Ex Vitro Rooting and Simultaneous Micrografting of the Walnut Hybrid Rootstock ‘Paradox’ (Juglans hindsi × Juglans regia) cl. ‘Vlach’

Abstract

In vitro micropropagation is already a current multiplication tool for walnut self-rooted cultivars and rootstocks, but walnut grafting is still performed in the field or in greenhouses, mainly using seedlings as rootstocks. The present work describes a new approach to obtain clonal walnut-grafted plants, involving in vitro shoot production of ‘Paradox’ (Juglans hindsi × Juglans regia) cl. ’Vlach’, to be used as rootstock, and J. regia cv. ‘Chandler’, to be used as scion. After completing the in vitro multiplication phase and a seven-day root induction treatment, ‘Vlach’ explants are transferred to ex vitro conditions for root expression while being simultaneously grafted using the in vitro produced ‘Chandler’ scions. The importance of the presence of leaves on both the scion and the rootstock for the success rate of the technique was evaluated. Under optimal conditions, average success rates of 82% for rootstock rooting, 72% for micrografting survival, and 84% for grafted plant acclimatization were achieved. This rooting/grafting combination technique seems able to compete with the traditional techniques of nursery grafting, allowing obtaining high-quality walnut-grafted plants independently of the external weather conditions in a significantly shorter time.

In Vitro Micrografting of Horticultural Plants: Method Development and the Use for Micropropagation

“…This stable in vitro environment and the probable pathogen-free status of micro-scion/rootstock may favor callus formation and rapid establishment of vascular reconnection between scions and rootstocks required for grafting success [34,35]. Micrografting protocols have been developed for many fruit crops including almond [18], apple [36], apricot [23], avocado [37], cacao [38], cashew [39], cherimoya [19], cherry [21], citrus [40,41], guava [4], grape [34], jujube [42], mulberry [43], hazelnut [44], kiwifruit [25], passion fruit [26], olive [45], peach [46], pear [47], pistachio [17], plum [48], walnut [49,50], and watermelon [51].…”

“…Several devices have been used to enable fast and effective union between the rootstock and scion, such as the elastic electric-wire tube [44], aluminum foil [66,76], Parafilm ® strip [42], silicon tube [13,79,80], paper bridge [59], silicone chip [30], plastic clamps [50] or alginate gel beads [44,75,81]. These grafting devices are used to support the graft and hold the scion and rootstock together during graft healing, particularly for the top-slit and top-wedge methods.…”

Microbiological Biostimulants in the Improvement of Extended Storage Quality of In Vitro-Derived Plants of Popular Ornamental Perennials

“…Simultaneous rooting and acclimatization of in vitro-produced plantlets represent a promising and efficient approach to plant production [11]. This innovative technique offers several advantages, including a reduction in labor and time required for plantlet production, and therefore, lowered costs, as well as enhanced survival rates during the transfer to ex vitro conditions [12].…”

Own-rooted Walnut Propagule of Four Walnut (Juglans) Rootstocks and Main Cultivated Cultivar Liaoning 1 Acquirement through Layering under Field Conditions

“…With the maturity and development of tissue culture technology, walnut micropropagation technology has been gained more attention and achieved tremendous progress in rootstock and cultivar propagation (Davis and Sankhla 1988;Gotea et al 2012;Leslie and McGranahan 1992;Liu et al 2018;Mc-Granahan et al 1987;McKenna and Sutter 1996;Payghamzadeh and Kazemitabar 2011;Pei et al 2007;Yegizbayeva et al 2021). Rootstock micropropagation for paradox cutting has been successful and used in commercial rootstock production (Ribeiro et al 2022).…”