Effects of plant growth regulators on vegetative development and seed production of birdsfoot trefoil (Lotus corniculatus L.) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University, Palmerston North, New Zealand

Effects of chemical manipulation of a crop of birdsfoot trefoil (Lotus corniculatus L.) grown for seed in two consecutive years were investigated in this study. In the first year, treatments included Cultar (paclobutrazol) at 0.5 or 1.0 kg a.i./ha, Cycocel (chlormequat chloride) at 1.5 or 3.0 kg a.i/ha and Alar (daminozide) at 2.0 or 4.0 kg a.i./ha applied twice at either the late vegetative stage (October) or at the early flowering stage (November). None of these treatments affected seed yield (average 549 kg/ha),or umbel components (pods per umbel, seeds per pod and thousand seed weight). In the second year, at the same stages of plant development, Cultar and Cycocel were applied at the same rates as previously, with an additional treatment added using RSW-0411 (triapenthenol) at 0.5 or 1.0 kg a.i./ha. Again, no seed yield improvement was obtained by any chemical treatment, but average seed yield being increased 27% from 769 kg/ha by 6 days delay in harvesting from 41 to 47 DAPF. Shoot length was reduced by chemical applications, especially at the time of rapid growth, and Cultar had the strongest and longest retarding capability. However, plant branching was not improved by any treatment. Although early flowering pattern was increased by October Cultar application at the higher rate and peak flowering pattern by November Cultar application at either rate, total reproductive structures at harvest in treated plants were similar to those in untreated plants due to flower abortion. Cultar applications in the first year had no carry-over effects on seed production in the second year, but delayed early plant growth in terms of ground cover. Plant growth regulators had no effect on the quality of the subsequently harvested seeds. Effects of Cultar, Cycocel and RSW-0411 applied at higher rates in October reproductive abortion were examined in flowers produced during the flowering season in the second year. Chemical treatments increased flower abortion by 20%, especially in the early flowers. However, there was no effect on abortion of pods in an umbel, on abortion of ovules or seeds in a pod, or on seed weight. Time of flowering also modified flower abortion rate (late flowers having up to 48% greater flower survival than early flowers), and seed development rate (being slower in early season flowers), had no effect on pod abortion and seed abortion (average 44% and 70%, respectively). Flower abortion was first found as early as 10 DAOF. Pod abortion occurred consistently after flower opening, and ovule or seed abortion occurred particularly in the early stages of seed development