Interspecific Grafting Research Articles

Interspecific grafting promotes poplar growth and drought resistance via regulating phytohormone signaling and secondary metabolic pathways

Populus cathayana (C) grafted onto P. deltoides (D) (C/D) can promote growth better than self-grafting (C/C and D/D). However, the mechanisms underlying growth and resistance to drought stress are not clear. In this study, we performed physiological and RNA-seq analysis on the different grafted combinations. It was found that C/D plants exhibited higher growth, net photosynthetic rate, IAA content and intrinsic water use efficiency (WUEi) than C/C and D/D plants under both well-watered and drought-stressed conditions. However, most growth, photosynthetic indices, and IAA content were decreased less in C/D, whereas ABA content, WUEi and root characteristics (e.g., root length, volume, surface area and vitality) were increased more in C/D than in other grafting combinations under drought-stressed conditions. Transcriptomic analysis revealed that the number of differentially expressed genes (DEGs) in leaves of C/D vs C/C (control, 181; drought, 121) was much lower than that in the roots of C/D vs D/D (control, 1639; drought, 1706), indicating that the rootstocks were more responsive to drought resistance. KEGG and GO functional enrichment analysis showed that the enhanced growth and drought resistance of C/D were mainly related to DEGs involved in the pathways of ABA and IAA signaling, and secondary metabolite biosynthesis, especially the pathways for lignin and dopamine synthesis and metabolism. Therefore, our results further demonstrated the dominant role of rootstock in drought resistance, and enriched our knowledge on the mechanism of how interspecific grafting enhanced the growth and drought resistance in poplar.

Integrated transcriptome and DNA methylome analysis reveal the biological base of increased resistance to gray leaf spot and growth inhibition in interspecific grafted tomato scions.

Grafting is widely used as an important agronomic approach to deal with environmental stresses. However, the molecular mechanism of grafted tomato scions in response to biotic stress and growth regulation has yet to be fully understood. This study investigated the resistance and growth performance of tomato scions grafted onto various rootstocks. A scion from a gray leaf spot-susceptible tomato cultivar was grafted onto tomato, eggplant, and pepper rootstocks, creating three grafting combinations: one self-grafting of tomato/tomato (TT), and two interspecific graftings, namely tomato/eggplant (TE) and tomato/pepper (TP). The study utilized transcriptome and DNA methylome analyses to explore the regulatory mechanisms behind the resistance and growth traits in the interspecific graftings. Results indicated that interspecific grafting significantly enhanced resistance to gray leaf spot and improved fruit quality, though fruit yield was decreased compared to self-grafting. Transcriptome analysis demonstrated that, compared to self-grafting, interspecific graftings triggered stronger wounding response and endogenous immune pathways, while restricting genes related to cell cycle pathways, especially in the TP grafting. Methylome data revealed that the TP grafting had more hypermethylated regions at CHG (H = A, C, or T) and CHH sites than the TT grafting. Furthermore, the TP grafting exhibited increased methylation levels in cell cycle related genes, such as DNA primase and ligase, while several genes related to defense kinases showed decreased methylation levels. Notably, several kinase transcripts were also confirmed among the rootstock-specific mobile transcripts. The study concludes that interspecific grafting alters gene methylation patterns, thereby activating defense responses and inhibiting the cell cycle in tomato scions. This mechanism is crucial in enhancing resistance to gray leaf spot and reducing growth in grafted tomato scions. These findings offer new insights into the genetic and epigenetic contributions to agronomic trait improvements through interspecific grafting.

