Effects of different light intensities on the healing and growth of grafted seedlings in two-stage grafting of tomato seedlings

Tomato is one of the most popular vegetable crops with the largest facility cultivation in China. Succession barriers, soil-borne diseases, and environmental stresses can often occur in actual production, leading to decreasing quality and yield. Fortunately, grafting has been one of the most effective operations to control the major diseases for the high resistance in recent years. Among them, two-stage grafting of tomatoes can be expected to cultivate high-quality seedling resistance. It is of great significance to precise control the light environment for better grafting during the healing and cutting stages. However, it is unclear on the specific parameters of the light environment during two-stage grafting. This study aims to explore the effects of different light intensities on the healing and growth of grafted seedlings in the two-stage grafting of tomatoes. The double-cut grafted seedlings rapidly healed and then took root after cutting under a high-density environment. The strong seedlings were cultivated after optimization. The grafted seedlings were then placed in a self-developed container made of acrylic and high-density foam board. The light intensity was selected to regulate the light environment at the ratio of red, blue, and green light during the healing period. The tomato variety 'Fendu 153' was used as the scion, while the 'Jinzuan' was used as the rootstock. The healing status and root regeneration of grafted seedlings were investigated under different light intensity gradients of 30-60-90 (CK), 40-80-120 (T1), 50-100-150 (T2), 60-120-180 (T3), and 70-140-210 (T4) μmol/(m²·s) during the healing period (1-2 d, 3-4 d, and 5 d). The grafted seedlings were cut under different light intensities after high-density healing for 1 d, 3 d, and 5 d, respectively, in order to evaluate the growth of plants. The growth indexes were measured, such as the plant height, stem diameter, leaf area, shoot ratio, and length, as well as surface area, diameter, and volume of root. The results showed that a higher survival rate of grafted seedlings was achieved in the T1 and T2 treatments. There was no significant difference, compared with the CK. The grafted seedlings under T1 treatment shared the fastest healing, the higher activities of antioxidant enzymes, the content of photosynthetic pigment, and the lower content of superoxide anion at the incision. There was a higher survival rate of cuttings after 3 d of treatment with the different light intensities. Among them, T1 and T2 treatments presented the highest. There was no significant difference among the treatments at 1 d of treatment with different light intensities. But the survival rate of cuttings decreased after 5 d. After evaluation on the growth of cutting grated seedlings, the root and above-ground growth of grafted seedlings were the best after T1 treatment for 1 d, 3 d, and 5 d, followed by T2, T3 at 5 d. In summary, the most favorable healing was achieved in the light intensity mode of 40-80-120 μmol/ (m²·s) at 1-2 d, 3-4 d, and 5 d, respectively. The best performance was obtained to cut within 3 d during the high-density healing stage of two-stage grafted tomato, in terms of the survival rate and the quality of grafted seedlings. The finding can also provide technical support to the two-stage grafted seedling of tomatoes.