Article

Early Season Growth, Yield, and Fruit Quality of Standard and Mini Watermelon Grafted onto Several Commercially Available Cucurbit Rootstocks

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Abstract

Grafting watermelon (Citrullus lanatus) is a common practice in many parts of the world and has recently received increased interest in the United States. The present study was designed to evaluate early season growth, yield, and fruit quality of watermelon in response to grafting and in the absence of known disease pressure in a fumigated system. Field experiments were conducted using standard and mini watermelons (cv. Exclamation and Extazy, respectively) grafted onto 20 commercially available cucurbit rootstocks representing four species: giant pumpkin (Cucurbita maxima), summer squash (Cucurbita pepo), bottle gourd (Lagenaria siceraria), and interspecific hybrid squash [ISH (C. maxima × Cucurbita moschata)]. Nongrafted ‘Exclamation’ and ‘Extazy’ were included as controls. To determine early season growth, leaf area was measured at 1, 2, and 3 weeks after transplant (WAT). At 1 WAT, nongrafted ‘Exclamation’ produced the smallest leaf area; however, at 3 WAT, nongrafted ‘Exclamation’ produced the largest leaf area in 2015, and no differences were observed in 2016. Leaf area was very similar among rootstocks in the ‘Extazy’ study, with minimal differences observed. Marketable yield included fruit weighing ≥9 and ≥3 lb for ‘Exclamation’ and ‘Extazy’, respectively. In the ‘Exclamation’ study, highest marketable yields were observed in nongrafted ‘Exclamation’, and ‘Exclamation’ grafted to ‘Pelops’, ‘TZ148’, and ‘Coloso’, and lowest marketable yields were observed when using ‘Marvel’ and ‘Kazako’ rootstocks, which produced 47% and 32% of nongrafted ‘Exclamation’ yield, respectively. In the ‘Extazy’ study, the highest marketable yield was observed in nongrafted ‘Extazy’, and ‘Kazako’ produced the lowest yields (48% of nongrafted ‘Extazy’). Fruit quality was determined by measuring fruit acidity (pH), soluble solids concentration (SSC), lycopene content, and flesh firmness from a sample of two fruit from each plot from the initial two harvests of each year. Across both studies, rootstock had no effect on SSC or lycopene content. As reported in previous studies, flesh firmness was increased as a result of grafting, and nongrafted ‘Exclamation’ and ‘Extazy’ had the lowest flesh firmness among standard and mini watermelons, respectively. The present study evaluated two scions with a selection of 20 cucurbit rootstocks and observed no benefits in early season growth, yield, or phytonutrient content. Only three of 20 rootstocks in each study produced marketable yields similar to the nongrafted treatments, and no grafted treatment produced higher yields than nongrafted ‘Exclamation’ or ‘Extazy’. Because grafted seedlings have an associated increase in cost and do not produce increased yields, grafting in these optimized farming systems and using fumigated soils does not offer an advantage in the absence of soilborne pathogens or other stressors that interfere with watermelon production. © 2018, American Society for Horticultural Science. All rights reserved.

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... Several studies found no difference or even reduced yields with grafted than with ungrafted watermelon, particularly in the absence of disease pressure. 1,68 Because grafted seedlings have an associated cost increase and do not produce increased yields, grafting in optimized farming systems that use fumigated soils does not offer an advantage in the absence of soil-borne pathogens or other stressors that would interfere with watermelon production. ...
... 23 Future efforts in watermelon rootstock breeding should take into consideration the matching of rootstock to the specific growing region, soil type, weather conditions, growth cycle and other environmental and horticultural factors, aiming to enhance fruit quality and extend shelf life. 68,69 Grafting also may be used to supplement classical breeding programs for intra-and interspecific watermelons, particularly in Israel where Biblical law (Leviticus 19:19) prohibits intergeneric grafting. Therefore, in Israel, in recent years, great efforts have been devoted to finding or breeding watermelon rootstocks, mainly of citron watermelon (Citrullus amarus Schrad.) 10 However, a rootstock considered for adoption into a crop system as a tool to control a biotic stressor should not only be resistant to the target organism, but also be grafting-compatible with respect to providing satisfactory plant development and production, as well as high postharvest fruit quality. ...
