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Key message: When grafting is used in breeding, the choice of the rootstock should not be underestimated. Its impact on grafted individuals can be either beneficial for reducing tree size or enhancing flowering such as in seed orchards or detrimental if it is a source of bias in clonal testing. This is demonstrated in an experimentation with Larix where the impact of grafting on the same or a different species rootstock is studied on several traits. Context: Grafting is heavily used by forest tree breeders to vegetatively propagate clones for establishment of clonal archives and seed orchards but also for clonal testing. Although of high importance in fruit trees and vines breeding, the selection of rootstocks in forest trees has drawn little attention. Aims: Our objective was to test the relative impact of rootstock and scion selection with contrasted characteristics on the performance of grafted trees. Methods: We performed three grafting experiments with larch (Larix sp.) combining either rootstocks and scions of the same species but with contrasted characteristics (high and low vigour and flowering capacity) or rootstocks and scions of the same and different species (homo- and hetero-plastic grafting). The performances of these combinations were monitored for over 10 years and compared for growth, wood properties, reproduction and some other traits. Results: The scion strongly affected performance but, in most cases, there was no significant interaction between scion and rootstock. Rootstock effects depended on the trait under consideration and the type of grafting. The choice of rootstock had little effect on wood properties. In case of homo-grafting, some significant rootstock effects were observed for growth although these effects were much weaker than those of scion and their relative weight decreased over time, making their practical importance minor. Notably, the mean performance of the grafted trees was unaffected by the vigour of the rootstocks or by their flowering capacities. In addition, the performance of individual clones was unaffected by the choice of clonal rootstock. Rootstocks had no significant effect on reproduction, whatever their vigour or flowering capacity. Flowering abundance was maximised when using scions from heavy flowering clones. When testing for different species grafting associations, the choice of rootstock had significant effects on multiple traits: hybrid larch rootstocks outperformed Japanese larch for growth traits but the latter yielded slightly but significantly delayed flushing and superior stem straightness. Additionally, European larch rootstocks led to heavier flowering than Japanese ones. Conclusion: The choice of the grafting type should be governed by breeders' objectives. Hetero-grafting should be preferred in cases where modification of traits such as tree size or production of flowers and cones is desired, as in seed orchard management. Conversely, no positive or negative impact on traits is wanted when evaluating genotype values for purposes such as clonal testing. In such cases, homo-grafting should be preferred to limit bias due to grafting. [ABSTRACT FROM AUTHOR]

Grafting, the careful selection of rootstocks and scions, has played a crucial role maintaining Chilean avocado fruit quality standards in a scenario in which climate change and drought-related issues have considerably decreased avocado fruit production in the last fifteen years. The historical use of seedling rootstocks in Chile has experienced a recent shift towards clonal rootstocks, driven by the potential to produce more consistent and predictable crops. This research aims to compare Hass avocado plants grafted on Mexicola seedling and Dusa® clonal rootstocks in a soilless and protected system using (i) a differential expression analysis of root and leaf samples and (ii) a fruit transcriptomic and metabolomic integration analysis to improve our understanding of rootstock–scion interaction and its impact on avocado tree performance and fruit quality. The results demonstrated that no significant transcriptomic and metabolomic differences were identified at fruit level in the ready-to-eat (RTE) stage for Hass avocado fruit from both rootstocks. However, Hass avocados grafted on the clonal rootstock showed greater aerial growth and slightly increased fruit size than the seedling rootstock due to the enrichment of cell wall-remodeling genes as revealed in leaves and fruit at harvest stage. [ABSTRACT FROM AUTHOR]

Grapevine leafroll-associated virus (GLRaV) infections are accompanied by symptoms influenced by host genotype, rootstock, environment, and which individual or combination of GLRaVs is present. Using a dedicated experimental vineyard, we studied the responses to GLRaVs in ripening berries from Cabernet Franc grapevines grafted to different rootstocks and with zero, one, or pairs of leafroll infection(s). RNA sequencing data were mapped to a high-quality Cabernet Franc genome reference assembled to carry out this study and integrated with hormone and metabolite abundance data. This study characterized conserved and condition-dependent responses to GLRaV infection(s). Common responses to GLRaVs were reproduced in two consecutive years and occurred in plants grafted to different rootstocks in more than one infection condition. Though different infections were inconsistently distinguishable from one another, the effects of infections in plants grafted to different rootstocks were distinct at each developmental stage. Conserved responses included the modulation of genes related to pathogen detection, abscisic acid (ABA) signalling, phenylpropanoid biosynthesis, and cytoskeleton remodelling. ABA, ABA glucose ester, ABA and hormone signalling-related gene expression, and the expression of genes in several transcription factor families differentiated the effects of GLRaVs in berries from Cabernet Franc grapevines grafted to different rootstocks. These results support that ABA participates in the shared responses to GLRaV infection and differentiates the responses observed in grapevines grafted to different rootstocks.