A Grafting Procedure for Gossypium hirsutum Based on In Vitro Grown Seedlings

Intervarietal grafting, and in some cases interspecific grafting, practiced mainly in horticultural crops has many practical applications. Grafting can also be a useful tool to perform basic physiological, biochemical, and molecular studies to better understand communication between shoot and root in a row crop, such as cotton. We have established a grafting protocol for upland cotton (Gossypium hirsutum L.) genotypes. Although less efficient, it can be used to create grafts between upland and Pima (G. barbadense) or Old-world cottons (G. arboreum or G. herbaceum). The procedure used 8-day-old seedlings grown in culture under sterile conditions to obtain the scion and rootstock. The scion consisted of the shoot apical meristem with a few leaf primordia, epicotyl, and a small portion of the hypocotyl with the cotyledons removed. The rootstock retained 2 to 3 cm of basal hypocotyl portion with the roots trimmed. Cleft grafts were assembled under aseptic conditions followed by their culture in vitro. Once established, as indicated by the healthy growth of three to four true leaves and roots, the grafts were moved to soil in small pots. After hardening the grafts on a laboratory bench for few weeks, they were transferred to larger pots and grown to maturity in a greenhouse to obtain seeds. The success rate using our protocol ranged from 90 to 100% for Coker 312 genotype and its derivative transgenic and gene edited lines. The method was also applicable to generate intervarietal and interspecific graft unions among various types of cotton plants.

Transcriptome and metabolome analyses reveal improvement in blueberry fruit quality by interspecific grafting

Transcriptome and metabolome analyses reveal improvement in blueberry fruit quality by interspecific grafting

Trends and gaps in tomato grafting literature: a systematic approach

Aim of study: To investigate the trends and existing research gaps in tomato grafting by employing scientometric methods. Area of study: In silico at SCOPUS database. Material and methods: Research articles were retrieved by combining the search terms related to tomato and grafting. The articles were selected according to pre-established criteria. Temporal trends and scientometric indexes were determined. Bibliometric mappings were conducted to determine the main countries, authors, and journals that published articles on tomato grafting; and to acquire collaboration and keywords co-occurrence networks. Technical aspects of tomato grafting were analyzed. Main results: A total of 397 research articles published from 1944 to 2020 were analyzed. The number of publications on tomato grafting increased at an annual rate of 8.8%. The USA and Spain are notable in terms of the number of published and cited articles. The USA and European countries had the highest number of collaborations. European authors had the strongest research connections. Interspecific grafts (61.83%) and experiments in controlled conditions (82.87%) predominated. The growing interest in tomato grafting has been observed as a means of overcoming environmental issues as well as yield and quality improvement. Research highlights: Collaboration among research groups contributed to a higher research impact on the theme. The mitigation of abiotic stresses and fruit quality has risen as significant concerns for tomato crops.

Effects of interspecific grafting of Coffea arabica and elevation on coffee growth, yield, and quality attributes in Costa Rica

Interspecific grafting of Coffea arabica scions on C. canephora rootstock has been proposed as a strategy against nematode infestation, but also for cultivation of coffee under environmental stressors (such as temperature extremes). An agroforestry-like microclimate was established using artificial shade nets (30% light interception) across a multi-site elevation trial (from 1000 to 1450 m above sea level) in Costa Rica (Alajuela region). The effects of interspecific grafting of scions from modern C. arabica varieties (‘Villa Sarchi’ and an F1 hybrid called ‘H3’) onto C. canephora (‘Nemaya’) rootstock were tested under these conditions. The interactions between grafting, genotype and elevation were determined on the above- and below ground growth, agronomic traits, photosynthesis as well as bean and cup qualities.Variation in the protuberance of the graft union (trunk vs. below graft union collar diameters) were detected. However, no physical vascular blockages were observed in any of the interspecific grafted plants. Generally, interspecific grafting negatively affected most aerial and root traits as well bean yields for both ‘H3’ and ‘Villa Sarchi’ varieties compared to the non-grafted plants. A significant reduction in the photosynthesis of grafted ‘H3’ (in terms of Vcmax and ΦCO2max) was also observed. However, there were no impacts of grafting on the final bean attributes nor cup quality. Genetics of the scions largely determined coffee yields, with higher yields produced by ‘H3’ compared to ‘Villa Sarchi’. The scion also controlled agronomic traits, bean qualities and belowground biomass (dry weight of taproot, secondary root mass and overall root system). This was observed when either C. arabica or C. canephora scion material was used. Increasing elevation significantly reduced the trunk, branches and shoot system, chlorophyll fluorescence parameters and other agronomic traits. However no significant interactions were found between grafting and elevation (within the range tested). Our results show how interspecific grafting of C. arabica onto C. canephora can reduce plant biomass and productivity under shade and across an elevational gradient, especially when the composite plant involves a vigorous and high yielding F1 hybrid.

