Grafting between tobacco plants to enhance salinity tolerance

We analysed the technique of grafting as a tool to increase salt-stress resistance in tobacco plants. With this aim, we performed two experiments. First, we selected, from among 6 commercial tobacco cultivars (cv. BB-162, cv. H-20, cv. Jarandilla, cv. ZB-3, cv. Havana II and cv. Havana 307) those most tolerant and sensitive to salinity, studying the response of certain nutritional and biochemical indicators of resistance in these plants. In the second experiment, we analysed the response to salinity in grafted tobacco plants using the rootstock of the most tolerant plants, and the scion of the most sensitive ones. In addition, these plants were subjected to salinity to test the viability and efficiency of this grafting technique, assessing the production of foliar biomass and the different quality parameters in this crop. In the first experiment, we found that the most tolerant tobacco cultivars were cv. BB-162 and cv. H-20, which were characterized by reduced uptake and foliar accumulation of Na⁺ and Cl⁻, together with greater synthesis of sucrose and proline, thereby reducing lipid peroxidation and thus oxidative damage, reflected in higher foliar biomass with respect to the other cultivars studied (primarily cv. Jarandilla, defined as the most salt-sensitive). In the second, we demonstrated that the grafting of salt-sensitive tobacco scions to salt-tolerant rootstocks improves the production and quality of tobacco leaves under conditions of saline stress. Our results show that the rootstocks cv. BB-162 and cv. H-20 best induced salt resistance in tobacco cv. Jarandilla, registering the lowest foliar concentrations of Na⁺ and Cl⁺, the lowest lipid peroxidation, and the highest proline and sugar concentrations. Overall, this is reflected in better biomass production and quality of the aerial part of the plant.     

Grafting raises the salt tolerance of tomato through limiting the transport of sodium and chloride to the shoot

With the aim of determining whether grafting could improve salinity tolerance of tomato (Lycopersicon esculentum Mill.), and what characteristics of the rootstock were required to increase the salt tolerance of the shoot, a commercial tomato hybrid (cv. Jaguar) was grafted onto the roots of several tomato genotypes with different potentials to exclude saline ions. The rootstock effect was assessed by growing plants at different NaCl concentrations (0, 25, 50, and 75 mM NaCl) under greenhouse conditions, and by determining the fruit yield and the leaf physiological changes induced by the rootstock after 60 d and 90 d of salt treatment. The grafting process itself did not affect the fruit yield, as non-grafted plants of cv. Jaguar and those grafted onto their own root showed the same yield over time under non-saline conditions. However, grafting raised fruit yield in Jaguar on most rootstocks, although the positive effect induced by the rootstock was lower at 25 mM NaCl than at 50 and 75 mM NaCl. At these higher levels, the plants grafted onto Radja, Pera and the hybrid VolgogradskijxPera increased their yields by approximately 80%, with respect to the Jaguar plants. The tolerance induced by the rootstock in the shoot was related to ionic rather than osmotic stress caused by salinity, as the differential fruit yield responses among graft combinations were mainly related to the different abilities of rootstocks to regulate the transport of saline ions. This was corroborated by the high negative correlation found between fruit yield and the leaf Na(+) or Cl(-) concentrations in salt-treated plants after 90 d of salt treatment. In conclusion, grafting provides an alternative way to enhance salt tolerance, determined as fruit yield, in the tomato, and evidence is reported that the rootstock is able to reduce ionic stress.     

Does grafting provide tomato plants an advantage against H2O2 production under conditions of thermal shock?

Non-grafted tomato plants ( Lycopersicon esculentum L. cv. Tmknvf₂) and grafted tomato plants ( L. esculentum L. cv. Tmknvf₂ ×  L. esculentum L. cv. RX-335) were grown for 30 days at three different temperatures (10°C, 25°C and 35°C). In the leaves of these plants, the enzymatic activities of SOD, GPX, CAT, APX, DHAR and GR were analysed, as were the concentrations of total H₂O₂, ascorbate and glutathione as well as foliar DW. Regardless of whether the plant was grafted or not, our results indicate that the thermal stress occurred mainly at 35°C, with the following effects: (1) high SOD activity; (2) H₂O₂ accumulation; (3) foliar-biomass reduction; (4) low GPX, CAT, APX, DHAR and GR activities; and (5) high concentrations of ascorbate and glutathione. In addition, our data show these effects to be much weaker in grafted than in non-grafted plants, directly reflected in greater biomass production. Therefore, the use of grafted plants under excessively high temperatures may offer an advantage over non-grafted plants in terms of resistance against thermal shock.     

