Fruit set and productivity in almond as related to self-compatibility, flower morphology and bud density

SummaryFruit set was studied over three years in ten almond selections of the Zaragoza breeding programme, previously selected for their fruit and kernel traits and self-compatibility. Five pollination treatments were applied: open pollination (control), open pollination of a reduced number of flowers (control D), artificial self- and cross-pollination after emasculation, and autogamy in bagged branches. Highly significant differences were observed in all cases: among selections, among years and among treatments. There was also a highly significant interaction for selection × year and selection × treatment, but not for year × treatment. The interaction of the three variables together was also highly significant. In general the higher fruit sets were observed for the control D treatment, showing that the flowers left had a better ability to set fruit, probably due to their less competitive conditions. Also cross-pollinations as a whole produced better fruit sets than self-pollinations, but not in all cases, showing differences in the ability to set self fruit among the selections. Fruit set in the bagged branches was the lowest, showing the differences in autogamy ability of each selection. These fruit sets could be related to the genetic self-compatibility as deduced by the pollen tube growth as well as to the flower morphology, allowing the contact of stigma and anthers. Fruit set was also related to flower density and fruit size to define the real productivity level of each selection, as selections showed highly significant differences for their productivity by open pollination and by autogamy. The year effects observed, affecting the treatments and the selections at different levels, stress the need for evaluation of autogamy for more than one year for such an important commercial trait as fruit set in almond.