Bridging the Gap: Genetic Insights into Graft Compatibility for Enhanced Kiwifruit Production

Abstract

Kiwifruit, with its unique flavor, nutritional value, and economic benefits, has gained significant attention in agriculture production. Kiwifruit plants have traditionally been propagated without grafting, but recently, grafting has become a more common practice. A new and complex disease called Kiwifruit Vine Decline Syndrome (KVDS) has emerged in different kiwifruit-growing areas. The syndrome was first recognized in Italy, although similar symptoms had been observed in New Zealand during the 1990s before subsequently spreading worldwide. While kiwifruit was not initially grafted in commercial orchards, the expansion of cultivation into regions with heavy soils or other challenging environmental conditions may make grafting selected kiwifruit cultivars onto KVDS-resistant or -tolerant rootstocks essential for the future of this crop. Grafting is a common horticultural practice, widely used to propagate several commercially important fruit crops, including kiwifruits, apples, grapes, citrus, peaches, apricots, and vegetables. Grafting methods and genetic compatibility have a crucial impact on fruit quality, yield, environmental adaptability, and disease resistance. Achieving successful compatibility involves a series of steps. During grafting, some scion/rootstock combinations exhibit poor graft compatibility, preventing the formation of a successful graft union. Identifying symptoms of graft incompatibility can be challenging, as they are not always evident in the first year after grafting. The causes of graft incompatibility are still largely unknown, especially in the case of kiwifruit. This review aims to examine the mechanisms of graft compatibility and incompatibility across different fruit crops. This review's goal is to identify potential markers and techniques that could enhance grafting success and boost the commercial production of kiwifruit.

Keywords: Actinidia; graft union formation; micrografting; primary and secondary metabolites; rootstock/scion.

Figure 1

Graphical representation of different types of grafting (G. De Mori drawing). (A). Bud-grafting; (B). cleft grafting; (C). twin cleft whip grafting; (D). splice grafting; (E). ring grafting; (F). crown grafting.

Figure 2

Field grafting in kiwifruit: (A) whip-cutting preparation; (B) approximation of rootstock and scion; (C) connection and binding; (D) vegetative development of the variety’s bud (scion).

Figure 3

Micrografting steps in kiwifruit. (A) In vitro micropropagation of rootstock and scion plantlets; (B) micrografting; (C) micrografting results in a solid connection between the tissues of the rootstocks and scions after 10 days; (D) rooted micrografted plantlet; (E) First-year development of micrografted plant.

Figure 4

Illustration of a compatible graft in kiwifruit. Graft compatibility results from the synergy of multiple factors: activation of genes involved in oxidative processes, genetic distance between scion and rootstock, hormonal regulation, and the involvement of primary and secondary metabolites.

Figure 5

Graphical representation of the signal exchanges occurring between rootstock and scion.