Watermelon Rootstocks Research Articles

Farklı Anaçlar Üzerine Aşılı Bazı Karpuz Hatlarının Sera Koşullarında Yaprak Besin İçerikleri Üzerine Etkileri

The aim of this study is to examine how grafting affects the concentration of plant nutrients in watermelon plants with different rootstocks and various skin color. This study was carried out in the greenhouses and laboratories of Mersin Alata Horticultural Research Institute in the 2020 spring/summer growing season. As rootstock, from the Lagenaria spp. group Argentario, from the Cucurbita maxima×C. moschata group Nun9075 and TZ148; and from the Citrullus amarus group PI 296341 were used. Turkey is an important producer for Nun9075 and TZ148, which are used as rootstocks for watermelon. B1, B2, S1 and S2 pure lines were used as scions. Pure lines S1 and S2 with striped rind ground pattern and pure lines B1 and B2 with dark green rind ground color were used. As a result, no direct relationship was found between rootstocks and watermelon lines in terms of plant nutrient uptake. Nitrogen (N) content was highest in Argentario (2.58%) rootstocks and S1 line (2.60%). Phosphorus (P) and iron (Fe) content did not show a statistically significant difference among rootstocks and lines. The highest potassium (K) content was found on Argentario (2.83%) and NUN9075 (2.82%) rootstocks and S1 (2.88%) and B1 (2.81%) lines. While the highest Mg content was obtained from NUN 9075 (0.39%) and B2 lines, it had high values in other lines and was included in the same group. While the highest Zn content was obtained from NUN 9075 (40.03 ppm) rootstock, it was in the same group with high values in other rootstocks. The highest Mn content was obtained from rootstock 3335 (58.80 ppm) and B1 line (52.01 ppm).

Non-Invasive Micro-Test Technology and Reciprocal Grafting Provide Direct Evidence of Contrasting Na+ Transport Strategies between Cucurbita moschata and Cucurbita maxima

Cucurbita species are widely used as rootstocks for cucumber, watermelon, and other plants for the restriction of toxic Na+ transport from root to shoot. Previous studies have found distinct salt tolerance strategies between Cucurbita moschata and Cucurbita maxima; the former accumulates a large amount of Na+ in the root, while the latter accumulates Na+ in the shoot. To further study the mechanism of Na+ transport in plants, four reciprocal grafts were made between MB (C. moschata) and JHL (C. maxima), denoted as MB/MB, JHL/JHL, MB/JHL, and JHL/MB (scion/rootstock). The results showed that using MB as the rootstock effectively reduced the accumulation of Na+ in the scion. Conversely, JHL rootstock tended to transfer more Na+ to the scion. To clarify this phenomenon, the velocities of Na+ flows on the root surface, stem, and vein of grafting combinations were measured using non-invasive micro-test technology. Compared with the seedlings using JHL as rootstock, the grafted combination with MB as rootstock had a higher root Na+ efflux and lower Na+ fluxes in the stem and vein. qRT-PCR analyses revealed the critical roles of salt overly sensitive 1 and high-affinity potassium as components of the mechanism enabling Na+ exclusion from the root and Na+ unloading from the stem xylem. Compared with the seedlings using MB as rootstocks, the JHL-grafted plants showed more rapid stomatal closure and decreased transpiration rate in the first three hours after salt stress but maintained a higher level under prolonged salt treatment (120 h). The tissue tolerances of JHL and MB were assessed using the isolated leaves under NaCl to exclude the influence of the root and stem. The results showed that the salinity inflicted more serious damage to MB leaves than to JHL leaves. qRT-PCR analyses indicated that the intracellular Na+/H+ transporter in the leaf vein was involved in this process. All these findings indicated that C. moschata and C. maxima adopted different strategies for regulating Na+ transport, and grafting can be used as a tool to create more salt-tolerant plants.

