Influence of Pollination on the Low Fruit Set in Japanese Plum

Some Japanese plum (Prunus salicina L.) cultivars are prone to erratic fruit set. However, the causes of this behaviour are not entirely clear. Since a number of factors intervene in the process leading to final fruit set, a limitation in its study is the difficulty in ascertaining to what extent it is caused by pollination deficiencies. In this work, two Japanese plum cultivars are studied to ascertain the influence of inadequate pollination in fruit set. The evaluation of pollen tube behaviour and fruit set, in open-, self- and cross-pollinated flowers of 'Songold' and 'Black Amber' in two locations, shows that fruit set in these conditions is limited by the absence of compatible pollen. Field and laboratory experiments confirmed that 'Songold' and 'Black Amber' behave as self-incompatible. Likewise, crossings with cultivars from the orchards were also incompatible. Finally, the S-alleles of the cultivars studied were determined by PCR in order to establish which cultivars could be used as pollinators of 'Songold' and 'Black Amber'.