Effects of light intensity and relative humidity on photosynthesis, growth and graft-take of grafted cucumber seedlings during healing and acclimatization

Abstract

Healing and acclimatization are key processes for the survival of grafted plants. This study evaluated the influence of light intensity (photosynthetic photon flux, PPF) and relative humidity during the healing and acclimatization period on the photosynthetic characteristics, graft-take, and growth of grafted cucumber (Cucumis sativus L.) seedlings, using a system for the continuous measurement of the CO2 exchange rate, in order to establish optimum environmental conditions for the healing and acclimatization of grafted cucumbers seedlings. Cucumbers (Cucumis sativus L. cv. Joeun Baekdadaki) were grafted onto rootstocks (Cucurbita maxima D. × C. moshata D. cv. New Shintozwa). Six combinations of two levels of relative humidity (95 and 90%) and three levels (0, 142, and 237 mol m -2 s -1 ) of light intensity were set up during healing and acclimatization. Increasing light intensity significantly increased CO2 exchange rates during healing and acclimatization. At 95 and 90% relative humidity, the CO2 exchange rates at 237 mol m -2 s -1 light intensity were 1.5 and 1.8 times higher than those at 142 mol m -2 s -1 light intensity, respectively. The light intensity during healing and acclimatization also affected the amount and distribution of chloroplasts in scion cotyledon. The amount of chloroplasts increased with the increase of PPF during healing and acclimatization, which covered most of cell wall with little open space left, compared with that of dark condition. As PPF increased, the shoot length, ratio of shoot to root, and specific leaf area decreased but the hypocotyl diameter, leaf area, dry weight, and percent dry matter increased. On the other hand, the relative humidity ranging from 90 to 95% did not significantly affect the CO2 exchange rates during healing, acclimatization, and growth of grafted cucumber seedlings. As a result, PPF during healing and acclimatization affected the growth and quality of grafted cucumber seedlings. This showed that higher PPF condition may improve the growth and quality of grafted cucumber seedlings.Additional key words: CO2 exchange rate, Cucumis sativus L., Cucurbita maxima D. × C. moshata D., graft Hort. Environ.

Effect of Acclimatization Temperature and Light Intensity on the Graft-Take of Cucumber Seedlings

“…It indicates that when the light intensity increased from 0 to 5400 Lux, the average shoot length of the grafted cucumber seedling significantly decreased from 8.326 to 8.101 cm. These results agreed with those obtained by [13] in which the shoot length of grafted cucumber seedlings was decreased by light during acclimatization. The results also indicate that the shoot length ranged from 8.254 and 8.131 cm at truss and flat tunnel, respectively.…”

“…The results showed that increasing of light intensity during acclimatization to improve the growth and quality of grafted cucumber seedlings. These results agreed with those obtained by [12,13] in which the stem diameter of grafted cucumber seedlings was enhanced by light during acclimatization. The results also indicate that the stem diameter ranged from 4.636 and 4.476 mm in truss and flat tunnel, respectively.…”

“…Ten cucumber seedlings representing each replicate on day 8 after grafting were taken as recommended by [13] to determine stem diameter, shoot length, number of leaves, root volume and shoot and root dry weight. Fresh shoots and roots of seedlings were weighed and placed in drying oven with circulating air at 65°C for 48 h then weighed for dry weight.…”

“…Grafted plants were usually healed and acclimatized in the past under specific environmental conditions such as high relative humidity (RH ≥ 95%) and low light intensity in order to produce a healthy plant that survived and grew [11]. However, several recent papers have reported that the photosynthesis, growth, and quality of grafted plants were improved by increasing the light intensity under highly controlled conditions during the healing and acclimatization periods [12,13].…”

Effect of Light Intensity and Temperature on Growth and Quality Parameters of Grafted Vines

“…Relative humidity of the first year was higher than that of the second year under all growth conditions. According to Jang et al (2011) generally, 75-85% relative humidity levels accelerate the photosynthesis rate. In grapevines, carbohydrates in roots and wood portions play important roles for vine longevity and quality.…”