Rootstock control of scion response to water stress in grapevine

Rootstocks play a major role in grapevine tolerance to water stress by controlling and adjusting the water supply to shoot transpiration demand. This study aimed to characterize the influence of rootstock genotypes in the adaptive response of scions to water limiting conditions. The effect of rootstock genotype (140Ru and SO4) was observed in the different availability of water provided to the scions (Cabernet Sauvignon, Grenache, Merlot, Syrah), while scions influenced stomatal control of water transpiration. Implication on the cell-to-cell component of plant water transport in both rootstock and scion impacted on embolisms formation in roots and on hydraulics of leaves. The main conclusion of the present study was that rootstock and scion genotypes are able to confer to the plant traits of drought adaptability influencing respectively the capacity of water extraction from the soil and the sensitivity of the stomatal control.     

Scion and Rootstock Effects on ABA-mediated Plant Growth Regulation and Salt Tolerance of Acclimated and Unacclimated Potato Genotypes

Tolerance of salt stress in potato (Solanum tuberosum L.) increased when the plants were pre-exposed to low concentrations of salt (salt acclimation). This acclimation was accompanied by increased levels of abscisic acid (ABA) in the shoot. To further study the role of roots and shoots in this acclimation process, reciprocal grafts were made between a salt-tolerant (9506) and salt-sensitive ABA(−) mutant and its ABA(+) normal sibling potato genotype. The grafted plants were acclimated with 75 or 100 mM NaCl for 3 weeks and then exposed to 150–180 mM NaCl, depending on the salt tolerance of the rootstock. After 2 weeks of exposure to the salt stress, the acclimated and unacclimated plants were compared for physiologic and morphologic parameters. The response to the salt stress was strongly influenced by the rootstock. The salt-tolerant 9506 rootstock increased the salt tolerance of scions of both the ABA-deficient mutant and its ABA(+) sibling. This salt tolerance induced by the rootstock was primarily modulated by salt acclimation and manifested in the scion via increased plant water content, stem diameter, dry matter accumulation, stomatal conductivity, and osmotic potential, and is associated with a reduction in leaf necrosis. There was also a pronounced scion effect on the rootstock. Using 9506 as a scion significantly increased root fresh and dry weights, stem diameter, and root water content of ABA(−) mutant rootstocks. Specific evidence was found of the role of exogenous ABA in the enhancement of water status in grafted plants under salt stress beyond that of grafting alone. This was verified by more positive stomatal conductivity and upward water flow in ABA-treated grafted and nongrafted plants and the absence of upward water flow in nontreated grafted plants through NMR imaging. Grafting using either salt-tolerant scions or rootstocks with inherently high ABA levels may positively modify subsequent responses of the plant under salt stress.     

不同砧穗组合葡萄植株对部分根区干旱的生理生化响应

利用自制木箱对嫁接在3309C、420A和110R砧木上的玛瓦斯亚葡萄（M）进行双侧根区交替灌溉（AI）和单侧灌溉（UI）两种水分胁迫处理,以探讨不同葡萄砧穗组合对干旱的适应能力.结果表明：水分胁迫导致葡萄叶片ABA浓度大幅度增加,AI和UI的3种组合平均分别提高了267.5％和394.7％,而气孔导度和蒸腾速率显著下降.UI处理的3种组合叶片SOD和CAT活性显著增加,脯氨酸（Pro）含量极显著增加,且均以M/110R增幅较大,M/3309C增幅较小;而AI处理的SOD和CAT活性增加较小,但Pro含量显著增加.干旱胁迫导致葡萄叶片质膜透性、MDA和H₂O₂含量极显著增加,以M/3309C增加最多,M/110R增加较少.不同砧穗组合适应干旱逆境的能力主要取决于砧木品种,110R适应干旱逆境的能力强于420A和3309C,其对应的嫁接植株的生长量亦呈同样趋势.与根区单侧灌溉相比,双侧根区交替灌溉对植株造成的伤害较小,是可推广的节水灌溉方式.     

