THE USE OF MOLECULAR MARKERS TO ANALYZE THE INHERITANCE OF MORPHOLOGICAL AND DEVELOPMENTAL TRAITS IN APPLE

Five morphological and developmental traits (branching habit, vegetati ve budbreak, reproductive budbreak, bloom time, and root suckering) we re anayzed in a family obtained from the apple (Malus domestica Borkh) cross 'Rome Beauty' x 'White Angel'. The phenotypic variation in thes e 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 ap peared to be controlled by at least two loci. One of these, Tb, govern ed the presence or absence of lateral branches, particularly on the lo wer half of shoots. The locus was heterozgous in 'White Angel' and was mapped to a 5 cM interval on linkage group 6. At least one other locu s 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 chromosom al region in which the Tb gene is located and may be a pleiotropic eff ect of this gene. Time of reproductive budbreak correlated with segreg ation at the isozyme marker, Prx-c; on linkage group 5. Variation in t ime of bloom and later stages in flower development appeared to be con trolled by different genes not linked to Prx-c. The tendency to produc e root suckers cosegregated with a marker on 'White Angel' linkage gro up 1, suggesting control by a single locus, Rs. Data from a 'Rome Beau ty' x 'Robusta 5' family provided additional information on the inheri tance of these traits.