Effects of different substrate formulations on growth and physiological characteristics of Vernicia fordii budding rootstock grafted seedlings

In order to determine the optimal substrate combinations, and to provide scientific theories and technical guidance for container seedling nursery of tung tree seedlings with hypocotyle rootstocks.

Using yellow soil, peat, perlite, vermiculite, and coir as substrate raw materials, a total of 8 different substrate formulations were designed. The survival rate, growth traits, fruiting capacity, biomass, root indexes, root indicators, and photosynthetic properties were measured on the grafted seedlings of shoot anvil cultivated by different substrate formulations, and the quality of the grafted seedlings were comprehensively evaluated by combining the correlation analysis, principal component analysis and the value of the subordinate function.

1）The grafted seedlings cultivated with T1 (pure yellow soil) and T6 (60% yellow subsoil + 20% peat soil + 20% vermiculite) exhibited high graft survival rate and final survival rate, reaching over 87% and 74% respectively. In contrast, the T5 treatment (10% yellow soil +50% peat soil +20% vermiculite +20% perlite) had the lowest initial graft survival rate and final survival rate, which were only 71.11% and 57.78% respectively. This indicates that the substrate ratio treatments with higher yellow soil content yielded higher seedling initial graft survival rate and final survival rate compared to those with lower yellow soil content; 2) During seedling growth, the bud-seedling rootstock grafted seedlings of Vernicia fordii (tung oil tree) showed the best growth performance under the T6 substrate ratio. In the same year, their seedling height reached 27.31 cm, which was 98.47% and 99.49% higher than those of T7 and T8 respectively, with significant differences (P<0.05). The ground diameter was 10.06 mm, second only to that of T5. The total fresh weight was 34.03 g, which was 126.41% and 155.86% higher than those of T1 and T7 respectively, with significant differences (P<0.05). The total root length was 1 062.70 cm, which was 180.93% and 167.00% higher than those of T7 and T8 respectively, with significant differences (P<0.05); 3) Bud-seedling rootstock grafting technique enables flowering and fruiting of grafted seedlings in the following year. Among them, the grafted seedlings under T5 and T6 substrate ratios showed high fruiting rates, which were 26.47% and 23.33% respectively. The seedling height of fruiting branches under all substrate ratios was significantly lower than that of non-fruiting branches. Therefore, to achieve high yield in the 3rd year, it is recommended to prioritize removing fruits in the 2nd year after grafting; 4) A comprehensive analysis of 15 indicators (including seedling height, ground diameter, total fresh weight, total dry weight, total root length, root surface area, root diameter, root volume, chlorophyll a content, chlorophyll b content, etc.) was conducted using the entropy weight method. Among these, the T6 substrate ratio obtained the highest score of 1.007, followed by T2, T3, T4, and T5 substrate ratios (ranging from 0.425 to 0.531), while T7 had the lowest score of 0.111. The comprehensive scores of grafted seedlings under different substrate ratios ranked from highest to lowest as T6, T4, T5, T3, T2, T8, T1, T7.

The grafted tung tree seedlings with hypocotyle rootstocks grown in the T6 substrate mixture performed best and can be used as a suitable substrate for grafting and seedling cultivation in production.