Revisão sobre a cultura da pitaya e concentrações de ácido bórico e temperaturas na conservação de grãos de pólen de diferentes espécies

Abstract

The pitayas (Hylocereus sp.) are tropical cacti, but they adapt to temperate regions, originating in Mexico and the Americas, with a stem classified as cladode and with the presence of small thorns. One of the great difficulties encountered in the production of pitaya is pollination, as producers are not always able to carry it out, since the flowers are nocturnal. Knowing how to properly store the pollen grain, for its conservation, is a big step for studies of genetic improvement. One of the methods used to obtain information about pollen viability is in vitro germination and one of the compounds that influence this germination is boric acid. Among the existing varieties, the self-compatible and incompatible ones stand out, and the incompatible ones require artificial pollination, where pollens from other cultivars are used and unfortunately, the flowering of these cultivars occurs at different times and with different climatic conditions, harming, often its fruiting. The objective of the present study was to bring available and updated information about the pitaya culture in Brazil, as well as to assess the viability of the pollen grain when kept in the refrigerator and to determine the boric acid concentration and temperature that provide the longest pollen tube length and percentage of in vitro germination of pollen grains from different pitaya species. The culture media used in the tests contained 6 g L-1 agar, 100 g L-1 sucrose and 518 mg L-1 calcium nitrate. In the first experiment, five concentrations of boric acid (0, 150, 350, 550 and 750 mg L-1) were tested in two species of pitaya of the genus Hylocereus (H. undatus and H. polyrhizus). The second experiment had three pitaya species (Hylocereus undatus, Hylocereus polyrhizus and Selenicereus setaceus) and pollen grain evaluation days (2, 4, 6 and 7). In the third experiment, a 6 x 5 factorial scheme was used (six pollen donor varieties x five temperatures for pollen grain germination, 20°, 25°, 30°, 35° and 40° C), with three replications for each variety of pitaya at each of the temperatures evaluated. The variables analyzed were germination percentage and pollen tube length (μm). In the first experiment, the highest germination percentage and the longest pollen tube length for both species were obtained at concentrations of 0 and 150mg L-1 and the storage time in the refrigerator that promoted the highest germination averages was 48 hours in the three different pitaya species and Selenicereus setaceus obtained the longest pollen tube length. In the third experiment, the highest percentage of pollen grain germination occurred at temperatures of 25° and 30° C in all varieties studied, and the longest pollen tube length was observed in the Golden variety submitted to 30° C.