How to regulate the light environment of grafted seedlings and cutting seedlings?

LED semiconductor lighting network vegetable grafting is an important way to obtain high yield and control pests and diseases. In grafting, especially for rootstock plants, increasing the length of hypocotyls has a practical significance in improving grafting speed and protecting fragile scions from contact with soil during transplanting. Moreover, grafting of melon rootstocks can often carry out rootless grafting to increase grafting efficiency, and then regenerate roots during callus.

Morphological control of seedlings is very important for the production of transplanted seedlings in greenhouses. Rootstock plants are required to have longer hypocotyls. The commercial standard for the length of hypocotyls of melon rootstocks is greater than 7 cm. More importantly, it is important to cultivate well-knotted rootstocks and scion seedlings to improve the efficiency of mechanized grafting operations. However, the hypocotyl elongation rate of rootstocks produced in a greenhouse environment is affected by seasonal illumination changes, and artificial light intervention adjustment is necessary.

Ma Zhiyu and others believe that cultivating robust, tidy, and uniform grafted vegetable seedlings is also an important prerequisite for automated grafting operations. The growth and development of vegetable seedlings is a very complicated process, and the light source is an important factor affecting plant growth. To this end, the effects of different light sources (red, blue, red and blue) on the hypocotyl growth of three melon rootstocks were studied. The results showed that the red-treated seedlings had the highest hypocotyls and thin stems; the red-blue-treated rootstocks had the highest hypocotyls and thick stems. For grafted rootstock seedlings, red light treatment has photosynthetic activity, which is beneficial to the energy accumulated by rootstock seedlings and promotes the growth of seedling hypocotyls. Thus, the morphology control of the seedlings is very important for the production of greenhouse transplanted seedlings, and the rootstock plants are required to have a long hypocotyl. The commercial standard of the hypocotyl length of the melon rootstocks is greater than 7 cm. More importantly, it is important to cultivate well-knotted rootstocks and scion seedlings to improve the efficiency of mechanized grafting operations. However, the hypocotyl elongation rate of rootstocks produced in a greenhouse environment is affected by seasonal illumination changes, and artificial light intervention adjustment is necessary. EOD (End-of-day) light quality treatment is an effective technical method for effectively controlling the elongation of stems and hypocotyls, and is also an economically viable and non-polluting method for controlling plant morphology.

Previous studies have shown that EOD red and far red light treatment can inhibit or promote the elongation rate of stem and hypocotyl, which is the plant response under the regulation of plant phytochrome. EOD light treatment affects phytochrome regulation response, such as plant height. Vegetable grafting requires the production of long hypocotyls. Chia and Kubota studied the effects of EOD red and far red light ratios on the elongation of hypocotyls of tomato rootstocks.

Compared to no fill light, EOD incandescent lamp (R/FR = 0.47) treatment increased the hypocotyl length of Aloha seedlings by 20%. Incandescent lamp treatment by light quality filtration (R/FR = 0.05) induced a greater hypocotyl elongation 44% higher than incandescent lamp treatment. The results show that ERD treatment is better with low R/FR or purer FR light source. In the EOD-FR dose response test, increasing the FR intensity or extending the FR treatment time increased the length of the hypocotyls of the two rootstocks (Figure 7-2).

Figure 7-2 EOD far red light treatment dose—the hypocotyl elongation response curve of pumpkin rootstock, the light dose increasing sequence from left to right

The dose saturation curve for hypocotyl length versus FR illumination can be described using the Michaelis-Menten type model. Based on the model, the 90% saturated FR doses of the two rootstocks were estimated to be 5-14 mmol/square meter per day and 8-15 mmol/square meter per day, respectively. The actual saturated dose was 2~4 mmol/per. Square meters per day. EOD-FR treatment did not affect the dry weight and stem diameter of the plants, and the hypocotyls were prolonged and undamaged. Yang et al. studied the effect of EOD-FR treatment on hypocotyl extension of melon rootstocks using mobile and fixed illumination devices. The pumpkin seedling mobile light source unit is a 120 cm metal strip equipped with FR- LEDs with a moving speed of 0.78 mm/s and 3.13 mm/s. Under the condition that the FR light dose is 4.0 mmol/square meter per day, the hypocotyl extension of the plants treated by the mobile and fixed illumination devices is the same regardless of the moving speed. The hypocotyls of the light-filled treatment were 55% to 69% longer than the control (Table 7-2).

Table 7-2 Pumpkin rootstock EOD far red light treatment hypocotyl length (mm)

Taiwan, China has also reported on the research of light source biology of LED light source. Taiwan University's Jao and Fang have developed a light source device consisting of red and blue LEDs that can adjust red and blue light intensity, red and blue light intensity ratio, frequency and duty cycle. This device is compared with tubular fluorescent lamps under continuous illumination. The growth of cultured potato tissue culture seedlings. 5.53 mmol / square meter per day, 16 / 8h photoperiod adjustment, red and blue light coexisting more than red and blue light is more conducive to the growth of potato tissue culture seedlings. Jao et al. studied the effects of LED red and blue light on the growth of tube seedlings and the formation of tuber after transplanting in the same day. The processing is shown in Table 7-3.

Table 7-3 Several light quality processing details

The results showed that the chlorophyll content and dry weight of colored calla under tubular fluorescent lamp treatment were higher than those of LED light source. There was no difference in plant dry weight and growth rate between different LED light source treatments, but the chlorophyll content and height of the plants increased after blue light, indicating that blue light is involved in the formation mechanism of chlorophyll and plant height (Table 7-4), so Blue light is an important factor affecting the height and chlorophyll formation of colored calla seedlings. The plants were transplanted to the greenhouse for growth, and there was no significant effect on the formation of the colored calla lily bulbs after the 6-month cultivation period (Table 7-5). The author believes that the cost of blue LED is much higher than that of red LED. It is suggested that it is feasible to cultivate colored calla seedlings with AC-powered red LED.

Table 7-4 Chlorophyll content, plant height and biomass of several calla seedlings

Table 7-5 Distribution of bulb formation after 6 months of transplanting of color calla seedlings in greenhouse