Plant–soil biota represent a unique living system crucial for improving crops' adaptation to climate change. In vineyards, plant–soil relations are mediated by rootstock–scion interaction, with grafted vines being the main plant material employed in vineyard planting. The interaction between two deeply different biological systems such as Vitis vinifera sativa and the American Vitis species may modify vines' adaptation to abiotic stress. The aim of this study was to investigate the physiological response (chlorophyll content—CHL; stomatal conductance—gs) of grafted and ungrafted vines and assess the involvement of Arbuscular Mycorrhizal Fungi (AMF) in this response. In two vineyards located in Central Italy, the presence of AMF was assessed in the roots of grafted and ungrafted cv 'Aleatico' vines. The morphological traits of AMF and root mycorrhizal colonization differed in the grafted and ungrafted vines. Under limited climate conditions, ungrafted vines showed better leaf resilience traits (high CHL and gs values) and larger AMF storage organs (vesicles). On the other hand, the grafted ones—which are more sensitive to climate conditions (lower gs and CHL)—involved AMF colonization strategies (greater abundance of arbuscoles and mycorrhizal colonization potential) linked to the improved uptake and transport of water from the bulk soil to the vine. Taken together, these findings highlight different mycorrhizal colonization strategies and storage behaviors in grafted and ungrafted vineyards and with respect to different physical and chemical soil traits. [ABSTRACT FROM AUTHOR]

Grafting, the careful selection of rootstocks and scions, has played a crucial role maintaining Chilean avocado fruit quality standards in a scenario in which climate change and drought-related issues have considerably decreased avocado fruit production in the last fifteen years. The historical use of seedling rootstocks in Chile has experienced a recent shift towards clonal rootstocks, driven by the potential to produce more consistent and predictable crops. This research aims to compare Hass avocado plants grafted on Mexicola seedling and Dusa® clonal rootstocks in a soilless and protected system using (i) a differential expression analysis of root and leaf samples and (ii) a fruit transcriptomic and metabolomic integration analysis to improve our understanding of rootstock–scion interaction and its impact on avocado tree performance and fruit quality. The results demonstrated that no significant transcriptomic and metabolomic differences were identified at fruit level in the ready-to-eat (RTE) stage for Hass avocado fruit from both rootstocks. However, Hass avocados grafted on the clonal rootstock showed greater aerial growth and slightly increased fruit size than the seedling rootstock due to the enrichment of cell wall-remodeling genes as revealed in leaves and fruit at harvest stage.

It is generally recognized that the root uptake capacity of grafted plants strongly depends on the rootstocks' well-developed root system. However, we found that grafted plants showed different nitrate uptake capacities when different varieties of oriental melon scion were grafted onto the same squash rootstock, suggesting that the scion regulated the nitrate uptake capacity of the rootstock root. In this study, we estimated the nitrate uptake capacity of grafted plants with the different oriental melon varieties' seedlings grafted onto the same squash rootstocks. The results indicated a significant difference in the nitrate uptake rate and activity of two heterologous grafting plants. We also showed a significant difference in CmoNRT2.1 expression in the roots of two grafting combinations and verified the positive regulation of nitrate uptake by CmoNRT2.1 expression. In addition, the two varieties of oriental melon scion had highly significant differences in CmHY5 expression, which was transported to the rootstock and positively induced CmoHY5-1 and CmoHY5-2 expression in the rootstock roots. Meanwhile, CmHY5 could positively regulate CmoNRT2.1 expression in the rootstock roots. Furthermore, CmoHY5-1 and CmoHY5-2 also positively regulated CmoNRT2.1 expression, respectively, and CmoHY5-1 dominated the positive regulation of CmoNRT2.1, while CmHY5 could interact with CmoHY5-1 and CmoHY5-2, respectively, to jointly regulate CmoNRT2.1 expression. The oriental melon scion regulated the nitrate uptake capacity of the melon/squash grafting plant roots, and the higher expression of CmHY5 in the oriental melon scion leaves, the more substantial the nitrate uptake capacity of squash rootstock roots. [ABSTRACT FROM AUTHOR]

