Tolerant Rootstocks Research Articles

Grafting onto an Appropriate Rootstock Reduces the Impact on Yield and Quality of Controlled Deficit Irrigated Pepper Crops

In this study, hybrid pepper rootstock NIBER® is tested for its ability to overcome water stress situations under soil conditions. The impact of deficit irrigation (DI) on yield and fruit quality, irrigation water use efficiency is evaluated, and consequently, the agronomic impact of employing water-stress tolerant rootstock is compared to ungrafted pepper plants. For this purpose, plants of the California-type sweet pepper ‘Maestral F1’ grafted onto NIBER® underwent a sustained DI regime during seasons 2018 and 2019 and were compared to their respective controls. Plants were drip-fertirrigated, and volumetric soil water content was continuously monitored by capacitance sensors. Gas exchange and leaf water potential measurements were taken early in the morning and midday 58, 79, and 114 days after transplanting. Plant and fruit dry biomass, marketable quality, blossom-end rot incidence and harvest index were also determined. For consecutive years, our results confirmed that grafting a pepper cultivar onto an appropriate rootstock (NIBER® in this case) as part of a DI strategy can overcome the negative effects of sustained water stress conditions. The plant biomass production and fruit yields of grafted plants were less affected by DI due to less sensitivity to water stress. This can be attributed to a less marked reduction in shoot dry weight in the grafted plants, which allowed greater whole photosynthesis by maintaining sink activity compared to ungrafted plants.

Desempenho produtivo de maracujazeiro amarelo em área com Fusarium solani

The use of tolerant rootstocks has shown good results in the control of Fusarium wilt in yellow passion fruit, which is considered one of the main problems in the crop as it affects the plant’s root system and has no chemical control. The present study aimed to evaluate the survival rates, the agronomic performance of the plants and the physical characteristics of the yellow passion fruit (Passiflora edulis Sims) grafted on different rootstocks in area with Fusarium wilt. The experiment was carried in Pracinha, in the State of São Paulo, Brazil, from August 2014 to May 2015, and a randomized block design was adopted, with five treatments, five replications and four plants per plot. The treatments were constituted by the following rootstocks: Passiflora alata Dryand, Passiflora gibertii N.E. Brown, Passiflora caerulea Linnaeus, double grafting P. gibertii x P. edulis and plants without grafting. The stem diameter of rootstock and the graft, the lenght of secondary branches, the number of tertiary branches, the number of surviving plants, the longitudinal and transversal diameters of the fruits, the number and mass of fruits and the productivity were evaluated. The largest diameter of the rootstock was observed in Passiflora alata while in the graft it was in plants of Passiflora edulis. The length of the secondarty branches and the number of tertiary branches were affected by the type of grafting and the rootstock used. The highest survival rates were observed in Passiflora alata (90%) and Passiflora gibertii (100%). The highest number of fruits per plant and productivity occurred in plants grafted on Passiflora gibertii. The adoption of double grafting using Passiflora gibertii x Passiflora edulis and simple grafting with Passiflora caerulea were not effective in the control of this disease. The species Passiflora gibertii and Passiflora alata showed the potential to be used as a rootstock for yellow passion fruit.

Comprehensive analysis of the apple rhizobiome as influenced by different Brassica seed meals and rootstocks in the same soil/plant system