Factors influencing stomatal conductance in response to water availability in grapevine: a meta‐analysis

The main factors regulating grapevine response to decreasing water availability were assessed under statistical support using published data related to leaf water relations in an extensive range of scion and rootstock genotypes. Matching leaf water potential (Ψ_leaf) and stomatal conductance (g_s) data were collected from peer‐reviewed literature with associated information. The resulting database contained 718 data points from 26 different Vitis vinifera varieties investigated as scions, 15 non‐V. vinifera rootstock genotypes and 11 own‐rooted V. vinifera varieties. Linearised data were analysed using the univariate general linear model (GLM) with factorial design including biological (scion and rootstock genotypes), methodological and environmental (soil) fixed factors. The first GLM performed on the whole database explained 82.4% of the variability in data distribution having the rootstock genotype the greatest contribution to variability (19.1%) followed by the scion genotype (16.2%). A classification of scions and rootstocks according to their mean predicted g_s in response to moderate water stress was generated. This model also revealed that g_s data obtained using a porometer were in average 2.1 times higher than using an infra‐red gas analyser. The effect of soil water‐holding properties was evaluated in a second analysis on a restricted database and showed a scion‐dependant effect, which was dominant over rootstock effect, in predicting g_s values. Overall the results suggest that a continuum exists in the range of stomatal sensitivities to water stress in V. vinifera, rather than an isohydric–anisohydric dichotomy, that is further enriched by the diversity of scion‐rootstock combinations and their interaction with different soils.     

Water status indicators of lemon trees in response to flooding and recovery

Potted 2-year-old lemon trees [Citrus limon (L.) Burm. fil, cv. Verna] grafted on sour orange (C. aurantium L.) rootstock were subjected to flooding for 3 d. Control plants were irrigated daily to field capacity. Continuously (sap flow, trunk diameter fluctuations) and discretely (predawn and midday leaf water potential, leaf conductance) measured plant-based water status indicators were compared. The sensitivity of the maximum daily trunk shrinkage signal intensity to flooding and its behaviour during the recovery period demonstrated that this indicator is more feasible than the others for use in automatic irrigation. The responses to flooding of continuously and discretely measured plant-based water status indicators were very similar to those observed in response to drought stress indicating that it necessary to use soil water measurement automatic sensors to detect the cause of the stress. The results underlined the robustness of the compensation heat-pulse technique for estimating instantaneous and daily transpiration rates on flooding stress and recovery.     

Shifts in xylem vessel diameter and embolisms in grafted apple trees of differing rootstock growth potential in response to drought

We investigated responses of plant growth rate, hydraulic resistance, and xylem cavitation in scion-rootstock-combinations of Malus domestica L. cv. Honeycrisp scions grafted onto a high-shoot vigor (HSV) rootstock, (semi-dwarfing Malling111), or onto a low-shoot vigor (LSV) rootstock, (dwarfing Budagovsky 9), in response to substrate moisture limitation. Adjustments in xylem vessel diameter and frequency were related to hydraulic resistance measurements for high- versus low- vigor apple trees. We observed a greater tolerance to water deficit in the high-shoot compared to the low-shoot vigor plants under water deficit as evidenced by increased growth in several plant organs, and greater scion anatomical response to limited water availability with ca. 25% increased vessel frequency and ca. 28% narrower current season xylem ring width. Whereas water limitation resulted in greater graft union hydraulic resistance of high-shoot vigor trees, the opposite was true when water was not limiting. The graft union of the low-shoot vigor rootstock exhibited higher hydraulic resistance under well-watered conditions. Scions of high-shoot vigor rootstocks had fewer embolisms at low plant water status compared to scions of low-shoot vigor rootstocks, presumably as a result of large differences in xylem vessel diameter. Our results demonstrated that anatomical differences were related to shifts in hydraulic conductivity and cavitation events, a direct result of grafting, under limited soil water.     

