Mechanisms Underlying Graft Union Formation and Rootstock Scion Interaction in Horticultural Plants

Abstract

Grafting is a common practice for vegetative propagation and trait improvement in horticultural plants. A general prerequisite for successful grafting and long term survival of grafted plants is taxonomic proximity between the root stock and scion. For the success of a grafting operation, rootstock and scion should essentially be closely related. Interaction between the rootstock and scion involves complex physiological-biochemical and molecular mechanisms. Successful graft union formation involves a series of steps viz., lining up of vascular cambium, generation of a wound healing response, callus bridge formation, followed by vascular cambium formation and subsequent formation of the secondary xylem and phloem. For grafted trees compatibility between the rootstock/scion is the most essential factor for their better performance and longevity. Graft incompatibility occurs on account of a number of factors including of unfavorable physiological responses across the graft union, transmission of virus or phytoplasma and anatomical deformities of vascular tissue at the graft junction. In order to avoid the incompatibility problems, it is important to predict the same at an early stage. Phytohormones, especially auxins regulate key events in graft union formation between the rootstock and scion, while others function to facilitate the signaling pathways. Transport of macro as well as micro molecules across long distances results in phenotypic variation shown by grafted plants, therefore grafting can be used to determine the pattern and rate of recurrence of this transport. A better understanding of rootstock scion interactions, endogenous growth substances, soil or climatic factors needs to be studied, which would facilitate efficient selection and use of rootstocks in the future. Protein, hormones, mRNA and small RNA transport across the junction is currently emerging as an important mechanism which controls the stock/scion communication and simultaneously may play a crucial role in understanding the physiology of grafting more precisely. This review provides an understanding of the physiological, biochemical and molecular basis underlying grafting with special reference to horticultural plants.

Rootstock-Mediated Genetic Variance in Cadmium Uptake by Juvenile Cacao (Theobroma cacao L.) Genotypes, and Its Effect on Growth and Physiology

“…However, our study is the first in suggesting an analogous mechanism at the rootstock × scion interface, typically regarded as leading to emergent heterotic properties ( Reyes-Herrera et al, 2020 ). This conflict may be due to underlying additive and combined physiological drivers ( Loupit and Cookson, 2020 ), such as water and nutrients uptake and transport, hormone production and transport, and large-scale movement of molecules during grafting and through time ( Rasool et al, 2020 ).…”

Inheritance of Rootstock Effects in Avocado (Persea americana Mill.) cv. Hass

“…Genotyping-by-sequencing (Elshire et al, 2011;Cortés and Blair, 2018), re-sequencing (Fuentes-Pardo and Ruzzante, 2017), RNAseq (Jensen et al, 2012;Sun, 2012;Reeksting et al, 2016) and single-cell sequencing (Tang et al, 2019) across different tissues of the grafted tree, including the graft interface (Cookson et al, 2019), will enable understanding the genetic architecture of rootstock-mediated traits and the rootstock-scion interaction. Ultimately, these approaches may help discern among additive and combined processes how plant tissues and physiological (Loupit and Cookson, 2020;Rasool et al, 2020) processes (such as water and nutrients uptake and transport, hormone production and transport, and large-scale movement of molecules) behave during grafting.…”

“…Rootstock effects can go further and influence properties typically attributed to the clonal scion such as fruit sensorial and nutritional quality-e.g., texture, sugar content, acidity, pH, flavor, and color (Giorgi et al, 2005;Gullo et al, 2014;Balducci et al, 2019), cold tolerance and shoot pest and pathogen resistance (Rubio et al, 2005;Goldschmidt, 2014). These combined effects are influenced by phylogenetic distance and stem anatomy (Wulf et al, 2020) and are mechanistically due to large-scale movement of water, proteins, and nutrients (Little et al, 2016) or long-distance signaling (Lu et al, 2020) via hormones, messenger RNAs, and small RNAs (Wang et al, 2017;Loupit and Cookson, 2020;Rasool et al, 2020). Despite shared physiological processes account for the overall trait variation, the interconnection of all contributing variables (i.e., rootstock genotype, scion genotype, and environment) obscures individual contributions to phenotypic variation (Albacete et al, 2015;Warschefsky et al, 2016).…”

The Impact of Metabolic Scion–Rootstock Interactions in Different Grapevine Tissues and Phloem Exudates

“…Grafting also improves plant growth under environmental stresses, such as drought [6,7] and salt stress [8,9]. In addition, the effects of rootstock-scion interaction on growth, fruit quality, and stress tolerance have been widely reviewed [10,11]. Therefore, understanding scion-rootstock interactions is crucial for choosing the most suitable graft combinations for specific environments and good fruit quality [10].…”

“…In addition, the effects of rootstock-scion interaction on growth, fruit quality, and stress tolerance have been widely reviewed [10,11]. Therefore, understanding scion-rootstock interactions is crucial for choosing the most suitable graft combinations for specific environments and good fruit quality [10]. Nevertheless, grafting also constitutes a source for pathogen dissemination given that, by grafting fungal, bacterial, and viral biomes of grafted plants interact and might have a role in the healing of the graft union and the final performance of the plant.…”