Replant disease refers to the poor growth of trees when attempting to establish the same or related species on old orchard sites. The use of pre-plant Brassicaceae seed meal (SM) soil amendments in combination with apple replant disease-tolerant rootstock genotypes has been shown to be a promising strategy for the control of apple replant disease (ARD). However, optimizing microorganism-driven protection of apple roots from infection by multiple soil-borne pathogens requires a more comprehensive understanding of how “effective” vs. “ineffective” Brassicaceae seed meal × rootstock genotype disease control systems modulate the composition of rhizosphere microbial communities. In particular, the community of oomycetes associated with the apple rhizosphere remains relatively unexplored compared with bacteria and fungi. To address these issues, we sequenced the root associated bacterial, fungal, and oomycete communities of apple replant disease tolerant (G.210) and susceptible (M.26) rootstocks when grown in an orchard replant soil amended with different Brassicaceae seed meal formulations (Brassica juncea + Sinapis alba, B. juncea, and Brassica napus) previously shown to provide varying levels of replant disease control. Multiple microbial components were associated with observed growth differences between “effective” and “ineffective” disease control systems including the absolute abundance of Ilyonectria/Cylindrocarpon in fine root tissue. Amplicon sequencing provided a more detailed picture of the genetic diversity of oomycete groups in the apple rhizosphere than previously appreciated, and highlighted the variability in oomycete community structure between different rootstock × seed meal disease control systems. In Brassica juncea + Sinapis alba SM-structured rhizospheres, the ARD-tolerant rootstock (G.210) harbored higher relative abundances of Peronosporales with reduced potential to infect apple roots and incite replant disease (such as Peronospora destructor and P. acanthicum), whereas the Peronosporales community associated with the sensitive rootstock (M.26) was dominated by the ARD-specific pathogen Phytophthora cactorum. In addition, Brassica juncea + Sinapis alba SM-structured microbiomes were characterized by numerous bacterial and fungal taxa with the potential for biocontrol, biodegradation and bioremediation. Taken together, these results support the hypothesis that particular Brassicaceae SM soil amendments not only provide “effective” disease control, but also promote microbiomes which are likely to contribute to long-term orchard soil health in many other ways. Overall, this comprehensive analysis highlights the significance of the rootstock × seed meal interaction on bacterial, fungal, and oomycete communities within the apple rhizosphere of “effective” vs. “ineffective” disease control systems and the potential influence of these elements on the dynamics of apple replant disease.

Role of rootstocks to mitigate biotic and abiotic stresses in tropical and subtropical fruit crops: A review

Fruit cultivation not only plays a crucial role in nutritional security but also offers employment opportunities, higher income and productivity to the farming community. Biotic and abiotic stresses are the most ominous factors in fruit production, which reduces the growth and productivity thereby resulting in an impact on global fruit production and availability. Biotic and abiotic stresses, including drought, extremes of temperature, various pest and diseases, salinity in soil and water are problems which are becoming acute. There is an urgent need to improve biotic and abiotic stress tolerance in fruit crops by using traditional breeding and biotechnology approaches like gene silencing and transgrafting. Nowadays, the virus resistance transgenic rootstocks are developed by using small interfering RNA s (silencing RNA) method. Rootstock breeding in fruit crops is a great challenge due to difficulty in identification of tolerant or resistance rootstock for various purposes. In this paper, we have discussed the various biotic and abiotic stresses, resistance mechanisms, and available resistant rootstocks so far as well as challenges in rootstock breeding which can be helpful to manage stress conditions in fruit cultivation. Further research is needed to develop the resistance rootstocks by using modern rootstock breeding methods with various biotechnological approaches.

Rootstocks increase grapevine tolerance to NaCl through ion compartmentalization and exclusion

The productivity of Vitis vinifera L. is limited by salinity, especially under water and drainage deficits, and could aggravate with climate change. The use of tolerant rootstocks is a strategy against salinity that helps yield maintenance. Some Argentinean grapevine cultivars show tolerance to salinity, although the mechanisms are yet unknown. The physiology of Malbec vines was evaluated with 4 V. vinifera rootstocks: Torrontes Riojano (TR) and Torrontes Sanjuanino (TS) Argentine varieties, and the hybrids 3309 Courdec (3309C, salinity sensitive) and 1103 Paulsen (1103P, tolerant), submitted to NaCl 0, 50 or 100 mM during 65 days. Mild and high salinity levels reduced vegetative growth (50 and 70%, respectively), photosynthesis and leaf water content. Midday ΨL reached − 1.16 MPa (moderate water stress) with 100 mM NaCl, which expressed as oxidative damage in mature leaves, thus affecting protein content, membrane integrity and lipid peroxidation. Proline accumulation in leaves increased in 1103P and TR under 50 mM, while 1103P showed the highest value in 100 mM NaCl. An increased vegetative expression and vigor were induced by TS. Accumulation of Na+ and Cl− ions in roots was found in TR and TS, suggesting a compartmentalization strategy, while 1103P excluded them.

