Effect of Training Method to Separate Sink and Source Organs on the Fresh Yield and Dry Matter Production of Cucumber (Cucumis sativus L.) under Greenhouse Conditions

In Japan, greenhouse cucumber production is generally conducted as either a long-term, one cropping system or a short-term, two cropping system; short-term cultivation requires time for crop replacement, which may result in lower yields. It is important to increase plants’ intercepted light to increase yield, which requires maintaining a high leaf area index. In this study, a new training method (separating method), in which the sink and source are separated, was developed for the short-term cultivation of cucumber (Cucumis sativus L.) under greenhouse conditions. In the separating method, the main stem had only leaves and the lateral branch had only fruits. The main stem was trained vertically and pinched when it reached a 1.8 m high training wire, while the lateral branch continued to grow horizontally at approximately 40 cm above the floor. A hydroponic system was used from October 2020 to February 2021. During this period, we assessed the yield productivity of the new training method and compared it with that of the lowering method (training method for growing the main stem without pinching) based on yield components. We observed that the fresh yield of the separating method was lower than that of the lowering method owing to a decrease in the number of fruits as result of fruit picking from the main stem. Conversely, total dry matter under the separating method was higher than that under the lowering method, and this could be attributed to the greater increase in leaf area index under the separating method. In terms of photosynthetic rate, values for the upper leaves were lower than those for the lowering method in the separating method approximately one month after pinching. These results suggested that the separating method could produce yields comparable to those of the lowering method in short-term cultivation. In addition, this method may contribute to mechanical harvesting because the fruit is always in a fixed location.