Across- and along-row pollen dispersal in high-density apple orchards: Insights from allozyme markers

The organization of most high-density orchards of apple (Malus x domestica Borkh.) into single-cultivar rows is often viewed as an impediment to effec tive pollen dispersal and pollination; however, few direct estimates of pol len dispersal are available to assess the extent of this problem. We estima ted the magnitude of pollen dispersal across rows (pollinator cultivars: Id ared, Vista Bella, Granny Smith), and along rows, (pollinator cultivars Fuj i, Paulared, Golden Russet), in two high-density orchards in Ontario, Canad a. Fruit were sampled from trees at regular intervals along transects that extended beyond (either across or along row) each pollinator cultivar and t he percentage of seeds that were sired by the pollen donor was estimated us ing allozyme markers. Seeds sired by the pollinator cultivar were found fro m seven ('Granny Smith') to 18 rows ('Idared') from the nearest pollinator tree and from seven ('Fuji', 'Paulared') to five trees ('Granny Smith') dow n the same row. Measured in metres, the maximum pollen dispersal distance w as greater across rows (62.4 m) than along rows (13.7 m). However, the aver age dispersal distance across rows, expressed in metres or trees, (17.4 m /- 3.6, 3.6 +/- 0.7 trees) did not differ from that along rows (5.8 m +/- 4 .1, 2.7 +/- 0.8 trees). These results are at odds with previous studies tha t indicate that honeybees move farther along rows than across, and have imp ortant implications for the design of commercial apple orchards.