Determination of Criteria and Drought Tolerance of Prope-Legitimate Cocoa Seed Through Polyethylene Glycol Induction

The availability of drought tolerant rootstock becomes one of solution to obtain tolerant cocoa clone at drought condition. The production of rootstock is easier and faster by using prope-legitimate seeds as plant materials. Seed germination selection phase can accelerate the obtainment of tolerant cocoa rootstocks. The tolerance trait of prope-legitimate seeds can be determined by seed germination on media induced by polyethylene glycol (PEG) solution. To determine the tolerant seeds, it is effective by using a specific character as selection criteria. This study aimed to obtain criteria and selection character to determine droughttolerant characteristic of prope-legitimate seed through PEG 6000 induction in the germination phase. The research was conducted at the Agronomy Laboratoryof the Indonesian Coffee and Cocoa Research Institute, Jember, East Java, Indonesia, used split plot design with five replications as experimental design. The main plot was solution of 0% and 6% PEG 6000, while the subplot were prope-legitimate seeds of 13 cocoa clones. The result showed that germination ability and sprout fresh weight were suitable as selection criteria to determine tolerant characteristic of prope-legitimate seeds to drought stress. Based on the value of tress susceptible index and clustering analysis, the tested prope-legitimate seeds were divided into three groups. The group of tolerant genotype consisted of Sca 06, while the group of medium tolerant were ICCRI 03, Sulawesi 02, KW 641, TSH 858, KEE 02, Sulawesi 03, and KW 617. The susceptible group consisted of six genotypes, namely ICS 60, KKM 22, KW 516, Sulawesi 01, and MCC 02.

COMPARATIVE GROWTH PERFORMANCE AND ACTIVITY OF DEFENSE RELATED ENZYMES AND GENE EXPRESSION IN RUBBER CLONES AGAINST RIGIDOPORUS MICROPORUS INFECTION

Rigidoporus microporus is the causal agent of rubber white root disease (WRD). Control of this is commonly carried out by chemical treatment. The use of tolerant rootstocks may present an effective method to lessen its impact. The screening of rubber rootstocks for tolerance of WRD was investigated by both defense-related enzymes and gene expression, and assessment of disease symptoms.Two recommended clones in Thailand (RRIT251 and RRIT408) and RRIM623 (Malaysian clone) were screened and compared with susceptible clones (RRIM600 and BPM24) and tolerant clone (PB5/51) by inoculating young rubber seedling with R. microporus. The expression of PRs and PAL were analyzed at 0, 1, 3, 5, and 7 days post inoculation (dpi) along with the defense-related enzyme activities. Based on observed transcriptional level of PRs and PAL genes, CHI, PAL, and POD enzyme activities, and also evidence from WRD symptom assessment in the field, we concluded that PB 5/51 had the best tolerance with the lowest disease incidence, high PAL and POD enzyme activities, with the next best being RRIM 623 and RRIT 251, respectively. Meanwhile, BPM 24, RRIM 600, and RRIT 408 clones are moderately susceptible to WRD. The study introduces new possibilities for the control of WRD using alternative rubber rootstock clones.

Genomics-assisted prediction of salt and alkali tolerances and functional marker development in apple rootstocks

BackgroundSaline, alkaline, and saline-alkaline stress severely affect plant growth and development. The tolerance of plants to these stressors has long been important breeding objectives, especially for woody perennials like apple. The aims of this study were to identify quantitative trait loci (QTLs) and to develop genomics-assisted prediction models for salt, alkali, and salt-alkali tolerance in apple rootstock.ResultsA total of 3258 hybrids derived from the apple rootstock cultivars ‘Baleng Crab’ (Malus robusta Rehd., tolerant) × ‘M9’ (M. pumila Mill., sensitive) were used to identify 17, 13, and two QTLs for injury indices of salt, alkali, and salt–alkali stress via bulked segregant analysis. The genotype effects of single nucleotide polymorphism (SNP) markers designed on candidate genes in each QTL interval were estimated. The genomic predicted value of an individual hybrid was calculated by adding the sum of all marker genotype effects to the mean phenotype value of the population. The prediction accuracy was 0.6569, 0.6695, and 0.5834 for injury indices of salt, alkali, and salt–alkali stress, respectively. SNP182G on MdRGLG3, which changes a leucine to an arginine at the vWFA-domain, conferred tolerance to salt, alkali, and salt-alkali stress. SNP761A on MdKCAB, affecting the Kv_beta domain that cooperated with the linked allelic variation SNP11, contributed to salt, alkali, and salt–alkali tolerance in apple rootstock.ConclusionsThe genomics-assisted prediction models can potentially be used in breeding saline, alkaline, and saline-alkaline tolerant apple rootstocks. The QTLs and the functional markers may provide insight for future studies into the genetic variation of plant abiotic stress tolerance.