The appropriate selection of rootstock-scion combinations to improve yield and fully realize grafting benefits requires an in-depth understanding of rootstock-scion synergy. Toward this end, we grafted two determinate-type scions [grape tomato (‘BHN 1022’) and beefsteak tomato (‘Skyway’)] onto four rootstocks with dierent characteristics to examine plant growth, yield performance, biomass production, and fruit mineral nutrient composition. The study was conducted during two growing seasons (spring and fall plantings in Florida) under organic production in high tunnels with the non-grafted scions as controls. Rootstocks had previously been designated as either “generative” (‘Estamino’) or “vegetative” (‘DR0141TX’) by some commercial suppliers or had not been characterized [‘RST-04-106-T’ and ‘SHIELD RZ F1 (61-802)’]. Also, ‘Estamino’, ‘DR0141TX’, and ‘RST-04-106-T’ had been described as more vigorous than ‘SHIELD RZ F1 (61-802)’. In both planting seasons (with low levels of soilborne disease pressure), the “vegetative” and “generative” rootstocks increased marketable and total fruit yields for both scions except for the beefsteak tomato grafted with the “vegetative” rootstock in fall planting. Positive eects of ‘RST-04-106-T’ on fruit yield varied with scions and planting seasons, and were most manifested when grafted with the beefsteak tomato scion in fall planting. ‘SHIELD RZ F1 (61-802)’ led to similar yields as the non-grafted controls except for grafting with the grape tomato scion in fall planting. For vegetative and fruit biomass, both the “vegetative” and “generative” rootstocks had positive impacts except for the beefsteak tomato in fall planting. For fruit mineral composition, the “vegetative” and “generative” rootstocks, both highly vigorous, consistently elevated fruit P, K, Ca, Zn, and Fe contents on a dry weight basis, whereas the other rootstocks did not. Overall, although the more vigorous rootstocks enhanced tomato plant productivity and fruit minerals, the evidence presented here does not support the suggestion that the so-called “vegetative” and “generative” rootstocks have dierent impacts on tomato scion yield, biomass production, or fruit mineral contents More studies with dierent production systems and environmental conditions as well as contrasting scion genotypes are needed to further categorize the impacts of rootstocks with dierent vigor and other characteristics on plant biomass production and their implications on fruit yield development. [ABSTRACT FROM AUTHOR]

The appropriate selection of rootstock-scion combinations to improve yield and fully realize grafting benefits requires an in-depth understanding of rootstock-scion synergy. Toward this end, we grafted two determinate-type scions [grape tomato (‘BHN 1022') and beefsteak tomato (‘Skyway')] onto four rootstocks with different characteristics to examine plant growth, yield performance, biomass production, and fruit mineral nutrient composition. The study was conducted during two growing seasons (spring and fall plantings in Florida) under organic production in high tunnels with the non-grafted scions as controls. Rootstocks had previously been designated as either “generative” (‘Estamino') or “vegetative” (‘DR0141TX') by some commercial suppliers or had not been characterized [‘RST-04-106-T' and ‘SHIELD RZ F1 (61-802)']. Also, ‘Estamino', ‘DR0141TX', and ‘RST-04-106-T' had been described as more vigorous than ‘SHIELD RZ F1 (61-802)'. In both planting seasons (with low levels of soilborne disease pressure), the “vegetative” and “generative” rootstocks increased marketable and total fruit yields for both scions except for the beefsteak tomato grafted with the “vegetative” rootstock in fall planting. Positive effects of ‘RST-04-106-T' on fruit yield varied with scions and planting seasons, and were most manifested when grafted with the beefsteak tomato scion in fall planting. ‘SHIELD RZ F1 (61-802)' led to similar yields as the non-grafted controls except for grafting with the grape tomato scion in fall planting. For vegetative and fruit biomass, both the “vegetative” and “generative” rootstocks had positive impacts except for the beefsteak tomato in fall planting. For fruit mineral composition, the “vegetative” and “generative” rootstocks, both highly vigorous, consistently elevated fruit P, K, Ca, Zn, and Fe contents on a dry weight basis, whereas the other rootstocks did not. Overall, although the more vigorous rootstocks enhanced tomato plant productivity and fruit minerals, the evidence presented here does not support the suggestion that the so-called “vegetative” and “generative” rootstocks have different impacts on tomato scion yield, biomass production, or fruit mineral contents. More studies with different production systems and environmental conditions as well as contrasting scion genotypes are needed to further categorize the impacts of rootstocks with different vigor and other characteristics on plant biomass production and their implications on fruit yield development.

