Self-grafted Controls Research Articles

Combination of resistant rootstock and non-fumigant nematicide for the management of Meloidogyne floridensis on tomato

Summary Meloidogyne floridensis is one of the emerging species of root-knot nematodes in vegetable production in the Southern USA. It can reproduce on commercial vegetable cultivars that have resistance to the common tropical root-knot nematode species (i.e., M. incognita, M. arenaria and M. javanica). The objective of this study was to evaluate the Solanum sisymbriifolium line Sis Syn II as rootstock, in combination with drench application of a non-fumigant nematicide, fluazaindolizine, for managing M. floridensis on tomato. This study was conducted in artificially infested microplots under field conditions at two different locations in Georgia, USA in 2021. Treatments were arranged in a randomised complete block design with eight replications at one location and four replications at the other. The tomato cultivar ‘Roadster’ was used as the scion. Control treatments included non-grafted, and ‘Roadster’ grafted onto ‘Roadster’ rootstock (self-grafted). Our results showed that, in both experiments, Sis Syn II (reproduction factor: 0.07) significantly reduced the population of M. floridensis compared to the non-grafted (4.37) and self-grafted (6.86) controls. Similarly, the galling index was lower for Sis Syn II (0.61) compared to the non-grafted (4.13) and self-grafted (3.90) controls. Moreover, grafting onto Sis Syn II increased the average biomass and yield of the tomato in both experiments. However, fluazaindolizine drenching did not exhibit any effect on M. floridensis populations or the yield increment of tomato. Our study demonstrates that Sis Syn II is effective in management of M. floridensis. Grafting the desirable tomato cultivar onto this rootstock can significantly suppress M. floridensis population and increase crop yield.

High-altitude accessions of Capsicum baccatum and C. pubescens as rootstocks to enhance suboptimal-temperature tolerance of pepper

This study evaluated the effectiveness of rootstocks germplasm to enhance the chilling tolerance of Capsicum annum L. We compared 2 accessions of C. baccatum, i.e., CB 5 and CB 9, and 3 accessions of C. pubescens, i.e., CP 2, CP 3, and CP 4, together with commercial controls across 3 experiments. Experiment 1 (Exp 1) aimed to evaluate these genotypes adaptation compared to rootstock cv. ‘Capsifort’ to chilling temperatures and was performed in growth chambers for 28 days under two thermal regimes, i.e. optimal (25–15 °C for 12 h/day) and suboptimal (15–5 °C for 12 h/day). In Exp 2 the scion cv. Tiberio was grafted onto these rootstocks and grown under suboptimal temperature for 28 days in comparison to ungrafted control. Exp 3 evaluated the same graft combinations in a commercial greenhouse, to assess the effects of grafting on fruit yield and quality of the scion ‘Tiberio’ compared to ungrafted and self-grafted controls. In Exp 1, CP 3 showed the best photosynthetic performances, whereas CP 2 and CP 3 outperformed ‘Capsifort’ for plant biomass under suboptimal temperature. In Exp 2, chlorophyll fluorescence was higher in the combination ‘Tiberio’/CB 9 than in ‘Tiberio’, while ‘Tiberio’/CP 3 had a higher photosynthetic rate. The stomatal conductance was higher in ‘Tiberio’/CP 3 and ‘Tiberio’/CP 4 than in ‘Tiberio’. All the graft combinations reduced the leaf proline content compared to the ungrafted plants. In Exp 3 the graft combinations ‘Tiberio’/‘Capsifort’, ‘Tiberio’/CB 5, ‘Tiberio’/CB 9 and ‘Tiberio’/CP 3 produced the highest marketable yields, but ‘Tiberio’/’Capsifort’, ‘Tiberio’/CB 5, and ‘Tiberio’/CB 9 had the highest number of discarded fruits per plant. ‘Tiberio’/CP 2 fruits had lower titratable acidity values than ‘Tiberio’, whereas ‘Tiberio’/CB 9 had the highest antioxidant activity. Overall, our results showed that CB 9 and CP 3 consistently proved positive performance on ‘Tiberio’, while CP 2 performed well under low temperature conditions only.

