationship with the main vegetative and reproductive phenophases. Carbohydrate storage in the stem during the Summer is essential for the development and productivity of this species in semiarid environments, mainly because the vegetative and reproductive growth occur during the dry season that begins at the end of the Fall, and ends up at the end of the Summer.