Effect of Selection for Dark Respiration Rate of Mature Leaves on Crop Yields of Lolium perenne cv. S23

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Abstract
Growth and nutritive quality of two polycross progeny (GL 83 and GL 112) from F1 plants of Lolium perenne ex cv. S23 showing slow dark respiration rates of mature leaves were compared in the field with S23 in 3 years. Plots were cut either nine (simulated grazing) or five (conservation) times annually. In the first trial, sown in 1977, dry matter yields from plots of GL 83 were compared with S23 during 1978 and 1979. A similar trial sown in 1979 compared GL 83, S23 and GL 112 during 1980. The slow respiration populations displayed consistently greater (6–13 per cent) annual dry matter yields than S23, mostly during mid to late summer. In the first trial the difference in yield was greater in 1979 than 1978 and more under conservation than simulated grazing. In the second trial GL 83 and GL 112 yielded 11 and 13 per cent more dry matter than S23 under simulated grazing and 5–6 per cent under conservation. There were no consistent differences in dry matter digestibility, water soluble carbohydrates or protein between the populations. Cellulose content of GL 83 and to a much lesser extent GL 112, tended to be greater than that of S23 from July to September. Analysis of one harvest from another trial revealed no significant difference in energy value, as measured by adiabatic bomb calorimetry, between GL 83 and S23. Thus, it appears that the greater dry matter production of the progeny with slower mature leaf dark respiration rates reflected a true increase in total energy yield not apparently associated with any agronomically undesirable characteristics. The general significance of the results for crop improvement are discussed.