Segregation in an ‘Imperial’ mandarin ‘Ellendale’ tangor family for characteristics that contribute to the seedless phenotype

SummaryThe ability of hybrids from a cross between ‘Imperial’ mandarin and ‘Ellendale’ tangor to produce seedless fruit was evaluated over three seasons by imposing a series of pollination treatments at the time of flowering. These involved covering limbs with mesh bags before flowering occurred, emasculating and withholding pollen from flowers, or emasculating and self-pollinating flowers, then assessing the seediness of the fruit that developed along with similar fruit from open-pollinated flowers. Hybrids segregated for parthenocarpic ability in a ratio of 9:23 ( 2 = 0.0008; ns), which favoured non-parthenocarpic hybrids and suggested the action of three dominant complementary genes. Variability in self-pollen reactions at the stigma indicated that the hybrids segregated for viable and non-functional pollen. Seedless fruit from self-pollinated flowers also suggested that the hybrids segregated for self-incompatibility. Variation between hybrids for floral characteristics concerning the presentation and availability of pollen in flowers, for which transgressive segregation was evident, was assessed in terms of the potential for self-pollination without vector intervention (auto-pollination), and the expression of parthenocarpy. The results are discussed in the context of selecting for parthenocarpy, coupled with pollen sterility or self-incompatibility in breeding new seedless Citrus cultivars.