Frequency and Characteristics of Nucellar and Zygotic Seedlings in Three Cultivars of Trifoliate Orange

Seedling populations of three cultivars of trifoliate orange [ Poncirus trifoliata (L.) Raf.] were grown in a greenhouse from seed collected in three different years and four different locations. Starch gel electrophoresis of four heterozygous loci was used to distinguish nucellar (apomictic) seedlings from zygotic seedlings. Minimum estimates of the frequency of zygotics among 23 seed samples ranged from 0% to 76%, with an overall mean of 18%. All zygotics apparently originated from self-pollination or pollination by other trees of trifoliate orange. Samples collected from the same tree in different years had significantly different frequencies of zygotics. Differences among cultivars in frequency of zygotics were obscured by the large environmental effects. Samples stored for 8 months before planting generally did not differ in frequency of zygotics from those stored for 5 months. Mean height of zygotics was less than that of nucellars in all samples measured, significantly less in most samples. However, many zygotics were so similar to nucellars in height, leaf size, thorn length, petiole length, and stem diameter that they would be difficult to identify using these traits.