Pollen source, fruit set and xenia in mandarins

The effects of pollen source on fruit set and fruit quality characteristics (xenia effects) were examined in three commercial cultivars of mandarin, I mperial, Ellenor, and Murcott. Six trees of each cultivar received six poll ination treatments: three cross-pollen sources, self-pollination, bagging a nd bagging with emasculation. Pollen tube growth, percentage fruit set, fru it weight, seediness, sugar and acid content were assessed in all treatment s. Significant xenia effects, including effects on sugar content, were foun d in all cultivars. 'Imperial' was found to be self-incompatible as self-po llen tubes were inhibited in the upper style. This resulted in a lower frui t set in self-pollinated fruits (P<0.01), a very low fruit weight (33-55 g, compared with 92-103 g, P<0.01), and fruits containing few or no seeds. In addition, 'Ellenor' and 'Murcott' pollen significantly increased sugar con tent of fruit by between 0.9-1.6% compared with self-pollinated and unpolli nated treatments (P<0.05). Widespread problems of variable production and p oor fruit quality in 'Imperial' may be alleviated by interplanting with app ropriate pollen sources such as 'Ellenor' and 'Murcott'. Pollen source sign ificantly affected fruit set, seed number and sugar content but not fruit w eight of cv. Ellenor. In particular, 'Murcott' pollen produced a significan tly higher fruit set, relatively low seed number, and the highest mean suga r content (13.2%), significantly higher than 'Imperial' pollen, bagged, and unpollinated treatments (>12.5%, P<0.01). Fruit production, seediness and sugar content of 'Ellenor' mandarin may be improved by interplanting with ' Murcott'. Cross-pollination significantly increased seed number of 'Murcott ' (15-21 seeds per fruit, compared with 13-17 seeds per fruit, P<0.01). 'Mu rcott' could be planted in pure blocks since self-pollinated 'Murcott' frui t had slightly fewer seeds than crosses, without any significant loss of si ze or quality. These results demonstrate the need for careful consideration of interplanting of cultivars and management of pollinators such as the ho neybee, Apis mellifera L. to maximize fruit production and quality in manda rins.