Drought response and recovery mechanisms of grapevine rootstocks grafted to a common Vitis vinifera scion

As grapevine production is converting into irrigated systems worldwide, understanding rootstock-scion interactions at different stages of moderate drought can help to better manage water resources and the choice of rootstock. This study compared the physio-morphological drought response and recovery of a drought-sensitive (Riparia Gloire (Vitis riparia)) and a drought-tolerant rootstock (Ramsey (Vitis champinii)) grafted with Cabernet Sauvignon (Vitis vinifera), and the self-grafted control in a pot study. Ramsey had lower root-to-shoot ratio but higher performance of the root system under drought, explained by the lower root tissue density and tip suberization and higher VviPIP2;1 aquaporin expression, and faster recovery of root hydraulic conductivity and stomatal conductance after re-watering than Riparia. Riparia maintained better water status under moderate drought by early root suberization, but it was less able to restore water uptake capacity and support scion growth and leaf gas exchange after re-watering. This study shows a suite of rootstock traits that improve scion growth in response to moderate drought. Thus, these results identify traits for breeding programs and the selection of rootstocks for sustainable management of water resources under irrigated production.

How Does Watermelon Grafting Impact Fruit Yield and Quality? A Systematic Review

Globally, there has been an increase in stringent regulations governing the use of chemical soil fumigants for controlling diseases, pests, and weeds. Grafting has been identified as an effective alternative to soil fumigation for managing soilborne diseases and pests in intensive vegetable cropping systems. The majority of watermelon (Citrullus lanatus) grafting research confirms that selected rootstocks play a role in improving plant resistance or tolerance to common soilborne diseases. Currently, there is a lack of evidence-based literature on the effects of grafting on watermelon fruit quality attributes and yield components. Previous reviews report wide variation in the impact of grafting on watermelon production, depending on rootstock–scion combinations and environmental conditions. This review employed evidence-based synthesis methods to comprehensively and methodically summarize research results of the impact of grafting on watermelon, with a focus on fruit quality and yield. In this systematic review, 548 citations (studies published during 2011–21) were screened against strict inclusion criteria, and data were extracted from 47 studies. Meta-analysis of percent differences between the grafted watermelon treatment and the nongrafted or self-grafted watermelon control was performed using extracted data of yield components and a wide range of fruit quality attributes. Meta-analysis of research data with variance measures was also conducted based on a rather limited number of studies. Our findings showed higher levels of total yield, average fruit weight, fruit length and width, fruit lycopene and soluble solids content, rind thickness, flesh firmness, lightness, chroma, and flesh nitrogen (N) content in grafted watermelon treatments compared with the nongrafted or self-grafted control. In particular, total yield, average fruit weight, and flesh firmness exhibited significant increases of a more than 10% difference. In contrast, grafted plants demonstrated decreases in fruit pH, hue angle, and flesh calcium content, although the reduction was not greater than 10% relative to the control. Meta-analysis of research data with variance measures further confirmed significantly greater total yield and flesh N content in grafted watermelon treatments compared with the nongrafted or self-grafted control. In addition, the meta-analysis results confirmed greater benefits of watermelon grafting in the presence of known soilborne disease pressure in contrast to the production scenarios without soilborne disease problems.

