Photosynthetic characteristics of three asparagus cultivars differing in yield

The physiological basis of yield in asparagus (Asparagus offincinalis L.) is poorly understood, but some reports have inferred a link between lateral fern photosynthesis (A) and annual spear yield. Gas exchange measurements were made on single lateral ferns of mature asparagus plants in the field and younger, potted plants. Among three cultivars with different levels of yield, the light-saturated rate of photosynthesis (A(sat)) was positively associated with crop yield in both sets of plants. There was a highly significant correlation between A(sat) and stomatal conductance (gs). A(sat) also increased with fern nitrogen, chlorophyll, and soluble protein concentrations across the cultivars. These data imply that differences in both gs and photosynthetic capacity contributed to the variation in A(sat), and this was supported by A/CI (internal CO2 concentration) analysis. Variation in photosynthetic capacity was related to genotypic differences in cladophyll diameter and thus the content (per unit surface area) of photosynthetic biochemical constituents and, possibly, mesophyll resistance to COL diffusion. The possibility of genotypic variation in other photosynthetic parameters was also noted. It is concluded that fern A(sat), might be a predictor of yield in asparagus, and of potential use in early selection for breeding, but confirmation of such a relationship requires investigation in a wider range of genotypes.