Cultivar differences in carbon assimilation and partitioning of primocane-fruiting raspberry

Field experiments were conducted during 1994 to examine the influence of genotype and ground-cover on leaf gas exchange, leaf chlorophyll content, and carbon partitioning of primocane fruiting (PF) raspberry. A split-split plot experimental design was used with the whole plot, split plot, and split-split plot factors consisting of cultivar(cvs. Autumn Bliss, Heritage, and Summit), infrared transmitting plastic film, and straw mulch, respectively. Significant cultivar (CV) effects on carbon partitioning were pre sent at the end of the growing season with 'Autumn Bliss' and Heritage' having 37 and 34% less total dry weight, 38 and 57% less dry shout weight, and 83 and 92% less dry berry weight respectively, than 'Summit.' Differences in root architecture were also present at the end of the growing season with the roots systems of 'Autumn Bliss, 'Heritage,' and 'Summit' bring shallow and diverse, slightly deeper and diverse, and very deep and nondiverse respectively. Significant differences in reproductive yield components were also present with 'Autumn Bliss,' 'Heritage,' and 'Summit' having a total floral number of 13.7, 3.09, 162; from which 12.2, 1.18, and 24.4 berries were harvested; with a berry weight of 2.65, 2.32, and 2.61 g respectively. Leaf gas exchange rates among the cultivars also differed with 'Summit' having the highest net photosynthesis (Pn) and transpiration rates, followed by 'Heritage' and 'Autumn Bliss: These cultivar differences in Pn (source supply) observed may have bern regulated by assimilate demand (i.e., sink strength) with the total plant dry weights complimenting the Pn rate of the three cultivars examined. Ultimately, this study provides valuable insight Into the genotypic regulation of carbon assimilation and partitioning, and illustrates the importance for the continued selection of earlier fruiting, heavier cropping primocane fruiting cultivars with important physiological traits such as carbon, water use, and yield efficiency, and stress and pest tolerance.