Response to Selection for Dark Respiration Rate of Mature Leaves in Lolium perenne and its Effects on Growth of Young Plants and Simulated Swards

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Abstract
Selections for slow and for fast rate of dark respiration of mature leaves were made from within Lolium perenne cv. S23. Selected parents were pair-crossed to provide 15 F1 families with slow respiration and 15 with fast. Dark respiration was inherited and families with contrasting rates were subjected to sequentially harvested growth analyses from the third leaf stage to that of 95 per cent light interception in a growth room. Seven periods of regrowth of simulated swards of the families were then recorded. During development of the primary canopy, growth of the selections did not differ until the final harvest interval. At this stage slow respiration families had faster (P < 0.05) net assimilation rate and greater plant dry weight (P < 0.05) and leaf area index (P < 0.05) than the fast respiration group. Relative growth rate followed the same trend. In the swards after each regrowth dry matter yield of the slow respiration group was greater than that of the fast. In another experiment, simulated swards of six slow respiration families yielded more than swards of six fast respiration families over sequential regrowth periods in a glasshouse from May to November: S23 was intermediate. Differences were most during August and September. Crop growth rate at each harvest correlated (P < 0.05 or P < 0.01) with previously determined leaf respiration at 25 °C. Leaf protein levels in August weakly correlated (r = +0.57, P < 0.05) with respiration rate per unit dry weight but there was a significant residual negative correlation (r = −0.67, P < 0.05) between the rate per unit protein and growth at that time. Results are discussed in relation to the concept of ‘maintenance-relàted’ respiration.