Construction of a high-density genetic linkage map and QTL analysis of morphological traits in an F1 Malusdomestica × Malus baccata hybrid

Apple is considered the most commonly grown fruit crop in temperate regions that brings great economic profits to fruit growers. Dwarfing rootstocks have been extensively used in apple breeding as well as commercial orchards, but the molecular and genetic basis of scion dwarfing and other morphological traits induced by them is still unclear. At present, we report a genetic map of Malusdomestica × Malus baccata with high density. The F₁ population was sequenced by a specific length amplified fragment (SLAF). In the genetic map, 5064 SLAF markers spanning 17 linkage groups (LG) were included. Dwarf-related and other phenotypic traits of the scion were evaluated over a 3-year growth period. Based on quantitative trait loci (QTL) evaluation of plant height and trunk diameter, two QTL clusters were found on LG 11, which exhibited remarkable influences on dwarfing of the scion. In this analysis, QTL DW2, which was previously reported as a locus that controls dwarfing, was confirmed. Moreover, three novel QTLs for total flower number and branching flower number were detected on LG2 and LG4, exhibited the phenotypic variation that has been explained by QTL ranging from 8.80% to 34.80%. The findings of the present study are helpful to find scion dwarfing and other phenotypes induced by rootstock in the apple.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12298-021-01069-0.     

Quantitative trait loci associated with constitutive traits control water use in pearl millet [Pennisetum glaucum (L.) R. Br.]

There is substantial genetic variation for drought adaption in pearl millet in terms of traits controlling plant water use. It is important to understand genomic regions responsible for these traits. Here, F₇ recombinant inbred lines were used to identify quantitative trait loci (QTL) and allelic interactions for traits affecting plant water use, and their relevance is discussed for crop productivity in water‐limited environments. Four QTL contributed to increased transpiration rate under high vapour pressure deficit (VPD) conditions, all with alleles from drought‐sensitive parent ICMB 841. Of these four QTL, a major QTL (35.7%) was mapped on linkage group (LG) 6. The alleles for 863B at this QTL decreased transpiration rate and this QTL co‐mapped to a previously detected LG 6 QTL, with alleles from 863B for grain weight and panicle harvest index across severe terminal drought stress environments. This provided additional support for a link between water saving from a lower transpiration rate under high VPD and drought tolerance. 863B alleles in this same genomic region also increased shoot weight, leaf area and total transpiration under well‐watered conditions. One unexpected outcome was reduced transpiration under high VPD (15%) from the interaction of two alleles for high VPD transpiration (LG 6 (B), 40.7) and specific leaf mass and biomass (LG 7 (A), 35.3), (A, allele from ICMB 841, B, allele from 863B, marker position). The LG 6 QTL appears to combine alleles for growth potential, beneficial for non‐stress conditions, and for saving water under high evaporative demand, beneficial under stressful conditions. Mapping QTL for water‐use traits, and assessing their interactions offers considerable potential for improving pearl millet adaptation to specific stress conditions through physiology‐informed marker‐assisted selection.     

Rootstock scion somatogenetic interactions in perennial composite plants

The ancient plant production practice of grafting which instantly imparts new physiological properties to the desirable scion still remains shrouded in mystery. Yet, grafting remains a widely used technique in the production of several horticultural species. In a composite grafted plant, rootstocks control many aspects of scion growth and physiology including yield and quality attributes as well as biotic and abiotic stress tolerance. Broadly, physical, physiological, biochemical and molecular mechanisms have been reviewed to develop an integrated understanding of this enigmatic process that challenges existing genetic paradigms. This review summarizes the reported mechanisms underlying some of the economically important traits and identifies several key points to consider when conducting rootstock scion interaction experiments. Study of the somatogenetic interactions between rootstock and scion is a field that is ripe for discovery and vast improvements in the coming decade. Further, utilization of rootstocks based on a better understanding of the somatogenetic interactions is highly relevant in the current agricultural environment where there is a need for sustainable production practices. Rootstocks may offer a non-transgenic approach to rapidly respond to the changing environment and expand agricultural production of annual and perennial crops where grafting is feasible in order to meet the global food, fiber and fuel demands of the future.     

Profiling of sugar transporter genes in grapevine coping with water deficit

The profiling of grapevine (Vitis vinifera L.) genes under water deficit was specifically targeted to sugar transporters. Leaf water status was characterized by physiological parameters and soluble sugars content. The expression analysis provided evidence that VvHT1 hexose transporter gene was strongly down-regulated by the increased sugar content under mild water-deficit. The genes of monosaccharide transporter VvHT5, sucrose carrier VvSUC11, vacuolar invertase VvGIN2 and grape ASR (ABA, stress, ripening) were up-regulated under severe water stress. Their regulation in a drought-ABA signalling network and possible roles in complex interdependence between sugar subcellular partitioning and cell influx/efflux under Grapevine acclimation to dehydration are discussed.     