Crossbreeding Rootstocks Improve Nitrogen Efficiency of Grafted Watermelon by Inducing Leaf Physiological and Root Morphological Responses

This is the first hydroponic study that evaluated the role of the heterotic plant characters of crossbreeding progenies and accessions which were used as rootstock for watermelon (scion) to improve the nitrogen (N) efficiency of this crop by grafting. The target of the research was to evaluate if grafting could enhance the nitrogen efficiency of watermelon through examining the responses of heterotic plant characters of crossbreeding rootstocks in the shoot development at the agronomical stage, root developments at the morphological stage, and leaf growth at various physiological stages. A hydroponic experiment was conducted by using an aerated deep-water culture (DWC) system in a well-equipped growth chamber of Erciyes University’s Plant Physiology Laboratory located at Kayseri, Türkiye. A watermelon cultivar Crimson Tide (CT) was grafted onto watermelon cultivars of Calhoun Gray (CG), Charleston Gray (Cha. G), and accessions of PI 296341 and PI 271769, the crossbreed progenies of Calhoun Gray × PI 296341, Calhoun Gray × PI 271769, and Charleston Gray × PI 296341. Plants were grown in 8 L plastic containers filled continuously with aired stock nutrient solution under two nitrogen (N) doses (low dose N: 0.3 mM unit N, and high dose N: 3.0 mM unit N) in a completely randomized block design (RBD) which was replicated three times, for six weeks. The grafted plants usually showed a higher crop growth performance than the self-grafted control plants, illustrating that nitrogen efficiency was significantly enhanced with respect to rootstocks of crossbreed progenies under a low N dose and high N dose. The N efficiency of grafted watermelon (CT) was improved by the high manifestation of heterosis in some root morphological characters (vigor root development and active root mechanism) of some of the crossbreeding rootstocks (Calhoun Gray × PI 271769) particularly in low-N conditions. Additionally, some of the crossbreeding rootstocks (Charleston Gray × PI 296341) exhibited high heterosis, which led to improving the N efficiency of grafted watermelon (CT) by inducing leaf physiological responses under high N supply. This clearly indicated that heterosis plays a crucial role in exploiting the genetic diversity in the N efficiency of watermelon. Therefore, these heterotic plant traits may be vital for the selection and breeding of nitrogen-efficient rootstocks for both small-scale and large-scale commercial farming in the nearby future.

Effects of Temperature and Grafting on Yield, Nutrient Uptake, and Water Use Efficiency of a Hydroponic Sweet Pepper Crop

In areas characterized by mild winter climate, pepper is frequently cultivated in unheated greenhouses in which the temperature during the winter may drop to suboptimal levels. Under low temperature (LT) conditions, the uptake of nutrients may be altered in a different manner than that of the water and thus their uptake ratio, known as uptake concentration, may be different than in greenhouses with standard temperature (ST) conditions. In the present study, pepper plants of the cultivars “Sammy” and “Orangery”, self-grafted or grafted onto two commercial rootstocks (“Robusto” and “Terrano”), were cultivated in a greenhouse under either ST or LT temperature conditions. The aim of the study was to test the impact of grafting and greenhouse temperature on total yield, water use efficiency, and nutrient uptake. The LT regime reduced the yield by about 50% in “Sammy” and 33% in “Orangery”, irrespective of the grafting combination. Grafting of “Sammy” onto both “Robusto” and “Terrano” increased the total fruit yield by 39% and 34% compared with the self-grafted control, while grafting of “Orangery” increased the yield only when the rootstock was “Terrano”. The yield increase resulted exclusively from enhancement of the fruit number per plant. Both the water consumption and the water use efficiency were negatively affected by the LT regime, however the temperature effect interacted with the rootstock/scion combination. The LT increased the uptake concentrations (UC) of K, Ca, Mg, N, and Mn, while it decreased strongly that of P and slightly the UC of Fe and Zn. The UC of K and Mg were influenced by the rootstock/scion combination, however this effect interacted with the temperature regime. In contrast, the Ca, N, and P concentrations were not influenced by the grafting combination. The results of the present study show that the impact of grafting on yield and nutrient uptake in pepper depend not merely on the rootstock genotype, however on the rootstock/scion combination.

