EFFECTS OF SHADING AND SODIUM HYDROSULFIDE, A HYDROGEN SULFIDE DONOR, APPLICATION ON PHYSIOLOGICAL RESPONSES IN CACAO UNDER CHILLING STRESS
Authors: Kondo, T.1*, Kawai, K.2, Nishioka, K.3 and Matsuzaka, Y.4
Journal Issue: Malaysian Cocoa Journal, Volume 17 2025
Keywords: Light intensity, low temperature, maximum quantum yield of photosystem II, oxidative stress, photosynthetic rate
Published On: 5/11/2025
Abstract
Due to global warming, cacao cultivation has been beginning at subtropical regions such as Okinawa Island, which is located at around 26-27°north latitude. During winter, the minimum temperature on Okinawa Island often falls below 10°C, and overcoming chilling stress remains the biggest challenge to cacao cultivation in Okinawa Island. So, cultivation methods for overcoming chilling stress are currently demanded in Okinawa Island. Chilling stress generally causes oxidative stress in the leaves, which leads to leaf damage. Thus, the effects of shading at approximately 80% and hydrogen sulfide (H2S) application, which have the effects of reducing oxidative stress, on the physiological responses in one-year old cacao seedling grown in unheated greenhouse at Kyoto University were determined from October to December 2021 and October to November 2022. In the greenhouse, the minimum temperatures fell below 10°C from late October. Shading enhanced photosynthetic rate, relative chlorophyll content (SPAD value) and maximum quantum yield of photosystem II (Fv/Fm), which can be used as an indicator of leaf damage, in cacao under chilling stress, while transpiration rate and stomatal conductance were not enhanced. The application of sodium hydrogen (NaHS), H2S donor, to the soil did not enhance photosynthetic rate, SPAD value and Fv/Fm, though transpiration rate and stomatal conductance were enhanced slightly. Therefore, under chilling stress where the minimum temperatures were lower than 10°C, shading has the effect of reducing chilling stress, while H2S application has no effect. Shading is a relatively inexpensive method and easy to introduce for farmers on Okinawa Island.