Rootstock Genotypes Research Articles

Rootstock effects on leaf function and isotope composition in apple occurred on both scion grafted and ungrafted rootstocks under hydroponic conditions.

Rootstocks are used in modern apple production to increase productivity, abiotic and biotic stress tolerance, and fruit quality. While dwarfing for apple rootstocks has been well characterized, the physiological mechanisms controlling dwarfing have not. Previous research has reported rootstock effects on scion water relations. Root architecture and variability in soil moisture across rooting depths can also contribute to these differences among rootstocks in the field. To exclude these effects on rootstock behavior, scions were grafted onto four different rootstocks with varying effects on scion vigor (B.9, M.9, G.41 and G.890). Non-grafted rootstocks were also grown to examine whether the effects of rootstock occurred independently from scion grafting. Plants were grown in a greenhouse under near steady-state hydroponic conditions. Carbon (δ13C), oxygen (δ18O) and nitrogen (δ15N) isotope composition were evaluated and relationships with carbon assimilation, water relations, and shoot growth were tested. Rootstocks affected scion shoot growth, aligning with known levels of vigor for these four rootstocks, and were consistent between the two scion cultivars. Furthermore, changes in water relations influenced by rootstock genotype significantly affected leaf, stem, and root δ13C, δ18O, and δ15N. Lower δ13C and δ18O were inconsistently associated with rootstock genotypes with higher vigor in leaves, stems, and roots. G.41 had lower δ15N in roots, stems, and leaves in both grafted and ungrafted trees. The effects of rootstock on aboveground water relations were also similar for leaves of ungrafted rootstocks. This study provides further evidence that dwarfing for apple rootstocks is linked with physiological limitations to water delivery to the developing scion.

Early rootstock selection under ‘tahiti’ acid lime crown in Capitão Poço, Pará State, Brazil

Citrus represents one of the main fruit crops grown in the world, highlighting the ‘Tahiti’ acid lime tree. The objective was to compare rootstock varieties combined with this scion to identify those with the best agronomic performance and precocity of production, in addition to Phytophthora gummosis resistance. The experiment was carried out in Capitão Poço, northeast region of Pará, and the following seven rootstock genotypes were evaluated: ‘Sunki Tropical’, ‘BRS O S Passos’, ‘BRS Bravo’, ‘BRS Donadio’, ‘Citrandarin Indio’, ‘BRS Matta’, and ‘LVK x LCR-038’. A randomized block experimental design was used, with three replications and 10 plants per plot. The evaluated characteristics were: plant height (m); crown volume (m3); number of ripe fruit per plant; total yield of ripened fruit per plant (kg plant-1); cumulative fruit yield (fruit kg plant-1); and average productive efficiency (fruit kg m-3 of crown). The average productive efficiency was high. For early selection, the best rootstocks in terms of yield, stability and adaptability were Sunki Tropical, BRS O S Passos, and Cintradarin Indio. The fruit number had the greatest direct effect on fruit yield, and crown pruning was directly harmful. Further studies to understand the complex interaction of G x E for BRS Donadio and Sunki Tropical should be carried out.

Improvement of Citrus Rootstock Hybrids Derived by 2x × 2x Intra Crosses with the Aid of Embryo Rescue and Ploidy Detection

Diploid Citrus × Poncirus hybrids have significantly contributed to citrus rootstock evaluation. In Türkiye, common sour orange rootstock is used in many different climates and soil conditions at almost 85% of citrus plantations, but this rootstock is susceptible to Citrus tristeza virus disease. This study was conducted to improve new rootstock genotypes by traditional hybridization. Common sour orange (CSO) and Common mandarin (Citrus deliciosa Ten.) (CM) were crossed with Troyer citrange (TC) while King mandarin (KM) was crossed with Carrizo citrange (CC). Embryos obtained from crosses were taken on 110, 120 and 130 days after artificial pollination (DAP), and were germinated on MT culture media. The embryos of 120 DAP of combinations had the highest germination rate within CSO×TC, 95.15%; CM×TC, 96.25%; KM×CC, 95.23%. The trifoliate rates for each combination at subculture (CSO×TC, 17.40%; CM×TC, 11.11%; KM×CC; 6.17%) were obtained from 110 DAP embryos. Survival rates of the genotypes were ranged between 72.13% and 90.28% in subculture and varied from 40.17% and 64.71% in the greenhouse. As a result of the ploidy analysis by flow cytometry, the nuclear DNA content of diploid genotypes were found between 0.78 pg/2C and 0.93 pg/2C. One of the genotypes derived from CM×TC hybridization on 120 DAP was determinated as a triploid plant.

