Carbon partitioning and sucrose metabolism in two field-grown asparagus (Asparagus officinalis) cultivars with contrasting yield

The aim of this study was to investigate the roles of carbon partitioning and sucrose metabolism in regulating cultivar differences in spear yield in asparagus (Asparagus officinalis L.). In the two cultivars studied, maximum net photosynthetic rate (Amax) was positively correlated with sucrose phosphate synthase (SPS) activity (r²=0.86), which was in turn linked to increases in sucrose content in cladophyll tissue. The high-yielding cultivar ASP-69 exhibited greater SPS activity and sucrose content than the low-yielding cultivar ASP-03, in fully-expanded and mature cladophyll tissue. ASP-69 also displayed a higher percentage of soluble solids in stem cell sap than did ASP-03. Sucrose synthase (SS) activity in storage roots in ASP-69 was significantly greater than in ASP-03 during fern growth season. Total non-structural carbohydrate (TNC) in storage roots did not differ in the two cultivars. Biomass analysis revealed that ASP-69 had a greater root/shoot ratio than ASP-03, suggesting that the total carbohydrate storage pool, rather than carbohydrate concentration, is an important determinant of asparagus yield. The overall results substantiate the conclusion that carbohydrate partitioning in the two asparagus cultivars studied is a property of the entire plant, and is influenced by both source and sink properties. This is highlighted by greater Amax, SPS activity and sucrose concentrations in cladophyll tissue in ASP-69, and greater SS activity and total carbohydrate content in storage root tissue in ASP-69.