Article
Grafting of vegetable seedlings is a unique horticultural technology, practiced for more than 5 decades, to overcome problems associated with intensive cultivation on limited arable land. Grafting can protect vegetables against soil‐borne diseases and nematodes, against abiotic stresses such as high or low temperatures, salinity, drought or excessive soil‐water content, and against elevated soil concentrations of heavy metals and organic pollutants. Watermelon is one of the most popular vegetable that is grafted, and more than 90% of the plants worldwide are commercially grafted. This mini review aims to summarize the latest available information about the effects of rootstock/scion combinations in enhancing or impairing watermelon fruit‐quality. A better understand of the influence of rootstock/scion compatibility or incompatibility on fruit‐quality parameters will facilitate decision making by growers and direct breeding programs to produce high quality grafted fruits in a cost‐effective manner. This article is protected by copyright. All rights reserved.
... It is used extensively to ameliorate the biotic stress, such as that caused by fungi and viruses, of crops (Cohen et al., 2000(Cohen et al., , 2005(Cohen et al., , 2007Ioannou, 2001;Nisini et al., 2002), enhance abiotic stress tolerance to extreme temperatures and other environmental factors (Zhou et al., 2007). Grafting can also induce alterations in fruit traits, such as size (Garcia-Lozano et al., 2020), rind thickness (Fredes et al., 2017), and flesh firmness (Bertucci et al., 2018). ...
... Grafting has long been used to regulate plant growth and improve biotic and abiotic stress tolerance in the production of horticultural plants . Grafting has been studied for its striking effects on fruit quality (Bertucci et al., 2018;Zhao et al., 2018;Garcia-Lozano et al., 2020), physiological responses (Ren et al., 2018), and photosynthesis . Furthermore, heterografting is a powerful tool for identifying horizontal DNA movement (Yu et al., 2017) and the long-distance transport of mRNAs (Banerjee et al., 2006;Ham et al., 2009;Xu et al., 2016;Huang et al., 2018), ncRNAs (Mok and Mok, 2001;Yoo et al., 2004; FIGURE 1 | Proposed model for the selective movement of mRNA and protein from companion cells to sieve elements in grafted cucurbits. ...
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Grafting is widely used in fruit, vegetable, and flower propagation to improve biotic and abiotic stress resistance, yield, and quality. At present, the systemic changes caused by grafting, as well as the mechanisms and effects of long-distance signal transport between rootstock and scion have mainly been investigated in model plants (Arabidopsis thaliana and Nicotiana benthamiana). However, these aspects of grafting vary when different plant materials are grafted, so the study of model plants provides only a theoretical basis and reference for the related research of grafted vegetables. The dearth of knowledge about the transport of signaling molecules in grafted vegetables is inconsistent with the rapid development of large-scale vegetable production, highlighting the need to study the mechanisms regulating the rootstock-scion interaction and long-distance transport. The rapid development of molecular biotechnology and “omics” approaches will allow researchers to unravel the physiological and molecular mechanisms involved in the rootstock–scion interaction in vegetables. We summarize recent progress in the study of the physiological aspects (e.g., hormones and nutrients) of the response in grafted vegetables and focus in particular on long-distance molecular signaling (e.g., RNA and proteins). This review provides a theoretical basis for studies of the rootstock–scion interaction in grafted vegetables, as well as provide guidance for rootstock breeding and selection to meet specific demands for efficient vegetable production.
... It's widely used to help crops recover from biotic and abiotic stress, such as that produced by insect pests, pathogens and other climatic factors. Grafting can also influence fruit characteristics such size, rind thickness (Fredes et al., 2017), and flesh firmness (Bertucci et al., 2018). The processes that control the rootstock-scion relationship can have an impact on plant growth and development, as well as physiological and biochemical features. ...
... Volatiles in the rind and flesh of four watermelon cultivars (Captivation, Exclamation, Excursion, and Fascination) were identified in this study for the first time, though their sensory profiles have been reported previously [30]. Horticultural traits of Captivation, Exclamation, and Fascination have also been reported [42][43][44]. ...
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Watermelon rind is treated as agricultural waste and commonly discarded, causing environmental issues and biomass loss. This study aimed to identify volatile profiles of watermelon rind and flesh and their cultivar difference. Volatiles were analyzed using solid-phase microextraction–gas chromatography–mass spectrometry (SPME-GC-MS). A total of 132 volatiles were identified, including aldehydes, alcohols, ketones, terpenes/terpenoids, esters, lactones, acids, and sulfides. In both rind and flesh, the most dominant compounds in numbers and abundance (peak area) were aldehydes and alcohols, which accounted 94–96% of the total volatile abundance in the rind and 85–87% in the flesh. Total volatile in watermelon rind was only 28–58% of the corresponding flesh samples. Both rind and flesh shared nine-carbon aldehydes and alcohols, though the rind lacked additional diversity. Volatile difference between rind and flesh was greater than the difference among cultivars, although volatiles in the rind could be two times difference between Fascination and other three watermelons (Captivation, Exclamation, and Excursion). This study provides the first-hand knowledge regarding watermelon rind volatile profiles and cultivar difference and shows the potential use of rind in food or beverages due to its naturally contained nine-carbon compounds.