Grafting tomato (Solanum lycopersicum) onto the rootstock of a high-altitude accession of Solanum habrochaites improves suboptimal-temperature tolerance

Grafting is regarded as a promising tool to broaden the temperature optimum of elite tomato cultivars. However, suitable low-temperature tolerant tomato rootstocks are not yet available and its breeding is hampered by a lack of variation in low-temperature tolerance within the cultivated tomato. In this study, therefore, the impact of grafting tomato (Solanum lycopersicum Mill. cv. Moneymaker, Sl) onto the rootstock of a cold-tolerant high-altitude accession of a related wild species (Solanum habrochaites LA 1777 Humb. & Bonpl., Sh) was examined at different combinations of optimal (25 °C) and/or suboptimal (15 °C) air/root-zone temperatures (RZT), i.e. 25/25, 25/15, 15/25 and 15/15 °C. Self-grafted tomato plants were used as controls. Both scion/rootstock combinations, Sl/Sl and Sl/Sh, were grown hydroponically and compared for biomass production and partitioning, plant morphology, carbohydrate partitioning and leaf C and N status. Grafting tomato onto Sh increased the relative growth rate of shoots with 26 and 11% at 25/15 and 15/15 °C, respectively. This increase could be attributed to stimulation of the leaf expansion rate. Graft combinations with Sh rootstocks were characterized by higher root mass ratios, particularly at 15 °C RZT. Suboptimal RZT strongly reduced the relative growth rate of Sl roots but not of Sh. This was correlated to differences in inhibition of root elongation. In contrast to tomato grafted onto Sh, leaf total C and total N concentrations increased in self-grafted tomato plants in response to 15 °C RZT. The increase in leaf total C concentration of Sl/Sl graft combinations at 15 °C RZT could be ascribed largely to starch accumulation. This study illustrates that growth of vegetative tomato plants at suboptimal temperature is for a significant part inhibited by its poor root development. Grafting tomato onto a low-temperature rootstock provides an alternative tool to reduce, in part, the grow-limiting effects of suboptimal RZ temperature on the shoot. To improve the low-temperature tolerance of existing commercial tomato rootstocks, S. habrochaites LA 1777 appeared to be a valuable germplasm pool.     

Investigation of the ameliorating effects of eggplant, datura, orange nightshade, local Iranian tobacco, and field tomato as rootstocks on alkali stress in tomato plants

Among the most important quality parameters of irrigation water used for greenhouse crops, alkalinity of water is considered critical due to its impact on soil or growing medium solution pH. In this study, plant growth, Fe content, photosynthetic pigment content, maximal quantum yield of PSII photochemistry (F_v/F_m), performance index (PI), leaf relative water content (LRWC), and soluble sugars concentration were investigated in nongrafted and grafted tomato (Lycopersicon esculentum Mill. cv. Red stone) plants onto five rootstocks of eggplant (Solanum melongena cv. Long purple), datura (Datura patula), orange nightshade (Solanum luteum Mill.), local Iranian tobacco (Nicotiana tabacum), and field tomato (Lycopersicon esculentum Mill. cv. Cal.jn3), exposed to 0, 5, and 10 mM NaHCO₃ concentrations, to determine whether grafting could improve alkalinity tolerance of tomato. Significant depression of leaf area, leaf and stem dry mass, shoot and root Fe content and LRWC under high NaHCO₃ level was observed in both grafted and ungrafted plants. The highest reduction in the shoot Fe content was observed at 10 mM sodium bicarbonate in control plants (greenhouse tomato). Moreover, at high HCO₃ ^? level, the highest percentage of LRWC reduction was also recorded in ungrafted plants. Values of F_v/F_m and PI decreased significantly at 5 and 10 mM NaHCO₃ irrespective of rootstock type. The present study revealed that soluble sugars content, photosynthetic pigments content, F_v/F_m and PI values in plants grafted onto datura rootstock were higher than those in nongrafted and rest of the grafted plants. Thus, the use of datura rootstock could provide a useful tool to improve alkalinity tolerance of tomato plants under NaHCO₃ stress.     