PHENOPSIS, an automated platform for reproducible phenotyping of plant responses to soil water deficit in Arabidopsis thaliana permitted the identification of an accession with low sensitivity to soil water deficit

The high-throughput phenotypic analysis of Arabidopsis thaliana collections requires methodological progress and automation. Methods to impose stable and reproducible soil water deficits are presented and were used to analyse plant responses to water stress. Several potential complications and methodological difficulties were identified, including the spatial and temporal variability of micrometeorological conditions within a growth chamber, the difference in soil water depletion rates between accessions and the differences in developmental stage of accessions the same time after sowing. Solutions were found. Nine accessions were grown in four experiments in a rigorously controlled growth-chamber equipped with an automated system to control soil water content and take pictures of individual plants. One accession, An1, was unaffected by water deficit in terms of leaf number, leaf area, root growth and transpiration rate per unit leaf area. Methods developed here will help identify quantitative trait loci and genes involved in plant tolerance to water deficit.     

Consequences of insect herbivory on grape fine root systems with different growth rates

Herbivory tolerance has been linked to plant growth rate where plants with fast growth rates are hypothesized to be more tolerant of herbivory than slower-growing plants. Evidence supporting this theory has been taken primarily from observations of aboveground organs but rarely from roots. Grapevines differing in overall rates of new root production, were studied in Napa Valley, California over two growing seasons in an established vineyard infested with the sucking insect, grape phylloxera (Daktulosphaira vitifoliae Fitch). The experimental vineyard allowed for the comparison of two root systems that differed in rates of new root tip production (a 'fast grower', Vitis berlandieri x Vitis rupestris cv. 1103P, and a slower-growing stock, Vitis riparia x Vitis rupestris cv. 101-14 Mgt). Each root system was grafted with a genetically identical shoot system (Vitis vinifera cv. Merlot). Using minirhizotrons, we did not observe any evidence of spatial or temporal avoidance of insect populations by root growth. Insect infestations were abundant throughout the soil profile, and seasonal peaks in phylloxera populations generally closely followed peaks in new root production. Our data supported the hypothesis that insect infestation was proportional to the number of growing tips, as indicated by similar per cent infestation in spite of a threefold difference in root tip production. In addition, infested roots of the fast-growing rootstock exhibited somewhat shorter median lifespans (60 d) than the slower-growing rootstock (85 d). Lifespans of uninfested roots were similar for the two rootstocks (200 d). As a consequence of greater root mortality of younger roots, infested root populations in the fast-growing rootstock had an older age structure. While there does not seem to be a trade-off between potential growth rate and relative rate of root infestation in these cultivars, our study indicates that a fast-growing root system may more readily shed infested roots that are presumably less effective in water and nutrient uptake. Thus, differences in root tip production may be linked to differences in the way plants cope with roots that are infested by sucking insects.     

Comparison of continuously recorded plant-based water stress indicators for young lemon trees

Continuously recorded plant-based water stress indicators (sap flow and parameters derived from trunk diameter fluctuations) were compared in potted young lemon trees (Citrus limon (L.) Burm. fil, cv. Verna) grafted on sour orange (C. aurantium L.) rootstock submitted to deficit irrigation. Daily maximum (MXTD) and minimum (MNTD) trunk diameters and daily trunk diameter shrinkage (MDS) were directly influenced by the water supply to the trees from the soil. The continuously recorded plant-based water stress indicators presented different degrees of sensitivity when used to estimate the water status of the plants. Sap flow (SF) and MDS were more immediate and sensitive than MXTD and MNTD. However, the higher signal intensity: noise for SF and the fact that its signal intensities remained clearly above unity during the stress period, indicating that the soil water was depleted, point to the greater reliability of this indicator. Also, the possibility of developing further baseline relationships between SF and air vapour pressure deficit in fully irrigated trees in field conditions increases the feasibility of using this parameter in automatic irrigation systems.     

Genetic analysis of physiological components of salt tolerance conferred by Solanum rootstocks. What is the rootstock doing for the scion?