Intra and Inter-specific Variability of Salt Tolerance Mechanisms in Diospyros Genus

Saline stress is one of most important problems that agriculture must face in the context of climate change. In the Mediterranean basin, one of the regions most affected, persimmon production can be compromised by this effect, due to the limited availability of salt tolerant rootstocks. Seedlings coming from four populations from the Diospyros genus have been exposed to salt stress in order to identify salt tolerance genotypes within these populations. Morphological, physiological, and transcriptomic approaches have revealed different mechanisms of tolerance among the population studied. An HKT1-like gene has been shown to have different root expression related to the salt tolerance phenotypes among and within populations. Additionally, we have observed differences in salt-responsive expression among PIP aquaporin genes. Genetic variability for salt tolerance can be generated in Diospyros species through crossings and used for overcome salt stress. Furthermore, differences in water use efficiency (WUE) have been obtained between and within populations. The information gathered at transcriptomic and physiological level demonstrated natural and heritable variability among Diospyros genus which is the key for salt-tolerant rootstock breeding programs.

Phytophthora nicotianae Infection of Citrus Leaves and Host Defense Activation Compared to Root Infection.

Currently, little is known about the host pathogen interaction between Phytophthora spp. and citrus roots versus leaves. Therefore, we compared the molecular events occurring in citrus roots and leaves after zoospore inoculation with Phytophthora nicotianae. We analyzed the physical characteristics and genetic responses to P. nicotianae infection of leaves and roots for susceptible and tolerant citrus rootstocks to examine the potential for leaves to model root responses to P. nicotianae infection. Leaves responded faster and stronger to P. nicotianae infection than roots, and leaves showed greater differential response than roots. In addition to differences in hormonal responses, sugar, phospholipase D (PLD), and phospholipase A (PLA) involvement in the interaction between citrus and P. nicotianae was identified. This work, for the first time, creates a solid P. nicotianae zoospore infection protocol, reports P. nicotianae infection on citrus leaves through stomata, and provides evidence that different host organs respond to the pathogen differentially in timing and magnitude. This work identifies the hormones, sugars, pathogenesis-related genes, PLDs, and PLAs that are involved in the molecular events occurring in citrus under infection of P. nicotianae zoospore, and advances our understanding of the mechanisms underlying the interaction.

Assessment of Fusarium wilt resistant Citrullus sp. rootstocks for yield and quality traits of grafted watermelon

The experiments were conducted to characterize eighteen Fusarium wilt resistant Citrullus accessions for their root parameters and to evaluate their performance as rootstocks for vigour, earliness, quality, yield and tolerance to sudden wilt disease of grafted watermelon in comparison with Cucurbita and Lagenaria rootstocks. Significant variations were observed among the rootstocks for all the root traits under study. The length and diameter of the rootstock hypocotyl were found to be an indicator of the robustness of the root system. A significant influence on vine length and earliness of the grafted crop was observed across different rootstocks. The grafts on Citrullus rootstocks could maintain the oblong fruit shape of the scion compared to those onto Cucurbita hybrid and Lagenaria rootstocks which yielded from flat-globe to spherical shaped fruits. A wide variation of TSS and carotenoid content was observed upon grafting while the pulp pH remained largely unaffected. An increase of average fruit weight by 82.37% and yield per plant by 112.15% in grafts onto RS-18 and RS-10 respectively were recorded. The grafts onto rootstocks viz., RS-10, RS-21 and RS-25 also exhibited reduced severity of sudden wilt; hence are of value in regions prone to both Fusarium wilt and sudden wilt diseases. Overall, the Citrullus accessions viz., RS-10, RS-11 and RS-18 were found to be promising in comparison to Cucurbita hybrids and Lagenaria rootstocks. Grafting onto resistant rootstocks can help in environment-friendly management of Fusarium and sudden wilt diseases in watermelon without compromising the yield and quality.

