Discrimination of cross incompatibility by number of seeds per fruit and fruit set percentage in apples

The number of seeds per fruit and fruit set percentage after bagging and without emasculation was investigated to evaluate the possibility of parthenocarpy and self-compatibility. In the present study, 213 cultivars and strains were examined. Ten cultivars and strains persisted in bearing fruit until harvest time (4.7% of the total number). Only three cultivars and strains contained seeds. The number of seeds was very low in 'Yingqiu' (1.33), which included most of the seeds from all of the tree cultivars and strains. When the seeds number of 'Yingqiu' was compared to the average number of seeds per fruit in cross-compatible combinations (6.81), it thus appeared easy to distinguish parthenocarpy and/or self-compatibility from cross-compatibility. These results suggest that emasculation is unnecessary for the evaluation of incompatibility performed by using the number of seeds per fruit. The rate of cultivars and strains belonging to 0% fruit set was 87.3%, that of less than 15% fruit set was 93.3%, that of less than 20% fruit set was 94.4%. Most plants were of these type. However, the cultivars with the high fruit set percentage were rarely observed (e.g. 'Orin'). Therefore, if cross pollinations are performed without emasculation for the evaluation of incompatibility, it is better to compare experimental samples against a control without emasculation and pollination, especially when evaluating compatibility according to the fruit set. To establish criteria for distinguishing cross-incompatibility from cross-compatibility by cross pollination, the number of seeds per fruit and fruit set percentage were investigated in 659 cross combinations. When we judged the incompatible combinations, reliable evaluations were obtained by using two parameters, namely, number of seeds per fruit and fruit set percentage; only one parameter would have been insufficient