Grafting desirable crop varieties on stress-tolerant rootstocks provides an opportunity to increase crop salt tolerance. Here, a commercial hybrid tomato variety was grafted on two populations of recombinant inbred lines developed from a salt-sensitive genotype of Solanum lycopersicum var. cerasiforme, as female parent, and two salt-tolerant lines, as male parents, from S. pimpinellifolium, the P population, and S. cheesmaniae, the C population, to identify an easy screening method for identifying rootstocks conferring salt tolerance in terms of fruit yield. Potential physiological components of salt tolerance were assessed in the scion: leaf biomass, [Na⁺], nutrition, water relations and xylem ABA concentration. A significant correlation between scion fruit yield and scion leaf fresh weight, water potential or the ABA concentration was found in the C population under salinity, but the only detected QTL did not support this relationship. The rootstocks of the P population clearly affected seven traits related to the sodium, phosphorous and copper concentrations and water content of the scion leaf, showing heritability estimates around 0.4 or higher. According to heritability estimates in the P population, up to five QTLs were detected per trait. QTLs contributing over 15% to the total variance were found for P and Cu concentrations and water content of the scion leaf, and the proportion of fresh root weight. Correlation and QTL analysis suggests that rootstock-mediated improvement of fruit yield in the P population under salinity is mainly explained by the rootstock’s ability to minimise perturbations in scion water status.     

Control of scion vigour by kiwifruit rootstocks is correlated with spring root pressure phenology

Root pressure was measured continuously over spring in eight clonal kiwifruit rootstocks selected from seven Actinidia species (A. chrysantha, A. deliciosa, A. eriantha, A. hemsleyana, A. kolomikta, A. macrosperma, A. polygama), using pressure transducers and miniature compression fittings. Rootstocks that promoted scion vigour developed root pressures up to 0.15 MPa before or during scion budburst, whereas those that reduced scion vigour developed root pressure up to 0.05 MPa only after scion shoot expansion. When several seasons were compared, the date of onset of root pressure and the magnitude of pressure achieved were consistent for each rootstock. Root pressure was first recorded between late July and early September in vigour-promoting rootstocks, while scion budburst and initial shoot growth were in late August and early September. Vigour-reducing rootstocks did not develop significant root pressure until October. The date of onset was similar for the grafted rootstock and ungrafted plant of the same clone, but was not clearly related to the timing of shoot growth by the ungrafted plant. In the grafted plants the leaf and xylem water potentials of the scion were more negative, midday turgor was 0.3-0.5 MPa lower, and wilting was sometimes observed in developing shoots growing on low-vigour rootstocks, indicating that water stress was contributing to reductions in growth. Leaf turgor was correlated with average root pressure but not pressure measured during the day, suggesting that root pressure was not supporting transpiration during peak flows and was, instead, indicative of higher root hydraulic conductance. The rapid temporal rise in root pressure observed each spring in the various rootstocks was not accompanied by changes in xylem sap solute potential, but when rootstock clones were compared those that developed higher root pressures had higher sap solute potentials. Xylem sap solute potential varied between rootstocks from -0.07 MPa to -0.15 MPa, while root pressures measured at the same time varied between 0.0 MPa and 0.09 MPa, suggesting that an osmotic mechanism could account for the observed root pressure. Differences in phenology between the rootstocks and scion appeared to account for the rootstock effects on shoot growth, and changes in root pressure provided a useful indication of seasonal changes in root hydraulic properties and solute transport behaviour.     

A Rootstock Provides Water Conservation for a Grafted Commercial Tomato (Solanum lycopersicum L.) Line in Response to Mild-Drought Conditions: A Focus on Vegetative Growth and Photosynthetic Parameters

