Graft Incompatibility Research Articles

Mapping Quantitative Trait Loci Associated With Graft (In)Compatibility in Apricot (Prunus armeniaca L.).

Graft incompatibility (GI) between the most popular Prunus rootstocks and apricot cultivars is one of the major problems for rootstock usage and improvement. Failure in producing long-leaving healthy grafts greatly affects the range of available Prunus rootstocks for apricot cultivation. Despite recent advances related to the molecular mechanisms of a graft-union formation between rootstock and scion, information on genetic control of this trait in woody plants is essentially missing because of a lack of hybrid crosses, segregating for the trait. In this study, we have employed the next-generation sequencing technology to generate the single-nucleotide polymorphism (SNP) markers and construct parental linkage maps for an apricot F1 population “Moniqui (Mo)” × “Paviot (Pa)” segregating for ability to form successful grafts with universal Prunus rootstock “Marianna 2624”. To localize genomic regions associated with this trait, we genotyped 138 individuals from the “Mo × Pa” cross and constructed medium-saturated genetic maps. The female “Mo” and male “Pa” maps were composed of 557 and 501 SNPs and organized in eight linkage groups that covered 780.2 and 690.4 cM of genetic distance, respectively. Parental maps were aligned to the Prunus persica v2.0 genome and revealed a high colinearity with the Prunus reference map. Two-year phenotypic data for characters associated with unsuccessful grafting such as necrotic line (NL), bark and wood discontinuities (BD and WD), and an overall estimate of graft (in)compatibility (GI) were collected for mapping quantitative trait loci (QTLs) on both parental maps. On the map of the graft-compatible parent “Pa”, two genomic regions on LG5 (44.9–60.8 cM) and LG8 (33.2–39.2 cM) were associated with graft (in)compatibility characters at different significance level, depending on phenotypic dataset. Of these, the LG8 QTL interval was most consistent between the years and supported by two significant and two putative QTLs. To our best knowledge, this is the first report on QTLs for graft (in)compatibility in woody plants. Results of this work will provide a valuable genomic resource for apricot breeding programs and facilitate future efforts focused on candidate genes discovery for graft (in)compatibility in apricot and other Prunus species.

Effect of the Rootstock and Cultivar on Graft Success and Sapling Development and Graft Incompatibility in Pear

This study was carried out to determine the effects of different rootstocks on graft success, sapling development and graft compatibility/incompatibility of ‘Deveci’ and ‘Williams’ pear cultivars in Samsun ecological conditions between 2014 and 2016 years. Graft incompatibility was attempted to be associated with morphological measurements in the graft union. Rootstock, cultivar and rootstockxcultivar interaction had a significant effect on the all examined parameters. In the study, graft take ratios were between 91.5-100.0%, graft sprout ratios were between 89.2-99.0% and survival ratios were between 83.7-99.0%. The graft sprout ratio was the highest in the OHxF333 and lowest was in the BA29 rootstock. The graft sprout and survival ratios were lower in quince rootstock than in pear rootstocks. Rootstock diameters were higher in the OHxF333 and seedling rootstocks than in the Fox11 and BA29 rootstocks. Graft union diameter and shoot diameter were lower in the Fox11 than the other rootstocks. Shoot length was higher in the OHxF333 than the other rootstocks. Especially considering the graft success and the diameter measurements made in the graft union, it has been found that some scion/stock combinations may show graft incompatibility. The ‘Williams’/BA29 combination may be incompatible due to the lower survival ratio and diameter values in the graft union than other combinations. Although graft success is sufficient, it should be noted that the ‘Williams’/Fox11, whose rootstock diameter and graft union diameter are lower than the others, may show graft incompatibility. ‘Deveci’ cultivar shows good compatibility with all rootstocks due to the higher graft success and sapling performance.

Mechanisms Underlying Graft Union Formation and Rootstock Scion Interaction in Horticultural Plants.