A comparative study of morphological characteristics in diploid and tetraploid (auto and allotetraploids) Citrullus genotypes

ABSTRACT In this study, ploidy levels were determined by stomatal observations and flow cytometry analysis of plants polyploidised by the application of 0.05% colchicine to seedlings at the first true leaf stage. In the study of developing polyploid watermelon rootstocks, the survival rate of the plants was 77%, and the polyploidisation rates were 11% and 3% according to stomatal observations and flow cytometry analysis, respectively. According to the results of flow cytometry, 22 polyploid genotypes were determined. Auto- (12) and allotetraploids (10) of Citrullus genotypes were developed, and their plant growth performance was determined in hydroponic culture in comparison with diploids, commercial rootstocks (RS841, ‘Argentario’) and watermelon cultivar (‘Crimson Tide’). Putative tetraploids and their diploid controls were grown in hydroponic culture for 21 days, and their vegetative growth performances were determined. The results showed that the increases in plant biomass depending on polyploidisation were 100% in autotetraploids and 156% in allotetraploids as compared to diploid controls.

Compatibility Evaluation and Anatomical Observation of Melon Grafted Onto Eight Cucurbitaceae Species.

Melon (Cucumis melo) is one of the top 10 fruits in the world, and its production often suffers due to soil-borne diseases. Grafting is an effective way to solve this problem. However, graft incompatibility between scion and rootstock limits the application of melon grafting. In this study, the melon was grafted onto eight Cucurbitaceae species (cucumber, pumpkin, melon, luffa, wax gourd, bottle gourd, bitter gourd, and watermelon), and graft compatibility evaluation and anatomical observation were conducted. Taking melon homo-grafted plants as control, melon grafted onto cucumber and pumpkin rootstocks was compatible, while melon grafted onto luffa, wax gourd, bottle gourd, bitter gourd, and watermelon rootstocks was incompatible based on the scion dry weight on day 42 after grafting. Meanwhile, we found that starch–iodine staining of scion stem base is an index to predict graft compatibility earlier, on day 14 after grafting. Further, microsection observations showed that there was more cell proliferation at graft junction of melon hetero-grafted combinations; vascular reconnection occurred in all graft combinations. However, excess callose deposited at graft junction resulted in the blockage of photosynthate transport, thus, leading to starch accumulation in scion stem base, and finally graft incompatibility. In addition, undegraded necrotic layer fragments were observed at graft junctions of melon grafted onto incompatible bitter gourd and watermelon rootstocks. The above results provide clues for the selection and breeding of compatible Cucurbitaceae rootstocks of melon and demonstrate that starch accumulation in scion base and callose deposition at graft junction is associated with melon graft compatibility.

Morphological and Physio-Biochemical Responses of Watermelon Grafted onto Rootstocks of Wild Watermelon [Citrullus colocynthis (L.) Schrad] and Commercial Interspecific Cucurbita Hybrid to Drought Stress

This study aimed to assess the morphological and physio-biochemical responses of a commercial watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) cv. ‘Crimson Sweet’ grafted onto a drought-tolerant rootstock of wild watermelon (bitter apple, Citrullus colocynthis (L.) Schrad, ‘Esfahan’) in comparison with an ungrafted ‘Crimson Sweet’ watermelon or one grafted onto a commercial interspecific Cucurbita hybrid (Cucurbita maxima Duch. × Cucurbita moschata Duch.) rootstock (‘Shintoza’) under water stress. The experiment was conducted in pots under a controlled environment in a greenhouse, and water stress was imposed by maintaining moisture level in pots at 100% (well water (WW)) or 50% (water deficit (WD)) of container capacity (CC). WD significantly decreased most of the morphological traits in ungrafted and grafted plants, while the decrease in growth traits was lower in grafted plants than ungrafted plants. The response of grafted plants onto wild watermelon rootstock (‘Esfahan’) for most of the affected parameters (shoot fresh and dry weight, vine length and internodal length) was, however, comparable to those grafted onto commercial Cucurbita hybrid rootstock (‘Shintoza’). Plants grafted onto bitter apple (wild watermelon) exhibited a relatively lower decrease in growth and biomass, besides showing higher antioxidant activity (e.g., guaiacol peroxidase) concomitant with the lower accumulation of malondialdehyde and electrolyte leakage in the leaf tissues in comparison with ungrafted plants. The overall growth performance, as well as those under water stress conditions in commercial rootstock-grafted watermelon, was related to its better plant water status (e.g., high relative water content) which was likely ascertained by its greater root efficiency. This suggests that watermelons grafted onto bitter apple rootstock and Cucurbita hybrid rootstock were constitutively more resistant to drought, with higher efficiency in mitigating oxidative stress than ungrafted treatment. The above findings demonstrated that bitter apple, a well-adapted desert species, can be used as an alternative rootstock to commercial rootstocks (e.g., ‘Shintoza’) for watermelon grafting under water stress conditions. In addition, bitter apple rootstock can be involved in rootstock breeding programs to improve drought tolerance in watermelon.

