EFFECT OF MECHANICAL AND MOISTURE-STRESS CONDITIONING ON GROWTH AND CUTICLE COMPOSITION OF BROCCOLI TRANSPLANTS

Epicuticular waxes were analyzed to explain the visible differences in the waxy bloom of conditioned broccoli (Brassica oleracea L. Group It alica 'Green Duke') transplants. Seedlings (22 days old) were subjecte d to brushing (40 cycles per minute, 1 minute twice daily), wind (7 m. s(-1) for 5 minutes twice daily), or moisture-stress conditioning (MSG ; visible wilt for 2 to 4 hours daily) for 16 (1987) or 21 (1988) days during transplant production in the greenhouse. The epicuticular waxe s of the uppermost fully expanded leaves were removed by dipping detac hed leaves into methylene chloride. The extract was derivatized with t rimethylsilyl reagents and subjected to capillary gas chromatography. The primary epicuticular wax components were the nonpolar C-29 compoun ds nonacosane, nonacosan-15-ol, and nonacosan-15-one, which were ident ified by mass spectrometry. In a Summer 1987 experiment, cuticle sampl es taken over time of treatment indicated acclimation to the condition ing treatments relative to untreated plants. After 9 days of treatment , the amount of total epicuticular waxes present on the leaves was red uced 38%, 31%, or 11% by wind, brushing, or MSC, respectively. However , after 15 days of treatment, the amount of cuticle present was reduce d 15% by brushing but only 6% by wind and was 17% greater in MSG-treat ed plants. Two weeks after transplanting to the field there were no di fferences in the amount or composition of the epicuticular waxes. In F all 1988, all treatments reduced plant growth, but only MSC tended to increase the amount of C-29 epicuticular components during greenhouse production. Differences in the amounts of epicuticular waxes were no l onger significant after 8 days in the field.