Transmission of RNA silencing signal through grafting confers virus resistance from transgenically silenced tobacco rootstocks to non-transgenic tomato and tobacco scions

We examined the transmission of RNA silencing signal in non-transgenic tomato and tobacco scions grafted onto the tobacco Sd1 rootstocks, which is silenced in both NtTOM1 and NtTOM3 required for tobamovirus multiplication. When the non-transgenic tomato scions were grafted onto the Sd1 rootstocks, RT-PCR analysis of the scions showed the reduced level of mRNA compared with that before grafting in both LeTH3 and LeTH1, tomato homologs of NtTOM1 and NtTOM3, respectively. siRNAs from both genes were detected in the scions after grafting but not before grafting. Further tomato scions were inoculated with Tomato mosaic virus (ToMV) and used for virus infection. They showed very low level of virus accumulation. Necrotic responding tobacco to tobamovirus was grafted onto the rootstock of Sdl. RT-PCR analysis showed low level expression of both NtTOM1 and NtTOM3 in the scions but siRNA was detected after grafting. When the leaves of scions were inoculated with ToMV or Tobacco mosaic virus, they produced very few local necrotic lesions (LNLs) while the control scions did many LNLs. These results suggest that RNA silencing was transmitted to non-transgenic tomato and tobacco scions after grafting onto the Sd1 rootstocks and that virus resistance was induced in the scions.     

A Graft Mimic Strategy for Verticillium Resistance in Tomato

Grafting vegetables for disease resistance has increased greatly in popularity over the past 10 years. Verticillium wilt of tomato is commonly controlled through grafting of commercial varieties on resistant rootstocks expressing the Ve1 R-gene. To mimic the grafted plant, proteomic analyses in tomato were used to identify a suitable root-specific promoter (TMVi), which was used to express the Ve1-allele in susceptible Craigella (Cs) tomato plants. The results indicate that when infected with Verticillim dahliae, race 1, the transformed plants are comparable to resistant cultivars (Cr) or grafted plants.     

Grafting influence on the weight and quality of tomato fruit under salt stress

Two commercial tomato cultivars were used to determine whether grafting could prevent decrease of fruit weight and quality under salt stress conditions. The cultivars Buran F1 and Berberana F1 were grafted onto rootstock ‘Maxifort’ and grown under three levels of elevated soil salinity (EC 3.80 dS m^?1, 6.95 dS m^?1 and 9.12 dS m^?1). Fruit weight reduction of grafted plants was lower (about 20–30%) in comparison with non‐grafted ones. Salt stress at the second salinity level (EC 6.95 dS m^?1) induced the highest alteration of examined growth and quality parameters. The total increase of phenols, flavonoids, ascorbate and lycopene content in the fruits of both grafted and non‐grafted plants for both cultivars had a similar trend and intensity, though some inter‐cultivar variation was observed. The possibility of grafting tomato plants to improve salt tolerance without fruit quality loss is discussed.     

Interaction between photoperiod, photosynthesis and ethylene formation in tomato plants (Lycopersicon esculentum cv. Ailsa Craig and ACC‐oxidase antisense pTOM13)

Wild‐type and ACC‐oxidase antisense tomato plants ( Lycopersicon esculentum Mill. cv. Ailsa Craig and pTOM13) were grown in environment‐controlled rooms for 21 days under photoperiods of 8, 16 or 23.5 h at an irradiance of 300 µmol m⁻² s⁻¹. Photosynthetic pigments, photosynthesis, soluble carbohydrates, starch and ethylene were measured on the last fully expanded leaf. Increasing the photoperiod from 8 to 16 h stimulated all measured growth parameters in both cultivars. However, when the photoperiod was increased to 23.5 h, foliar yellowing and deformation were observed in the wild‐type Ailsa Craig whereas no change was observed in pTOM13. It was not possible to relate these foliar changes in Ailsa Craig to destruction of the photosynthetic apparatus by excess carbohydrate levels in the leaves. Because pTOM13 was antisense to ACC‐oxidase. it is proposed that yellowing and deformation in leaves of wild‐type tomato plants grown under long photoperiods may be caused by stress ethylene induced by a long photoperiod.     