Grapevine bacterial communities display compartment-specific dynamics over space and time within the Central Valley of California

BackgroundPlant organs (compartments) host distinct microbiota which shift in response to variation in both development and climate. Grapevines are woody perennial crops that are clonally propagated and cultivated across vast geographic areas, and as such, their microbial communities may also reflect site-specific influences. These site-specific influences along with microbial differences across sites compose ‘terroir’, the environmental influence on wine produced in a given region. Commercial grapevines are typically composed of a genetically distinct root (rootstock) grafted to a shoot system (scion) which adds an additional layer of complexity via genome-to-genome interactions.ResultsTo understand spatial and temporal patterns of bacterial diversity in grafted grapevines, we used 16S rRNA amplicon sequencing to quantify soil and compartment microbiota (berries, leaves, and roots) for grafted grapevines in commercial vineyards across three counties in the Central Valley of California over two successive growing seasons. Community composition revealed compartment-specific dynamics. Roots assembled site-specific bacterial communities that reflected rootstock genotype and environment influences, whereas bacterial communities of leaves and berries displayed associations with time.ConclusionsThese results provide further evidence of a microbial terroir within the grapevine root systems but also reveal that the microbiota of above-ground compartments are only weakly associated with the local soil microbiome in the Central Valley of California.

Influence of Soil Type, Land Use, and Rootstock Genotype on Root-Associated Arbuscular Mycorrhizal Fungi Communities and Their Impact on Grapevine Growth and Nutrition

Soil characteristics, land management practices, and plant genotypes influence arbuscular mycorrhizal fungi (AMF) communities, leading to the proliferation of AMF taxa with different growth and nutritional outcomes in their hosts. However, the specific patterns driving these relationships are still not well understood. This study aimed to (1) evaluate the influence of soil characteristics, land use, and rootstock on AMF diversity and community structure and (2) assess the effect of those AMF communities on grapevine growth and nutrition. Soil samples were collected from vineyard and non-agricultural areas in Lisbon and Pegões, Portugal, and trap cultures established using Richter 110 and 1103 Paulsen rootstocks. After 3.5 months growth under greenhouse conditions, root-associated AMF communities were assessed by amplicon metagenomic sequencing using AMF-specific primers. Alpha diversity was only influenced by the soil type, while in β-diversity, an interaction was found between the soil type and land use. Both diversity measures were positively correlated with foliar K and negatively with leaf Mn and Mg. Notably, the concentrations of these nutrients were highly correlated with the relative abundance of operational taxonomic units (OTUs) within the genera Glomus, Rhizophagus, and Claroideoglomus. These results are valuable for supporting AMF selection for improved plant nutrition based on varying soil types and land uses.

Host Genetic Traits Underlying the Composition and Assembly of the Citrus Microbiome

Although plant genotypes are known to be a determinant of microbiome composition, the genetic mechanisms underlying how genotypes affect the microbiome are poorly understood. Citrus is an important, perennial fruit crop that normally contains scion grafted on the rootstock. Here, we investigated the genetic traits underlying the citrus microbiome. We sequenced the metagenome of leaf, root, and rhizosphere soil samples and the genome of corresponding citrus genotypes, which included 66 unique rootstock–scion combinations (56 scion genotypes and 9 rootstock genotypes) from one location using deep shotgun sequencing. Using a genome-wide association study (GWAS) analysis, we identified significant associations between citrus genes and a subset of genera and functional traits of the microbiome. Intriguingly, we found that bacterial secretion systems and mobility-related genes were present in single-nucleotide polymorphism-associated microbial functional traits of leaf and root microbiomes but not in the rhizosphere microbiome, indicating that they are important factors for bacteria to colonize inside or on leaf and root tissues but less so in the rhizosphere. We also discovered that chemotaxis and flagella genes play critical roles for bacteria colonizing leaf tissues but not in root tissues and the rhizosphere. Microbiome-associated host genes were mainly involved in plant immunity, transporters, hormones, cell walls, and the metabolism of carbohydrates, amino acids, and nitrogen. We identified genetic determinants that are associated with the abundance of Bacillus, Bradyrhizobium, Burkholderia, and Cellvibrio, genera that are known to comprise many beneficial bacteria for citrus. This study unraveled the genetic traits underneath the mutual selection of citrus and microbes via GWAS analyses. This study provides useful information that aids the utilization of genotypes and key members of a healthy microbiota for microbiome engineering as well as the editing of specific genes to improve host microbiota. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Identification of genes involved in almond scion tree architecture influenced by rootstock genotype using transcriptome analysis