Grapevine viruses: a multitude of diverse species with simple but overall poorly adopted management solutions in the vineyard

Eighty-six viruses have been isolated to date from grapevines worldwide. Some of these viruses are associated with economically damaging diseases such as leaf mottling and deformation, vein clearing, leafroll, degeneration and red blotch. They belong to the families Betaflexiviridae, Caulimoviridae, Closteroviridae, Secoviridae and Geminiviridae, and are transmitted by diverse vectors such as mealybugs (Hemiptera: Pseudococcidae), soft scale insects (Hemiptera: Coccidae), an aphid (Hemiptera: Aphididae), dagger nematodes (Nematoda: Longidoridae), a treehopper (Hemiptera: Membracidae) and eriophyid mites (Acari: Eriophyidae). Management of these viruses primarily relies on preventive measures to limit their presence in the propagation and planting material. In the vineyard, specific disease scenario-based strategies such as rogueing in combination with agrochemical applications to limit vector populations, if appropriate, and the removal of entire parcels and their replacement with clean planting material, including vector tolerant rootstocks, if opportune, are implemented to reduce their incidence, prevent their spread and mitigate their impact. These solutions are simple but their implementation is often suboptimal and their adoption is largely low. Some of the uncertainties that hinder their endorsement are captured here, and options to refine them and to enhance their adoption are discussed.

The Use of a Tomato Landrace as Rootstock Improves the Response of Commercial Tomato under Water Deficit Conditions

Grafting onto drought tolerant rootstocks has been proposed as a useful strategy to overcome future water scarcity periods. The ‘de Ramellet’ tomato is a drought tolerant landrace selected under semiarid Mediterranean summer conditions under rain-fed or low irrigation. In this manuscript, the responses of a commercial hybrid ‘de Ramellet’ genotype grafted onto a traditional ‘de Ramellet’ (RL) and a commercial Maxifort (Mx) tomato rootstocks under commercial greenhouse conditions are studied. Non-grafted (NON) and self-grafted (SELF) plants were used as controls. Two water regimes were established: well-watered (WW, covering plant water demands) and water deficit (WD, reducing 50% irrigation as compared to WW). The results confirm an improvement in agronomic performance of Mx as compared to NON, but also show a similar improving effect of RL. Grafting enhanced plant growth regardless of the rootstock under WW conditions. Similarly, water-use efficiency (assessed as leaf carbon isotope composition) increased in grafted plants under WD treatment as compared to NON. Despite the lack of significant differences, RL tended to promote higher fruit production and fruit number than Mx, irrespective of the water treatment, whereas RL was the single graft combination with higher fruit production than NON under WD. In conclusion, the results uncover the potential of drought-adapted landraces to be used as rootstocks in order to increase plant growth and fruit production under both well-watered and water deficit cultivation conditions.

Management of Verticillium Wilt of Avocado Using Tolerant Rootstocks.

The global avocado industry is growing, and farmers are seeking to expand their plantations. However, many lands suitable for avocado planting were previously cultivated with hosts of the soil-borne fungal pathogen Verticillium dahliae, which is the causal agent of Verticillium wilt (VW). VW can seriously impair avocado orchards, and therefore, planting on infested soil is not recommended. The use of different rootstock types allows avocado cultivation in various regions with diverse biotic and abiotic constraints. Hence, we tested whether genetic variance among rootstocks may also be used to manage avocado VW. Six hundred trees, mostly Hass and some Ettinger, grafted on 23 selected rootstocks were evaluated for five years in a highly V. dahliae-inoculated plot for VW symptoms, fungal infection, and productivity. The selected rootstocks displayed a significant variation related to VW tolerance, and productive avocado rootstocks with potential VW tolerance were identified. Moreover, the rootstock productivity appears to correlate negatively to the susceptibility level. In conclusion, planting susceptible rootstocks (e.g., VC66, VC152, and VC26) in infested soil increases the likelihood of massive tree loss and low productivity. Whereas, tolerant rootstocks (e.g., VC804 and Dusa) may restrict VW and enable avocado cultivation on infested soils.

A cross population between D. kaki and D. virginiana shows high variability for saline tolerance and improved salt stress tolerance.