... The first reports of grafting were from Japan, in which watermelons were grafted to gourd rootstocks to provide Fusarium wilt resistance in watermelon cropping (Reddy, 2016). However, it has been used to improve plant environmental stress tolerance and enhance produce and quality in fruits such as flesh sturdiness, rind texture and other fruit traits (Bertucci et al., 2018;García-Mendívil et al., 2019). Louws et al. (2010) suggested the increasing soil pathogen abundance owed to the intensification of cropping methods, dependence on vulnerable cultivars to meet target markets, and invasion of new pathogen species increased the use of grafting. ...
Article
The suppressiveness of soils to inhibit pathogens mostly require rich microbiome harbouring plant growth-promoting microbes in the soil, especially rhizosphere. The present study evaluates the suppressiveness of the rhizosphere of a grafted eggplant under biochar amendment and its effects on the microbial communities involved. This study used four treatments consisting of grafted (CB) and self-rooted (CA) eggplants, with 10 t/ha biochar addition each (as BB and BA). Results revealed that BB significantly suppressed the incidence of Verticillium wilt by more than 70% and improved the yield of eggplant compared with the control. Treatment of CB and BB showed significant effects on the community structure and abundance of bacteria and fungi. The bacteria diversity and richness of CB and BB were higher than those of the BA and CA, respectively. For bacteria, the analysis showed the genus Bacillus to be abundant in the rhizosphere of both CB and BB, while genera Humicola, Chaetomium, Mortierella, and Tausonia were the dominant fungi, suggesting they may play an active part in disease suppression. Based on Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis, the results showed that CB and BB harbored more genes responsible for disease resistance than CA and BA. In summary, grafting with the addition of biochar was effective in suppressing Verticillium wilt of eggplant and can be given as a recommendation to eggplant growers to alleviate Verticillium wilt.
... There are six distinct weight categories: mini (1.5 to 4.0 kg), icebox (4.0 to 5.5 kg), small (5.0 to 8.0 kg), medium (8.0 to 11 kg), large (11.0 to 14 kg) and giant (>14 kg). Commercially, fruits are grouped by the number that fits into 24" bins, such as 36-count (7.7 to 10 kg per fruit), 45-count (6.4 to 7.7 kg per fruit) and 60-count (4.5 to 6.4 kg per fruit) [4]. Mini size watermelons are packaged into cartons of four to six fruits per carton. ...
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Watermelon is the most important horticultural crop in Texas and is grown across the state under diverse environments. Our study was conducted in the southern region of Texas to understand genotype-by-environment interactions and the contribution of yield components to yield. To accomplish this, twenty genotypes were evaluated for important traits and characteristics at two locations, Uvalde and Weslaco TX, for two years, 2018 and 2019. The genotypes were evaluated for total yield, total fruit count, total soluble solids, rind thickness, fruit length, diameter and weight. Genotype-by-environment (G x E) interaction was not significant, possibly due to similarity in climatic conditions and nutrient management practices. In the grouped analysis, cultivars Crimson Diamond, Sunshade and the breeding line TAM 2 had a higher total yield. Path analysis showed a high direct effect for total fruit count and fruit diameter of 0.89 and 0.85, respectively. However, total fruit count had a high indirect effect of −0.44. Fruit weight was the only trait that showed a significant (p < 0.01) correlation towards total yield at r = 0.58. Neither of the high direct effects, total fruit count and fruit diameter, had a significant correlation. The study inferred that breeding resources could be optimized by reducing the testing location to only one representative location for measured traits in southern Texas. The indirect selection of total fruit or fruit diameter could result in better yield. The study suggested selecting for optimum total fruit and fruit diameter for higher yield.
... Grafting was essential for crop survival in the contaminated soils at Qalya and Bet She'an, and improved both plant performance and postharvest fruit quality, but was not a factor in the noncontaminated soils at Newe Ya'ar, as shown in Table 2. Because grafted seedlings have an associated increase in cost and do not produce increased yields on non-contaminated media [21], grafting in these optimized farming systems does not offer an advantage in the absence of soil-borne pathogens or other stress factors that interfere with watermelon production [22]. ...
