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  • Author or Editor: Junpei Zhang x
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Informative DNA fingerprints from 50 walnut cultivars (Juglans regia) in China were generated using amplified fragment length polymorphism (AFLP) markers to reveal their genetic diversity and relationships. Nine primer combinations were selected from 64 EcoR I/Mse I primer combinations to amplify the accessions. An average of 132 polymorphic loci per primer set was detected from the nine primer combinations. The discrimination power of each polymorphic marker (estimated by the polymorphism information content) ranged from 0.00 to 0.37 with an average of 0.19. A moderate level of genetic diversity was observed among the 50 cultivars. Their expected heterozygosity varied from 0.38 to 0.50 (average, 0.44), and Dice's similarity coefficient ranged from 0.53 to 0.86 (average, 0.70). The cluster analysis conducted using the unweighted pair group method of arithmetic averages method showed that all of the cultivars fell into five groups at Dice's similarity coefficient of 0.68. According to the comprehensive analyses based on the specific loci, similarity coefficient, and clustering results, six cultivars (Liaoning 1, Zixin, Shanhe 4, Zha 343, Tulare, and Chandler) were considered important germplasms of walnut cultivars.

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Cotyledon explants of walnut (Juglans regia) have been shown to generate adventitious roots on growth regulator-free medium. The spatial distribution of endogenous indole-3-acetic acid (IAA) and its dynamic changes during adventitious root formation were investigated using an in situ immunohistochemical approach. Before root induction, IAA signal was distributed throughout the freshly excised cotyledon explants. During provascular bundle differentiation, the IAA signal was mainly located in the provascular bundles. At the stage of annular meristematic zones formation, the IAA signal was mainly distributed in the meristematic zones and decreased in the vascular bundles and cotyledonous parenchyma. As primordia formed, the IAA signal became localized in the root primordia and gradually disappeared in the meristematic zones. In emerging roots, the IAA signal was mainly localized in the root cap and root meristem. These results suggest that accumulation of IAA in the provascular bundles may induce vascular differentiation and the increase in IAA through meristematic zones may be responsible for the adventitious root formation from walnut cotyledons. The direct evidence presented here indicates that IAA accumulated in the meristematic zones is not the sole signal needed to induce adventitious root.

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Walnut, a woody plant, is regarded as having difficulty rooting when propagated by vegetative methods, such as cutting and layering. A layering experiment was conducted in 2018 and 2022. In 2018, some Juglans species, including J. regia L. seedling (JR), J. regia cv. Liaoning 1 (JR LN1), J. hopeinesis Hu seedling (JH), J. mandshurica Maxim seedling (JM), and J. nigra L. seedling (JN), were the mother plants. The specific research hypotheses were that own-rooted walnut propagule could be obtained through layering. the rooting capacity of different Juglans species would be different, and the rooting ability of JN would be the highest among the samplings. The results indicated that all of these species in the experiment could be rooted by etiolation and indole-3-butyric acid (IBA) treatment and that root occurrence was found 6 to 7 weeks after IBA treatment. The layers (shoots from the mother plant) on the seedlings of JR, JH, and JM obtained rooting percentages (RP) of 75.55%, 84.45%, and 86.67%, respectively, and root numbers (RNs) of 21.8, 42.8, and 38.8, respectively, after 20 days of etiolation and 1% IBA treatment. JR LN1 had difficulty rooting in equal conditions and had a RP of 31.11%. In 2022, JR LN1 was the only mother plant and the IBA concentration was increased to obtain satisfactory RP and RN. With the 4% and 8% IBA treatments, RPs of 88.9% and 93.3% and RNs of 40.3 and 27.7, respectively, were achieved. During the experiment, the RP, RN, root length (RL), and root diameter (RD), as well as the layer height (LH) and layer diameter (LD), were investigated and evaluated. Layers with low vigor were more likely to root, as shown by a nonparametric test conducted for the height and diameter of the layers of the rooting and nonrooting groups. A significantly negative correlation (r = −0.548) was observed between RN and LH. Moreover, the quality of the best results of JR LN1 layering propagule and that with ‘liaoning 1’ 1-year-old seedling were compared. Our results provide more support for the possibility of vegetative propagation of walnut by layering and more information regarding the clonal cultivation of walnut trees and the own-rooted seedling establishment of walnut cultivars.

Open Access