Promoted graft healing and quality of watermelon seedlings by environmental manipulation

Abstract

In the Republic of Korea, the demand for high quality grafted vegetable plug seedlings by crop growers has been increasing year by year. However, because of climate change and some extreme weather conditions encountered during the summer and winter seasons in the country, the quality of grafted vegetable seedlings has been affected, and the increasing demand for quantity and quality cannot always be met. Therefore, improving quality of plug seedlings become a critical research topic, especially of grafted seedlings of fruiting vegetables, accomplished through environmental manipulation in greenhouses. In this study, light (quality, intensity, and duration), and relative humidity (RH), which have been found to be common issues, were the target factors. As the model plants for all experiments, two cultivars of watermelon (Citrullus vulgaris Schrad.) 'Speed' and 'Sambok Honey' grafted onto the 'RS Dongjanggun' bottle gourd (Lagenaria siceraria Standl.) rootstock were used. The LEDs amplifying red and blue wavelength promoted graft healing and quality of grafted seedlings during or after the graft healing period. The light intensity of 100 mu mol m(-2) s(-1) photosynthetic photon flux density (PPFD) was sufficient as the main light source during the graft healing period or supplemental light source after the healing period for grafted seedlings. The lighting duration of 16 h (on)/8 h (off) was most effective for graft healing and improving the quality of grafted seedlings, especially after the graft healing period. As compared to a saturated RH, a low vapor pressure deficit such as 97-98% RH (VPD of 0.4-0.7 g m(-3)) accelerated graft healing.