Improving the Mineral Nutrition in Grafted Watermelon Plants: Nitrogen Metabolism

Watermelon (Citrullus lanatus [Trumb.] Mansfeld cv. Early Star), was used as scion grafted onto three cultivars of pumpkin (Cucurbita pepo L. cvs. Brava, Shintoza and Kamel) used as rootstocks and ungrafted Early Star plants were used as control. The rootstocks showed a high capacity for N uptake and transport to the scion where N reduction and assimilation improved growth of the scion in grafted plants with respect to the control.     

Slight vapor deficit accelerates graft union healing of tomato plug seedling

The application of grafting in tomato production has substantially improved tomato quality and yields. It has been demonstrated that humidity plays an important role in the graft healing of seedlings. This study focuses on the optimum relative humidity (RH) conditions for scion and rootstock healing of grafted tomato (Solanum lycopersicum L.) seedlings. Two tomato cultivars, ‘Super Sunload’ and ‘Super Dotaerang’, grafted onto ‘B-Blocking’ rootstock were subjected to one of three RH regimens: 70–80, 80–90, or 90–100%. The results showed that the scions of both cultivars showed apparent wilting under the 70–80 and 80–90% RH treatments. On this basis, the 90–100% RH treatment was subdivided into 95–96, 97–98, and 99–100% RH treatments, which were then applied. Among these subdivided RH treatments, the fresh weights of the scions and rootstocks significantly increased in response to the treatments of 97–98 and 99–100% RH, and the graft union connection of both cultivars was also enhanced after two days of healing. Furthermore, lower levels of endogenous H₂O₂ and less activity of antioxidant enzymes were observed in both cultivars in response to treatment with 95–96 or 97–98% RH, which indicated that less oxidative stress occurred. Overall, it is suggested that 97–98% is the optimal RH level for the graft healing of tomato seedlings.     

Rootstock-mediated changes in xylem ionic and hormonal status are correlated with delayed leaf senescence, and increased leaf area and crop productivity in salinized tomato

Tomato crop productivity under salinity can be improved by grafting cultivars onto salt-tolerant wild relatives, thus mediating the supply of root-derived ionic and hormonal factors that regulate leaf area and senescence. A tomato cultivar was grafted onto rootstocks from a population of recombinant inbred lines (RILs) derived from a Solanum lycopersicum  ×  Solanum cheesmaniae cross and cultivated under moderate salinity (75 m m NaCl). Concentrations of Na⁺, K⁺ and several phytohormones [abscisic acid (ABA); the cytokinins (CKs) zeatin, Z; zeatin riboside, ZR; and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC)] were analysed in leaf xylem sap in graft combinations of contrasting vigour. Scion leaf area correlated with photosystem II (PSII) efficiency ( F _v/ F _m) and determined fruit productivity. Xylem K⁺ (but not Na⁺), K⁺/Na⁺, the active CK Z, the ratio with its storage form Z/ZR and especially the ratio between CKs and ACC (Z/ACC and Z + ZR/ACC) were positively loaded into the first principal component (PC) determining both leaf growth and PSII efficiency. In contrast, the ratio ACC/ABA was negatively correlated with leaf biomass. Although the underlying physiological mechanisms by which rootstocks mediate leaf area or chlorophyll fluorescence (and thus influence tomato salt tolerance) seem complex, a putative potassium–CK interaction involved in regulating both processes merits further attention.     

南方根结线虫对不同砧木嫁接番茄苗活性氧清除系统的影响

采用盆栽人工接种方法,对番茄嫁接苗进行了抗性评价,研究了番茄嫁接苗叶片中抗氧化酶活性和活性氧代谢的动态变化。结果表明,接种南方根结线虫(J2)后,砧木嫁接苗表现为高抗,自根嫁接苗为高感。通过嫁接换根,与自根嫁接苗相比,砧木嫁接苗明显提高了接穗叶片的超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性,降低了超氧阴离子(O.2-)产生速率以及过氧化氢(H2O2)和丙二醛(MDA)含量。表明番茄植株体内的活性氧水平和抗氧化酶活性的高低与其抗根结线虫的能力密切相关,较低的活性氧水平和较高的抗氧化酶活性有利于减轻对膜系统的伤害,提高番茄植株的抗根结线虫能力。     

