Population Analysis of Vigor and Growth Pattern of Apple Seedlings with Short Internode Parentage

The vigor of growth and branching pattern of about 2000 apple seedlings were assessed. The seedlings were 8 years of age and were obtained by intercrossing 4 ‘Goldspur Delicious’ × ‘Redspur Delicious’ hybrids. The seedlings differed considerably in their vigor; the largest tree measured 16 times larger than the smallest one. The short internode condition seemed to exert some dwarfing effect on tree size but was not, however, the sole factor accounting for the degree of dwarfing observed. Measurements revealed that short internode conditions occurred within the most vigorous tree class as well as within the least vigorous one. A continuous variation rather than discontinuous segregation was observed with regard to both vigor of the trees and presence of spurs. Branching pattern also differed with the most numerous pattern being trees with upright branches, some of which produced only a limited number of third-order branches while the others produced a more pronounced number of second-order laterals. Trees with spread-shape crowns consisted of about 20% of the total count, while trees with natural-shape crowns, only 8%.