Growth and development of ‘Illini Hardy’ blackberry (Rubus subgenus Eubatus Focke) under shaded systems

摘要

Blackberries (Rubus subgenus Eubatus Focke) of the Eastern United States commonly grow along forest edges and in disturbed sites, though the potential for introducing improved cultivars into managed forest systems has been little explored in agroforestry literature. Bare root ‘Illini Hardy’ blackberry plants were grown under three neutral shade cloth levels (20, 50, and 70 % irradiance relative to full sunlight) and a full sun control in an orchard system over one growing season. The plants were then excavated from the shade plots and the floricanes forced to fruit in a heated greenhouse after receiving a chilling treatment consistent with data published about the cultivar. Potential yield reflected by primocane yield components was only marginally affected by the light treatments, with no significant differences in primocane counts, cane length, or the numbers of nodes. Cane diameter and attributes of primocane architecture were significant, affecting crown geometries and resulting in the highest percent light interception among plants grown at 70 % relative irradiance. Maximum net photosynthesis rates increased at higher irradiance levels with little increase above 70 % full sunlight, although no differences were observed in whole plant biomass or biomass allocation. Flowering and harvest periods were more concentrated from plants receiving 70–100 % relative irradiance during flower initiation. These results suggest that vegetative phases of ‘Illini Hardy’ blackberry may benefit from partial shading with an optimum light intensity approximating 70 % of full sunlight, but that floral bud differentiation is delayed or incomplete at lower irradiance levels produced by whole canopy or intracane shading.