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Mohamed Badrane Erhioui, M. Dorais, A. Gosselin and A.P. Papadopulos

Most experiments on the effects of cover materials on greenhouse crops have provided no real statistical replication for the cover materials. This study was conducted in Winter 1996 at the Harrow Research Centre (Ontario) in nine minihouses covered with glass (single-glass), D-poly (double inflated polyethylene film), and acrylic (rigid twin acrylic panel) offering a 3 × 3 latin square experimental design. Tomato plants (Lycopersicon esculentum L.) were grown in CO2-enriched atmosphere (1000 ppm) under three covering materials, and two light treatments (natural light, and supplemental light at 65 μmol·m–2·s–1) in order to determine the effects of supplemental light on growth, photosynthesis, reproductive carbon allocation, and evolution of carbohydrates synthesis in the diurnal cycles. Overall, the application of supplemental light increased photosynthesis rate, yields, harvest index, total chlorophyll content, and starch accumulation in all treatments, regardless of the type of cover materials. Early marketable yield in acrylic and D-poly houses was higher than in glasshouses. Plants grown under enhanced light intensity flowered earlier and produced 12% more marketable fruits than those grown under natural light. The photosynthetic rate of plants grown in acrylic houses was higher than that of plants grown in glasshouses and those grown in D-poly. The leaves of plants grown in acrylic and D-poly houses had higher dry mass contents and much higher specific leaf weight (>10%) than plants in glasshouses. The net photosynthesis dropped after 3 months of treatment, accompanied by a high accumulation of carbohydrates in the leaves. These results indicate that a photosynthetic acclimation occurs earlier during the growth period suggesting a limitations in carbon metabolism.

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Badrane M. Erhioui, André Gosselin, Xiuming Hao, Athanasios P. Papadopoulos and Martine Dorais

A study was conducted in mini-greenhouses covered with single-glass (glass), double inflated polyethylene film (D-poly), or rigid twin acrylic panels (acrylic) to determine the effects of covering materials and supplemental lighting (SL) (65 μmol·m-2·s-1 at 1 m from the ground, providing a 16-hour photoperiod) on growth, yield, photosynthesis, and leaf carbohydrate concentration of `Trust' greenhouse tomato plants (Lycopersicon esculentum Mill.). Regardless of the light treatment, the marketable yield (kg·m-2) and the number of fruit per square meter in D-poly houses were higher (P ≤ 0.05) by 15% to 16% and 13% to 17%, respectively, than in glasshouses. Under supplemental lighting (SL), similar results were observed in acrylic houses compared to glasshouses. Covering materials had no significant effect on photosynthesis and leaf chlorophyll (chl) concentration. SL increased the number of leaves (March) by 15% (P ≤ 0.05) in glasshouses, marketable fruit yield by 23% (P ≤ 0.01) in acrylic houses, leaf specific weight by 19% to 33% (P ≤ 0.05) in all houses, total chl concentration by 10% to 14% (P ≤ 0.01) in acrylic houses, and photosynthetic rate (March) by 22% (P ≤ 0.01) in glasshouses. Under nonsupplemental lighting (nonSL, daily solar radiation of 8.42 MJ·m-2), plant height in acrylic houses was significantly higher (P ≤ 0.05) than in glasshouses. Neither covering materials nor SL affected (P ≤ 0.05) dry matter allocation to the fruit. Results suggest that D-poly and acrylic houses with SL provide the best environment for the early yield (February to March) under southwestern Ontario growing conditions. The photosynthetic rate decreased (P ≤ 0.05) by 18% in acrylic, and 15% in D-poly and glasshouses after 2 months of growth under nonSL. Conversely, the decrease in carbon exchange rate was not significant in D-poly houses and glasshouses under SL. As a result, the photosynthesis decline observed in the present study could not be explained by leaf starch accumulation in March.