Tillering, Leaf Expansion and Growth of Plants of Two Cultivars of Perennial Ryegrass Grown using Hydroponics at Two Water Potentials

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Abstract
Tillering and growth parameters of perennial ryegrass cultivars Wendy (diploid) and Condesa (tetraploid) were determined in a glasshouse experiment using hydroponics at low (−1·3 MPa) and normal water potential (0 MPa). At −1·3 MPa, leaf extension rate was reduced by 36%. Final plant tiller number was 20% lower at −1·3 MPa because of a 12% reduction in the leaf appearance rate in the first weeks after the start of the treatments. Site filling, the relative increase in tiller number per leaf appearance interval, was high (0.61)-but still lower than theoretically possible-and was only slightly affected by water potential. Site filling was shown to be strictly related to the number of inhibited plus unemerged tiller buds. Dry matter production was 64% lower at −1·3 MPa. Relative growth rate (RGR) was, on average, 17% lower at −1·3 MPa, but the reduction was greater just after the treatments started. Also, net assimilation rate (NAR) was reduced more by low water potential just after the start of the treatments. Specific leaf area (SLA) was 13 % lower at −1·3 MPa for Wendy, but not significantly reduced for Condesa. Contrary to expectations based on the theory of the functional balance between root and shoot, leaf weight ratio was slightly higher at −1·3 MPa. From comparison of the results of this study with published data, it is concluded that effects of drought in the field on tillering cannot be attributed only to low water potential.

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