The Use of Molecular Markers to Analyze the Inheritance of Morphological and Developmental Traits in Apple

Abstract

Five morphological and developmental traits (branching habit, vegetative budbreak, reproductive budbreak, bloom time, and root suckering) were analyzed in a family obtained from the apple (Malus domestica Borkh) cross `Rome Beauty' × `White Angel'. The phenotypic variation in these traits was compared with a selected set of marker loci covering the known genome of each of the parents to locate genes with major effects on the traits. The contrasting branching habits of the two parents appeared to be controlled by at least two loci. One of these, Tb, governed the presence or absence of lateral branches, particularly on the lower half of shoots. The locus was heterozygous in `White Angel' and was mapped to a 5 CM interval on linkage group 6. At least one other locus conditioning spur-type branching appeared to be segregating, but the locus or loci could not be linked to segregating markers. The timing of initial vegetative growth was tightly associated with the chromosomal region in which the Tb gene is located and maybe a pleiotropic effect of this gene. Time of reproductive budbreak correlated with segregation at the isozyme marker, Prx-c, on linkage group 5. Variation in time of bloom and later stages in flower development appeared to be controlled by different genes not linked to Prx-c. The tendency to produce root suckers cosegregated with a marker on `White Angel' linkage group 1, suggesting control by a single locus, Rs. Data from a `Rome Beauty' x `Robusta 5' family provided additional information on the inheritance of these traits.