ISHS Acta Horticulturae 56: Symposium on Juvenility in Woody Perennials

Visser, T., Verhaegh, J.J. and de Vries, D.P. 1976. A COMPARISON OF APPLE AND PEAR SEEDLINGS WITH REFERENCE TO THE JUVENILE PERIOD. I. SEEDLING GROWTH AND YIELD. Acta Hort. (ISHS) 56:205-214
http://www.actahort.org/books/56/56_22.htm

Abstract: Several thousand apple and pear seedlings of many progenies were studied in connection with their juvenile period (J.P.). The initially significant inverse relation between the vigour (stem diameter) and the J.P. of seedlings became insignificant as the trees grew older, due to a retardation of growth occurring when the seedlings become generative. This relation can be used effectively in preselecting for vigour in the nursery. Cumulative yields were higher when the J.P. was shorter, but there was no evident link between the J.P. and annual yield in full bearing, that is to say, precocity and productivity are not directly connected. Better growing conditions and pre-selection have shortened the mean progeny J.P. of either crop by three years since the 1950's. Generally, the pear seedlings appear to grow faster, to become generative slower and to yield lower than comparable apple seedlings. The mean J.P. of apple and pear progenies averaged 4.2 and 6.0 years respectively. The difference between apple and pear may be attributable to a greater selection pressure on both precocity and productivity with apple than with pear.

This possibly also led to a smaller tree in the productive phase on the assumption that tree size at first flowering — small at a short, large at a long, J.P. — expresses reproductive efficiency and as such is reflected in the size of the adult tree.

Visser, T. 1976. A COMPARISON OF APPLE AND PEAR SEEDLINGS WITH REFERENCE TO THE JUVENILE PERIOD. II. MODE OF INHERITANCE. Acta Hort. (ISHS) 56:215-218.
http://www.actahort.org/books/56/56_23.htm

Abstract: Analysis of two incomplete half-diallel schemes of crosses, involving 22 apple and 33 pear progenies with 2 500 and 5 400 seedlings respectively, showed a highly significant general combining ability (GCA) and an insignificant specific combining ability (SCA) variance for the juvenile period (J.P.). This indicates that the inheritance of the J.P. is of an additive nature, a mode of inheritance which is a function of the inheritance of a complex of factors governing "growth". The mean J.P. of apple progenies varied between 3.4 and 5.0 years, that of pear progenies between 4.7 and 7.0 years. The implications for breeding are discussed.