Rootstock Effect on Grafted Tomato Transplant Shoot and Root Responses to Drying Soils

Improvement of crop water use is imperative. Plants’ responses to limited water can dictate their ability to better use available resources and avoid prolonged and severe stress. The following study was conducted to determine how tomato (Solanum lycopersicum) rootstocks with different root system morphologies respond to drying soils. Plants were grown in pots containing an inorganic substrate composed of calcined clay and sand in a greenhouse on North Carolina State University’s campus. The heirloom tomato cultivar Cherokee Purple was used as the scion for ‘Beaufort’ and ‘Shield’ rootstocks as well as the self-grafted control. These rootstocks were assigned either normal or reduced irrigation treatments. Plants grown under the normal irrigation schedule were weighed and watered daily to maintain container capacity for one week. Those receiving reduced irrigation had all water withheld for one week, at which point strong midday wilting became evident. Shoot physiological and morphological data as well as root morphological data were collected at the end of the study. A constitutive positive increase on relative water content, leaf area, stomatal conductance (gS), and net CO2 assimilation rate was observed with scions grafted on ‘Beaufort’. In addition, this rootstock had a significantly longer total root system (118.6 m) compared with ‘Shield’ (94.9 m) and the self-grafted control (104.2 m). Furthermore, 76.4% of the total root length observed in ‘Beaufort’ was composed of very thin diameter roots ( <0.5 mm), which was higher than ‘Shield’ (73.67%) and the self-grafted control (69.07%). The only significant rootstock irrigation interaction observed was for effective quantum yield of photosystem II (φPSII). At normal irrigation there were no differences among the rootstock treatments; however, at reduced irrigation ‘Beaufort’ had significantly higher φPSII than both ‘Shield’ and the self-grafted control. These results may explain some of the improved production and water use efficiency observed in field trials using ‘Beaufort’ rootstock, and data secured may allow for better screening of rootstocks for improved water use efficiency in the future.

Grafting the Indeterminate Tomato Cultivar Moneymaker onto Multifort Rootstock Improves Cold Tolerance

Tomato (Solanum lycopersicum L.) is a warm-season, cold-sensitive crop that shows slower growth and development at temperatures below 18 °C. Improving suboptimal temperature tolerance would allow earlier planting of field-grown tomato and a reduction in energy inputs for heating greenhouses. Grafting tomato onto high-altitude Solanum habrochaites (S. Knapp and D.M. Spooner) accessions has proven effective at improving scion suboptimal temperature tolerance in limited experiments. This study was conducted to determine whether commercially available tomato rootstocks with differing parental backgrounds and root system morphologies can improve the tolerance of scion plants to suboptimal temperature. Two controlled environment growth chambers were used and maintained at either optimal (25 °C day/20 °C night) or suboptimal (15 °C day/15 °C night) temperatures. The cold-sensitive tomato cultivar Moneymaker was used as the nongrafted and self-grafted control as well as scion grafted on ‘Multifort’ (S. lycopersicum × S. habrochaites), ‘Shield’ (S. lycopersicum), and S. habrochaites LA1777 rootstocks. Plants were grown for 10 days in 3.8 L plastic containers filled with a mixture of calcined clay and sand. ‘Multifort’ rootstock significantly reduced the amount of cold-induced stress as observed by larger leaf area and higher levels of CO2 assimilation and photosystem II quantum efficiency. ‘Multifort’ had significantly longer roots, having 42% to 56% more fine root (diameter less than 0.5 mm) length compared with the other nongrafted and grafted treatments. Leaf starch concentration was significantly lower in ‘Multifort’-grafted plants at suboptimal temperatures compared with the self-grafted and nongrafted controls and the ‘Shield’-grafted plants at the same temperature. The ability for ‘Multifort’ to maintain root growth at suboptimal temperatures may improve root system sink strength, thereby promoting movement of photosynthate from leaf to root even under cold conditions. This work demonstrates that a commercially available rootstock can be used to improve suboptimal temperature tolerance in cold-sensitive ‘Moneymaker’ scions.

