Yield, Flower Quality, and Photo-Physiological Responses of Cut Rose Flowers Grafted onto Three Different Rootstocks in Summer Season

Abstract

The thermal stress caused by high temperatures on cut rose flowers grown in greenhouses is a major environmental impact that reduces the yield of growing cut rose flowers during summer. To confirm the resistance of grafted cut rose flowers to high-temperature stress, roses were grown in a greenhouse during the summer season and analyzed for yield, quality, root activity, and photo-physiological characteristics. A morphological change was observed in the stomata of the grafted cut rose flowers, which were larger in size than the scion or rootstocks. As a result of cultivating cut rose flowers by lowering the temperature of the greenhouse through shading in summer, it was confirmed that all of the scions, rootstocks, and grafted cut rose flowers were not in a stressed state by observing the maximal quantum yield of primary photochemistry (FV/FM) values on the chlorophyll-a fluorescence. However, the rate of electron transport flux from the primary acceptor (QA) to the secondary acceptor (QB) per the photosystem II reaction center (ET0/RC) value was found to be significantly higher on grafted cut rose flowers, compared with that of the scions. The efficiencies of the photosynthesis rate, the transpiration rate, and the stomatal conductance were increased when grafted compared with non-grafted. When the root activity was confirmed by the formazan content, it was found that the root activity was improved grafting. Furthermore, when grafted, morphological changes such as flower size and the number of petals on spray roses were also observed. Although there was a difference depending on the type of rootstock, the yield of the grafted cut rose flowers increased by 11–20%, compared with the scion rose. Therefore, grafting cultivation during the summer season with high temperatures is an effective method in terms of photo-physiological response and yield.