The development of water stress resistant lines of commercial tomato by breeding or genetic engineering is possible, but will take considerable time before commercial varieties are available for production. However, grafting commercial tomato lines on drought resistant rootstock may produce drought tolerant commercial tomato lines much more rapidly. Due to changing climates and the need for commercial production of vegetables in low quality fields there is an urgent need for stress tolerant commercial lines of vegetables such as tomato. In previous observations we identified a scion root stock combination (‘BHN 602’ scion grafted onto ‘Jjak Kkung’ rootstock hereafter identified as 602/Jjak) that had a qualitative drought-tolerance phenotype when compared to the non-grafted line. Based on this initial observation, we studied photosynthesis and vegetative above-ground growth during mild-drought for the 602/Jjak compared with another scion-rootstock combination (‘BHN 602’ scion grafted onto ‘Cheong Gang’ rootstock hereafter identified as 602/Cheong) and a non-grafted control. Overall above ground vegetative growth was significantly lower for 602/Jjak in comparison to the other plant lines. Moreover, water potential reduction in response to mild drought was significantly less for 602/Jjak, yet stomatal conductance of all plant-lines were equally inhibited by mild-drought. Light saturated photosynthesis of 602/Jjak was less affected by low water potential than the other two lines as was the % reduction in mesophyll conductance. Therefore, the Jjak Kkung rootstock caused aboveground growth reduction, water conservation and increased photosynthetic tolerance of mild drought. These data show that different rootstocks can change the photosynthetic responses to drought of a high yielding, commercial tomato line. Also, this rapid discovery of one scion-rootstock combination that provided mild-drought tolerance suggests that screening more scion-rootstock combination for stress tolerance may rapidly yield commercially viable, stress tolerant lines of tomato.     

Genetic architecture of aerial and root traits in field-grown grafted grapevines is largely independent

Key message

QTLs were identified for traits assessed on field-grown grafted grapevines. Root number and section had the largest phenotypic variance explained. Genetic control of root and aerial traits was independent.

Abstract

Breeding new rootstocks for perennial crops remains challenging, mainly because of the number of desirable traits which have to be combined, these traits include good rooting ability and root development. Consequently, the present study analyzes the genetic architecture of root traits in grapevine. A segregating progeny of 138 F1 genotypes issued from an inter-specific cross between Vitis vinifera cv. Cabernet-Sauvignon × V. riparia cv. Gloire de Montpellier, used as rootstock, was phenotyped in grafted plants grown for 2 years in the field. Seven traits, related to aerial and root development, were quantified. Heritability ranged between 0.44 for aerial biomass to 0.7 for root number. Total root number was related to the number of fine roots, while root biomass was related to the number of coarse roots. Significant quantitative trait loci (QTLs) were identified for all the traits studied with some of them explaining approximately 20% of phenotypic variance. Only a single QTL co-localized for root and aerial biomass. Identified QTLs for aerial-to-root biomass ratio suggest that aerial and root traits are controlled independently. Genes known to be involved in auxin signaling pathways and phosphorus nutrition, whose orthologues were previously shown to regulate root development in Arabidopsis, were located in the confidence intervals of several QTLs. This study opens new perspectives for breeding rootstocks with improved root development capacities.

     

Role of Grafting in Resistance to Water Stress in Tomato Plants: Ammonia Production and Assimilation

In general, drought depresses nutrient uptake by the root and transport to the shoot due to a restricted transpiration rate, which may contribute to growth limitation under water deprivation. Moreover, water stress may also restrict the ability of plants to reduce and assimilate nitrogen through the inhibition of enzymes implicated in nitrogen metabolism. The assimilation of nitrogen has marked effects on plant productivity, biomass, and crop yield, and nitrogen deficiency leads to a decrease in structural components. Plants produce significant quantities of NH₄ ⁺ through the reduction of NO₃ ^? and photorespiration, which must be rapidly assimilated into nontoxic organic nitrogen compounds. The aim of the present work was to determine the response of reciprocal grafts made between one tomato tolerant cultivar (Lycopersicon esculentum), Zarina, and a more sensitive cultivar, Josefina, to nitrogen reduction and ammonium assimilation under water stress conditions. Our results show that when cv. Zarina (tolerant cultivar) was used as rootstock grafted with cv. Josefina (ZarxJos), these plants showed an improved N uptake and NO₃ ^? assimilation, triggering a favorable physiological and growth response to water stress. On the other hand, when Zarina was used as the scion (JosxZar), these grafted plants showed an increase in the photorespiration cycle, which may generate amino acids and proteins and could explain their better growth under stress conditions. In conclusion, grafting improves N uptake or photorespiration, and increases leaf NO₃ ^? photoassimilation in water stress experiments in tomato plants.