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Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/16/1996 Publication Date: N/A Citation: N/A Interpretive Summary: A selection of sweet orange known as 'Cipo' bears normal sweet orange fruit on trees with an unusual short stature and horizontal growth of branches. Trees that are naturally smaller in stature may be of significant value for backyard use and commercial production. To evaluate the potential for breeding new smaller citrus hybrids using 'Cipo', two populations of hybrids were made using a common mandarin as the female parent and either 'Cipo' or another sweet orange with normal growth and appearance as the male parent. These two populations, along with suitable control populations, were examined in detail for two measurable traits that have been associated with the unusual growth of 'Cipo'. About half of the hybrids between the mandarin and 'Cipo' had normal growth, while the other half had "Cipo type" horizontal growth. None of the hybrids between mandarin and normal sweet orange had "Cipo type" horizontal growth. The recovery of many hybrids with horizontal growth when 'Cipo' is used as a parent indicates that the trait is under simple genetic control and that breeding for smaller cultivars using 'Cipo' is possible. Technical Abstract: 'Cipo' sweet orange combines typical midseason fruit characteristics with a unique procumbent growth habit. This distinctive habit may be of value in breeding for smaller and more procumbent scion cultivars if it can be genetically transmitted to hybrid seedlings. Two sibling populations were created using 'Clementine' mandarin as the common parent and either 'Cipo' sweet orange or 'Pineapple', another midseason sweet orange with a more typical upright growth habit. Progeny from the 'Clementine' x 'Cipo' cross yielded many hybrids with the procumbent habit, many with the upright habit, and some that appeared intermediate. Both hybrid populations were compared with nucellar seedling populations from 'Cipo' and 'Pineapple' using two morphological characteristics that have been found to differentiate between the procumbent habit of 'Cipo' and the upright habit of 'Pineapple'. Quantification of these two characteristics indicated that the 'Clementine' x 'Cipo' progeny segregated into two groups on the basis of growth habit, but all the 'Clementine' x 'Pineapple' hybrids were of upright growth habit. The two measured characteristics were tightly linked in the segregating population, and it seems likely they are pleiotropic effects of the same genetic mutation. The observed population distributions were as expected if the procumbent habit in 'Cipo' is controlled by a single dominant allele in the heterozygous condition. |
