Artificial pollination can improve fruit set and quality in the ice cream tree (Casimiroa edulis)

Ice cream fruit (Casimiroa edulis La Llave) is a member of the Rutaceae family native to South America, which has recently been introduced to China. In order to improve the yield of ice cream fruit, we carried out a hybridization experiment with paired pollination. Pollen was collected in the morning and carefully stored, before it was applied to the stigmata of sprouted flowers, using a cotton swab or tweezers. This artificial pollination is repeated at different times of the day. This was continued until the stamens fall off the flowers, the stigmata withered, and the fruit began to develop. Fruit yield and quality were recorded as the principal metrics of the success of each hybrid. At the Hainan Tropical Fruit Window Agricultural Company, nine different ice cream fruit varieties were selected and divided into three groups (abundant pollen, little pollen and no pollen) according to the amount of pollen that each variety naturally produced. Four experimental conditions were investigated: 1. No artificial pollination (natural self-pollination); 2. Artificial self-pollination; 3. Cross-pollination (no emasculation); 4. Cross-pollination (with emasculation). The results indicated that the fruit from cultivars producing abundant pollen generally had poor quality, smaller size, average sweetness, and a medium rate of natural fruit set. In contrast, cultivars producing little pollen showed better fruit quality, higher fruit fertility and increased success rates for artificial pollination. The N2 ice cream fruit cultivar showed the best characteristics as the paternal line (pollen source), while the 4P cultivar showed the best characteristics as the maternal line (flower source). The New varieties (N2 × 4P) performs well in fruit quality, fruit size, fruit sweetness and fruit setting rate. Consequently, this cross-pollinated cultivar is recommended for agricultural production and planting.