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ABSTRACT
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 hand- 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.
Abbreviations: FAA, formalin-acetic acid-ethyl alcohol.
STUDIES ON CROP pollination by native and nonnative insects are becoming increasingly critical because of a perceived global decline in pollinator stocks, a subject of much current debate with great economical and conservation consequences (Ghazoul, 2005a, 2005b; Steffan-Dewenter et al., 2005). Insect pollination is determinant or beneficial for agriculture since more than 65% of the 1500 cultivated species are pollinated by animals (Roubik, 1995). However, detailed studies of crop pollination systems are incomplete or out of date (Klein et al., 2006). To adequately evaluate the importance of animal pollination for food production and the impact of pollinator losses due to different anthropogenic disturbances, one of the first steps is to determine the pollination needs of different cultivated plants (Klein et al., 2006). Even when some highly productive crops may benefit from insect pollination, generalizations on pollinator requirements are usually based on results obtained from one or a few cultivars (Crane and Walker, 1984; Free, 1993; Roubik, 1995), a practice that can lead to misleading conclusions and mismanagement with great potential economical...