Development of Bottle Gourd Lines Resistant to Zucchini Yellow Mosaic Virus Using Ethyl Methanesulfonate Mutagenesis

Zucchini yellow mosaic virus (ZYMV) causes serious damage to cucurbit crops worldwide and can be spread by aphids, by mechanical injury, and in seeds. With the popularization of cucurbit grafting, the use of susceptible rootstock has increased the risk of ZYMV infection in cucurbit crops. In China, the bottle gourd (Lagenaria siceraria) is a widely used rootstock in grafted watermelon production. However, few resistant bottle gourds are available commercially. This study developed bottle gourd lines resistant to ZYMV using ethyl methanesulfonate (EMS) mutagenesis. A new mutated bottle gourd population (M1) was generated by treating seeds with EMS. Diverse phenotypes were observed in the seedlings, flowers, and fruit of M2 plants, some of which are of potential commercial interest, such as dwarfing and different fruit shapes. Based on the M2 phenotypes, 106 M3 lines were selected and screened for resistance to ZYMV by mechanical inoculation and agroinfiltration. Nine M3 lines were resistant to ZYMV during three tests. One inbred M4 line (177-8) was developed and showed stable resistance and no virus when tested using a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and polymerase chain reaction. These resistant lines are promising materials for developing watermelon rootstock and exploring resistance genes as new ZYMV-resistant resources. EMS induction could be a practical strategy for creating resistant cucurbit crops.

Effect of wild watermelon rootstocks and water stress on chemical properties of watermelon fruit

Drought is one of the most important abiotic factors that restrict the production of agricultural plants. An effective way to avoid the negative effects of drought on crops is to cultivate high-yielding varieties by grafting them onto drought-tolerant rootstocks with a strong root system. For this purpose, five different plant materials were used: wild watermelon rootstock, i.e., wild watermelon (A1 and A2), open-pollinated Lagenaria siceraria (gourd) rootstocks (A3), Cucurbita maxima Duchesne × Cucurbita moschata Duchesne (TZ-148) F1 watermelon rootstocks (A4), and the ungrafted control. Five different irrigation depths were applied considering irrigation water (IW)/cumulative pan evaporation (CPE) rations (I100: 1.0 IW/CPE, I75:0.75 IW/CPE, I50:0.50 IW/CPE, I35:0.35 IW/CPE, and I0:rain-fed). The results showed that the use of rootstock and water stress increased the rate of sugar content in the fruit. The highest positive relationship was found between glucose and total sugar, whereas the highest negative relationship was observed between sucrose and malic acid. Parameters such as glucose, total sugar, and citric acid showed significant changes in drought stress. Fructose and malic acid showed significant differences between the rootstocks. Principal Component Analysis (PCA) revealed that the A2I50 application was located in the positive region of both components and showed important results in these parameters. The TZ148 rootstock contributed significantly to the quality of watermelon. In addition, the A2 wild watermelon rootstock showed respectable results, especially under water stress conditions. Based on these results, we conclude that the use of wild watermelon rootstock will contribute to the fruit quality in arid and semi-arid areas with limited water resources.