Persimmon (Diospyros kaki Thunb.) production is facing important problems related to climate change in the Mediterranean areas. One of them is soil salinization caused by the decrease and change of the rainfall distribution. In this context, there is a need to develop cultivars adapted to the increasingly challenging soil conditions. In this study, a backcross between (D. kaki x D. virginiana) x D. kaki was conducted, to unravel the mechanism involved in salinity tolerance of persimmon. The backcross involved the two species most used as rootstock for persimmon production. Both species are clearly distinct in their level of tolerance to salinity. Variables related to growth, leaf gas exchange, leaf water relations and content of nutrients were significantly affected by saline stress in the backcross population. Water flow regulation appears as a mechanism of salt tolerance in persimmon via differences in water potential and transpiration rate, which reduces ion entrance in the plant. Genetic expression of eight putative orthologous genes involved in different mechanisms leading to salt tolerance was analyzed. Differences in expression levels among populations under saline or control treatment were found. The ‘High affinity potassium transporter’ (HKT1-like) reduced its expression levels in the roots in all studied populations. Results obtained allowed selection of tolerant rootstocks genotypes and describe the hypothesis about the mechanisms involved in salt tolerance in persimmon that will be useful for breeding salinity tolerant rootstocks.

Grafting Tomato as a Tool to Improve Salt Tolerance

Salinity in soil or water is a serious threat to global agriculture; the expected acreage affected by salinity is about 20% of the global irrigated lands. Improving salt tolerance of plants through breeding is a complex undertaking due to the number of traits involved. Grafting, a surgical mean of joining a scion and rootstock of two different genotypes with the desired traits, offers an alternative to breeding and biotechnological approaches to salt tolerance. Grafting can also be used to circumvent other biotic and abiotic stresses. Increasing salinity tolerance in tomato (Solanum lycopresicum L.), a highly nutritious and economical vegetable, will have greater impact on the vegetable industry, especially in (semi) arid regions where salinity in soil and water are more prevalent. Besides, plants also experience salt stress when water in hydroponic system is recycled for tomato production. Grafting high yielding but salt-susceptible tomato cultivars onto salt-resistant/tolerant rootstocks is a sustainable strategy to overcome saline stress. Selection of salt-tolerant rootstocks though screening of available commercial and wild relatives of tomato under salt stress conditions is a pre-requisite for grafting. The positive response of grafting exerted by tolerant rootstocks or scion-rootstock interactions on yield and fruit characteristics of tomato under saline conditions is attributed to several physiological and biochemical changes. In this review, the importance of tomato grafting, strategies to select appropriate rootstocks, scion-rootstock interaction for growth, yield and quality characteristics, as well as the tolerance mechanisms that (grafted) plants deploy to circumvent or minimize the effects of salt stress in root zones are discussed. The future challenges of grafting tomato are also highlighted.

Vegetative and reproductive performance of species of the genus Passiflora

As passion fruit gains market share, it becomes important to evaluate the agronomic and phenological traits of cultivated and wild genotypes for genetic improvement and understand the influence of time of cultivation on plant behavior. This study aimed to investigate agronomic and phenological parameters of Passiflora suberosa, P. alata, P. maliformis, P. quadrangularis, P. foetida, P. mucronata, P. cincinnata and hybrids BRS Rubi do Cerrado, BRS Gigante Amarelo, and BRS Pérola do Cerrado. Key traits for genetic improvement were also assessed. Two experiments were carried out for 12 months, the first starting in December 2015 and the second in May 2016. Plots were organized in a randomized block design, and analyses were performed monthly. The following vegetative characteristics were evaluated: length and diameter of orthotropic and plagiotropic branches, internode length, leaf length and width of orthotropic and plagiotropic branches, and number of plagiotropic branches. Flowering and fruiting were dichotomized as presence or absence. Ten microsatellite markers were used to estimate genetic diversity. The wild species P. suberosa differed markedly from cultivated genotypes and had the lowest values for all vegetative parameters. The hybrid BRS Gigante Amarelo differed from other plants in orthotropic branch diameter. In Experiment II, plants differed in plagiotropic branch diameter and leaf length of plagiotropic branches. Most plants had similar cumulative growth curves as well as flowering and fruiting patterns. Clustering of genotypes based on microsatellite data revealed similarities in growth parameters, flowering time, and fruiting time. Some genotypes showed similar phenological patterns and are potential candidates for developing novel hybrids, and some wild species may find application as resistant and tolerant rootstocks.