Grafting is a common practice for vegetative propagation and trait improvement in horticultural plants. A general prerequisite for successful grafting and long term survival of grafted plants is taxonomic proximity between the root stock and scion. For the success of a grafting operation, rootstock and scion should essentially be closely related. Interaction between the rootstock and scion involves complex physiological-biochemical and molecular mechanisms. Successful graft union formation involves a series of steps viz., lining up of vascular cambium, generation of a wound healing response, callus bridge formation, followed by vascular cambium formation and subsequent formation of the secondary xylem and phloem. For grafted trees compatibility between the rootstock/scion is the most essential factor for their better performance and longevity. Graft incompatibility occurs on account of a number of factors including of unfavorable physiological responses across the graft union, transmission of virus or phytoplasma and anatomical deformities of vascular tissue at the graft junction. In order to avoid the incompatibility problems, it is important to predict the same at an early stage. Phytohormones, especially auxins regulate key events in graft union formation between the rootstock and scion, while others function to facilitate the signaling pathways. Transport of macro as well as micro molecules across long distances results in phenotypic variation shown by grafted plants, therefore grafting can be used to determine the pattern and rate of recurrence of this transport. A better understanding of rootstock scion interactions, endogenous growth substances, soil or climatic factors needs to be studied, which would facilitate efficient selection and use of rootstocks in the future. Protein, hormones, mRNA and small RNA transport across the junction is currently emerging as an important mechanism which controls the stock/scion communication and simultaneously may play a crucial role in understanding the physiology of grafting more precisely. This review provides an understanding of the physiological, biochemical and molecular basis underlying grafting with special reference to horticultural plants.

Identifying Molecular Markers of Successful Graft Union Formation and Compatibility.

Grafting is a technique used for millennia for vegetative propagation, especially in perennial fruit crops. This method, used on woody and herbaceous plants, can improve several agronomic characteristics, such as yield or vigor, as well as tolerance to biotic and abiotic stresses. However, some scion/rootstock combinations suffer from poor graft compatibility, i.e., they are unable to form and/or sustain a successful graft union. Identifying symptoms of graft incompatibility is difficult because they are not always present in the first years after grafting and in most cases the causes of incompatibility are still poorly understood. Studies of changes in transcript abundance during graft union formation indicate that grafting responses are similar to responses to wounding and include the differential expression of genes related to hormone signaling, oxidative stress, formation of new vascular vessels, cell development, and secondary metabolites, in particular polyphenols. This review summarizes current knowledge of the changes in transcript abundance, redox status and metabolites accumulation during graft union formation and in cases of graft incompatibility. The goal of this review is to discuss the possibility of identifying marker transcripts, enzyme activities and/or metabolites of grafting success and graft compatibility which could be used to score grafting success for genetic research and in breeding programs. We highlight gaps in current knowledge and potential research directions in this field.

Hybrid Rootstocks for Valencia Sweet Orange in Rainfed Cultivation Under Tropical Savannah Climate

The performance of Valencia sweet orange grafted onto 41 hybrid citrus rootstocks was evaluated for 11 years in rainfed cultivation under tropical savannah climate (Aw type) in Brazil, in addition to three selections of the standard drought-tolerant Rangpur lime and two selections of Sunki mandarin. Drought tolerance, assessed by visual score of leaf wilting, was directly related to the mean fruit yield. Indio and Riverside citrandarins, Tropical Sunki mandarin and the hybrid TSKC × CTSW-028 were grouped with the most productive selections of Rangpur lime, all of them inducing large tree size, intermediate fruit production efficiency, and high drought tolerance. The hybrid TSK × TR English-CO was similar except by inducing a higher mean soluble solids concentration in the orange juice. A third group of rootstocks induced high yield and drought tolerance, and a mean 30% reduction in tree size that led to high production efficiency, which comprised the hybrids HTR-053, TSKC × (LCR × TR)-017 and-059, TSKC × CTSW-041, LCR × TR-001 and San Diego citrandarin. The tree mortality on Rangpur lime selections was as least as 46%, while more than 80% of trees grafted onto the aforementioned rootstocks survived without visual symptoms of citrus sudden death disease or graft incompatibility. The selected hybrids and Tropical Sunki mandarin also induced fruit quality, mainly soluble solids, superior to the Rangpur lime and, therefore, are potential rootstocks for rainfed cultivation of Valencia sweet orange.