EFFECTIVENESS OF SIX ROOTSTOCKS FOR FUSARIUM WILT CONTROL IN CUCUMBER AND THEIR INFLUENCE ON GROWTH, YIELD AND FRUIT QUALITY CHARACTERISTICS

Six rootstocks were evaluated against fusarium wilt of cucumber, in a greenhouse experiment, in two successive years. The susceptible Cretan cv. ‘Knossos’ was grafted on the commercial Cucurbita interspecific hybrid rootstocks ‘Leon’, ‘Mirage’, ‘Mammoth’, ‘Vivere’, and on species Cycios angulatus and Lagenaria ciseraria. Self-grafted plants of cv. ‘Knossos’ were used as controls. Disease severity, plant growth, yield, and fruit quality characteristics were compared in 27 cucumber plants from each rootstock-scion combination, artificially inoculated with Fusarium oxysporum f. sp. cucumerinum. Plants grafted on all tested rootstocks were significantly more resistant to fusarium wilt than self-grafted controls. In addition, all of the tested rootstocks prevented vigor and yield loss in diseased plants. Positive influence on stem length and root biomass was observed by all rootstocks, in both healthy and diseased plants, as compared to the control, but effects were not consistent in the two different years, except for root biomass in healthy plants. In the presence of the pathogen rootstocks increased yield, compared to the control. None of the tested rootstocks affected fruit quality characteristics.

Solanum habrochaites introgression line grafted as rootstock in cultivated tomato maintains growth and improves yield under cold and drought stresses

ABSTRACTGrafting tomato (Solanum lycopersicum L.) onto introgression lines (ILs) derived from S. habrochaites with introgression of a quantitative trait locus (QTL), stm9, for shoot turgor maintainer located on chromosome 9 has been suggested for improving yield under abiotic stresses. However, the physiological and agronomic responses of grafts with IL rootstocks to low root-zone temperature (RZT) and drought stresses are not yet clearly understood. Therefore, recurrent parent (RP) grafted onto IL and donor (D) rootstocks, and self-grafted IL and RP were examined at different combinations of optimal (20°–26°C RZT and well-watered) and suboptimal (10°C RZT and well-watered, and 20°–26°C RZT and cyclic drought) temperatures. Graft combinations were compared with self-grafted controls for dry weights, stomatal conductance (gs), leaf parameters, osmotic adjustment, and stress tolerance index. The RP grafted onto IL rootstocks regulated gs efficiently, retained the green trait, and produced higher biomass than the self-grafted RP. The IL rootstocks improved tolerance of the scion to drought and low RZT. Potential of IL rootstocks for improving tomato production under stressed conditions is discussed.

Nutritional Quality of Field-grown Tomato Fruit as Affected by Grafting with Interspecific Hybrid Rootstocks

In this study, the effects of grafting with interspecific hybrid rootstocks on field-grown tomato fruit quality were evaluated over a 2-year period. Fruit quality attributes from determinate ‘Florida 47’ tomato plants grafted onto either ‘Beaufort’ or ‘Multifort’ rootstocks were compared with those from non- and self-grafted controls. Grafted plants had higher fruit yields than non- and self-grafted plants, and increased production of marketable fruit by ≈41%. The increased yield was accompanied by few major differences in nutritional quality attributes measured for these fruit. Although grafting with the interspecific rootstocks led to consistently small, but significant increases of fruit moisture (≈0.6%), flavor attributes such as total titratable acidity (TTA) and the ratio of soluble solids content (SSC) to TTA were not significantly altered. Among the antioxidants evaluated, ascorbic acid concentration was reduced by 22% in fruit from grafted plants, but significant effects were not evident for either total phenolics or antioxidant capacity as assayed by oxygen radical absorbance capacity (ORAC). Levels of carotenoids (lycopene, β-carotene, and lutein) were similar in fruit from grafted plants with hybrid rootstocks compared with non- and self-grafted controls. Overall, the seasonal differences outweighed the grafting effects on fruit quality attributes. This study showed that grafting with interspecific hybrid rootstocks could be an effective horticultural technique for enhancing fruit yield of tomato plants. Despite the modest reduction in ascorbic acid content associated with the use of these rootstocks, grafting did not cause major negative impacts on fruit composition or nutritional quality of fresh-market tomatoes.