Anatomical and biophysical basis for graft incompatibility within the Solanaceae.

Interspecies grafting is an economically relevant technique that allows beneficial shoot and root combinations from separate species to be combined. One hypothesis for the basis of graft compatibility revolves around taxonomic relatedness. To test how phylogenetic distance affects interspecific graft compatibility within the economically important Solanaceae subfamily, Solanoideae, we characterized the anatomical and biophysical integrity of graft junctions between four species: tomato (Solanum lycopersicum), eggplant (Solanum melongena), pepper (Capsicum annuum), and groundcherry (Physalis pubescens). We analyzed the survival, growth, integrity, and cellular composition of the graft junctions. Utilizing various techniques, we were able to quantitatively assess compatibility among the interspecific grafts. Even though most of our graft combinations could survive, we show that only intrageneric combinations between tomato and eggplant are compatible. Unlike incompatible grafts, the formation of substantial vascular reconnections between tomato and eggplant in the intrageneric heterografts likely contributed to biophysically stable grafts. Furthermore, we identified 10 graft combinations that show delayed incompatibility, providing a useful system to pursue deeper work into graft compatibility. This work provides new evidence that graft compatibility may be limited to intrageneric combinations within the Solanoideae subfamily. Further research amongst additional Solanaceous species can be used to test the extent to which our hypothesis applies to this family.

Transcriptome and physiological analyses reveal new insights into delayed incompatibility formed by interspecific grafting

Pinus elliottii used as rootstock instead of homologous rootstock, have been proved to accelerate early growth of the scion (Pinus massoniana), for cultivation of large diameter wood. However, the basal diameter of scions in heterologous grafts was significantly smaller than self-graft 10 years later, according to field investigation, which was opposed to cultivation objectives. Although advantage of heterologous grafts has been reported, less is known about the long term effect of heterologous rootstock on scions of P. massoniana. The aim of present study was to investigate the mechanism of the above difference. Toward this aim, the growth traits and physiological characteristics of scions in the two graft groups were studied, and the underlying mechanism was preliminarily explored through transcriptome sequencing technology. Results showed that scions of heterologous grafts had less TSCA compared to self-grafts, while no significant difference of plant height, number of branches and canopy volume between two graft groups. Besides, scion leaves of heterologous grafts displayed higher antioxidant enzyme activity and lower chlorophyll content. And interactions between rootstocks and scions had also changed the mineral element composition of scion leaves. Compared with homologous grafts, scion leaves of heterologous grafts accumulated more K+, Mg2+ and Zn2+, but less Ca2+,which have been proved to be conducive to the growth of stem diameter of P. massoniana. Moreover, a comparative transcriptome analysis of two graft groups showed that DEGs between them were mainly caused by the specificity of rootstock. GO and KEGG analysis found that heterologous rootstock had different gene expression preferences, and the gene expression level between rootstocks and scions were significantly different, such as auxin auxin-related genes and stress responsive genes. That may imply that auxin pathway played an important role not only in grafting healing process, but also in maintaining the growth between scion and stock. Summary of all above results, we concluded that the long term effect of heterologous rootstock on scions may be unsatisfactory with the later rapidly growth of scion, probably due to delayed graft incompatibility between scion and stock of heterologous grafts. This study may remind us that the long-term growth of the scion deserves attention as well as the healing process, which could also provide a basis for delayed graft incompatibility.

