Comparison of growth and carbohydrate accumulation in seedlings of two varieties of Lolium perenne

Following the identification of suitable traits, the genetic basis of physiological processes such as growth and carbohydrate accumulation can be examined with QTL analysis. Seedling growth was studied in two varieties of perennial ryegrass (Lolium perenne L.) at two stages (following germination and after defoliation) during transitions from reserve-driven growth to current-photosynthate-driven growth. Total water-soluble carbohydrate contents of leaf blades, sheaths and roots were also measured. Aurora (a high-sugar variety) was capable of rapid growth, and grew faster than Perma when growth was reserve-driven. Perma had a low reserve carbohydrate content and grew slowly when growth was reserve-driven. When growth was fuelled by current photosynthate, Perma grew faster than Aurora and replaced its carbohydrate reserves more rapidly. Changes in growth rate appeared to precede changes in water-soluble carbohydrate content. It is concluded that the extent of water-soluble carbohydrate accumulation was inversely related to constitutive growth rate, and that neither process appeared to be limited by photosynthate supply. Traits amenable to QTL analysis are identified.