New Sources of Resistance in Winter Squash (Cucurbita moschata) to Phytophthora Crown Rot and Their Relationship to Cultivated Squash

Butternut squash (Cucurbita moschata) is an important vegetable crop grown and consumed in most states in the United States. C. moschata lines and interspecific hybrids between Cucurbita species are also used as rootstocks for grafting watermelon and melon. However, currently most commercially available C. moschata squash varieties are highly susceptible to crown and root rot caused by the oomycete pathogen Phytophthora capsici, especially in the southeastern United States. All available plant introductions (PIs) of C. moschata (319 PIs) were evaluated for resistance to crown rot. Four-week-old plants were inoculated with 104 zoospores from a local South Carolina isolate of P. capsici. Plants were rated for disease severity 3 weeks after inoculation using a 0 to 5 rating scale (0 = no symptoms and 5 = plant dead). The majority (87%) of the C. moschata PIs were highly susceptible to crown rot in the first evaluation and were rated as 5. Reevaluation of the promising PIs identified several potential new sources of resistance (e.g., Grif 935, PI 442272, PI 442264, PI 512142, PI 438724, PI 438778, and PI 442280). Variability in resistance reaction among plants within a PI was also observed, and not all plants exhibited resistance. Further evaluation of S1 generation from the most resistant plants (rated ≤1) demonstrated that highly resistant plants could be selected from these PIs to develop lines for use in breeding programs. These new sources of resistance can be utilized for developing new crown and root rot resistant rootstocks for watermelon grafting and for developing resistant varieties for human consumption.

Effect of Deficit Irrigation and Rootstocks on Fruit Weight During Post-Harvest Controlled Storage of Watermelon

Grafted seedlings are used not only for protection from soil-borne diseases but also to increase tolerance to abiotic stress conditions, improve fruit quality and increase nutrient uptake in the soil. In this study, it was aimed to determine the effect of different watermelon rootstocks on weight loss of watermelon fruits, which were obtained at deficit irrigation levels and they were stored under controlled conditions for different periods. For this purpose, 2 citron watermelons, 1 open bottle gourd and 1 hybrid TZ-148 which is widely used for watermelon in Turkey were used as rootstock. The "Crimson Tide" commercial cultivar was grafted onto these rootstocks and non-grafted applications were used as control lots. 5 different irrigation levels were applied according to the plant pan coefficient such as kcp1 = 1.00 (I100), kcp2 = 0.75 (I75), kcp3 = 0.50 (I50), kcp4 = 0.33 (I33) and kcp5 = 0.00 (I0) non-irrigated. According to the results, all watermelon rootstocks caused by less fruit weight loss compared to non-grafted applications and it has been demonstrated that using grafted rootstocks is an advantage in watermelons to be stored. On the other hand, TZ-148 commercial rootstock and citron melon 1 rootstock determined as the best rootstock in post-harvest storage. The I100 and I75 irrigation levels have approximately the same weight loss.

How do rootstocks of citron watermelon (Citrullus lanatus var. citroides) affect the yield and quality of watermelon under deficit irrigation?

Deficit irrigation practices and utilization of rootstocks that are tolerant to water stress are critical strategies for the protection of water resources and sustainable irrigation management, especially in arid and semi-arid areas. Therefore, this study was carried out to investigate the yield and quality of watermelon grafted onto different rootstocks under deficit irrigation conditions during 2017 and 2018 in the Konya Plain of Turkey, where the semi-arid climate is prevalent. In this study, five different plant materials, such as citroides1 (A1), citroides2 (A2), gourd (A3), hybrid TZ148 (A4) rootstocks grafted with the Crimson Tide variety, and non-grafted Crimson Tide as control (K1), were used as the main-plots. Five different irrigation levels, calculated by taking into account the amounts of cumulative water (Ep) that evaporated at 7-day intervals from Class A Pan (I100 = 1.00Ep; I75 = 0.75Ep; I50 = 0.50Ep; I35 = 0.35Ep, and I0 = rain-fed), were used as the sub-plots.When the average of experimental years was considered, the highest rate of evapotranspiration (ET) was found in the plot A4I100 (615 mm). The highest fruit yield was obtained from the A4I100 (93.4 t/ha), and an increase in yield of up to 35 % was achieved in the A4I100, compared to non-grafted plants applied I100 irrigation level (K1I100). The analysis of data by both separate evaluation and principal component analysis (PCA) revealed that the yield values obtained from plants grafted onto A4, A1, and A2 rootstocks applied I75 irrigation level were higher than non-grafted plants applied I100 irrigation level. The water productivity (WP) and irrigation water productivity (IWP) ranged between 7.1–17.4 kg/m3 and 11.7–25.0 kg/m3, respectively, and a significant increase in the values of WP and IWP was achieved by grafting. This two-year study revealed that the performances of citron watermelon rootstocks were found close to the TZ148 rootstock in terms of fruit yield, certain yield components, WP, and IWP. Thus, it has also been demonstrated that the citron watermelons could be used commercially as watermelon rootstocks, and citron watermelon rootstocks could be used as watermelon rootstocks in breeding programs, in order to save water, especially in arid and semi-arid regions.