اثر روش‌های مختلف پیوند بر رشد رویشی و عملکرد میوه گوجه‌فرنگی رقم "اس‌وی 8320"

Introduction: Today in order to produce vegetable fruits tolerant to adverse environmental conditions and increase growth, yield and fruit quality, grafting methods have been created. Tomato (Solanum lycopersicum) is one of the most important greenhouse products. Heirloom tomato cultivars lack disease genetic resistance and are particularly susceptible to epidemics in the field. Grafting can be used to unite the soil borne disease resistance and enhanced vigor of hybrid tomato cultivars with the high fruit quality of heirloom cultivars. There are deficiencies in vegetable grafting including skills for grafting operation performance and after the grafting, having enough knowledge to select rootstock, farm management in application of required fertilizers, graft incompatibility, excessive vegetative growth of grafting plant and physiological abnormalities, and fruit quality reduction. For grafting herbaceous plants such as vegetables, depending on the type of plant, plant size, grafting purpose, available equipment, preference and experience of the grafting plant producer and post-grafting management, different grafting methods have been introduce which is for different species and the used method is completely different. Each method has its own advantages and disadvantages, which are effective in the survival and development of grafting plants. This experiment was conducted in order to evaluate the effect of grafting methods on yield and vegetative growth of tomato plants. Material and Methods: Three common grafting methods, splice, cleft and approach grafting were evaluated for tomato SV 8320 cultivar grafted on Rimac rootstock. Executive operations were conducted in a completely randomized design with three replications at greenhouse of Lorestan Agriculture Faculty. Plant height, number of auxiliary shoot, number and length of internodes, number of fruit cluster, number of flower in cluster, root fresh and dry weight, number of fruit cluster, number of fruit in cluster, width and diameter of fruit, fruit weight, fruit fresh and dry weight, length of fruit tail, fruit tissue firmness, total soluble solid, pH, diameters of hypocotyl, pre, middle and total yield , ratio of the marketable fruits to second degree fruits, and fruit tissue firmness were recorded. Data was analyzed using SPSS software and means were compared by Duncan’s multiple range test. Results and Discussion: Grafting method had significantly effect on plant height, number and length of internode, root fresh and dry weight, number of fruit cluster, width and diameter of fruit, fruit weight, fruit fresh and dry weight, length of fruit tail, fruit tissue firmness, pH, pre, middle and total yield, the ratio of the marketable fruits to second degree fruits at 5% of probability level. Vegetative characteristics and yield in grafted plants were higher compared to non-grafted plants. Conclusion: According to results of this experiment using different grafting methods lead to stimulate growth in grafting plants, increasing production and product quality. Changes caused by the rootstock are controlled through water absorption, synthesis and transition of water, minerals and herbal hormones. Signal generation in the rootstocks and transition of them to the scion, causes changes in the physiology and morphology of the grafted plant. Grafting success varied between grafting methods, so that splice grafting is better than other methods. Graft compatibility was shown by the ability of tissue to regenerate and the vessels ability in wound tissues to rejoint together then grow and develop as a vigorous composite plant. Attempts to increase the productivity of grafted plant should be followed by the application of good agricultural practices.

Chimeric plants-the best of both worlds.

Overcoming graft incompatibility between species could protect future crop yields