Salinity restricts plant growth and production by specific ions toxicity to particular plants. Cl ion is exceptionally toxic to citrus. Citrus rootstock and scion has a significant effect on each other under unfavourable conditions. Nevertheless, their specific response can be different depending on the way to translocate and compartment the toxic ions, or to induce antioxidant systems. In this paper, we studied the behaviour of diploid (2x) and tetraploid (4x) Volkamer lemon rootstocks grafted with commercial cultivar Kinnow mandarin (KM/VM2x and KM/VM4x, respectively) when exposed to moderate (75 mM) and high salt stress (150 mM). Both genotypes showed a decrease in their photosynthetic variables (Pn, gs, E, Fv/Fm, Fv′/Fm′, NPQ), and the decline was more significant in KM/VM2x plants as compared to KM/VM4x. The highest increase in the concentration of stress indicators (MDA and H2O2) was observed in leaves and roots of KM/VM2x at 75 and 150 mM of salt stress. The KM/VM4× showed the maximum increase in antioxidative enzymes (SOD, CAT, POD, APx, GR) and osmolytes (PRO, GB) in leaves and roots at 75 and 150 mM. Minerals (Cl ion, Na, K, P, N, Ca) accumulation was also significantly affected in leaves and roots of KM/VM2x and KM/VM4x under moderate and high NaCl stress. Overall, our results showed that Cl ion accumulation presents a robust correlation with stress indicators and their scavenging enzymes in leaves and roots. Moreover, 2x scion significantly mitigated by the 4x rootstock and showed more tolerance as compared to grafted on 2x rootstock. [ABSTRACT FROM AUTHOR]

Key message: Rootstock provides more abscisic acid (ABA) content to scions to increase the chilling tolerance of seedlings. H2O2 is involved in ABA regulation of grafting-induced chilling tolerance of cucumber. Here we examined the role of ABA in the response of grafted cucumber to chilling stress. The data showed chilling induced an increase in leaf and root ABA content and there was a positive correlation between ABA content and the chilling tolerance of the varieties. The increase of ABA content and NCED mRNA abundance in the leaf of both Cs/Cs (self-root) and Cs/Cm (grafted with pumpkin as rootstock) showed a delay under aerial stress compared with those under whole plant and root-zone stress. Intriguingly, an increase in ABA in xylem was found under whole-plant and root-zone chilling stress but was not detected under aerial stress, implying the increases in ABA content in leaves were mainly from root ABA transportation. Compared to Cs/Cs, a higher ABA content and NCED mRNA abundance were observed in Cs/Cm, which showed that Cm could output more ABA than Cs. The removal of endogenous ABA decreased the difference in chilling tolerance induced by Cm, as evidenced by the observed similar oxidative stress levels and photosynthetic capacity between Cs/Cs and Cs/Cm after chilling stress. Moreover, we found that the H2O2 signal in grafted cucumber could respond to chilling stress earlier than the H2O2 signal in self-rooted cucumber. The inhibition of endogenous H2O2 decreased the chilling tolerance of grafted cucumber induced by ABA by reducing photosynthesis and the mRNA abundance of CBF1 and COR. Thus, our results indicate that H2O2, as the downstream signal, participated in the rootstock-induced chilling tolerance of grafted seedlings induced by ABA. [ABSTRACT FROM AUTHOR]