Plant Grafting Shapes Complexity and Co-occurrence of Rhizobacterial Assemblages.

Grafting is a basic technique which is widely used to increase yield and enhance biotic and abiotic stress tolerance in plant production. The diversity and interactions of rhizobacterial assemblages shaped by grafting are important for the growth of their hosts but remain poorly understood. To test the hypothesis that plant grafting shapes complexity and co-occurrence of rhizobacterial assemblage, four types of plants, including ungrafted bottle gourd (B), ungrafted watermelon (W), grafted watermelon with bottle gourd rootstock (W/B), and grafted bottle gourd with watermelon rootstock (B/W), were cultivated in two soil types in a greenhouse, and the rhizosphere bacterial communities were analyzed by 16S rRNA gene high-throughput sequencing. Both the soil type and grafting significantly influenced the bacterial community composition. Grafting increased bacterial within-sample diversity in both soils. Core enriched operational taxonomic units (OTUs) in the W/B rhizosphere compared with the other three treatments (B, W, and B/W) were mainly affiliated with Alphaproteobacteria, Deltaproteobacteria, and Bacteroidetes, which are likely related to methanol oxidation, methylotrophy, fermentation, and ureolysis. Co-occurrence network analysis proved that grafting increased network complexity, including the number of nodes, edges, and modules. Moreover, grafting strengthened the structural robustness of the network in the rhizosphere, while ungrafted watermelon had the lowest network robustness. Homogeneous selection played a predominant role in bacterial community assembly, and the contribution of dispersal limitation was increased in grafted watermelon with bottle gourd rootstock. Grafting increased the diversity and transformed the network topology of the bacterial community, which indicated that grafting could improve species coexistence in the watermelon rhizosphere.

RESISTANCE OF CUCURBITA SPP. TO FUSARIUM SOLANI FOR USE AS ROOTSTOCK

ABSTRACT Fusarium solani f. sp. cucurbitae (Fsc) is a soil pathogen and the adoption of resistant rootstocks is an effective method of control. Hybrids of Cucurbita spp. are the main rootstock used for watermelon. This study aimed to evaluate the virulence of Fsc race 1 (Fsc1) in three cucurbits and check the reaction of Cucurbita spp. genotypes to the fungus for its use as rootstock. Four experiments were performed. The virulence of Fsc1 in melon, watermelon and Cucurbita spp. was evaluated in experiment I. In experiment two and three the severity of the pathogen in 19 cucurbits was analyzed. And experiment four evaluated the compatibility of these genotypes as a rootstock for watermelon. Cucurbita spp. proved to be more resistant to Fusarium solani f. sp. cucurbitae race 1 than the melon. The high frequency of plants resistant to Fsc1 was found in the genotypes BGC622, BGC620, BGC567, BGC530, BGC186, BGC381, BGC692, BGC082, ES0061 and ES0062. In addition, the evaluated genotypes may be used as watermelon rootstocks, except for the ES530 strain, which was incompatible with the cultivar BRS Opara, but could be used in pumpkin breeding programs, as well as other resistant genotypes.

