Pollination Requirements of Pigmented Grapefruit (Citrus paradisi Macf.) from Northwestern Argentina

The consequence of a proposed pollinator decline for agriculture is a subject of much ongoing debate. However, pollination requirements of many cultivated plants remain unknown. Citrus is complex in terms of pollination needs because of great variation in breeding systems among and within species, and even among and within cultivars. The objective of this study was to evaluate pollinator dependence of three cultivars of grapefruit ( Citrus paradisi Macf.) planted in northwestern Argentina. Bagged flowering branches were assigned to different pollination treatments: emasculation, spontaneous self‐pollination, hand self‐pollination, and hand cross‐pollination, and the results compared with those from open‐pollinated flowers. We counted the number of pollen grains and pollen tubes in the style, fruit set, and seed production. We also assessed differences in germination rates of self‐ vs. cross‐pollen grains. We found that handߚ and open‐pollinated flowers set about six times more fruit than emasculated and bagged (insect excluded) flowers. In addition, cross‐pollen performed better in terms of grain germination and tube growth than self‐pollen. Although being fully self‐compatible, apomixis and wind pollination are not important factors for grapefruit reproductive success. Thus, insect pollinators represent a critical and potential limiting resource for seedless grapefruits from northwestern Argentina.