Plant–soil biota represent a unique living system crucial for improving crops’ adaptation to climate change. In vineyards, plant–soil relations are mediated by rootstock–scion interaction, with grafted vines being the main plant material employed in vineyard planting. The interaction between two deeply different biological systems such as Vitis vinifera sativa and the American Vitis species may modify vines’ adaptation to abiotic stress. The aim of this study was to investigate the physiological response (chlorophyll content—CHL; stomatal conductance—gs) of grafted and ungrafted vines and assess the involvement of Arbuscular Mycorrhizal Fungi (AMF) in this response. In two vineyards located in Central Italy, the presence of AMF was assessed in the roots of grafted and ungrafted cv ‘Aleatico’ vines. The morphological traits of AMF and root mycorrhizal colonization differed in the grafted and ungrafted vines. Under limited climate conditions, ungrafted vines showed better leaf resilience traits (high CHL and gs values) and larger AMF storage organs (vesicles). On the other hand, the grafted ones—which are more sensitive to climate conditions (lower gs and CHL)—involved AMF colonization strategies (greater abundance of arbuscoles and mycorrhizal colonization potential) linked to the improved uptake and transport of water from the bulk soil to the vine. Taken together, these findings highlight different mycorrhizal colonization strategies and storage behaviors in grafted and ungrafted vineyards and with respect to different physical and chemical soil traits.

The cropping potential of almond (Prunus amygdalus (L.) Batsch, syn P. dulcis (Mill.)) cultivars is determined by their adaptation to edaphoclimatic and environmental conditions. The effects of scion–rootstock interactions on vigor have a decisive impact on this cropping success. Intensively planted orchards with smaller less vigorous trees present several potential benefits for increasing orchard profitability. While several studies have examined rootstock effects on tree vigor, it is less clear how rootstocks influence more specific aspects of tree architecture. The objective of this current study was to identify which architectural traits of commercially important scion cultivars are influenced by rootstock and which of these traits can be useful as descriptors of rootstock performance in breeding evaluations. To do this, 6 almond cultivars of commercial significance were grafted onto 5 hybrid rootstocks, resulting in 30 combinations that were measured after their second year of growth. We observed that rootstock choice mainly influenced branch production, but the effects were not consistent across the different scion–rootstock combinations evaluated. This lack of consistency in response highlights the importance of the unique interaction between each rootstock and its respective scion genotype. [ABSTRACT FROM AUTHOR]

Vegetable grafting is extensively used today in agricultural production to control soil-borne pathogens, abiotic and biotic stresses and to improve phenotypic characteristics of the scion. Commercial vegetable grafting is currently practiced in tomato, watermelon, melon, eggplant, cucumber, and pepper. It is also regarded as a rapid alternative to the relatively slow approach of breeding for increased environmental-stress tolerance of fruit vegetables. However, even though grafting has been used for centuries, until today, there are still many issues that have not been elucidated. This review will emphasize on the important mechanisms taking place during grafting, especially the genomic interactions between grafting partners and the impact of rootstocks in scion’s performance. Special emphasis will be drawn on the relation between vegetable grafting, epigenetics, and the changes in morphology and quality of the products. Recent advances in plant science such as next-generation sequencing provide new information regarding the molecular interactions between rootstock and scion. It is now evidenced that genetic exchange is happening across grafting junctions between rootstock and scion, potentially affecting grafting-mediated effects already recorded in grafted plants. Furthermore, significant changes in DNA methylation are recorded in grafted scions, suggesting that these epigenetic mechanisms could be implicated in grafting effects. In this aspect, we also discuss the process and the molecular aspects of rootstock scion communication. Finally, we provide with an extensive overview of gene expression changes recorded in grafted plants and how these are related to the phenotypic changes observed. Τhis review finally seeks to elucidate the dynamics of rootstock-scion interactions and thus stimulate more research on grafting in the future. In a future where sustainable agricultural production is the way forward, grafting could play an important role to develop products of higher yield and quality in a safe and “green” way.