Cucurbitaceae Germplasm Resistance to Verticillium Wilt and Grafting Compatibility with Watermelon

Grafting is used in watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai] production as a means to combat soilborne diseases. To support the development of new rootstock cultivars in the United States, we screened cucurbit germplasm accessions for resistance to verticillium wilt (caused by Verticillium dahliae Kleb.) and for compatibility as watermelon rootstocks. Screening was done using a field naturally infested with V. dahliae [5 and 7.5 colony-forming units (cfu)·g−1 soil in 2017 and 2018, respectively], and plants were inoculated at transplanting (1.5 and 104 cfu of V. dahliae per plant in 2017 and 2018, respectively). In 2017, 56 germplasm accessions from three genera commonly used as rootstocks, Cucurbita, Lagenaria, and Benincasa, were sourced from the U.S. Department of Agriculture (USDA) National Plant Germplasm System and area under the verticillium wilt (disease) progress curve (AUDPC) values ranged from 16 to 397. The 14 accessions with the lowest AUDPC values and good germination (>40%) were used as rootstocks along with the commercial rootstock cv. Tetsukabuto (control), and all were grafted with watermelon cv. Secretariat as the scion in 2018. Grafted plant survival rate was greatest for ‘Tetsukabuto’ (90%) and the accession PI 381840 (L. siceraria) (89%), and ranged from 22% to 85% for all other accessions. All grafted treatments that produced mature fruit in 2018 tended to flower at the same time as nongrafted ‘Secretariat’, with first male and female flowers occurring in 45 to 50 days and 44 to 51 days after transplanting, respectively. There were no significant differences in AUDPC values due to grafting or when accessions were compared with ‘Tetsukabuto’. Only six accessions produced mature fruit when grafted with ‘Secretariat’, indicating they were compatible for watermelon grafting. Fruit weight and number as well as total soluble solids, pH, lycopene content, rind firmness and thickness, and dry matter content were similar for all accessions and ‘Tetsukabuto’ grafted on ‘Secretariat’. Only fruit flesh firmness differed and was highest for ‘Secretariat’ grafted on ‘PI 491316’ and lowest for ‘Secretariat’ grafted on ‘PI 49174’. The six verticillium wilt-tolerant accessions that were compatible with watermelon could potentially be used as rootstocks or as sources of genetic resistance in rootstock breeding programs.

Transcriptome changes in reciprocal grafts involving watermelon and bottle gourd reveal molecular mechanisms involved in increase of the fruit size, rind toughness and soluble solids.

Transcriptome landscape reveals the molecular mechanisms involved in the improvement of fruit traits by the grafting of watermelon and bottle gourd. Grafting has been used as a sustainable alternative for watermelon breeding to control soil-borne pathogens and to increase tolerance to various abiotic stresses. However, some reports have shown that grafting can negatively affect the quality of fruits. Despite several field studies on the effects of grafting on fruit quality, the regulation of this process at the molecular level has not been revealed. The aim of this study was to elucidate various molecular mechanisms involved in different tissues of heterografted watermelon and bottle gourd plants. Grafting with bottle gourd rootstock increased the size and rind thickness of watermelon fruits, whereas that with watermelon rootstock produced bottle gourd fruits with higher total soluble solid content and thinner rinds. Correspondingly, genes related to ripening, softening, cell wall strengthening, stress response and disease resistance were differentially expressed in watermelon fruits. Moreover, genes associated mainly with sugar metabolism were differentially expressed in bottle gourd fruits. RNA-seq revealed more than 400 mobile transcripts across the heterografted sets. More than half of these were validated from PlaMoM, a database for plant mobile macromolecules. In addition, some of these mobile transcripts contained a transfer RNA-like structure. Other RNA motifs were also enriched in these transcripts, most with a biological role based on GO analysis. This transcriptome study provided a comprehensive understanding of various molecular mechanisms underlying grafted tissues in watermelon.

