ORIGIN AND INHERITANCE OF DWARFING BY THE CITRUS ROOTSTOCK PONCIRUS-TRIFOLIATA FLYING-DRAGON

'Flying Dragon' Poncirus trifoliata L. Raf. is a dwarfing rootstock for citrus. Inheritance of dwarfing ability was studied in a population of open-pollinated seedlings of 'Flying Dragon'. Molecular marker genotypes suggest that all seedlings originated from selfing. Progeny seedlings were budded with 'Cutter Valencia' orange and planted in the field to evaluate the dwarfing effect of the seedling rootstock. At 5 years after planting, rankit analysis of the frequency distributions of trunk cross-sectional area and canopy volume suggested the presence of two overlapping distributions of 34 dwarf trees and 7 nondwarf. This ratio is consistent with inheritance of rootstock dwarfing as a single dominant gene for which 'Flying Dragon' is' heterozygous. Two morphological characteristics of 'Flying Dragon', curved thorns and twisted trunk growth, were closely linked to, or pleiotropic effects of, the dwarfing gene. Bulked segregant analysis was used to identify three RAPD markers linked to the dwarfing gene. 'Flying Dragon' was identical to nondwarfing cultivars of trifoliate orange at 40 homozygous and heterozygous isozyme and RFLP markers; therefore, it is likely that 'Flying Dragon' originated as a mutant of a nondwarfing genotype and has not undergone sexual recombination since this event.