| Begonia x cheimantha is a popular holiday crop in Europe. Its commercial production in the southern U.S. has been limited by the occurrence of mottled leaf chlorosis and necrosis, apparently due to environmental stress. B. x cheimantha 'Emma' was grown in the fall in a glass greenhouse at College Station, Texas under either 0, 60, or 88 percent shade. Total plant height, height to the top of the leaf, peduncle height, and time to first open flower per plant all decreased with decreasing shade. Plant quality improved significantly as shade level increased. A 60 percent shade level significantly improved plant quality compared to plants grown under no shade.; Long-day treatments had no significance on plant height, flower size, or leaf damage, but did influence date of first open flower. Plants were generally shorter and more compact but were significantly poorer quality and had more leaf damage under the no shade versus shade treatments. Shading with 60% black polyethylene increased chlorophyll content, internodal elongation and consequent plant height, and flower size compared to non-shaded plants.; Paclobutrazol sprays at 20 and 30 {dollar}rm mg{lcub}cdot{rcub}Lsp{lcub}-1{rcub}{dollar} reduced plant height 29% and 34%, respectively, compared to that of untreated control plants. Paclobutrazol had a significant effect on plant quality, number of leaves, number of flowers, but did not have any significance on flower size. The quality of the plants treated with paclobutrazol was improved by a darker color of leaves without yellow blotching compared to control plants. Plants that did not receive paclobutrazol had considerable yellow blotching, chlorosis, and necrosis. Leaves of treated plants had a relatively higher concentration of soluble protein, chlorophyll, and enhanced activities of ascorbate peroxidase (AsA), dehydroascorbate (DHA) reductase, and monodehydroascorbate (MDHA) reductase than non-treated plants. An increase of these enzyme activities accumulated by paclobutrazol treatment led to improved plant quality and reduced yellow blotching.; The starch content of leaves grown under high irradiance levels was lower than those grown under shade. Consequently, lack of carbohydrates may prevent a successful acclimatization process. Since photosynthesis rate increased little above {dollar}rm{lcub}approx{rcub}400 mu mol{lcub}cdot{rcub}msp{lcub}-2{rcub}{lcub}cdot{rcub}ssp{lcub}-1{rcub},{dollar} the light saturation point was relatively low. |