Fruit quality assessment of watermelons grafted onto citron melon rootstock.

The grafting of watermelons (Citrullus lanatus) is a common technique that increases yield under stressful soil conditions. The most common rootstocks for watermelons are Cucurbita hybrids. However, they often have a negative impact on fruit quality. Exploiting novel Citrullus germplasm such as citron melon (Citrullus lanatus var. citroides) is an alternative to avoid these quality problems. Citron melon has been validated as watermelon rootstock, comparing its effects on watermelon quality to those of Cucurbita hybrids. Larger fruits with thicker rinds were observed in fruits from plants grafted onto both citron and Cucurbita rootstocks. The citron melon had no significant effect on flesh sugars or acid profiles compared to non-grafted watermelons, except for an increase in glucose and malic acid content, which also occurred in the Cucurbita rootstocks. The aroma profile of fruits produced on citron melon was similar to that of the non-grafted and self-grafted controls. The citron rootstock did not display the increased levels of (Z)-6-nonen-1-ol (a compound associated with pumpkin-like odors) found in fruits produced with Cucurbita hybrids. The low impact of citron melon rootstock on fruit quality, along with the enhanced resistance against nematodes, make the citron a promising alternative to Cucurbita rootstocks. © 2016 Society of Chemical Industry.

Eggplant relatives as sources of variation for developing new rootstocks: Effects of grafting on eggplant yield and fruit apparent quality and composition

We propose the utilization of eggplant ( Solanum melongena L.) interspecific hybrids derived from crosses with closely related species as an approach for developing new improved rootstocks for eggplant. Here we investigate rootstock effects on fruit yield, apparent quality and proximate and mineral composition of S. melongena ‘Black Beauty’ (BB) scions grafted on interspecific hybrid rootstocks developed from crosses of S. melongena with Solanum incanum L. (SI × SM) and Solanum aethiopicum L. (SM × SA). The results are compared with non-grafted (BB control) and self-grafted (BB/BB) controls and with S. melongena ‘Black Beauty’ scions grafted onto Solanum torvum Sw. (STO) and Solanum macrocarpon L. (SMA) rootstocks. All treatments were grown in a soil naturally infested with root-knot nematodes (mostly Meloidogyne incognita (Kofoid and White) Chitwood). SI × SM and SM × SA interspecific hybrids had high germination (≥90%) and total graft success (100%). Contrary to what occurred with all other treatments, no plants from scions grafted onto these hybrid rootstocks died during the experiment. In particular, the SI × SM hybrid rootstock conferred the highest vigour to the scion, which resulted in the highest values for fruit earliness and early and total yield. Little difference was observed among treatments for apparent fruit quality traits, except for a greater fruit calyx length and prickliness of fruit grafted onto SMA rootstocks. A similar result was obtained for fruit composition where phenolics content was higher in fruit from plants grafted onto SMA rootstocks. Grafting eggplant onto interspecific eggplant hybrids, especially on the SI × SM hybrid, has proved advantageous for eggplant production, as the high vigour and good compatibility of the rootstock with scion results in improved early and total yield without negative effects on apparent fruit quality or composition. Interspecific hybrids represent an alternative to the commonly used STO rootstock, which is a wild species with irregular germination.