Relationships between Rootstock-Scion Combinations and Growing Regions on Watermelon Fruit Quality

Grafting of vegetable plants is done primarily to reduce the potential for damage caused by soil-borne diseases. Most of the watermelons (Citrullus) grown in the Mediterranean Basin, including in Israel, are grafted, mainly on interspecific hybrid pumpkin (Cucurbita) rootstocks. Biblical law (Leviticus 19:19) does not allow intergeneric grafting, so in recent years, great efforts have been made in Israel to find or breed watermelon rootstocks. Both interspecific and intergeneric grafting can have negative or positive effects on fruit yield and quality after harvest. The inconsistencies in fruit quality and shelf-life parameters can be attributed to differences in production environments. However, many farmers are grafting and planting the same rootstock-scion combination all over the country, regardless of local soil, water, and climactic conditions. We studied the effect of similar rootstock-scion combinations on watermelon yield and fruit quality in three regions of Israel differing in soil type and altitude. Fruit-quality parameters were evaluated after 4 days at 21 °C (local marketing simulation). Fruit quality was significantly affected, mainly by the growing region, based on factorial analysis, but also by rootstock-scion combination, regardless of rootstock vigor. Therefore, the best rootstock-scion combination needs to be found and adopted for each growing region. Grafting was essential for watermelon crop survival in contaminated soils and improved both plant performance and postharvest fruit quality, but was not a factor in non-contaminated soils.

Response of two Citrullus amarus accessions to isolates of three species of Meloidogyne and their graft compatibility with watermelon

The response of two Citrullus amarus accessions, BGV0005164 and BGV0005167, was assessed against different Meloidogyne arenaria, Meloidogyne incognita, and Meloidogyne javanica isolates in pot experiments and against M. incognita in plastic greenhouse. In the pot experiments, plants were inoculated with a second-stage juvenile per cm3 of sterile sand and maintained in a growth chamber at 25 °C for 50 days. The watermelon cv. Sugar Baby was included as a susceptible control for comparison. At the end of the experiments, the number of egg masses and eggs per plant was determined, and the reproduction index was calculated as the percentage of the number of eggs produced in the C. amarus accessions with regard to that produced in the susceptible cv. Sugar Baby. In the plastic greenhouse experiment, the ungrafted watermelon cv. Sugar Baby and watermelons grafted onto each of the C. amarus accessions and onto the watermelon rootstock cv. Robusta were cultivated from May to August 2016 in plots with nematode densities from 46 to 1392 J2 per 250 cm3 of soil at transplantation. At the end of the experiment, the galling index and the number of eggs per plant were determined, and the reproduction index was calculated. Additionally, the compatibility of the two accessions with the watermelon cv. Sugar Baby and the effect on fruit quality (weight, size, shape, firmness, pH, total soluble solids, and flesh color) were assessed under a hydroponic system in a greenhouse. The commercial rootstocks cv. Cobalt and cv. Robusta were also included. All the Meloidogyne isolates produced less egg masses and eggs per plant on the accessions than on Sugar Baby. Both accessions performed as resistant against M. arenaria, and from highly to moderately resistant to M. incognita and M. javanica in pot experiments. In the plastic greenhouse experiment, both C. amarus accessions performed as resistant to M. incognita. Both C. amarus accessions were compatible with the watermelon cv. Sugar Baby, but only the BGV0005167 accession did not influence the fruit quality. Then, the BGV0005167 accession is a promising rootstock for managing the three tropical root-knot nematode species without influencing watermelon fruit quality.

Nitrogen Use Efficiency of Watermelon Grafted onto 10 Wild Watermelon Rootstocks under Low Nitrogen Conditions

Nitrogen availability is the key determinant of plant growth and development. The improvement of nitrogen use efficiency (NUE) in crops is an important consideration. In fruit and vegetables, such as watermelon, rootstocks are often utilized to control soil borne diseases and improve plant performance to a range of abiotic stresses. In this study, we evaluated the efficacy of 10 wild watermelon rootstocks (ZXG-516, ZXG-941, ZXG-945, ZXG-1250, ZXG-1251, ZXG-1558, ZXG-944, ZXG-1469, ZXG-1463, and ZXG-952) to improve the plant growth and nitrogen use efficiency (NUE) of the watermelon cultivar: Zaojia 8424. Nitrogen use efficiency (NUE) is a comprehensive parameter that represents the ability of a plant to absorb nitrogen (N) and convert the supplied resources to the dry biomass. Wild watermelon rootstocks substantially improved plant growth, rate of photosynthesis, stomatal conductivity, intercellular carbon dioxide concentration, rate of transpiration, nitrogen uptake efficiency, nitrogen use efficiency, and nitrogen utilization efficiency of watermelon. NUE of watermelon grafted onto ZXG-945, ZXG-1250, and ZXG-941 was improved by up to 67%, 77%, and 168%, respectively, at optimum N supply. Similarly, at low N supply (0.2 mM), NUE of watermelon grafted onto ZXG-1558 and ZXG-516 was improved by up to 104% and 175%, respectively. In conclusion, grafting onto some wild rootstocks can improve nitrogen use efficiency of watermelon, and this improved nitrogen use efficiency could be attributed to better N uptake efficiency of wild watermelon rootstocks.