Exploring graft incompatibility markers: Intraspecific and interspecific grafts of tomato (Solanum lycopersicum L.)

Grafting is an innovative and cost-efficient technique commonly practiced in solanaceous crops such as tomato (Solanum lycopersicum L.). However, incompatibility limits the far-reaching grafting approaches in sustainable food production worldwide. An early and precise graft incompatibility detection will have great significance, since graft compatibility between rootstock and scion is a pre-requisite for a successful grafting. The current study examined graft incompatibility in tomato self-grafts (Roma tomato grafted on Roma tomato), intraspecific grafts (Roma tomato grafted on Super red tomato) and interspecific grafts (Roma tomato grafted on Eggplant and Pepper plant) at 4, 8 and 16 DAG (days after grafting) to explore physiological, biochemical and metabolic changes at the graft junction that might be used as graft incompatibility markers. Results revealed that among grafted combinations intraspecific grafts depicted a vigorous resistance against oxidative damage by accumulating low hydrogen peroxide, minimum membrane permeability and lipid peroxidation coupled with high antioxidants activity compared to other grafted combinations while interspecific grafts with low survival rates showed high accumulation of total phenolic and flavonoid content at all three grafting stages (4, 8 and 16 DAG). During histological examinations of graft junctions, an apparent long adherence region at the graft junction of self-grafts and intraspecific grafts were observed while interspecific grafts present a small adhesion line. These variations at the structural, physiological and metabolic level may regulate incompatibility and may serve as markers for early detection of graft incompatibility. These findings may further help in the development of markers at molecular level valuable in rootstock development programs.

Pertumbuhan dan Hasil Kopi Grafting Robusta/Liberika pada Klon dan Waktu Pemupukan yang berbeda

Grafting of different coffee species (interspecific grafting) aims to take advantage of the superiority of the rootstock and promote the growth and production of the scion. For example, Robusta coffee is grafted with Liberika coffee as rootstock. One of the principles of fertilization is the application of fertilizer at the right time. This study aimed to determine the effect of clones of Robusta/Liberica interspecific grafting and different fertilization times on the growth and yield of Robusta coffee. The research was conducted in a 15-year-old coffee plantation with the rootstock of Liberika coffee of the Red Robinson variety which was grafted to the scion of multiclonal Robusta coffee. Planting distance of coffee was 2.5 m x 2.5 m and shade trees were Gliricidia sepium. This research used a split plot design arranged in a factorial (4x2) with three replications so that there were 24 experimental units. The main plot was the time of fertilization, namely in early April and October and in early May and November. As sub-plots, there were Robusta coffee clones, namely Korolla 1, Korolla 2, Tugu Bungkuk, and Darmani. The results showed that fertilization time, clones, and their interactions did not affect the number of primary branches, primary branch length, number of secondary branches, fruit weight of harvested samples, number of fruit per bunch, fruit weight per bunch, dry seed weight per bunch, and coffee yield per tree. The interaction of coffee clones and fertilization time had a significant effect on the number of pods per branch, the number of harvested samples, dry bean weight of harvested samples, dry bean weight per branch, and coffee yield per hectare. For Darmani coffee clones, delaying fertilization from April and October to May and November reduced coffee yield. Key words : Interspesific grafting, Liberica, Robusta, time of fertilization, yield

Peningkatan Produktivitas Kopi Sistem Sambung Interspesifik Robusta/Liberika

Lampung coffee farmers generally cultivate Robusta coffee and practice ethno-agronomy based on local wisdom, including cultivating coffee of Robusta/Liberica interspecific grafting system. This community service activity uses the method of face-to-face meetings, FGD, training, and making demonstration plots. The targets of this activity are management and members of Wijaya Muda farmer groups and farmers around the location at Pekon Sukajaya, Sumberjaya, West Lampung District.The results showed that based on evaluation results, the PKM activities was going well, with obtaining a total score of 12 (3 variables, scores 1-5) which indicated the level of participation was categorized as good. The evaluation of the results selected from 12 indicators of knowledge/skills showed an increase in the score of 53 to 73, which means that the level of knowledge skills increased from sufficient to good. The intensification of the Robusta/Liberica grafting system increased drought resistance and coffee production.
 
