THE RESPONSES OF PHOTOSYNTHESIS, FRUIT YIELD AND QUALITY OF MINI-CUCUMBER TO LED-INTERLIGHTING AND GRAFTING IN TROPICAL CONDITIONS

Resumo

Supplemental lighting is becoming a common practice for horticultural greenhouse industries, especially at high-latitude countries. This increase is because artificial light stimulates the photosynthetic process and enhances the total yield. However, no scientific reports were found on this topic in tropical climate countries. This study investigates the effects of LED-interlighting and grafting on photosynthetic response and yield and quality of snack cucumber fruit in southeastern Brazil. In the light treatment, at 15 cm of distance from the bar, the LED devices emitted a photon flux of 220 µmolm^-2 s^-1 by red light (80%) with a peak wavelength of 662 nm and blue light (20%) with a peak wavelength of 452 nm. Lighting was used for 10 h d^-1 from 30 days after seedling transplanting until the end of the growth period. Mini cucumber hybrid ʻLarinoʼ was grafted on rootstock cultivar ʻKeeperʼ (pumpkin hybrid) and rootstock cultivar ʻShelperʼ (C. moschata, pumpkin hybrid). The air temperature and relative humidity (RH) were maintained at 23.5 ± 4 °C and 72 ± 10 % during the light period, respectively. At night, average temperature was 18.6 °C ± 5 °C and the RH was 90 ± 5 %. The LED-interlighting treatment increased in 40% the plant CO₂ net assimilation rate compared to plants grown under natural light in the greenhouse. Plants grafted onto both rootstocks had higher CO₂ net assimilation rate (µmol CO₂ m^-2 s^-1), apparent carboxylation efficiency (µmol CO₂ mol ar^-1) and apparent electron transport rate (µmol electrons m^-2 s^-1). The early yield increased 11.6 % and 24% in response to LED-interlighting and grafting, respectively. The commercial yield also increased with LED light at rate of 13 % but did not enhance with grafting. Postharvest quality parameters as titratable acidity, total soluble solids and shelf life did not increase with the LED light supplementation. Our study shows that even in tropical climate conditions LED-interlighting can be used as a tool to improve commercial cucumber production.