Interactions of daminozide, 2, 2′-dipyridyl,and gibberellins A3, A9 and A20, in stem extension inChrysanthemum morifolium Ramat: an indication that daminozide may not inhibit the responses to GA9 or GA20 by blocking gibberellin hydroxylation

Interactions between the growth retardant daminozide (a substituted succinamic acid) and a subsequent application (1 or 10 g) of either gibberellin A₃, A₉ or A₂₀, on stem extension inChrysanthemum morifolium cv. Bright Golden Anne, indicated that pre-treatment of plants with daminozide largely prevented the response to GA₂₀ as well as to GA₉. The daminozide-GA₃ interaction on total stem length was dependent upon the dose of GA₃ such that, by flowering time, 1 g of GA₃ had virtually eliminated the retardant effect, while 10 g of GA₃ increased stem length to a value similar to that achieved by control shoots receiving 10 g of GA₃. In contrast, prior application of 2, 2-dipyridyl (an inhibitor of hydroxylation in some plant and animal systems) had no significant influence on the time courses of response to any of the GAs. In the absence of daminozide (and 2, 2-dipyridyl) all three GAs were very active in promoting internode extension soon after their application. If 2, 2-dipyridyl can block hydroxylation reactions in chrysanthemum tissues, the results do not support the hypothesis that daminozide restricts GA₉- (or GA₂₀-) induced stem elongation by preventing the hydroxylation of GA₉.     

Comparisons of a new triazole retardant PP 333 with ancymidol and other compounds on pot-grown tulips

PP 333 was compared with ancymidol, CGA 65993, dikegulac-sodium (as Atrinal) and maleic hydrazide for its ability to restrict stem extension in tulip cvs Paul Richter, Apeldoorn and Trance. Single, 300 ml compost drenches were applied one day after housing fully cooled bulbs grown in a sphagnum peat/sand compost (3:1 v/v).Experiments in 1979/1980 and 1980/1981 with mid- and late-season crops showed that PP 333, like ancymidol, could reduce stem extension without deleterious responses. However, higher amounts of PP 333 (0.8–33.3 mg a.i./pot) were required than of ancymidol (0.625–2.5 mg a.i./pot). Cv. Paul Richter was much less responsive to PP 333 and ancymidol than Apeldoorn, particularly when grown as a late-season crop. Dikegulac was the most effective chemical in the latter situation, especially as it restricted post-flowering extension growth. PP 333 and ancymidol were better able to control such growth in the mid-season crops. Other than for the above purpose, dikegulac proved unsuitable because it increased flower bud blasting and gave rise to abnormally coloured perianth segments. Similarly, marked reductions in stem length of Apeldoorn and Paul Richter with CGA 65993 were associated with unacceptable side-effects, namely, smaller flowers (both cvs) and more bud blasting in Apeldoorn. Maleic hydrazide (5–500 mg a.i./pot) had little influence on stem length in any of the three cultivars.The trials indicated the need to test each cultivar/retardant combination, as well as to take into account the time of forcing because, whereas Paul Richter and Apeldoorn were adequately dwarfed by PP 333 and ancymidol without adverse effects, both compounds caused about 50% of Trance flowers to blast. No treatment influenced flowering date in cv. Paul Richter but PP 333 delayed flowering by two days in Apeldoorn and Trance, as did the higher doses of ancymidol in Apeldoorn.