Effect of seed size and defoliation at three development stages on root and shoot growth of seedlings of some common pasture species

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Abstract
Plants of perennial ryegrass and red clover grown from low-weight seeds were smaller and had shorter root lengths and slower root elongation rates than plants from medium- and high-weight seed. Both these species had higher root elongation rates than the smaller-seeded cocksfoot and white clover, which in turn had a greater seed size and elongation rate than timothy and browntop. Within the four grasses and two clovers, plant size and root length were related to seed size, but the clovers had lower relative values than the grasses. Removal of all laminae resulted in rapid reduction in root elongation followed by gradual recovery in all six species. Recovery was more rapid when plants were defoliated at 8 weeks than at 6 or 10 weeks, and was slowest in browntop and most rapid in white clover, cocksfoot, and perennial ryegrass. The maximum depression of root elongation was greater in the grasses than in the clovers. There was no difference according to the age at which defoliation occurred. The results are discussed in relation to pasture establishment.