Greenhouse climate, plant organ temperature, and quantum yield
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Greenhouse production started in Uganda with flower growers who initially failed due to poor greenhouse designs among other factors. Some vegetable (sweet pepper, tomato, and cucumber) growers in Uganda are tending towards greenhouse production, however they are being disappointed by lower yields that cannot justify the price of purchasing the greenhouses. There are existing yield gaps for sweet pepper grown in Ugandan greenhouses and the causes are not clearly known. This study was conducted on two cultivars of sweet pepper in five greenhouses of different design. The general objective was to determine the basis for low yield in greenhouse grown Sweet pepper in Uganda. Measurements were conducted on greenhouse climate (temperature and relative humidity), organ (apical meristem, leaf, flower, fruit, and stem) temperature, and leaf (top, middle, and bottom) quantum yield. It was hypothesized that low yields in Ugandan greenhouses are attributed to poor greenhouse climatic conditions. Results show significantly higher temperatures experienced in all the five greenhouses during the day. Flower and fruit temperatures were also significantly higher than optimum that not only increase risks of flower and fruit abortion but also lead to abnormal development which leads to poor quality fruits. The average relative humidity experienced in the five greenhouses was significantly high leading to increased risk of fungal diseases. There were significant differences in the quantum yield of Starlet F1 cultivar during early morning, late morning, midafternoon and evening. No significant difference in quantum yield of Starlet F1 was observed among the four selected greenhouses in the study area. There was no significant difference in the quantum yield of Top, middle and bottom leaves of starlet F1 cultivar. In general, the quantum yield of the Sweet pepper plants in the study area was lower (0.57-0.63) than optimum (0.78-0.84), proving that plants were not photosynthesizing efficiently. This study shows that low yields for greenhouse grown sweet pepper can be attributed to sub optimal greenhouse climate, extremely high organ temperatures and low photosynthetic efficiency.