 Keywords: Biochar, grafting, interspesific, Robusta/Liberica, intensification

Physico-chemical and postharvest quality characteristics of intra and interspecific grafted tomato fruits

The objective of this study was to evaluate the physico-chemical and postharvest quality characteristics of intra- and interspecific grafted tomato fruit. Anna F1, a commercial tomato variety was interspecifically (Tomato Scion and African eggplant rootstock ( Solanum aethiopicum) ) and intraspecifically (Tomato Scion and bacterial wilt resistant hybrid tomato rootstock) grafted. The tomatoes were grown in a greenhouse and harvested at mature green, turning and ripe stages respectively. The tomatoes were analyzed for size, weight, cumulative weight loss, color changes, texture, respiration and ethylene gas production rates, vitamin C and lycopene content. Interspecific grafting on Manyire green, AB2, and intraspecific grafting on Armada, and B.B rootstocks significantly improved physical and physiological attributes of the tomato fruit. There was significant difference (p < 0.05) in size and weight of grafted tomatoes and control at all the three maturity stages. Intraspecific grafted tomato fruits on Armada rootstocks had the best quality characteristics in terms of firmness, low weight loss, respiration and ethylene production rates which are associated with extended postharvest shelf-life. Intraspecific grafting reduced respiration and ethylene gas production rates with tomatoes grafted onto Armada rootstocks attaining the least climacteric peaks of 20.20 ml CO 2 Kg -1 h -1 and 0.34 μL C 2 H 4 Kg -1 h -1 respectively at mature green stage, thus leading to extendend postharvest life of these tomatoes. Tomatoes grafted onto B.B rootstock had the highest vitamin C content (28.11 mg/100 g). In general, intraspecific grafting recorded the best quality traits over the interspecific grafting. However interspecific grafting of tomato onto African eggplant Manyire and AB2 rootstocks had lower but comparable fruit quality to intraspecific grafting. • The effect of grafting on tomato quality is dependent on scion/rootstock combination. • Tomatoes from Manyire and AB2 rootstocks grafts (interspecific), and Armada and B.B rootstocks (intraspecific) had improved physical, physiological qualities as compared to nongrafted control. • Fruits from the Armada rootstock reported the best quality characteristics in terms of firmness and low weight loss, respiration and ethylene production rates which are associated with prolonging shelf-life. • Lycopene content was not affected by grafting. • In general, intraspecific grafting had the best quality traits over the interspecific grafting. However interspecific grafting of tomato onto African eggplant Manyire and AB2 rootstocks has comparable fruit quality to intraspecific grafting especially for resource poor farmers.

Integrated DNA methylation, transcriptome and physiological analyses reveal new insights into superiority of poplars formed by interspecific grafting.

Plant grafting has a long history and it is extensively employed to improve plant performance. In our previous research, reciprocal grafts of Populus cathayana Rehder (C) and Populus deltoides Bart. Ex Marsh (D) were generated. The results showed that interspecific grafting combinations (scion/rootstock: C/D and D/C) grew better than intraspecific grafting combinations (C/C and D/D). To further understand differences in molecular mechanisms between interspecific and intraspecific grafting, we performed an integrated analysis, including bisulfite sequencing, RNA sequencing and measurements of physiological indicators, to investigate leaves of different grafting combinations. We found that the difference at the genome-wide methylation level was greater in D/C vs D/D than in C/D vs C/C, but no difference was detected at the transcription level in D/C vs D/D. Furthermore, the grafting superiority of D/C vs D/D was not as strong as that of C/D vs C/C. These results may be associated with the different methylation forms, mCHH (71.76%) and mCG (57.16%), that accounted for the highest percentages in C/D vs C/C and D/C vs D/D, respectively. In addition, the interspecific grafting superiority was found mainly related to the process of photosynthesis, phytohormone signal transduction, biosynthesis of secondary metabolites, cell wall and transcriptional regulation based on both physiological and molecular results. Overall, the results indicated that the physiological and molecular phenotypes of grafted plants are affected by the interaction between scion and rootstock. Thus, our study provides a theoretical basis for developing suitable scion-rootstock combinations for grafted plants.

