Testing female fertility in mandarin orange with controlled manual cross-pollinations

Although irradiation and triploidy can reduce fertility of mandarin cultivars, seediness in supposedly seedless cultivars through cross-pollinations is still an undesired characteristic. Female fertility was assessed (as part of a collaborative study between Spain, Morocco and South Africa) to determine whether controlled manual cross-pollination could be used as a methodology for distinguishing fertility differences between cultivars. Controlled manual cross-pollinations were made at anthesis and 6 days after anthesis on four female parents ('Nules', 'Nadorcott', 'Nova' and 'Marisol') using two male parents ('Nova' and 'Nadorcott') during the 2012 and 2013 citrus flowering seasons. Open-pollinated fruit were included as a control. Pollen germination was tested during flowering and the number of seed per fruit was determined at harvest. Pollen germination was higher in 'Nadorcott' compared with 'Nova'. The number of seed per fruit was higher in controlled manually cross-pollinated flowers compared with open-pollinated flowers. The number of seed decreased with later pollination dates, probably due to reduced stigma receptivity. 'Nadorcott' as pollinator resulted in larger numbers of seed in female parents in comparison with 'Nova' as pollinator, except when pollinated with itself. Female fertility is directly related to seediness, and the degree of female fertility can be determined with high accuracy by controlled manual cross-pollination. This methodology provides a simple means to describe cultivar-specific differences in female fertility.