Bazı hibrit kestane genotiplerinin anaçlık potansiyelleri

In Turkey chestnut cultivation is threaten by chestnut blight, chestnut root rot and Asian chestnut gall wasp. In order to obtain tolerant cultivars to the pests and diseases hybridization studies were performed. As a result, A14, A25, A41 and A100 hybrid chestnut genotypes were selected as superior. Some of these genotypes were registered by ‘Republic of Turkey Ministry of Agriculture and Forestry Variety Registration and Seed Certification Center’. A14 genotype named as ‘Akyüz’ and A100 named as ‘Macit 55’. Grafting studies were performed with these genotypes and cultivars. However, due to graft incompatibility survival ratio was found low. To avoid graft incompatibility, own seedlings may be better candidate as rootstocks because of the degree of compatibility. In this study seedling rootstock potential of ‘Akyüz’, ‘Macit 55’ cultivars and A25, A41 genotypes were examined. ‘Marigoule’ cultivar used as control. The study was conducted between 2013 and 2015 at Ondokuz Mayıs University, Samsun, Turkey. In the study healthy seed ratio (%), seed emerging ratio (%), suitable for grafting seedling ratio (%), seedling diameter (cm), coefficient of variation (CV) of seedling diameter and seedling productivity (%) were investigated. As a result of the study, all genotype and cultivars were found superior in terms of their generative rootstock characteristics. However, a great variation was observed among the rootstocks over the years. Therefore, studies should be conducted to determine the effect of xenia on rootstock candidates in nut species where generative rootstock use is necessary. Also, to find out the graft compatibility of these genotype and cultivars grafting studies should be done and they should be evaluated for long-term.

A Phenotypic Search on Graft Compatibility in Grapevine

Grafting is the most used propagation method in viticulture and is the unique control strategy against Phylloxera. Nevertheless, its practice remains limited mainly due to inconsistent graft success and difficulties in predicting graft compatibility responses of proposed scion–rootstock combinations, slowing down the selection of elite rootstocks. Aiming to identify optimal phenotypic parameters related to graft (in)compatibility, we used four clones of two grapevine cultivars that show different compatibility behavior when grafted onto the same rootstock. Several physiological parameters, internal anatomy of the graft union, chlorophyll fluorescence, and pigment contents of homo- and heterografts were monitored in a nursery-grafting context. The measurements highlighted enhanced performance of the heterografts due to rooting difficulties of Vitis vinifera homografts. This suggests that in viticulture, homografts should only be used as compatibility controls regarding qualitative attributes. By observing the internal anatomy of the union, we found that grapevines might require longer times for graft healing than anticipated. While Affinity Coefficients were not informative to assess incompatibility, leaf chlorophyll concentration analysis proved to be a more sensitive indicator of stress than the analysis of chlorophyll fluorescence. Overall, we conclude that graft take correlated best with callus formation at the graft junction three weeks after grafting.

Compatibility and horticultural performance of Pera sweet orange clones grafted to Swingle citrumelo rootstock

ABSTRACT Despite its interesting agricultural traits, Swingle citrumelo (Citrus paradisi Macfad. ‘Duncan’ × Poncirus trifoliata L. Raf.) rootstock exhibits severe incompatibility when grafted with Pera sweet orange [Citrus sinensis (L.) Osb.] scions, and this fact limits its use for propagation purposes. Nonetheless, the existence of certain Pera sweet orange clones that are compatible with Swingle citrumelo represents a substantial gain for the entire citrus industry. This study investigated the compatibility between seven Pera sweet orange clones and Swingle citrumelo rootstock, regarding the presence of a necrotic line at the graft union junction, the difference in diameter between rootstock and scion, the influence of clonal cleaning by micrografting, and the horticultural performance of the selected combinations. No trees died because of grafting incompatibility, even after twenty years (trial I), except for clone CV1, or after six years and nine months (trial II) from planting. The rootstock/scion trunk diameter ratio was not related to the presence of a necrotic line in the graft-union region. Additionally, these variables did not influence fruit yield and quality, and they were not affected by clonal cleaning or pre-immunisation of the old Pera sweet orange clones.

Living with Two Genomes: Grafting and Its Implications for Plant Genome-to-Genome Interactions, Phenotypic Variation, and Evolution.

Plant genomes interact when genetically distinct individuals join, or are joined, together. Individuals can fuse in three contexts: artificial grafts, natural grafts, and host-parasite interactions. Artificial grafts have been studied for decades and are important platforms for studying the movement of RNA, DNA, and protein. Yet several mysteries about artificial grafts remain, including the factors that contribute to graft incompatibility, the prevalence of genetic and epigenetic modifications caused by exchanges between graft partners, and the long-term effects of these modifications on phenotype. Host-parasite interactions also lead to the exchange of materials, and RNA exchange actively contributes to an ongoing arms race between parasite virulence and host resistance. Little is known about natural grafts except that they can be frequent and may provide opportunities for evolutionary innovation through genome exchange. In this review, we survey our current understanding about these three mechanisms of contact, the genomic interactions that result, and the potential evolutionary implications.