Monocotyledonous plants graft at the embryonic root-shoot interface.

Grafting is possible in both animals and plants. Although in animals the process requires surgery and is often associated with rejection of non-self, in plants grafting is widespread, and has been used since antiquity for crop improvement1. However, in the monocotyledons, which represent the second largest group of terrestrial plants and include many staple crops, the absence of vascular cambium is thought to preclude grafting2. Here we show that the embryonic hypocotyl allows intra- and inter-specific grafting in all three monocotyledon groups: the commelinids, lilioids and alismatids. We show functional graft unions through histology, application of exogenous fluorescent dyes, complementation assays for movement of endogenous hormones, and growth of plants to maturity. Expression profiling identifies genes that unify the molecular response associated with grafting in monocotyledons and dicotyledons, but also gene families that have not previously been associated with tissue union. Fusion of susceptible wheat scions to oat rootstocks confers resistance to the soil-borne pathogen Gaeumannomyces graminis. Collectively, these data overturn the consensus that monocotyledons cannot form graft unions, and identify the hypocotyl (mesocotyl in grasses) as a meristematic tissue that allows this process. We conclude that graft compatibility is a shared ability among seed-bearing plants.

Flowering Time and Productivity of Interspecific Grafts Between Pepper Species in Contrasting High Tunnel-sheltered and Open-field Production Environments in Costa Rica

The production of sweet peppers (Capsicum annuum) is often constrained in tropical environments by susceptibility to persistent soil-borne diseases, including bacterial wilt (Ralstonia solanacearum). However, the production of sweet peppers in high tunnels using sterile soilless media irrigated with nutrient solution offers the potential to reduce the incidence of bacterial wilt. An additional strategy for disease management is the use of sweet pepper scions grafted onto rootstocks that are resistant to soil-borne pathogens. Two sweet pepper cultivars grown extensively in the tropics, Nathalie and 4212, were used as scions and grafted onto the habanero pepper cultivar Habanero TEC (Capsicum chinense) and the aji pepper cultivar Baccatum TEC (Capsicum baccatum). Two cultivars related to the two rootstocks were prescreened for susceptibility to two virulent strains of bacterial wilt. Graft combinations were grown in two environments, a high tunnel with automatic nutrient solution irrigation of containers filled with sterile coconut fiber and an open field with known high levels of bacterial wilt inoculum. Self-grafted and nongrafted plants of scions were included as checks. The disease susceptibility screening showed that the area under the disease progress curve was consistently low for ‘Habanero TEC’ and ‘Baccatum TEC’ when inoculated with two virulent strains of bacterial wilt, suggesting that habanero pepper cultivars and, to a lesser degree, aji pepper cultivars may be useful as rootstocks in soils with bacterial wilt inoculum. Significant increases in yield, fruit number, and reduced time to flowering were observed in the high tunnel compared with the open-field environment. Individual fruit weight was reduced in the high tunnel compared with the field. Yield, fruit number, fruit weight, and time to flowering were consistent between scions regardless of rootstock. No differences were observed for yield, fruit number, fruit weight, or time to flowering of self-grafted and nongrafted scion checks. In the high tunnel, yield was higher in scions grafted onto ‘Habanero TEC’ compared with self-grafted and nongrafted checks. In the open field, yield and fruit number were highest on scions grafted onto ‘Habanero TEC’. Regardless of graft treatment, high-tunnel production in tropical environments can result in significant increases in yield and fruit number compared with open-field production. No advantage of grafted plants was observed in the high-tunnel production environment. In contrast, in the open-field environment, grafting sweet pepper scions onto pungent habanero rootstocks resulted in a significant increase in yield, fruit number, and fruit size compared with self-grafted and nongrafted checks. The increase was likely attributable to the resistance of habanero pepper cultivars to soil-borne diseases, including bacterial wilt.

