Effect of Light Quality on the Growth and Mechanical Property of Tomato Grafted Seedlings

Seedling quality is directly related to the success rate of automatic grafting. To select the suitable light quality for cultivating mechanically grafted tomato seedlings, the effects of different LED light qualities on the morphological parameters and mechanical properties of tomato seedlings were measured in an artificial light environment in a plant factory. Combination of red (R) and blue (B) LEDs as follows: R: B=100:0 (RLT), R: B=75:25(RBI), R: B=50:50(RBII), R: B=25:75(RBIII), R: B=0:100(BLT). The results showed that Red light is beneficial for the elongation of the hypocotyl of seedlings, Blue light is beneficial for the accumulation of dry matter in seedlings and monochromatic red light can reduce the seedling index. The effect of light quality on rootstocks and scions is different. Increasing the proportion of blue light is beneficial for increasing the stem diameter of scions, but it is not significant for the stem diameter of rootstocks. On the 25th to 30th day, the growth rate of stem diameter is the fastest. Based on morphological characteristics, the suitable light quality for rootstocks is RBI and RBII, and scions are RBII and RBIII. The mechanical properties of rootstocks and scions under different light -quality treatments were measured, and the results showed that the mechanical properties of scions were generally better than those of rootstocks. The rootstock has a significantly better bending strength than the scion, while the scion has a significantly better radial and axial compression force than the rootstock. Considering the automatic grafting process and mechanical characteristics, BLT and RBII were selected as the suitable light quality for rootstocks and scions. Based on the influence of comprehensive light quality on morphological and mechanical characteristics, the suitable light quality for cultivating mechanically grafted tomato seedlings is RBII.