Rootstocks improve cucumber photosynthesis through nitrogen metabolism regulation under salt stress

We examined the growth, photosynthetic parameters, initial and total ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity, the relative expression of rbcL, rbcS, and rca gene, and nitrogen metabolism of cucumber (Cucumis sativus L. cv. Jinchun No.2, CS) plants grafted onto figleaf gourd (Cucurbita ficifolia Bouché, CF) and pumpkin (Cucurbita moschata Duch. cv. Chaojiquanwang, CM) rootstocks. Growth inhibition under salt stress (90 mM NaCl) was characterized by the irreversible inhibition of CO₂ assimilation in the cucumber plants grafted onto cucumber rootstocks (CS/CS). In contrast, this effect was significantly alleviated by grafting the cucumber plants onto the CF and CM roots (CS/CF, CS/CM). Under NaCl stress, the CS/CF and CS/CM plants exhibited higher photosynthetic activity, higher initial and total Rubisco activity, and higher Rubisco-related gene expression than the CS/CS plants. Salinity resulted in a lesser increase in nitrate content and decrease in free amino acid content in the CS/CF and the CS/CM plants compared with the CS/CS plants. Accordingly, the activity of nitrate reductase, glutamine synthetase, and glutamate synthase decreased significantly, especially in the CS/CS plants. These results suggest that grafting cucumber plants onto salt-tolerant rootstocks enhances Rubisco activity and the expression of Rubisco-related genes by effectively accelerating nitrate transformation into amino acids under NaCl stress, thereby improving the photosynthetic performance of cucumber leaves.     

Photosynthetic response of drought- and salt-stressed tomato and turnip rape plants to foliar-applied glycinebetaine

The effect of foliar application of glycinebetaine (50 and 100 m M ) on photosynthesis, stomatal conductance, photorespiration and transpiration in tomato cv. Bos 3155 ( Lycopersicon esculentum Mill.) and summer turnip rape cv. Kulta ( Brassica rapa L. ssp. oleifera ) plants subjected to drought and salinity are reported. Glycinebetaine application increased net photosynthesis of stressed plants. This was mostly due to increased stomatal conductance following glycinebetaine application as there were no marked changes in light and CO₂ saturated rates of O₂ evolution. Moreover, glycinebetaine application resulted in a significant decrease of photorespiration both in drought- and salt-stressed plants.     

The effectiveness of grafting to improve salt tolerance in tomato when an ‘excluder’ genotype is used as scion

If the main effect of long-term exposure of tomato plants to salinity is the accumulation of toxic concentrations of Na⁺ and Cl⁻ in the leaves, then the selection of ‘excluder’ rootstocks should increase tolerance to salinity in grafted tomato plants, independently of the genotype used as the scion. The question addressed in this study is whether shoot genotypes with an ‘excluder’ character are able to increase their salt tolerance when grafted onto rootstocks of the same characteristics. Moneymaker (with excluder character) was grafted onto two root genotypes, Radja and Pera, selected for their very different ability to regulate the transport of saline ions to the shoot over time. Grafting onto either Pera or Radja improved fruit yield compared to the self-grafted plants of Moneymaker (M/M) when the plants were grown at 50 mM NaCl, whereas there was no effect of either rootstock or of grafting per se (M/M) on fruit yield in the absence of or at 25 mM NaCl. The relationship between the salt responses to mid- and long-term depended on the stress level; after 27 d of 150 mM NaCl treatment, both graft combinations enhanced similarly their salt tolerances as did in the long-term experiment. Moreover, the tolerance induced by rootstock was related to the low rates of saline ion accumulation in their leaves. However, the positive effect of rootstock was only observed with rootstock Pera when the grafted plants were grown at 50 mM NaCl (the same salt level used in the long-term experiment) for 35 d. According to the physiological changes induced by rootstock in the leaves, the different salt responses seem to be due to the fact that the osmotic effect predominated on the toxic effect under these last conditions. Consequently, in order to select rootstocks care must be taken in the timing of any selection process: the stress level and length of exposure to salinity must be sufficient for the true differences in salt tolerance for toxicity to be shown. Taken together, these results show the effectiveness of grafting to enhance fruit yield in tomato and provide evidence that the positive effect induced by rootstock is related to the re-establishment of ionic homeostasis.     