The emergence of almond (Prunus amygdalus (L.) Batsch, syn P. dulcis (Mill.)) intensive and semi-intensive cropping systems has created a necessity for new almond cultivars with vigor and shape adapted to these new circumstances. Hence, it is important to unravel which mechanisms are behind the regulation of the tree three-dimensional structure, or tree architecture, and what factors may play a role, like the choice of rootstock. In this study, we have analyzed the rootstock influence on the scion transcriptome, regarding the biological processes that control almond tree architecture. Three commercial almond cultivars were grafted onto three hybrid rootstocks known to confer different architecture to the scion, resulting in nine combinations, whose gene expression in shoot tips was analyzed via RNA-Seq. We report that differences in tree architecture phenotype are correlated with differential expression of genes involved in hormonal and molecular responses associated with the regulation of apical dominance, branch formation, plant growth, cell wall formation, or nitrogen assimilation. These results highlight the importance of the rootstock choice in selecting a desirable scion architecture and in establishing almond orchards.

Rapid In Vitro Screening of Prunus Genotypes for Resistance to Armillaria Root Rot Using Roots of Young Rootstocks

Armillaria root rot (ARR), caused by Armillaria species and Desarmillaria tabescens, is a severe disease that affects stone fruit trees in the United States. One strategy to mitigate the impact of this disease is to develop ARR-resistant rootstocks. However, current techniques to screen Prunus species for resistance to ARR are time-consuming, labor-intensive, and may not fully replicate field conditions. To address these limitations, we developed a new rapid in vitro screening assay, which uses roots of 2-year-old Prunus rootstock genotypes. We screened 12 Prunus genotypes against Armillaria mellea, Armillaria solidipes, and Desarmillaria tabescens in vitro. Freshly excavated root segments were placed next to or on top of fungal cultures. After 21 days, the circumferential percentage and horizontal length of the fungal colonization and the ability of the fungus to enter through root periderm were evaluated. The root tissue surrounding the infection was also evaluated to assess any response reactions against the ARR pathogens. Our results showed that inoculated root tissues displayed signs of fungal infection, and infection and host responses varied among the Prunus genotypes. Host responses similar to those observed in the field, such as compartmentalization of infected tissue with barrier zones, necrophylactic periderm formation, and callus formation on root surfaces, were observed and were more evident in less susceptible genotypes. In conclusion, our newly developed assay, which uses freshly excavated roots from 2-year-old rootstocks, can rapidly screen Prunus genotypes for resistance to ARR.

Relative contribution of season, site, scion and rootstock genotype, and susceptibility to European canker to the variability in bacterial and fungal communities in apple leaf scar tissues

AbstractNeonectria ditissima infects apple trees through wounds, causing European canker. In the UK, the most important entry site for N. ditissima is leaf scar. Specific apple endophytes may contribute to cultivar resistance/tolerance to the pathogen. We assessed the relative effect of location, sampling time (season), and rootstock/scion genotype on bacterial and fungal endophyte communities in the apple leaf scar tissues of current‐season extension shoots and identified Operational Taxonomic Units (OTUs) with differential abundance between canker resistant and susceptible scions, and between rootstocks. Leaf scar tissues were sampled from two orchards at three times (10/2018, 06/2019 and 10/2019) for eight scion cultivars, each grafted onto two rootstocks, for profiling 16S and ITS rRNA regions. Endophyte composition was primarily affected by season (autumn vs. spring) and location (sites and blocks within site). There was a significant reduction in the community size in the spring, particularly for fungi, and species turnover between autumn and spring. This seasonal dynamics suggest that to protect leaf scars from N. ditissima infection in the autumn specific endophytes suppressing canker may have to be augmented annually around the leaf‐fall time. Scion and rootstock genotypes had limited effects on the endophyte community. A group of resistant cultivars differed from a group of susceptible ones in the relative abundance of many bacterial and fungal OTUs, most of which had low reads numbers. Nevertheless, several OTUs with high reads numbers differed in their relative abundance between resistant and susceptible scions, including OTUs from Sphingomonas, Methylobacterium, Vishniacozyma and Rhodotorula babjevae, and warrant further investigation for their potential role in host resistance/tolerance against N. ditissima.

