SHOOT PREFORMATION IN CLONES OF FRAXINUS-PENNSYLVANICA IN RELATION TOSITE AND YEAR OF BUD FORMATION

Shoot preformation was investigated in buds of four clones of Fraxinus pennsylvanica var. subintegerrima (Vahl) Fern. at two sites in Manito ba in the second (1988) and third (1989) growing seasons after graftin g. More preformed primordia were produced in terminal buds in 1989 com pared to 1988 at each site. Both terminal and lateral buds at Morden c ontained significantly more primordia than those at Winnipeg. The numb ers of preformed primordia were significantly different among clones. Clone 3 produced the most and clone 1 the fewest primordia in terminal buds. Despite quantitative variation, the pattern was similar among c lones for terminal buds at each site and in each year. A similar patte rn was evident for lateral buds at the Winnipeg site in 1989 but at Mo rden, clones 4 and 1 had the largest number of preformed primordia. Da ta from 1989 revealed that numbers of primordia were correlated with b ud dimensions, parent shoot length, diameter and number of leaves, and location of the bud on the parent. Shoot dry weight was also related to these variables and revealed a non-linear increase in dry weight wi th shoot length. Multiple regression, with parent shoot length and loc ation of buds along the parent axis as independent variables provided a reliable indicator of preformation in the crown. Although there is a genotypic component to preformation, variation between sites, years a nd crown locations suggests plasticity in bud development.