Determination of cardinal temperatures for sugar apple ( Annona squamosa L.)

The sugar apple is highly dependent on the pollination and fruit tree pollen performance is crucial for successful fertilization and fruit set. The objective of this study was to determine the cardinal temperatures for in vitro pollen grains germination and evaluate the effect of temperature on pollen tube growth of sugar apple. The experimental design was in a completely randomized with eight treatments (10, 15, 20, 25, 30, 35, 40 and 45 oC), four replicates and each plot was constituted by two slides per parcel. The cardinal temperatures were determined by evaluating in vitro germination of pollen grains and pollen tube growth in standard culture medium. It also assessed the pollen tube growth and the percentage of germination in vitro depending on the type of pollen grain arrangement (monad, dyad, triad and tetrad). In vitro germination of pollen grains and pollen tube growth varied significantly with temperature. The maximum germination recorded (48.13%) and the maximum lengths of pollen tubes (536.45 μm) were obtained when pollen grains were cultivated at 25 oC. The estimated cardinal temperatures were 9.7, 26.9 and 44.2 oC. Among the pollen grain arrangements, tetrads pollen grains were observed in higher proportions, however, monads pollen grains presented higher germination percentage.