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Haishan An, Feixiong Luo, Ting Wu, Yi Wang, Xuefeng Xu, Xinzhong Zhang and Zhenhai Han

Fine root (≤2 mm in diameter) systems play a pivotal role in water and mineral uptake in higher plants. However, the impact of fine root architecture on tree growth and development is not fully understood, especially in apple trees. Here, we summarize a 6-year-trial study using minirhizotrons to investigate the relationships between fine root production, mortality, and longevity in ‘Red Fuji’ trees grafted on five different rootstocks/interstems. Based on root length density (RLD), fine root production and mortality were markedly lower in ‘Red Fuji’ trees growing on dwarfing M.9 (M.9) and Shao series no. 40 (SH.40) rootstocks than in trees on standard Malus robusta ‘Baleng Crab’ (BC) rootstock. The use of M.9 and SH.40 as interstems led to an extensive reduction in fine root production and mortality in comparison with BC rootstock. Root number density (RND), but not average root length (ARL), showed similar patterns to RLD. About one-half of fine roots in ‘Red Fuji’ tree growing on M.9 were scattered within the top 0–20 cm of topsoil, indicating shallow root system in M.9, whereas in trees on BC, 55.15% of fine roots were distributed between 100- and 150-cm soil depth, indicating a deep root architecture. The addition of interstems did not alter fine root soil-depth distribution. For all rootstocks/interstems, fine roots with a life span of less than 80 days were generated in spring and summer, but fine roots which lived for more than 81 days were produced almost all the year round. In conclusion, lower fine root numbers were associated with the dwarfing effect in dwarfing rootstocks/interstems, but ARL and shallower rooting were not.

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Haishan An, Jiajia Meng, Fangjie Xu, Shuang Jiang, Xiaoqing Wang, Chunhui Shi, Boqiang Zhou, Jun Luo and Xueying Zhang

Vegetative propagation by cuttings is a very popular method. However, blueberry propagation using cuttings is still a main factor limiting its expansion because its results can vary according to the blueberry cultivar and environmental factors. This study aimed to evaluate the rooting abilities of hardwood cuttings for six blueberry cultivars (O’Neal, Misty, Diana, Biloxi, Bluebeauty, and Coville) using three different exogenous indole-butyric acid (IBA) concentrations (1000, 2000, and 3000 ppm), and to determine if the cutting position (basal, central, apical) affects rooting performance. A control treatment (0 ppm IBA) was also performed. After 90 days of each treatment, rooting percentage, average root length, and average root number per cutting were assessed and used to calculate rooting index, which is a measure of rooting ability. The rooting percentages of hardwood cuttings differed largely among cultivars and were highest for ‘Bluebeauty’ (68.55%), followed by ‘Biloxi’ (68.01%). The rooting index values of these two cultivars (33.59 and 35.18, respectively) were significantly higher than those of the other four cultivars. The rooting response of blueberry hardwood cuttings to IBA concentrations was quadratic, and 1000 and 2000 ppm IBA were sufficient to express the maximum rooting percentage in most cultivars. The rooting abilities of basal, central, and apical cuttings were similar with treatments with high IBA concentrations. The effects of the cultivar, IBA concentration, and interaction between them on rooting percentage, average root length, and average root number were significant; however, the effects of the cutting position on the rooting percentage and average root length were not. This suggested that the rooting abilities of blueberry hardwood cuttings were significantly influenced by the cultivar and IBA concentration rather than by the cutting position.