Inheritance of self- and graft-incompatibility traits in an F1 apricot progeny.

Floral self-incompatibility affecting yearly yield in a weather-dependent manner and graft incompatibility affecting longevity of mature trees are two important traits for apricot production. However, genetic control of graft compatibility and relationship between these traits are unknown. Here, we analyzed its inheritance in an F1 apricot progeny from a cross between self- and graft- incompatible and self- and graft-compatible cultivars. Hybrid individuals were genotyped for establishing self-incompatibility status and grafted on the plum rootstock ‘Marianna 2624’. Phenotyping of graft incompatibility was done at two time points, one month and one year after grafting. Anatomical (necrotic layer, bark and wood discontinuity for two consecutive years) and cytomorphological (cell proliferation, cell arrangement and cell shape one month after grafting) characteristics related to graft compatibility displayed continuous variation within the progeny, suggesting a polygenic inheritance. Using the Pearson correlation test, strong and significant correlations were detected between anatomical and cytomorphological traits that may reduce the number of characters for screening genotypes or progenies for graft compatibility in segregating crosses. Furthermore, no correlation existed between self- and graft incompatibility traits suggesting that they are independent inheritance traits. Hence, screening an extended hybrid population is required for pyramiding these traits in breeding programs.

Validation of micrografting to identify incompatible interactions of rootstocks with virus‐infected scions of Cabernet Franc

Background and Aims Grafted grapevines are a key component of modern viticulture. Grafting provides not only resistance to soil-borne pests, but can also improve adaptability to the environment and can improve fruit yield and quality. Graft incompatibility induced by grapevine viruses causes damage to vineyards worldwide. The aim of the present study was to create a rapid and reliable means of evaluating graft incompatibility resulting from grafting virus-infected scions onto healthy grape rootstocks. Methods and Results Scions of Control (healthy Cabernet Franc), LR131 (Cabernet Franc infected with GLRaV-1) and LR132 (Cabernet Franc infected with GLRaV-1 and GVA) were grafted onto different rootstocks by micrografting, green grafting and bench grafting methods. All the micrografts infected with LR132 failed, while LR131 and Control micrografts had similar survival rates. The impact of LR132 was less severe on green grafted plants, followed by bench grafts. Analysis of variance showed an interaction of grafting method × virus variety × rootstock, affecting grafting survival. When grafted onto Freedom and 101-14, LR131 inhibited the growth of both scion and rootstock, but no significant impact was seen when LR131 was grafted onto St. George and AXR1. Well-established callus was visible between the surfaces of LR131 and the rootstocks. The virus GLRaV-1 was detected moving from the LR131 scion source to rootstocks 7 days after micrografting. Callus formation was delayed by LR132 between scion and rootstock surfaces, and a scion-rootstock vascular connection did not establish, resulting in the death of all micrografts. Conclusions Micrografting is a reliable and sensitive method to screen for virus tolerant graft combinations compared with green and bench grafting. Significance of the Study The results of the present study validate micrografting as a means of producing credible information for selection of virus tolerant rootstocks, and ultimately vineyards with higher rates of compatible grafts.

Peroxidase activity and initial growth of ‘Barbosa’ peach on clonal rootstocks

Abstract In the peach nursery trees production, the use of rootstocks with unknown genetic identity obtained from peach seeds in the canning industry is frequent. The hypothesis tested was that there are rootstocks that express greater graft compatibility, enabling greater survival and growth, and that peroxidase activity can be used as indication of graft incompatibility. The aim of this study was to evaluate the survival and the peroxidase activity efficiency in identifying graft incompatibility and the trunk diameter growth of ‘Barbosa’ peach grafted onto 18 Prunus clonal rootstocks, propagated by herbaceous cuttings, compared to own-rooted scion trees. The experimental design was three randomized blocks, with one tree per plot. The first three vegetative cycles of trees conducted in double Y (5.0m x 2.0m) without irrigation were evaluated. The highest trunk diameter growth was provided by ‘Okinawa’, ‘Tsukuba-1’, ‘Tsukuba-2’, Mexico F1 and ‘Flordaguard’ rootstocks, without differing from own-rooted ‘Barbosa’ peach. Peroxidase activity differs by rootstock effect at the beginning of the dormancy period, and is higher than in vegetative growth, especially in interspecific graft combinations. Peroxidase activity is a biochemical indicator of stress, but should not be used alone and generalized to characterize graft incompatibility.