Effect of Different Rootstocks on the Salt Stress Tolerance in Watermelon Seedlings

The selection of salt-tolerant watermelon rootstocks requires the evaluation of its underlying mechanism. The present study investigated the effect of applying 200 mmol·L−1 NaCl on various physiological and biochemical parameters of Citrullus lanatus ‘Jingxin No.2’ (abbreviated as W) seedlings grafted onto W, Cucurbita moschata ‘Quanneng Tiejia’ (P1), ‘Kaijia No.1’ (P2), and Lagenaria siceraria ‘Hanzhen No.3’ (G), which were grown hydroponically. All the measured growth parameters were significantly inhibited by salt stress, with W/P2 exhibiting superior growth. Salt stress increased Na+ uptake, which in turn disrupted K+/Na+ homeostasis in all grafting combinations. The photosynthetic capacity, chlorophyll concentration, and photochemical efficiency of photosystem II of all grafts significantly decreased with salt stress. However, W grafted onto G and P2 showed higher resistance than W grafted onto W and P1. Electrolyte leakage (EL) superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase activity were significantly affected by both grafting and salt stress. Minimum EL was observed in W/P2, which also exhibited superior antioxidative capacity. Physiological and biochemical assessment indicated that W grafted onto the P2 rootstock displayed the greatest salt tolerance. Plants grafted onto salt-resistant P2 accumulated less Na+ and reactive oxygen species (ROS) and exhibited superior growth, photosynthesis, and ROS-scavenging capacity compared to those grafted onto the other rootstocks.

Assessment of Rooting Capability and Rootstock Potentials of Some Turkish Bottle Gourd (Lagenaria siceraria) Accessions Used as Rootstocks for Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai

Assessment of Rooting Capability and Rootstock Potentials of Some Turkish Bottle Gourd (Lagenaria siceraria) Accessions Used as Rootstocks for Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai

Producción de sandía con portainjertos en suelos infestados con el virus de la mancha necrótica del melón


 
 
 México es uno de los principales productores de sandía a nivel mundial. Pero la presencia de patógenos del suelo como nematodos, Fusarium oxysporum f. sp. niveum y el virus de la mancha necrótica del melón (MNSV) representan un serio problema para los productores. El uso de plantas injertadas es una buena alternativa para hacer frente a estos problemas, ayudando a incrementar el rendimiento y calidad en sandía. Los portainjertos de sandía silvestre (Citrullus lanatus var. citroides) han demostrado ser eficaces para el control de la mayoría de las enfermedades que se transmiten a través del suelo, además de tener alta resistencia a nematodos; no obstante, no se tiene registro sobre su resistencia al MNSV. Se realizaron dos experimentos para evaluar la resistencia al MNSV de portainjertos para sandía. En el experimento 1 se evaluaron los portainjertos de híbridos interespecíficos “RS-841” “Ercole” (Cucurbita maxima×Cucurbita moschata) y de sandía silvestre los portainjertos “Robusta”, “RS0272” y “RS1833”. En el experimento 2 se evaluaron los portainjertos “RS-841”, “Ercole” y “Robusta”. En ambos casos en suelos infestados con MNSV. Los portainjertos de sandía silvestre fueron altamente susceptibles al MNSV, en cambio los híbridos interespecíficos mostraron resistencia a esta enfermedad. El portainjertos “RS-841” fue el que produjo los frutos de mejor calidad. El rendimiento fue inferior con diferencia significativa cuando se utilizaron los portainjertos de sandía silvestre.