Rootstocks Alter the Seasonal Dynamics and Vertical Distribution of New Root Growth of Vitis vinifera cv. Shiraz grapevines

Minirhizotron tubes were installed to monitor root growth dynamics of mature Shiraz grapevines in a rootstock trial established in the hot climate Riverina region of New South Wales, Australia. The vertical root distribution and seasonal root growth dynamics of Shiraz on own-roots and Shiraz grafted on the rootstocks Ramsey, 140 Ruggeri and Schwarzmann was studied for five seasons across a seven-year period to a depth of 60 cm. New root production was significantly influenced by genotype, soil depth, season, growth stage and year. Soil moisture and soil temperature were monitored at 10, 30 and 60 cm in the last two seasons. Soil moisture at 30 cm and soil temperature at all three depths were significant predictors of root growth. New root numbers were significantly higher in 140 Ruggeri than the other rootstocks. To the depth studied, 140 Ruggeri roots were evenly distributed from the topsoil down, whereas the majority of roots of Schwarzmann and Shiraz were located at intermediate depths in the 10–40 cm ad 20–40 cm zones respectively, while Ramsey roots were found at 20 cm or below. Depending on genotype, root growth occurred across several phenological stages but tended to peak at flowering. In some years we observed root growth in early and late winter at rates exceeding that of autumn, and this was associated with warmer temperatures during this period. In general, the seasonal dynamics of root growth attributes were found to be influenced by abiotic factors, but mainly determined by genotype. The insights gained from this study can help us better understand the interplay between rootstock, environment, and management, and predict how different rootstock genotypes may perform under changing climatic conditions.

Genotypic differences in root architecture and physiological characteristics in mango (Mangifera indica) under drought

An experiment was conducted at the research farm of ICAR-Indian Agricultural Research Institute, New Delhi during 2020 and 2021 to study the genotypic differences in root architecture and physiological characteristics in mango (Mangifera indica L.) under drought. One-year-old polyembryonic 7 mango rootstock genotypes were exposed to normal irrigation and drought conditions for 24 days. The drought-induced increased total plant weight and dry weight in Kurukkan. The shoot dry weight decreased in all genotypes ranging from 5.13% in OLP-Z-6/1 to 81.82% in Kurukkan. There was a lesser reduction in membrane stability index in Kurukkan and K-5, stomata count in Kurukkan, Olour and OPK-3-7/12 at the end of the drought period. Root surface area increased under drought in Kurukkan, while it decreased more in K-5. Correlation studies confirmed a strong positive relationship between relative water content (RWC) and membrane stability index (MSI), number of stomata (SC), number of leaves (NL), root tips (RT) and root forks (NRF); MSI and number of root tips (NRT); dry weight of the whole plant and root surface area (RSA); the dry weight of roots and root volume (RV), RSA, and plant height (Ph); root length (RL) and RSA, RT, and NRF. Kurukkan was identified as drought-tolerant based on a higher SC, RWC, RV, RSA, dry mass, NRT and NRF. Results indicated that the root indices offer a promising strategy for the screening of drought-tolerant mango genotypes.

The rootstock shape microbial diversity and functionality in the rhizosphere of Vitis vinifera L. cultivar Falanghina.