Graft compatibility for new releasedPrunusrootstocks

Graft compatibility for new Prunus rootstocks recently introduced into the Spanish market or under selection in public and private programmes is assessed in nursery trials. Part of the evaluated material belongs to the Aula Dei Experimental Station (EEAD-CSIC) selection program in Zaragoza, Spain. Another group of rootstocks under test is from the private nursery Agromillora Iberia, S.L. Some of those rootstocks showed good adaptation to Mediterranean growing conditions and resistance to root-knot nematodes. As control, peach-almond (‘GF 677’), peach × P. davidiana (‘Cadaman’), other interspecific plum-based rootstocks (‘Damas GF 1869’, ‘Ishtara’) and different plum species (P. cerasifera: ‘Adara’; P. domestica: ‘Constanti 1’; P. insititia: ‘Adesoto’ and other ‘Pollizo de Murcia’ clones, ‘Saint Julien A’) are used. New evaluated rootstocks include: ‘Densipac R 20’ (P. besseyi × P. cerasifera), ‘Nanopac R 40’ (P. dulcis × P. persica), ‘Replantpac RR’ (P. dulcis × P. cerasifera), ‘AP 45’ [(P. besseyi × P. salicina) × P. armeniaca], ‘Aprimed AP 65’ [(P. armeniaca L. × P. cerasifera Ehrh) × P. pumila L. var. besseyi], and ‘LC 52’ (P. cerasifera × P. maackii), among others. To determine graft-compatibility, commercial cultivars of different Prunus species were budded on some of the evaluated rootstocks. They include: ‘Moniqui’ and ‘Portici’ (apricot); ‘Lauranne’, ‘Nonpareil’, ‘Penta’ and ‘Soleta’ (almond); ‘Angeleno’ and ‘Golden Japan’ (Japanese plum); ‘Big Top’ and ‘Sumergrand’ (nectarine) and ‘Aida’, ‘Carmen’, ‘Cordia’, ‘Ferrovia’, ‘Kovics’, ‘Krupnoplodnaja’, and ‘Sandor’ (cherries). Several degrees of graft incompatibility have been observed for the ‘translocated’ type of incompatibility. In general, peach-almond hybrids and slow-growing plums (P. domestica and P. insititia plums as ‘Adesoto’ and other ‘Pollizo de Murcia’ clones) were graft-compatible with peach, almond and Japanese plum tested cultivars. However, in the case of P. cerasifera, P. besseyi and interspecific hybrids with these species, performance differed substantially depending on the evaluated genotype.

Long-term graft compatibility study of peach-almond hybrid and plum based rootstocks budded with European and Japanese plums