Pistacia vera L. genotypes; a potential rival for UCB-1 rootstock for cultivating under salt stress conditions

Abstract UCB-1(P. integerrima ×P. atlantica) is considered as a high tolerant hybrid rootstock to salt stress from Pistacia genus that widely used as rootstock for pistachio cultivars. This study was conducted to compare the response of five P. vera salt-tolerant genotypes with UCB-1 under salt stress. The experiment was carried out as a completely randomized design with factorial arrangement and four replications. Eight months old pistachio genotypes namely Akbari, Ahmad-Aghaee, Italiyayi, Ghazvini, Badami, and UCB-1 were subjected to salinity stress at three salinity levels (0.5 (control), 12 and 18 dS m−1) for 75 days. In order to select the most tolerant genotypes, some physiological and biochemical factors were measured. Leaf water potential, chlorophyll, and K content decreased while leaf total proline, phenolic content, lipid peroxidation, antioxidant enzyme activities, and Na leaf content increased with raising salinity levels regardless of genotypes. Comparison between genotypes indicated that for most of the measured factors, UCB-1 and Akbari showed better performance comparing to others. However, there was no significant difference between Akbari and UCB-1 regarding salt tolerance that shows the high potential of P. vera genotypes to be used instead of UCB-1. Furthermore, there was no significant difference between Akbari, Ahmad-Aghaee, and UCB-1 in malondialdehyde (MDA) and total phenolic content as well as ascorbate peroxidase (APX) activity. In conclusion, the studied rootstocks can be ordered based on their tolerance to salinity as the following: UCB-1 = Akbari > Ahmad-Aghaee > Italiyayi > Ghazvini > Badami.

UTILIZING BIOTECHNOLOGY TOOLS FOR SILECTING SALT TOLERANT ROOTSTOCK OF PEACH HASSAWI

This study was carried out with an aim of evaluation of performance of Hassawi peach rootstocks and testing their variance towards salinity stress thus to find out a quick effective modern technique for their reculture and re-propagation again in the region. Eight different concentrations of sodium chloride (NaCl) that represent progressive gradual levels of salinity were used to investigate tolerability of the explants towards variant levels of salinity stress. Thus to evaluate the performance of these Hassawi peach rootstocks (peach, plum ]ghwj[, and almond). Date and results declared the general superiority of bitter almond to the other rootstocks, as it vitally survived and tolerated salinity to 3500 ppm NaCl, followed by peach that tolerated salinity to 2500 ppm, and eventually ghwj that just survived with maximum tolerance of 2000 ppm of NaCl. The study recommends to count on bitter almond as a salinity tolerant rootstock followed by peach for grafting Hassawi peach rootstocks for its regeneration again in Al-Ahsa oasis, and to exclude plum rootstock because of its low salinity tolerance besides its very low harmonization with peach that negatively affect grafting process.

Chlorophyll Fluorescence, Photosynthesis and Growth of Tomato Plants as Affected by Long-Term Oxygen Root Zone Deprivation and Grafting

A greenhouse experiment was conducted to study the effects of the O2 root zone level and grafting on chlorophyll fluorescence, photosynthesis and growth of cherry tomato grown in a hydroponic system. Two O2 concentrations in the root zone, namely Ox (saturation level) and Ox- (2–3 mg L−1), were applied for 30 days on self-grafted cherry tomato Dreamer or grafted onto the hybrids Arnold, Beaufort, Maxifort and Top Pittam. Root hypoxia increased minimum fluorescence (by 10%) while it decreased variable fluorescence and the maximum quantum yield of PSII (up to 16 and 8%, respectively). Moreover, it reduced leaf photosynthesis, transpiration and stomatal conductance (by 12, 17 and 13%, respectively), whereas it increased leaf electrolyte leakage (by 2.1%). The graft combinations showed a different ability in buffering the effects of root hypoxia on plant growth and related components, and these differences were related to their root biomass. The minimum fluorescence was negatively correlated to plant growth, so it may be a useful indicator to select tolerant rootstocks to root hypoxia. Our results suggest the occurrence of both diffusive and metabolic constraints to tomato photosynthesis under root hypoxia, a condition that can be mitigated by selecting rootstocks with a more developed root system.