Effects of high grafting on tomato plants infected by Meloidogyne incognita and Ralstonia solanacearum

The root‐knot nematode Meloidogyne incognita is known to increase the severity of bacterial wilt in many solanaceous crops. In Japan, several bacterial wilt‐resistant rootstocks that have the M. incognita resistance (Mi) gene in their genome have been developed for tomatoes. In this study, we aimed to examine whether the presence of Mi gene‐breaking M. incognita population affects the development of bacterial wilt in bacterial‐wilt‐resistant tomato rootstocks with Mi in their genetic background. We also aimed to examine the possibility of using high‐grafted tomatoes to control bacterial wilt in plants infected by M. incognita. Our results indicate that the resistance to bacterial wilt was easy to break in usual‐grafted tomato plants infected with M. incognita and that M. incognita enhanced the vertical movement of Ralstonia solanacearum in the bacterial‐wilt‐resistant tomato rootstocks. In addition, our results suggest that high grafting led to significantly less wilting in the plants infected by M. incognita than did usual grafting.     

Effect of salinity on growth, ion content and CO2 assimilation rate in lemon varieties on different rootstocks

Citrus rootstocks as well as lemon scions differ in their ability to restrict sodium and chloride ions and in their sensitivity to saline stress. To determine the behaviour of different rootstock-scion combinations, 3 lemon cultivars on 3 different rootstocks were grown in containers in a greenhouse and irrigated with 5, 25 and 50 m M NaCl. Growth of the plants and foliar contents of sodium and chloride as well as physiological parameters including transpiration rate, gas exchange, stomatal conductance and chlorophyll content were evaluated. Shoot length of the plants on sour orange and on C. volkameriana showed a greater reduction with salinity than those on C. macrophylla . Accumulation of salt in the leaves was also scion dependent, cv. 'Eureka' having higher concentrations of sodium and chloride than the others. Assimilation rate of CO₂ and stomatal conductance were greatly reduced by salinity in the leaves of Verna and Eureka on sour orange. Gas exchange in the leaves was highly correlated with chloride and sodium contents in all lemon-rootstock combinations. C. macrophylla showed a higher resistance to salinity than C. volkameriana and sour orange. Inferences on the mechanisms of action of salt on lemon trees are discussed.     

Phytosterols and polyphenols in reciprocally grafted tobacco—tomato plants

Intact and reciprocally grafted tobacco and tomato plants were studied to examine their roles as scions and stocks in the formation, composition, and total amount of 3-β-hydroxysterol and polyphenols. Intact tobacco plants have a higher phytosterol content than do tomato plants. Tobacco leaves from the Tob/Tom grafted plants contained much less phytosterol than leaves from intact tobacco plants. The distribution of four major sterols, however, did not vary significantly. The concentration of total polyphenols in intact tobacco and tomato was about the same, but tobacco was high in chlorogenic acid, and tomato was high in rutin. Tobacco leaves from Tob/Tom grafted plants showed only a slight decrease in total polyphenol concentration compared with intact tobacco. Tomato roots appeared to contribute to the increased total polyphenol per plant in either intact tomato or in Tob/Tom grafted plants, despite the fact that no polyphenolic compounds were detected in the tomato root itself. Grafting may provide a limited technique for reducing the phytosterol concentration of tobacco leaves.     

Rootstock-imposed Alterations in Nitrate Reductase and Glutamine Synthetase Activities in Leaves of Rose Plants

The activities of nitrate reductase and glutamine synthetase in leaves of greenhouse grown rose plants (Rosa hybrida cvs. Ilseta and Mercedes) grafted on various rootstocks were compared with those in leaves of non-grafted, own-root plants of these cultivars. The results obtained showed that the enzymatic activities as well as nitrate content in the leaves were altered by the grafting and by type of the rootstock used. These rootstock-imposed alterations differed between the two cultivars used in the study. This revised version was published online in July 2006 with corrections to the Cover Date.