Cytological Studies on Graft Union Development with Perennial Chilli Rootstocks

Grafting technology in vegetable crops is becoming increasingly popular as an alternative tool to improve the biotic and abiotic resistance besides improvement in horticultural traits. By utilizing the right combination of resistant rootstock and scion, desired variability can be achieved to improve the yield and quality of vegetables. A study was conducted at the College orchard, Department of Vegetable science, Horticultural College and Research Institute, Tamil Nadu Agricultural University, Coimbatore during the year 2020-2021 to evaluate the graft compatibility with two chilli rootstocks. The experimental material consisted of two perennial rootstocks viz., CC-CBE-001 and CF-CBE-007 and three scion materials viz., TNAU Chilli Hybrid CO 1, Ranga hybrid and Bangaram hybrid. Wedge grafting was done using 60 days old rootstock and 45 days old scion seedlings with nine treatments. The adhesion line wall thickness of pith cells were determined at different stages after grafting. The wound healing of the scion-rootstock union was studied using microscopic examination of the grafting region on the 5th, 10th, 15th and 20th day after grafting. It was observed that ten days after grafting, vascular bundle was formed and a large amount of callus was produced to bridge the scion and rootstock. Despite interspecific grafting, callus formation, subsequent cell differentiation and vascular connection were established, resulting in effective graft compatibility, according to the anatomical and histological analysis.

Primary metabolism and initial development of grafted black pepper seedlings

The production of black pepper seedlings through grafting is a promising strategy to mitigate the effect of environmental stresses, such as drought, that limit its cultivation. However, studies on compatibility between grafts and rootstocks are still scarce, especially considering the wild species of the genus Piper and the cultivated genotypes of black pepper. The objective of this work was to evaluate the relationship between primary metabolism and the development of black pepper seedlings obtained through intra- and interspecific grafting. The method used was that of cleft lateral grafting, as graft the Bragantina cultivar, better known in the world as ‘Panniyur 1’, and ‘Kottanadan’ cultivar and three wild species (Piper hispidum, Piper aduncum and Piper tuberculatum) were used as root-stock. As a control, ´Bragantina` was grafted onto itself (homograft). The experiment was carried out for 110 days and the seedlings were evaluated for development, gas exchange, and carbohydrate allocation. The rootstock influences the development and primary metabolism of seedlings. P. aduncum showed greater initial compatibility among wild species, due to less impediment to carbohydrate flow. P. tuberculatum showed early incompatibility, as the grafts died. The seedlings grafted on P. hispidum and 'Kottanadan' had initial compatibility with an average of 78% survival and 60% budding, but they may have late incompatibility due to limitation of carbohydrate flow.

Effects of Interspecific Grafting Between Capsicum Species on Scion Fruit Quality Characteristics

