Long distance pollen flow in mandarin orchards determined by AFLP markers - Implications for seedless mandarin production

Abstract

Production of seedless mandarins such as 'Nules' clementine mandarin (Citrus Clementina Hort. Ex Tan.) and 'Afourer' mandarin [C. sinensis (L.) Osbeck x C. reticulata Blanco] is increasing in California as consumers' interest in seedless, easy peeling, and good tasting mandarins increases. The fruit would produce seeds if cross-pollination with compatible pollen source occurred. It is almost impossible to prevent cross-pollination between compatible mandarin cultivars by honeybees (Apis mellifera L.) within the multi-faceted agricultural environment in California. To produce seedless mandarin, growers either plant a single cultivar in a large solid block or try to use pollen-sterile navel oranges (C. sinensis) or satsuma mandarins (C. unshiu Marco.) as buffers to prevent cross-pollination. The question of how many rows of buffer trees or spacing can effectively prevent cross-pollination by honeybees between compatible mandarins is unclear. We initiated a study using fluorescent-labeled AFLP markers to determine the pollen parentages of 'Nules' clementine seedlings and 'Afourer' mandarin seedlings from two orchards in California. The longest distance of pollen flow at an orchard near Madera was 521 m. The pollen of 'Minneola' tangelo (C. reticulata x C. paradisi Macf.) was able to disperse across a minimum of 92 rows of 'Lane Late' navel oranges plus two rows of 'Afourer' mandarins to pollinate 'Afourer' mandarins. We also found that all the seedlings of 'Nules' clementine mandarin at an orchard near Bakersfield had been pollinated by 'Afourer' mandarin pollen. The pollen of 'Afourer' mandarin was able to disperse up to distances between 837 and 960 m to pollinate 'Nules' clementine. The pollen dispersal distance found in this study was at least 16 times longer than previously reported in a citrus orchard. Growers need to consider a much larger space or buffer rows to prevent cross-pollination and produce seedless mandarins in California.