EFFECTS OF LEAF SHEAR BREAKING LOAD ON THE FEEDING VALUE OF PERENNIALRYEGRASS (LOLIUM-PERENNE) FOR SHEEP .1. EFFECTS ON LEAF ANATOMY AND MORPHOLOGY

Two populations of perennial ryegrass (PRG) (Loliu perenne L.) were se lected for low (LS) and high leaf shear breaking load (HS) in 1984 at DSIR, Palmerston North. Leaf shear breaking load for the LS group was c. 41% lower than for the HS group and the LS selection had significan tly shorter, narrower leaves and smaller leaf cross-sectional areas th an the HS selection. LS leaves were c. 27% less resistant to shear tha n HS leaves per unit of cross-sectional area. The lower leaf shear str ength in the LS selection was associated with a significantly lower co ncentration of sclerenchyma tissues in the leaf cross-sectional area c ompared with the HS selection. The total shear load required to break down the same dry weight of leaves to 1 mm particle size (leaf index o f masticatory load) was calculated and shown to be influenced by the d ifferences in leaf morphology. LS leaves were estimated to have a 27% lower index of masticatory load than HS leaves when both were grown un der optimum climatic conditions.