The rhizosphere effect occurring at the root-soil interface has increasingly been shown to play a key role in plant fitness and soil functionality, influencing plants resilience. Here, for the first time, we investigated whether the rootstock genotype on which Vitis vinifera L. cultivar Falanghina is grafted can influence the rhizosphere microbiome. Specifically, we evaluated to which extent the 5BB and 1103P rootstocks are able to shape microbial diversity of rhizosphere environment. Moreover, we explored the potential function of microbial community and its shift under plant genotype influence. We investigated seven vineyards subjected to the same pedo-climatic conditions, similar age, training system and management and collected twelve rhizosphere soil samples for metagenomic analyses and composite soil samples for physical-chemical properties. In this study, we used 16S rRNA gene-based metagenomic analysis to investigate the rhizosphere bacterial diversity and composition. Liner discriminant analysis effect size (LEFSe) was conducted for metagenomic biomarker discovery. The functional composition of sampled communities was determined using PICRUSt, which is based on marker gene sequencing profiles. Soil analyses involved the determination of texture, pH, Cation Exchange Capacity (CSC), Organic Carbon (OC), electrical conductivity (EC), calcium (Ca), magnesium (Mg), potassium (K) content, Phosphorous (P), nitrogen (N). The latter revealed that soil features were quite homogenous. The metagenomic data showed that the bacterial alpha-diversity (Observed OTUs) significantly increased in 1103P rhizosphere microbiota. Irrespective of cultivar, Pseudomonadota was the dominant phylum, followed by Actinomycetota > Bacteroidota > Thermoproteota. However, Actinomycetota was the major marker phyla differentiating the rhizosphere microbial communities associated with the different rootstock types. At the genus level, several taxa belonging to Actinomycetota and Alphaproteobacteria classes were enriched in 1103P genotype rhizosphere. Investigating the potential functional profile, we found that most key enzyme-encoding genes involved in N cycling were significantly more abundant in 5BB rootstock rhizosphere soil. However, we found that 1103P rhizosphere was enriched in genes involved in C cycle and Plant Growth Promotion (PGP) functionality. Our results suggest that the different rootstocks not only recruit specific bacterial communities, but also specific functional traits within the same environment.

Unveiling Cacao Rootstock-Genotypes with Potential Use in the Mitigation of Cadmium Bioaccumulation.

The accumulation of high cadmium (Cd) levels in cacao beans (Theobroma cacao) generate several commercial and health issues. We hypothesized that cacao phenotypic and genotypic diversity could provide new insights to decrease Cd accumulation in cacao beans. Nine cacao rootstock genotypes were evaluated for up to 90 days under 0, 6, and 12 (mg·kg-1) of CdCl2 exposure and Cd content and plant growth dynamics were measured in leaves, stems, and roots. Data revealed that all cacao genotypes studied here were highly tolerant to Cd, since they presented tolerance index ≥ 60%. In shoots, EET61 and PA46 presented the higher (~270 mg·kg DW-1) and lower (~20 mg·kg DW-1) Cd concentration, respectively. Accordingly, only the EET61 showed an increase in the shoot cadmium translocation factor over the 90 days of exposure. However, when analyzing cadmium allocation to different organs based on total plant dry mass production, none of the genotypes maintained high Cd compartmentalization into roots, since P46, which was the genotype with the highest allocation of Cd to the roots, presented only 20% of total cadmium per plant in this plant organ and 80% allocated into the shoots, under Cd 12 (mg·kg-1) and after 90 days of exposure. Thus, genotypic/phenotypic variability in cacao rootstocks may provide valuable strategies for maximizing the reduction in Cd content in shoots. In this sense, IMC67 and PA46 were the ones that stood out in the present study.

The transcriptionally active bacterial communities of grapevine rhizosphere in dependence on rootstock and scion variety

The rhizosphere is where crucial processes for the productivity of viticultural systems occur. The composition of the bacterial communities associated with the rhizosphere of grapevines is known to depend on plant genotype. However, the genotype of grafted grapevines differs between scion and rootstock; the role of each genotype is unclear. To untangle the effect of scion and rootstock, the rRNA (V4–V5 region of 16S rRNA) extracted from the rhizosphere of the grape varieties Riesling and Mueller-Thurgau ungrafted vs grafted on different rootstocks was sequenced. The bioinformatic analysis with tools designed to be robust for compositional data showed that the investigated rootstocks or scions or combinations, respectively, recruited bacterial communities with distinguishable traits. Statistical differences were revealed between ungrafted Riesling vs Mueller-Thurgau, between grafted Riesling vs ungrafted Riesling, and between ungrafted Mueller-Thurgau vs grafted Mueller-Thurgau. Thus, confirming the role of scion and rootstock genotype as a driver of the structure and composition of bacterial communities in the rhizosphere of grapevines.