Performance of eggplant grafted onto cultivated, wild, and hybrid materials of eggplant and tomato

Eggplant (Solanum melongena) is amenable to grafting and this technique can be exploited to improve production of this vegetable crop. Here, we study the performance of the ‘Cristal F1’ eggplant cultivar grafted onto a total of 17 rootstocks, including five families, each of which is made by two parents and their hybrid, as well a commercial eggplant rootstock and a self-grafted control. Three families consist of eggplant rootstocks, including a S. melongena intraspecific family and two interspecific families of S. melongena with S. incanum and S. aethiopicum. Two other families are made of interspecific hybrids between tomato (S. lycopersicum) and S. habrochaites. Overall, eggplant rootstocks showed a good compatibility and graft success, while tomato rootstocks had a poor compatibility and only S. habrochaites rootstocks could be evaluated for yield and fruit production. Important differences were found for susceptibility to nematodes, with some S. melongena accessions showing the best results. Eggplant hybrids were intermediate to their parents in nematode resistance and tomato rootstocks proved to be very susceptible to nematodes. Yield, fruit number and earliness were higher in the most vigorous rootstocks, in particular in the S. melongena × S. aethiopicum hybrid. Good performance was also observed for some S. melongena accessions, but poor results were obtained when using S. incanum, S. aethiopicum and S. habrochaites rootstocks. Some differences were observed for fruit size and shape among the different rootstocks, but for the best rootstocks no differences of commercial relevance were apparent. The results suggest that S. melongena germplasm and both intraspecific and interspecific eggplant hybrids seem to be promising materials for developing new rootstocks for eggplant production.

Grafting Tomato with Interspecific Rootstock to Manage Diseases Caused by Sclerotium rolfsii and Southern Root-Knot Nematode.

Southern blight (Sclerotium rolfsii) and root-knot nematodes (Meloidogyne spp.) cause severe damage to fresh-market tomato (Solanum lycopersicum) throughout the southeastern United States. Grafting is an emerging technology in U.S. tomato production, and growers require information regarding the resistance characteristics conferred by rootstocks. In this study, southern blight (SB) and root-knot nematodes (RKN) were effectively managed using interspecific hybrid rootstocks. During 2007 and 2008, field trials were carried out at two locations that had soils naturally infested with S. rolfsii. At the end of the growing seasons, the mean SB incidence of nongrafted plants was 27 and 79% at the two sites. SB incidence among plants grafted onto rootstock cultivars Big Power (one location only), Beaufort, and Maxifort ranged from 0 to 5%, and area under the disease progress curve (AUDPC) values were lower than for nongrafted and self-grafted controls (P < 0.01). At one location, soils were naturally infested with RKN, and all three rootstocks reduced RKN AUDPC and RKN soil populations at first harvest (P < 0.01). Big Power was particularly effective at reducing RKN galling and RKN soil populations at final fruit harvest (P < 0.01). Fruit yield was higher when resistant rootstocks were utilized (P < 0.05), and in our study grafting was effective at maintaining crop productivity in soils infested with S. rolfsii and M. incognita.

Effects of cotton rootstock on endogenous cytokinins and abscisic acid in xylem sap and leaves in relation to leaf senescence

Leaf senescence varies greatly among cotton cultivars, possibly due to their root characteristics, particularly the root-sourced cytokinins and abscisic acid (ABA). Early-senescence (K1) and late-senescence (K2) lines, were reciprocally or self-grafted to examine the effects of rootstock on leaf senescence and endogenous hormones in both leaves and xylem sap. The results indicate that the graft of K1 scion onto K2 rootstock (K1/K2) alleviated leaf senescence with enhanced photosynthetic (Pn) rate, increased levels of chlorophyll (Chl) and total soluble protein (TSP), concurrently with reduced malondialdehyde (MDA) contents in the fourth leaf on the main-stem. The graft of K2 scion onto K1 rootstock enhanced leaf senescence with reduced Pn, Chl, and TSP, and increased MDA, compared with their respective self-grafted control plants (K1/K1 and K2/K2). Reciprocally grafted plants differed significantly from their self-grafted control plants in levels of zeatin and its riboside (Z+ZR), isopentenyl and its adenine (iP+iPA), and ABA, but not in those of dihydrozeatin and its riboside (DHZ+DHZR) in leaves in late season, which was consistent with variations in leaf senescence between reciprocally and self-grafted plants. The results suggest that leaf senescence is closely associated with reduced accumulation of Z+ZR, and iP+iPA rather than DHZ+DHZR, or enhanced ABA in leaves of cotton. Genotypic variation in leaf senescence may result from the difference in root characteristics, particularly in Z+ZR, iP+iPA, and ABA which are regulated by the root system directly or indirectly.

