Identifying Molecular Markers of Successful Graft Union Formation and Compatibility

Abstract

Grafting is a technique used for millennia for vegetative propagation, especially in perennial fruit crops. This method, used on woody and herbaceous plants, can improve several agronomic characteristics, such as yield or vigor, as well as tolerance to biotic and abiotic stresses. However, some scion/rootstock combinations suffer from poor graft compatibility, i.e., they are unable to form and/or sustain a successful graft union. Identifying symptoms of graft incompatibility is difficult because they are not always present in the first years after grafting and in most cases the causes of incompatibility are still poorly understood. Studies of changes in transcript abundance during graft union formation indicate that grafting responses are similar to responses to wounding and include the differential expression of genes related to hormone signaling, oxidative stress, formation of new vascular vessels, cell development, and secondary metabolites, in particular polyphenols. This review summarizes current knowledge of the changes in transcript abundance, redox status and metabolites accumulation during graft union formation and in cases of graft incompatibility. The goal of this review is to discuss the possibility of identifying marker transcripts, enzyme activities and/or metabolites of grafting success and graft compatibility which could be used to score grafting success for genetic research and in breeding programs. We highlight gaps in current knowledge and potential research directions in this field.

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 ).…”

“…However, after quantifying an additive component such as the inheritance of rootstock effects (i.e., rootstock-mediated genetic variance) across recombinant cacao saplings, a next step is to consider more thoroughly the complexity of the rootstock × scion interaction. After all, rootstock metabolites transcend the root system and could reach the grafted scion, i.e., rootstock’s additive contribution ( Loupit and Cookson, 2020 ; Rasool et al, 2020 ), which in turn may have contrasting consequences on rootstock traits, i.e., scion’s additive contribution ( Shu et al, 2017 ). These concurrent effects would ultimately feedback an emergent rootstock × scion interaction, a statistical interaction in the strict sense.…”

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 ).…”

Advances in Nursery Production of Hazelnut Plants in Serbia − Successful Grafting of Different Corylus avellana L. Cultivars and Clones Onto Corylus colurna L. Rootstock

“…However, ample body of evidence shows that nursery techniques, such as layering (Lagerstedt, 1983;Solar et al, 1994), softwood and hardwood cuttings (Kantarci and Ayfer, 1994;Ughini and Roversi, 2005), in vitro propagation (Damiano et al, 2005), and grafting are more suitable for use in the modern hazelnut industry. In perennial fruit crops in particular, grafting has been used for millennia for vegetative propagation, as it can improve some agronomic characteristics, such as yield or vigor, as well as tolerance to biotic and abiotic stresses (Loupit and Cookson, 2020). In Serbia, Corylus avellana L. cultivars are typically grafted on the Corylus colurna L. (Turkish filbert) rootstock, as this technology that has been developed and improved in this country results in high-quality planting material.…”