Identification of genes associated with the regulation of cold tolerance and the RNA movement in the grafted apple

In grafted apple, rootstock-derived signals influence scion cold tolerance by initiating physiological changes to survive over the winter. To understand the underlying molecular interactions between scion and rootstock responsive to cold, we developed transcriptomics and metabolomics data in the stems of two scion/rootstock combinations, ‘Gala’/‘G202’ (cold resistant rootstock) and ‘Gala’/‘M9’ (cold susceptible rootstock). Outer layers of scion and rootstock stem, including vascular tissues, were collected from the field-grown grafted apple during the winter. The clustering of differentially expressed genes (DEGs) and gene ontology enrichment indicated distinct expression dynamics in the two graft combinations, which supports the dependency of scion cold tolerance on the rootstock genotypes. We identified 544 potentially mobile mRNAs of DEGs showing highly-correlated seasonal dynamics between scion and rootstock. The mobility of a subset of 544 mRNAs was validated by translocated genome-wide variants and the measurements of selected RNA mobility in tobacco and Arabidopsis. We detected orthologous genes of potentially mobile mRNAs in Arabidopsis thaliana, which belong to cold regulatory networks with RNA mobility. Together, our study provides a comprehensive insight into gene interactions and signal exchange between scion and rootstock responsive to cold. This will serve for future research to enhance cold tolerance of grafted tree crops.

Inter-row cropping and rootstock genotype selection in a UK cider orchard to combat apple replant disease

Apple rootstock genotypes confer different levels of tolerance to apple replant disease (ARD) and vigour to a newly replanted apple tree. A hybrid management system of rotating the rootstock genotype planted between successive generations and inter-row planting in the alleyways of orchards may minimise the severity of ARD symptoms. High-throughput sequencing of the fungal ITS and bacterial 16S rDNA regions was used to investigate the diversity, and differential taxa present in soils displaying symptoms of ARD. Candidate pathogens and beneficial microorganisms were correlated with the above-ground establishment of each rootstock genotype in a UK cider orchard. Our results suggest that the same rootstock or rootstock with closely related parentage to the previous rootstock had more severe ARD symptoms. Planting in the alleyway appeared an effective strategy to minimise the severity of symptoms irrespective of rootstock genotype. The planting location effect had a higher contribution to the variation in the rhizosphere microbiome than that of the rootstock genotype. No predicted causal agents for ARD could be identified to a taxonomic level to predict their function but two species associated with mycorrhizae, Pteridiospora spinosispora and Paraglomus laccatum were identified as inversely correlated with ARD severity and could be candidate beneficial species for apple, warranting further investigation and research. Our findings suggest that planting in the alleyways and planting rootstocks genetically dissimilar to the previously planted rootstock can be beneficial for tree establishment. We have also identified species inversely associated with ARD severity, making candidates for future research to test the antagonistic effect of the species against ARD pathogens in apple roots.

Tissues and mechanisms associated with Verticillium wilt resistance in tomato using bi-grafted near-isogenic lines.

Host resistance is the primary means to control Verticillium dahliae, a soil-borne pathogen causing major losses on a broad range of plants, including tomato. The tissues and mechanisms responsible for resistance remain obscure. In the field, resistant tomato used as rootstocks does not confer resistance. Here, we created bi-grafted plants with near-isogenic lines (NILs) exhibiting (Ve1) or lacking (ve1) resistance to V. dahliae race 1. Ten days after inoculation, scion and rootstock tissues were subjected to differential gene expression and co-expression network analyses. Symptoms only developed in susceptible scions regardless of the rootstock. Infection caused more dramatic alteration of tomato gene expression in susceptible compared to resistant tissues, including pathogen receptor, signaling pathway, PR protein, and cell wall modification genes. Differences were observed between scions and rootstocks, primarily related to physiological processes in these tissues. Gene expression in scions was influenced by the rootstock genotype. A few genes were associated with the Ve1 genotype, which was independent of infection or tissue type. Several were physically clustered, some near the Ve1 locus on chromosome 9. Transcripts mapped to V. dahliae were dominated by secreted candidate effector proteins. These findings advance knowledge of molecular mechanisms underlying the tomato-V. dahliae interaction.

Effects of differentially expressed microRNAs induced by rootstocks and silicon on improving chilling tolerance of cucumber seedlings (Cucumis sativus L.)

