Effect of radicle excision treatment on the growth of pecan seedlings

Abstract:【Objective】This study investigated the effect of radicle excision treatments on the growth of pecan seedlings in order to provide technical support for the cultivation of pecan.【Methods】‘Pawnee’pecan seeds of the same size were selected for temperature-controlled germination. After germination, the pecan seeds were divided into three groups according to the radicle length. Group F had a radicle length no longer than 2 cm; group S between 2 and 4 cm; and group T longer than 4 cm. The control in these groups was designated as F1, S1, and T1, respectively. The treatments with root tip removal in the three groups were recorded as F2, S2, and T2. The treatment with 1/2 radicle removed in group S and group T was designated as S3 and T3, respectively, and the treatment with 2 cm radicle left in group T was assigned as T4. All the nine treatments had three replicates each with 30 seeds. The treated germi- nating seeds were planted in the same container, and then the seedling emergence rate was recorded. The growth index, root morphological index, and some physiological and biochemical indexes of the seedlings were measured and statistically analyzed in mid-June (early growth stage) and mid-Septem- ber (late growth stage).【Results】The seedling emergence rate of F2 was significantly increased by 14.8% compared with F1. No significant difference in the seedling emergence rate was found among treatments in group S. However, the seedling emergence rate in T1 was significantly higher than in T4. No significant difference in the length and ground diameter of the above-ground part in group S in the early stage of seedling growth. Compared to S1, the stem and leaf dry weights of S2 and S3 increased significantly by 48.3% and 81.8%, respectively. The dry root weight of S3, increased significantly by 22.7% and 25.2% compared to S1 and S2, respectively. The total dry weight of the seedlings in S3 was significantly higher than S1 and S2, by 30.0% and 27.7% respectively. In the late stage of seedling growth, the radicle excision treatments in groups F and T had no significant effect on the growth and root morphology of seedlings. Compared with S3, dry root weight and average root diameter of S1 in- creased by 18.7% and 23.5%, respectively. The total root volume of S1 increased by 52.3% compared with S3, while the diameter in S1 increased by 16.1% compared with S2. There were strong main roots in each treatment, and there was no significant difference in the lateral root number among treatments. There was no significant difference in chlorophyll content and photosynthetic parameters among differ- ent treatments in the later stages of seedling growth. Analysis of chlorophyll fluorescence revealed no significant differences in Fv/Fm, Fv/F0 in S and T groups. Meanwhile, Fv/Fm and Fv/F0 in F2 were signifi- cantly larger than those in F1. There was no significant difference in root activity among treatments in group F at the early stage of seedling growth. Root activity of S2 and S3 increased by 1.87 and 1.45 folds compared with S1, respectively. The root activity of T2, T3 and T4 increased by 62.3%, 43.0% and 42.5%, respectively, compared with T1. In the later stage of seedling growth, the soluble sugar con- tent in F2 was significantly higher than that in F1, and S1 was substantially higher than S2, suggesting that the seedling quality and resistance of F2 and S1 were better. On the other hand, no significant difference in soluble sugar content was found among treatment in T group.【Conclusion】Root tip removal of germinated seeds with radicle length less than 2 cm improved seedling emergence rate and quality. Inter- estingly, germinated seeds with a radicle length between 2 and 4 cm had better seedling quality and root growth without radicle excision. Meanwhile, for germinated seeds with a radicle longer than 4 cm, cutting off half of the radicle facilitated sowing and obtained a higher seedlings emergence rate.