EFFECTS OF ABSCISIC-ACID (ABA) AND ABA ANALOGS ON FREEZING TOLERANCE,LOW-TEMPERATURE GROWTH, AND FLOWERING IN RAPESEED

Brassica napus and B. campestris are grown in Western Canada in areas subject to unseasonable frosts. At the seedling stage, cultivars of Br assica are very sensitive to frosts of -2-degrees to -5-degrees-C, whi ch are either lethal or delay the development of the plant. Seedlings of B. napus and B. campestris, germinated and grown at 10-degrees-C (1 6-h photoperiod), were treated with a foliar spray of either 100 muM r acemic abscisic acid (ABA), 100 muM of various ABA analogs, 0.1% aceto ne, or were untreated. Freeze tests indicated 2-degrees-C of frost tol erance could be gained in B. napus following an application of three A BA analogs. In B. campestris, three analogs also increased freezing to lerance approximately 1.5-degrees-C. The analogs 2',3' dihydro ABA and acetylenic divinyl methyl-ABA were effective in both species. Plant f resh weight and dry weight increased in treated plants relative to con trol or acetone-treated plants after 3 weeks at 10-degrees-C. The effe ct of frost and/or analog treatment on flowering was determined in bot h species. In B. campestris and B. napus, a mild frost advanced flower ing by approximately 2 days compared with nonfrozen control plants. Th e promotive effect of frost on flowering decreased with increasing sev erity of the frost. Several of the analog treatments, particularly 2', 3' dihydro ABA and acetylenic divinyl ABA, advanced flowering by 2-3 d ays in both species. The benefit of these ABA analog treatments on flo wering was enhanced additionally by a mild frost. Plants treated with either ABA, 2',3' dihydro ABA, 2',3' acetylenic dihydro ABA, or acetyl enic divinyl ABA flowered up to 5 days earlier than control plants.