BackgroundRootstocks can improve the chilling tolerance of grafted cucumbers, but their effectiveness varies. Rootstocks with strong de-blooming capacity may result in lower chilling tolerance of grafted cucumbers compared to those with weak de-blooming capacity, while also reducing the silicon absorption. However, it remains unclear whether this reduction in chilling tolerance is due to differences in rootstock genotypes or the reduction in silicon absorption.ResultsThe chilling tolerance of cucumber seedlings was improved by using rootstocks and silicon nutrition. Rootstocks had a more significant effect than silicon nutrition, and the weak de-blooming rootstock ‘Yunnan figleaf gourd’ was superior to the strong de-blooming rootstock ‘Huangchenggen No. 2’. Compared to self-rooted cucumber, twelve miRNAs were regulated by two rootstocks, including seven identical miRNAs (novel-mir23, novel-mir26, novel-mir30, novel-mir37, novel-mir46, miR395a and miR398a-3p) and five different miRNAs (novel-mir32, novel-mir38, novel-mir65, novel-mir78 and miR397a). Notably, four of these miRNAs (novel-mir38, novel-mir65, novel-mir78 and miR397a) were only identified in ‘Yunnan figleaf gourd’-grafted cucumbers. Furthermore, six miRNAs (miR168a-5p, miR390a-5p, novel-mir26, novel-mir55, novel-mir67 and novel-mir70) were found to be responsive to exogenous silicon. Target gene prediction for 20 miRNAs resulted in 520 genes. Functional analysis of these target genes showed that ‘Yunnan figleaf gourd’ improves the chilling tolerance of cucumber by regulating laccase synthesis and sulfate metabolism, while ‘Huangchenggen No. 2’ and exogenous silicon reduced chilling stress damage to cucumber by regulating ROS scavenging and protein protection, respectively.ConclusionAmong the identified miRNAs, novel-mir46 and miR398a-3p were found in cucumbers in response to chilling stress and two types of rootstocks. However, no identical miRNAs were identified in response to chilling stress and silicon. In addition, the differential expression of novel-mir38, novel-mir65, novel-mir78 and miR397a may be one of the important reasons for the differences in chilling tolerance of grafted cucumbers caused by two types of rootstocks.

Variation in the Root System Architecture of Peach × (Peach × Almond) Backcrosses.

The spatial arrangement and growth pattern of root systems, defined by the root system architecture (RSA), influences plant productivity and adaptation to soil environments, playing an important role in sustainable horticulture. Florida's peach production area covers contrasting soil types, making it necessary to identify rootstocks that exhibit soil-type-specific advantageous root traits. In this sense, the wide genetic diversity of the Prunus genus allows the breeding of rootstock genotypes with contrasting root traits. The evaluation of root traits expressed in young seedlings and plantlets facilitates the early selection of desirable phenotypes in rootstock breeding. Plantlets from three peach × (peach × almond) backcross populations were vegetatively propagated and grown in rhizoboxes. These backcross populations were identified as BC1251, BC1256, and BC1260 and studied in a completely randomized design. Scanned images of the entire root systems of the plantlets were analyzed for total root length distribution by diameter classes, root dry weight by depth horizons, root morphological components, structural root parameters, and root spreading angles. The BC1260 progeny presented a shallower root system and lower root growth. Backcross BC1251 progeny exhibited a more vigorous and deeper root system at narrower root angles, potentially allowing it to explore and exploit water and nutrients in deep sandy entisols from the Florida central ridge.

Short-term water stress responses of grafted pepper plants are associated with changes in the hormonal balance.

Phytohormones play an important role in regulating the plant behavior to drought. In previous studies, NIBER® pepper rootstock showed tolerance to drought in terms of production and fruit quality compared to ungrafted plants. In this study, our hypothesis was that short-term exposure to water stress in young, grafted pepper plants would shed light on tolerance to drought in terms of modulation of the hormonal balance. To validate this hypothesis, fresh weight, water use efficiency (WUE) and the main hormone classes were analyzed in self-grafted pepper plants (variety onto variety, V/V) and variety grafted onto NIBER® (V/N) at 4, 24, and 48h after severe water stress was induced by PEG addition. After 48h, WUE in V/N was higher than in V/V, due to major stomata closure to maintain water retention in the leaves. This can be explained by the higher abscisic acid (ABA) levels observed in the leaves of V/N plants. Despite the interaction between ABA and the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), in relation to stomata closure is controversial, we observed an important increase of ACC at the end of the experiment in V/N plants coinciding with an important rise of the WUE and ABA. The maximum concentration of jasmonic acid and salicylic acid after 48h was found in the leaves of V/N, associated with their role in abiotic stress signaling and tolerance. Respect to auxins and cytokinins, the highest concentrations were linked to water stress and NIBER®, but this effect did not occur for gibberellins. These results show that hormone balance was affected by water stress and rootstock genotype, where NIBER® rootstock displayed a better ability to overcome short-term water stress.