Grafting is typically utilized to merge adapted seedling rootstocks with highly productive clonal scions. This process implies the interaction of multiple genomes to produce a unique tree phenotype. However, the interconnection of both genotypes obscures individual contributions to phenotypic variation (rootstock-mediated heritability), hampering tree breeding. Therefore, our goal was to quantify the inheritance of seedling rootstock effects on scion traits using avocado (Persea americana Mill.) cv. Hass as a model fruit tree. We characterized 240 diverse rootstocks from 8 avocado cv. Hass orchards with similar management in three regions of the province of Antioquia, northwest Andes of Colombia, using 13 microsatellite markers simple sequence repeats (SSRs). Parallel to this, we recorded 20 phenotypic traits (including morphological, biomass/reproductive, and fruit yield and quality traits) in the scions for 3 years (2015–2017). Relatedness among rootstocks was inferred through the genetic markers and inputted in a “genetic prediction” model to calculate narrow-sense heritabilities (h2) on scion traits. We used three different randomization tests to highlight traits with consistently significant heritability estimates. This strategy allowed us to capture five traits with significant heritability values that ranged from 0.33 to 0.45 and model fits (r) that oscillated between 0.58 and 0.73 across orchards. The results showed significance in the rootstock effects for four complex harvest and quality traits (i.e., total number of fruits, number of fruits with exportation quality, and number of fruits discarded because of low weight or thrips damage), whereas the only morphological trait that had a significant heritability value was overall trunk height (an emergent property of the rootstock–scion interaction). These findings suggest the inheritance of rootstock effects, beyond root phenotype, on a surprisingly wide spectrum of scion traits in “Hass” avocado. They also reinforce the utility of polymorphic SSRs for relatedness reconstruction and genetic prediction of complex traits. This research is, up to date, the most cohesive evidence of narrow-sense inheritance of rootstock effects in a tropical fruit tree crop. Ultimately, our work highlights the importance of considering the rootstock–scion interaction to broaden the genetic basis of fruit tree breeding programs while enhancing our understanding of the consequences of grafting.

The production of kiwifruit around the world is widely affected by the bacterial canker disease caused by Pseudomonas syringae pv. actinidiae (Psa). The use of resistant rootstock is considered to be an effective way to control diseases; however, there are few studies on the evaluation and utilization of Psa-resistant rootstocks in kiwifruit. A genotype Gui-1 in the Actinidia guilinensis species demonstrated strong resistance to Psa in our previous study, so it was used as a rootstock to evaluate its effect on the resistance of the highly susceptible cultivar 'Hongyang' (Actinidia chinensis) with an in vitro assay. The results show that Gui-1 significantly improved the resistance of 'Hongyang' scion to Psa without affecting the fruit quality, and also showed that the in vitro cane could still maintain the rootstock-induced resistance, but the resistance imparted to the scion by the rootstock might be spatially and temporally uneven. This study first provides the laboratory evidence of grafting-induced resistance to Psa, which provides a foundation for the application of resistant rootstock in kiwifruit production. The study also provides implications for the study of the mechanism of rootstock–scion interaction, especially those related to the resistance to non-soil-borne disease. [ABSTRACT FROM AUTHOR]

Vegetable grafting is extensively used today in agricultural production to control soil-borne pathogens, abiotic and biotic stresses and to improve phenotypic characteristics of the scion. Commercial vegetable grafting is currently practiced in tomato, watermelon, melon, eggplant, cucumber, and pepper. It is also regarded as a rapid alternative to the relatively slow approach of breeding for increased environmental-stress tolerance of fruit vegetables. However, even though grafting has been used for centuries, until today, there are still many issues that have not been elucidated. This review will emphasize on the important mechanisms taking place during grafting, especially the genomic interactions between grafting partners and the impact of rootstocks in scion's performance. Special emphasis will be drawn on the relation between vegetable grafting, epigenetics, and the changes in morphology and quality of the products. Recent advances in plant science such as next-generation sequencing provide new information regarding the molecular interactions between rootstock and scion. It is now evidenced that genetic exchange is happening across grafting junctions between rootstock and scion, potentially affecting grafting-mediated effects already recorded in grafted plants. Furthermore, significant changes in DNA methylation are recorded in grafted scions, suggesting that these epigenetic mechanisms could be implicated in grafting effects. In this aspect, we also discuss the process and the molecular aspects of rootstock scion communication. Finally, we provide with an extensive overview of gene expression changes recorded in grafted plants and how these are related to the phenotypic changes observed. Τhis review finally seeks to elucidate the dynamics of rootstock-scion interactions and thus stimulate more research on grafting in the future. In a future where sustainable agricultural production is the way forward, grafting could play an important role to develop products of higher yield and quality in a safe and "green" way. [ABSTRACT FROM AUTHOR]

