Tillering, lodging, dry matter partitioning, and seed yield in ryegrass (Lolium spp.) as affected by the plant growth regulator paclobutrazol Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2v23vz13k

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  • Seed yield in ryegrass (Lolium spp.) is the product of the number of fertile tillers per unit area and seed weight per spike at maturity. These components of yield develop through a series of growth stages beginning with tiller bud initiation and finishing with seed filling. Environmental conditions during plant growth control potential yield development and the efficiency with which it is utilized. Lodging in ryegrass can have dramatic effects upon the utilization of potential yield. It occurs when culm strength is inadequate to maintain the spike in its vertical position. High moisture and fertility stimulate vegetative growth, stem elongation, and produce premature or early lodging. The timing and severity of lodging directly determine its impact upon seed yield and its components. In these experiments, the effects of the plant growth regulator paclobutrazol upon tillering, lodging, dry matter partitioning, and seed yield were investigated under controlled environment and field conditions. Linn and Pennfine perennial ryegrasses under dry conditions (1982) lodged after anthesis with no significant effect upon yield. In 1983, Caravelle and Pennfine perennial ryegrasses lodged prior to the completion of anthesis which resulted in yield reductions when compared to unlodged plants. The plant growth regulator paclobutrazol delayed lodging by restricting stem elongation. This effect was concentrated in the basal internodes where both internode length and weight were reduced. In Pennfine and Caravelle perennial ryegrasses the strength of the internodal segments were found to be related to the dry weight per unit length of stem. Paclobutrazol increased the dry weight per unit length of stem, stem strength, and seed yield. Yield increases were attributed to increased number and weight of seeds per spike and larger number of fertile tillers. Paclobutrazol was found to influence plant growth in several ways. Paclobutrazol applied to annual ryegrass at the vegetative growth stage increased tiller number, decreased leaf length, and decreased leaf area. Treatment at the floret initiation stage decreased tiller length and increased the number of florets in the top spikelet. Tiller number was not significantly increased. This indicates that paclobutrazol had a variety of potential effects upon ryegrass development depending upon the growth stage at application and the rate applied.
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