The introduction of some new rootstocks requires knowledge of the potential ‘translocated’ and ‘localized’ graft incompatibilities before releasing these rootstocks into the market. Trials were established at the Aula Dei Experimental Station (Zaragoza, Spain) to assess graft compatibility between five European plum (Prunus domestica L.) and six Japanese plum (Prunus salicina L.) cultivars with thirty-eight rootstocks belonging to peach × almond hybrids, as well as slow-growing, fast-growing and interspecific hybrid plum groups. Some of these rootstocks are under process of selection and others are commercial rootstocks already introduced into the European market. External visual diagnosis of the scion-rootstock graft combinations was performed by observing symptoms of the ‘translocated’ incompatibility in the nursery. Visual symptoms of ‘translocated’ incompatibility were only found on the Japanese plum cv. ‘Golden Japan’ budded on the plum-apricot hybrid AP-45. The ‘localized’ graft incompatibility was assessed after internal macroscopically examination of graft unions. In the case of the European plum cvs., ‘President’ and ‘Reine Claude Tardive of Chambourcy’ exhibited good graft compatibility with all the tested rootstocks, with the exception of ‘President’ budded on the pentaploid plum hybrid rootstock Damas GF 1869. ‘Reine Claude Verte’ cv. showed ‘localized’ incompatibility with Myrobalan B and Myrobalan GF 3-1 since the second year after budding. ‘Stanley’ cv. showed ‘localized’ incompatibility with the six evaluated peach × almond hybrid rootstocks, although it was compatible with all plum based rootstocks. In the case of Japanese plums, four cultivars (‘Angeleno’, ‘Black Amber’,’ Delbarazur’ and ‘Songold’) did not show any graft incompatibility, but ‘Friar’ showed ‘localized’ incompatibility on Myrobalan B. In the case of peach-almond and P. cerasifera based rootstocks (Adarcias, GF 677, Damas GF 1869, Myrobalan B, Myrobalan 29 C, Myrobalan GF 3-1 and Marianna GF 8-1), ‘Golden Japan’ trees showed similar symptoms to those caused by TomRV in Myrobalan and peach rootstocks and ‘localized’ incompatibility. Finally, this study confirmed the interest of P. insititia specie as well as several interspecific Prunus hybrids as a good source of rootstocks for the plum industry.

Compatibility of tomato cultivar Santa Cruz Kada grafted on different Solanaceae species and control of bacterial wilt

ABSTRACT The objective of this work was to evaluate the compatibility, gas exchange and yield of tomato cultivar Santa Cruz Kada, susceptible to bacterial wilt (Ralstonia solanacearum) when grafted on different Solanaceae species. Rootstock sources were the mini-tomato RVTC-66, Cayenne pepper, Jerusalem cherry (Solanum pseudocapsicum), sticky nightshade (Solanum sisymbriifolium), and cultivar Santa Cruz Kada itself (self-grafting). Two materials were tested to promote the union between rootstocks and scions: grafting clips and biodegradable tape (Parafilm). Grafting success index (GSI) was evaluated and, for treatments using biodegradable tape, grafting incompatibility, gas exchange, agronomic characteristics and bacterial wilt epidemiology were assessed throughout the cycle. The use of biodegradable tape favored graft healing. Cayenne pepper, Jerusalem cherry, and sticky nightshade should not be employed as rootstocks for scions of tomato cultivar Santa Cruz Kada. The mini-tomato accession RVTC-66 showed low graft incompatibility, high photosynthetic efficiency and, when compared to self-grafting, the same fruit production, but with higher plant health index concerning the bacterial wilt.

Agronomic and Anatomical Indicators of Dwarfism and Graft Incompatibility in Citrus Plants

Poncirus trifoliata var. monstrosa (T. Ito) Swingle is a rootstock used in Brazilian citriculture for its potential to induce dwarfism and the viability of densified crops. Its recommendation is still restricted due to lack of research on the performance and compatibility of different types of scion under specific conditions of soil and climate. The aim of this study was to correlate plant size and productive efficiency with anatomical indicators of dwarfism or graft incompatibility between citrus scion cultivars and the ‘Flying Dragon’ trifoliate orange (FD) and ‘Rangpur Lime’ (RL) as rootstocks. The experimental design was of randomised blocks with split plots, with the experiment conducted in an orchard from the fourth to the sixth year of cultivation, under localised irrigation. The treatments consisted of two rootstocks (FD and RL) in the plots and five scion cultivars (Tahiti acid lime, and Natal, Navel, Lima Sorocaba and Pera oranges) in the sub-plots, with four replications per treatment. The agronomic performance of the plants was evaluated, together with the characteristics of samples containing the cambial zone and secondary xylem below, above and within the graft region. The FD rootstock gives the smallest size and greatest productive efficiency. The ‘Navel’ orange has good anatomical plasticity, adjusting itself more efficiently to the rootstocks. Visual symptoms of incompatibility between the ‘Pera’ orange grafted onto the FD can be seen at 64 months after planting. Vessel size and frequency, as well as the size and disposition of the cambial zone, are related to dwarfism and graft incompatibility.