Grafting is typically utilized to merge adapted seedling rootstocks with highly productive clonal scions. This process implies the interaction of multiple genomes to produce a unique tree phenotype. However, the interconnection of both genotypes obscures individual contributions to phenotypic variation (rootstock-mediated heritability), hampering tree breeding. Therefore, our goal was to quantify the inheritance of seedling rootstock effects on scion traits using avocado (Persea americana Mill.) cv. Hass as a model fruit tree. We characterized 240 diverse rootstocks from 8 avocado cv. Hass orchards with similar management in three regions of the province of Antioquia, northwest Andes of Colombia, using 13 microsatellite markers simple sequence repeats (SSRs). Parallel to this, we recorded 20 phenotypic traits (including morphological, biomass/reproductive, and fruit yield and quality traits) in the scions for 3 years (2015–2017). Relatedness among rootstocks was inferred through the genetic markers and inputted in a "genetic prediction" model to calculate narrow-sense heritabilities (h 2) on scion traits. We used three different randomization tests to highlight traits with consistently significant heritability estimates. This strategy allowed us to capture five traits with significant heritability values that ranged from 0.33 to 0.45 and model fits (r) that oscillated between 0.58 and 0.73 across orchards. The results showed significance in the rootstock effects for four complex harvest and quality traits (i.e., total number of fruits, number of fruits with exportation quality, and number of fruits discarded because of low weight or thrips damage), whereas the only morphological trait that had a significant heritability value was overall trunk height (an emergent property of the rootstock–scion interaction). These findings suggest the inheritance of rootstock effects, beyond root phenotype, on a surprisingly wide spectrum of scion traits in "Hass" avocado. They also reinforce the utility of polymorphic SSRs for relatedness reconstruction and genetic prediction of complex traits. This research is, up to date, the most cohesive evidence of narrow-sense inheritance of rootstock effects in a tropical fruit tree crop. Ultimately, our work highlights the importance of considering the rootstock–scion interaction to broaden the genetic basis of fruit tree breeding programs while enhancing our understanding of the consequences of grafting. [ABSTRACT FROM AUTHOR]

The cropping potential of almond (Prunus amygdalus (L.) Batsch, syn P. dulcis (Mill.)) cultivars is determined by their adaptation to edaphoclimatic and environmental conditions. The effects of scion–rootstock interactions on vigor have a decisive impact on this cropping success. Intensively planted orchards with smaller less vigorous trees present several potential benefits for increasing orchard profitability. While several studies have examined rootstock effects on tree vigor, it is less clear how rootstocks influence more specific aspects of tree architecture. The objective of this current study was to identify which architectural traits of commercially important scion cultivars are influenced by rootstock and which of these traits can be useful as descriptors of rootstock performance in breeding evaluations. To do this, 6 almond cultivars of commercial significance were grafted onto 5 hybrid rootstocks, resulting in 30 combinations that were measured after their second year of growth. We observed that rootstock choice mainly influenced branch production, but the effects were not consistent across the different scion–rootstock combinations evaluated. This lack of consistency in response highlights the importance of the unique interaction between each rootstock and its respective scion genotype.

In Hevea brasiliensis (Willd. ex A. Juss.) Müll. Arg., the genetic diversity of seedling rootstocks is considered as the major factor responsibles for intra-clonal variation in the latex yield. Genetically uniform clonal rootstock is used to reduce this variation. In this study, the effect of four rootstocks including three clonal rootstocks namely, CATAS 8813, Hai ken 2, Dafeng 99 and a seedling rootstock were investigated after grafted to PR 107 with respect to growth, rubber yield, biochemical parameters of latex and intra-clonal variation. Rootstocks significantly affected the sucrose, inorganic phosphorus and thiol contents. The clone CATAS 8813 and seedling rootstocks showed higher sucrose, inorganic phosphorus and thiol contents than the trees of Haiken 2 and Dafeng 99. Dry rubber yield was found to be highest in CATAS 8813 followed by Dafeng 99 and Haiken 2. The three clonal rootstocks reduced intra-clonal variation in latex yield, exhibiting lower range of latex yield and lower coefficient of variation, compared to the seedling rootstocks. The effect of the four rootstocks on the girth growth was not significantly different. The present study suggested that the clonal rootstock CATAS 8813 might be a potential source for improving rubber yield of scion PR 107. [ABSTRACT FROM AUTHOR]

Due to the rapid expansion of irrigated agriculture, effi cient use of the limited water resources in arid and semi-arid regions is becoming more and more vital. However, water salinity is a major problem due to its negative infl uence on the yields of many crops. It reduces citrus trees’ growth and causes physiological disorders. Primarily salt-stress lowers net CO2 assimilation, stomatal conductance, and water potential of citrus tree leaves, in addition to accumulation of excessive concentration of Chloride or Sodium in leaves. A great deal of research indicates that citrus have the genetic potential to be salt-sensitive; however inheritance studies in citrus are scarce. In this paper the adverse of effects of salinity on physiological aspects of citrus are reviewed. The review summarizes the prevailing state of knowledge about the responses and tolerance of citrus trees to salinity.

