Pollen Viability and Pollination in Sugar Apple (Annona squamosa) and 'Gefner' Atemoya (A. cherimola x A. squamosa) in South Florida

Fruit set of commercial Annonaceae by natural pollinators is generally insufficient to produce commercially acceptable yields. In addition, several investigations have reported the pollen source and age of the pollen affects the potential percentage of fruit set of sugar apple and atemoya. The objectives of present investigation were to determine the effect of pollen storage durations on pollen viability, the percentage of fruit set by hand pollination of ‘Red’ sugar apple, ‘Lessard Thai’ green sugar apple, and ‘Gefner’ atemoya and the resulting fruit characteristics as a result of pollen source in South Florida. Five treatments were applied: (1) pollen collected from male stage flowers and hand pollination performed immediately and pollen collected from late female stage flowers in the late afternoon and hand pollination performed either the morning of the (2) next, (3) second, (4) third, or (5) fourth day. The pollen sources were collected from late female stage flowers as they were transitioning to the functionally staminate stage and stored in paper bags refrigerated at 5 °C.  Hand pollination was made by using a number 2 water color paint brush. Pollen from three Annona cultivars and five pollination treatments were arranged in a completely randomized design with five replicates per treatment. In vitro pollen viability was determined by placing samples of pollen on a standard culture medium (5 g·L^-1 Agar, 1.27 mM Ca (NO₃)₂ 4H₂O, 0.87 mM MgSO₄ 7H₂O, 0.99 mM  KNO₃ and 1.62 mM H₃BO pH 7.0) supplied with 10% sucrose. Data was analyzed by ANOVA and Tukey’s test (5% probability). The percentage of in vitro pollen germination was the highest for ‘Red’ sugar apple when pollination was used immediately after male flower collection (26.5%), and when using female flowers collected late afternoon and pollination performed the next day (23%). For ‘Lessard Thai’ green sugar apple the best results were obtained in treatments 1, 2 and 3 with average of 33.1% in vitro pollen germination. ‘Gefner’ atemoya showed high levels of pollen germination (33.7%) in treatments 2, 3, and 4. The percentage of fruit set correlated to pollen germination. Hand pollination promoted high percentages of fruit set, > 80%. Fruit harvested as a result of the various pollen sources varied in fruit weight, fruit diameter, and number of seeds per fruit and will be discussed. Pollen from sugar apple and atemoya may be stored up to 2 and 3 days, respectively.