Tomato rootstock effects on gene expression patterns in eggplant scions

The grafting technique has been used in agriculture since ancient time to improve horticultural crops. Nonetheless, the mechanism by which the rootstocks impact the traits of scions remains elusive. Here, using carefully produced “tomato + eggplant” grafts, we studied a possible effect of tomato rootstocks on gene expression of eggplant scions. By taking strict precautions, including using inbred lines and employing both ungrafted and self-grafted controls, potential confounding influences were confidently ruled out. It was found that the tomato rootstock could up-or down-regulate gene expression of the eggplant scions. The effected genes are related to diverse functions, including general metabolism, signal transduction, stress-response, cell cycle/division, and transcription/translation. Possible mechanisms of the rootstock effects on gene expression of the scions are discussed.

Development of union abnormalities in grafts between lemon (Citrus limon) and Poncirus trifoliata

A complete ring of bark was exchanged between seedlings of P. trifoliata and those of seven lemon cultivars, thereby producing P. trifoliata seedlings with a ring of lemon bark and lemon seedlings with a ring of P. trifoliata bark. Self-grafted controls were also propagated. The incompatibility of Eureka lemon–P. trifoliata combinations was clearly manifested at the graft union 7–9 months after grafting. Union abnormalities were detected only in lemon seedlings with a ring of P. trifoliata bark. They were not detected in P. trifoliata seedlings with a ring of lemon bark, nor in self-grafted controls. Anatomical studies revealed that the initial disturbance occurred in the outer phloem and spread along the rays towards the cambium. After the cambial zone was affected, the excessive proliferation of ray parenchyma disrupted vascular continuity. Extensive necrosis and gum deposition were evident in severely affected unions. The investigation showed that an early diagnosis of incompatibility is possible by examining the structure of the union.

Symbiotic Nitrogen Fixation in Soybeans. III. Effect of Supplemental Nitrogen and Intervarietal Grafting1

Two field experiments were conducted to determine the effect of 1) grafting onto root genotypes with different nitrogen fixation rates, and 2) supplemental nitrogen applied at the time of declining nodule activity (end of flowering), on nodulation, seed yield, and protein yield of ‘Chippewa 64’ and ‘Clay’ soybeans (Glycine max (L.) Merr.). The experiments were conducted in situations of low available soil nitrogen to ensure a strong reliance on symbiotic nitrogen fixation. In the first study, seedling shoots of both varieties were grafted onto four roofstocks: ‘Wayne’, ‘Altona’, Chippewa 64 and Clay.Differences were evident among root genotypes, independent of shoot genotype, for acetylene reduction activity per plant, but not for nodule fresh weight. for Chippewa 64 shoots, seed yield and seed protein content were significantly altered by grafting onto other rootstocks, whereas for Clay shoots only seed protein content was significantly changed from that of the selfgrafted controls. The effects of the root genotypes on seed yield were related in part to the respective differences in ability to support nitrogen fixation.In the second study, supplemental nitrogen (0, 224, and 448 kg per ha) was applied as ammonium nitrate at the end of flowering to Chippewa 64 and Clay soybeans. The application of nitrogen caused a decline in acetylene reduction activity for both varieties. Seed yield and seed protein content for Clay, and seed protein content and vegetative protein yield for Chippewa 64, were all increased by the application of nitrogen.