Several dwarf plum genotypes (Prunus salicina L.), due to deficiency of unknown gibberellin (GA) signalling, were identified. A cDNA encoding GA 2-oxidase (PslGA2ox), the major gibberellin catabolic enzyme in plants, was cloned and used to screen the GA-deficient hybrids. This resulted in the identification of a dwarf plum hybrid, designated as DGO24, that exhibits a markedly elevated PslGA2ox signal. Grafting ‘Early Golden’ (EG), a commercial plum cultivar, on DGO24 (EG/D) enhanced PslGA2ox accumulation in the scion part and generated trees of compact stature. Assessment of active GAs in such trees revealed that DGO24 and EG/D accumulated relatively much lower quantities of main bioactive GAs (GA1 and GA4) than control trees (EG/M). Moreover, the physiological function of PslGA2ox was studied by determining the molecular and developmental consequences due to ectopic expression in Arabidopsis. Among several lines, two groups of homozygous transgenics that exhibited contrasting phenotypes were identified. Group-1 displayed a dwarf growth pattern typical of mutants with a GA deficiency including smaller leaves, shorter stems, and delay in the development of reproductive events. In contrast, Group-2 exhibited a ‘GA overdose’ phenotype as all the plants showed elongated growth, a typical response to GA application, even under limited GA conditions, potentially due to co-suppression of closely related Arabidopsis homologous. The studies reveal the possibility of utilizing PslGA2ox as a marker for developing size-controlling rootstocks in Prunus. [ABSTRACT FROM PUBLISHER]

• Plant physiology, plant water stress and plant morphology were severally affected by heat and deficit irrigation in citrus. • Water and heat responsive genes showed higher expression in tolerant and no or little expression in sensitive citrus genotypes. • Heat shock proteins and Major Intrinsic Proteins expression can contribute to avoiding the risks of oxidative stress incurred by water-conservative behavior in plant under stress. • Brazilian sour orange showed tolerance against heat, water deficit and combined heat and water deficit condition. Citrus is most important fruit crop of the world grown throughout the subtropics and semi-arid to humid tropics. Water deficit and high temperature are two major abiotic stresses that affect the plant physiology negatively and ultimately reduced crop yield and performance. The objective of this study was to evaluate the responses of ten genetically diverse citrus selections against the water deficit, heat, and their combinations. Treatments consisted of moderate and high heat (38 °C and 46 °C), water deficit (50% and 25% field capacity) and combined (38 °C with 50% field capacity and 46 °C with 25% field capacity) stress. We measured the effects of water potential, moisture contents and gas exchange on the expression of heat shock proteins (HSPs) and major intrinsic proteins (MIPs). Brazilian sour orange (Citrus aurantium L.) and Keen sour orage (C. aurantium L) performed well by avoiding desiccation and maintaining photosynthesis, stomatal conductance, water potential and moisture content under high temperature and low soil moisture. While, Savage citrange (Poncirus trifoliata × Citrus sinensis) proved the most sensitive to all stress conditions. Genome wide analysis indicated that CsHsp70 had NBD sugar kinase actin Hsp70 protein and molecular charpones Dnak, while CsHsp70.1 had chloroplast protein with Dnak and CsHsp90 had Hsp90 protein. Brazilian sour orange expressed HSPs under heat, MIPs under water deficit and both under combined stress conditions. CsHsp70, CsHsp70.1 and CsHsp90 showed high expression from 1.5 to 6.0 h and then gradually decreased till 24.0 h under heat and combined stress in Brazilian sour orange. CsHsp70 in Savage citrange exhibited slight expression under heat and combined stress after 6.0 h. High expression of CsTIP2 and CsTIP1 was observed from 1.5 to 24.0 h under water deficit, whereas CsTIP1 expressed under heat and combined stress after 1.5 h. Whereas, Savage citrange exhibited little expression of the same genes under stress. It was concluded that the differences among these varieties are in tolerance to heat and water deficit is associated with capacity for upregulation of HSPs and MIPs. [ABSTRACT FROM AUTHOR]