Use of phenotypic selection and hypocotyl properties as predictive selection criteria in pumpkin (Cucurbita moschata Duch.) rootstock lines used for grafted cucumber (Cucumis sativus L.) seedling cultivation

In recent years, grafted cucumber seedling use has been rapidly increasing worldwide, especially for providing tolerance to stress conditions and positively affecting yield potential. However, graft incompatibility is still an important issue in grafted seedling production. Hypocotyl properties of rootstocks and scions are of great importance for ensuring graft compatibility. This study aimed to select superior rootstock genotypes based on certain selection criteria, such as hypocotyl morphology, grafted seedling visual evaluation, and graft compatibility properties, of 42 pumpkin (Cucurbita moschata) genotypes that are included in the cucumber rootstock breeding program and are resistant to Fusarium oxysporum f. sp. cucumerinum. Three C. moschata and three C. maxima × C. moschata rootstocks were used as control cultivars. All genotypes were grafted with the Gordion F1 cucumber cultivar using the splice grafting method. In the pumpkin rootstock genotypes, the cross-sectional area of the hypocotyls varied between 3.47 mm2 and 10.42 mm2, pith cavity area varied between 0.59 mm2 and 4.14 mm2, and pith cavity rate varied between 10.3% and 65.2%. Vascular bundle numbers of the genotypes were between 6 and 12. In the rootstocks, success rates of the grafts ranged from 56% to 100%. Among the rootstock/scion combinations, 100% success rate was obtained in 19 inbred pumpkin rootstocks. Scion rooting never occurred in 11 of the pumpkin rootstocks. The correlation analysis of the investigated properties showed that there was a statistically nonsignificant relationship between the crosssectional area of the hypocotyl, vascular bundle number, and graft success rate (P > 0.05). The parameter with the greatest negative effect on graft success rate was scion rooting (r: -0.49, P < 0.05). The results showed that scion rooting depended on the pith cavity rate and decreased as the pith cavity rate decreased (r: 0.56, P < 0.05). The weighted-ranking method was employed to select the most promising pumpkin rootstock genotypes for grafted seedling production. According to the evaluations, 12 pumpkin rootstocks were selected as the most superior rootstock candidates. We aim to develop new hybrid rootstocks for cucumber in the near future by carrying out special combinations of tools from test-based hybridization studies among the selected pumpkin lines.

Anatomical graft compatibility study between apricot cultivars and different plum based rootstocks

Abstract The introduction of some new rootstocks requires knowledge of the extent and nature of (in)-compatibility reactions before releasing these rootstocks on the market, providing both nursery and fruit growers valuable information about the risk of weak unions (‘localized’ incompatibility). Therefore, trials were established at Aula Dei Experimental Station (Zaragoza, Spain) nurseries to assess graft compatibility between four apricot cultivars (‘Bulida’, ‘Canino’, ‘Moniqui’ and ‘Paviot’) and twenty-one plum based rootstocks. In general, ‘Paviot’ cv. exhibited good graft compatibility with all tested rootstocks, although several discontinuities in the bark were observed in the case of Ademir, Myrobalan 713 AD and Miral 3278 AD. ‘Bulida’ cv. was graft compatible with all rootstocks, with the exception of Marianna 2624 and Miral 3278 AD. They showed vascular and wood discontinuities in their graft unions. In the case of the exigent cvs. group (‘Canino’ and ‘Moniqui’) graft incompatibility was observed, in general, with all fast-growing plum rootstocks (mainly Prunus cerasifera) and some interspecific hybrid rootstocks. On the contrary, the hexaploid P. insititia plums showed good graft compatibility with all apricot cvs., with the exception of Montizo and PM 140 AD rootstocks. A positive and significant correlation (r = 0.628, P ≤ 0.01) of graft incompatibility occurrence was found between the first or second year and the fourth year after grafting. Finally, the study of the ratio ‘stem circumference / union circumference’ showed that most of the scion-rootstock graft combinations presenting a ratio inferior to 0.8 showed discontinuities in the bark and/or in the wood at the graft union.