Pollination compatibility of 'Sundrop' apricot and its progeny in the 'Clutha' series

Flowers of the apricot (Prunus armeniaca L.) cultivar, 'Sundrop' produced low fruitset when self-pollinated or caged to exclude bees during bloom. The level of fruit set improved when 'Sundrop' flowers were pollinated with another cultivar, even when the pollen came from trees of its own progeny (the 'Clutha' series). Levels of self-compatibility varied within the 'Clutha' series; seven selections were as self-compatible as one of their parents 'Moorpark' whereas six showed low self-compatibility, similar to that of their other parent, 'Sundrop'. Comparison of the flowering dates of these and other commercial cultivars which could be used as pollenisers showed that in four of the five years 'CluthaGold', 'CluthaStar', 'CluthaSun', and 'CluthaGem' all flowered with 'Sundrop'. However, one year demonstrated the need to include an earlier flowering polleniser for 'Sundrop'. Five of the six named 'Clutha' selections were compatible with 'Sundrop'; only lack of synchrony of flowering will affect their value as potential pollenisers for this cultivar. Three of the more commonly planted newer cultivars had low self-compatibility-'Sundrop', 'CluthaGold', and 'Valleygold'-thus revising the pollination status of apricot from a crop that does not require cross-pollination to one which generally does; care will be necessary in the planning of new plantings.