Production of Capsicum annuum peppers is often limited, especially in tropical environments, by susceptibility to soil pathogens including Ralstonia solanacearum. Grafting desirable cultivars onto selected rootstocks can increase adaptation to abiotic stress and is an alternative to pesticides for managing soilborne pathogens. Cultivars of two other pepper species, Capsicum baccatum and Capsicum chinense, are tolerant or resistant to an array of soilborne pathogens and have potential as rootstocks; however, knowledge of how interspecific grafting may affect scion fruit quality is lacking. Flowering time, yield, and fruit quality characteristics were evaluated in 2017 and 2020 for C. annuum cultivars Dulcitico, Nathalie (2017), Gypsy (2020), and California Wonder used as scions grafted onto Aji Rico (C. baccatum) and Primero Red (C. chinense) rootstocks, including self-grafted and nongrafted scion checks. In 2020, the rootstocks per se were evaluated. The two rootstocks (‘Aji Rico’ and ‘Primero Red’), three scions, and self- and nongrafted scions were evaluated using a factorial, replicated, completely randomized design in fields at the West Madison and Eagle Heights Agricultural Research Stations located in Madison, WI, in 2017 and 2020, respectively. Differences among the main effects for scion fruit quality characteristics were consistent with cultivar descriptions. No scion × rootstock interactions were observed. Rootstocks did not result in changes in total fruit number, yield, fruit shape (length-to-width ratio), or soluble solids of scion fruit compared with self- and nongrafted checks. The rootstock ‘Primero Red’ increased fruit weight and decreased time to flowering regardless of scion compared with self- and nongrafted checks. All scions were sweet (nonpungent) cultivars and both rootstocks were pungent cultivars. No capsaicinoids were detected in the fruit of sweet pepper scions grafted onto pungent pepper rootstocks. The results indicate that interspecific grafts involving ‘Aji Rico’ and ‘Primero Red’ will not have deleterious effects on fruit quality characteristics of sweet pepper scions.

Growth and Photosynthetic Characteristics of Interspecific Grafting Coffee under Different Mixed Substrate

Growth and Photosynthetic Characteristics of Interspecific Grafting Coffee under Different Mixed Substrate

Differential transcription pathways associated with rootstock-induced dwarfing in breadfruit (Artocarpus altilis) scions

BackgroundBreadfruit (Artocarpus altilis) is a traditional staple tree crop throughout the tropics. Through interspecific grafting, a dwarf phenotype with over 50% reduction in plant height was identified when marang (Artocarpus odoratissimus) rootstocks were used. However, the molecular mechanism underlying the rootstock-induced breadfruit dwarfing is poorly understood.ResultsAn RNA-sequencing study of breadfruit scions at 22 months after grafting identified 5409 differentially expressed genes (DEGs) of which 2069 were upregulated and 3339 were downregulated in scion stems on marang rootstocks compared to those on self-graft. The DEGs were predominantly enriched for biological processes involved in carbon metabolism, cell wall organization, plant hormone signal transduction and redox homeostasis. The down-regulation of genes encoding vacuolar acid invertases and alkaline/neutral invertases, was consistent with the decreased activity of both enzymes, accompanying with a higher sucrose but lower glucose and fructose levels in the tissues. Key genes of biosynthetic pathways for amino acids, lipids and cell wall were down regulated, reflecting reduction of sucrose utilisation for stem growth on dwarfing rootstocks. Genes encoding sugar transporters, amino acid transporters, choline transporters, along with large number of potassium channels and aquaporin family members were down-regulated in scion stems on marang rootstocks. Lower activity of plasma membrane H+-ATPase, together with the predominance of genes encoding expansins, wall-associated receptor kinases and key enzymes for biosynthesis and re-modelling of cellulose, xyloglucans and pectins in down-regulated DGEs suggested impairment of cell expansion. Signalling pathways of auxin and gibberellin, along with strigolacton and brassinosteroid biosynthetic genes dominated the down-regulated DEGs. Phenylpropanoid pathway was enriched, with key lignin biosynthetic genes down-regulated, and flavonoid biosynthetic genes upregulated in scions on marang rootstocks. Signalling pathways of salicylic acid, jasmonic acid, ethylene and MAPK cascade were significantly enriched in the upregulated DEGs.ConclusionsRootstock-induced disruption in pathways regulating nutrient transport, sucrose utilisation, cell wall biosynthesis and networks of hormone transduction are proposed to impair cell expansion and stem elongation, leading to dwarf phenotype in breadfruit scions. The information provides opportunity to develop screening strategy for rootstock breeding and selection for breadfruit dwarfing.