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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.
Article
Bottle gourd (Lagenaria siceraria (Molina) Standl.] and citron watermelon (Citrullus lanatus var. citroides (L. H. Bailey) Mansf. ex Greb.) are amongst the widely grown yet under-researched cucurbits genetic resources in sub-Saharan Africa (SSA). Fresh immature leaves, fruit and seed are used for food and medicinal purposes in the region. Furthermore, both species are used as rootstock and donors of novel genes for commercial production and breeding of sweet dessert watermelon cultivars. Despite their economic value and contribution to food and nutrition security in the region, bottle gourd and citron watermelon genetic resources remain under-utilized and largely un-explored for commercial product development. The objective of this review was to document the unique values of bottle gourd and citron watermelon for genetic improvement and development of value-added food and non-food products, and to highlight regional and global efforts on conservation , production, processing, commercialization and various enterprise development of these important indigenous species. The review discussed on the value of both crops as a rootstock to improve fruit yield and quality of cultivated watermelon. This is followed by important summaries on phenotypic and genetic variation of bottle gourd and citron watermelon genetic resources and implications for new cultivar design. Finally, the review highlighted value-added non-food and food-based products developed based on indigenous knowledge systems in SSA and availability and access to genetic resources of bottle gourd and citron watermelon for breeding, product design and deployment.
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Nematode and disease resistant rootstocks have been developed for many vegetable crops including tomato, eggplant, melon, watermelon, and cucumber and are being utilized by an increasing number of growers. Grafting commercially desirable vegetable scions on nematode and disease resistant rootstocks has been significantly stimulated by the need for an alternative to banned soil fumigation with methyl bromide, which had been the primary method for managing soil- borne nematodes, diseases, and weeds. Rootstocks resistant to root-knot nematodes (Meloidogyne spp.) and diseases including Fusarium wilt, Fusarium crown and root rot, Verticillium wilt, bacterial wilt, Southern blight, and sudden wilt have been developed and many are available commercially. New technologies such as transcriptomics, identification of differentially expressed genes, transgene rootstocks, and RNAi silencing are being used in the development of vegetable rootstocks which are resistant to pests, salt tolerant, and heat and cold tolerant. Overall, grafting has proven to be a successful and environmentally safe method for managing root-knot nematodes and soil-borne diseases by reducing infection, disease development, and inoculum build-up in the soil, which is especially important for growth of healthy subsequent crops. This article is protected by copyright. All rights reserved.
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Pythium species cause root and stem rot in watermelon (Citrullus lanatus), but cucurbit rootstocks used to graft watermelon have not been evaluated for resistance. P. aphanidermatum and P. myriotylum were inoculated onto 15 nongrafted watermelon, citron (Citrullus amarus), bottle gourd (Lagenaria siceraria), and interspecific hybrid squash (Cucurbita maxima × C. moschata) cultivars in a growth chamber. Watermelon was more susceptible than bottle gourd and interspecific hybrid squash at 20 and 30°C. Twenty-one cultivars were inoculated in a field with an equal blend of both Pythium species. Interspecific hybrid squash was less susceptible than bottle gourd and watermelon in 2018 and 2019. Seedless watermelon cultivar Tri-X 313 was grafted to one citron, one bottle gourd, and three interspecific hybrid squash rootstocks. Plants were inoculated in the field as described. Grafting to interspecific hybrid squash rootstocks reduced disease incidence compared with nongrafted controls in 2018 and 2019. Mefenoxam and propamocarb applied at transplanting did not affect disease compared with non-fungicide-treated plots. Grafting to interspecific hybrid squash Camelforce significantly increased total and marketable fruit numbers and total weight in 2019 compared with the nongrafted control. In summary, interspecific hybrid squash was consistently resistant to Pythium, demonstrating resistance and utility in watermelon grafting.
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Interspecific hybrid squash (Cucurbita maxima × Cucurbita moschata) rootstocks used to graft watermelon (Citrullus lanatus var. lanatus) are resistant to Fusarium oxysporum f. sp. niveum, the fungus that causes Fusarium wilt of watermelon, but they are susceptible to Meloidogyne incognita, the southern root knot nematode. A new citron (Citrullus amarus) rootstock cultivar Carolina Strongback is resistant to F. oxysporum f. sp. niveum and M. incognita. The objective of this study was to determine if an interaction between M. incognita and F. oxysporum f. sp. niveum race 2 occurred on grafted or nongrafted triploid watermelon susceptible to F. oxysporum f. sp. niveum race 2. In 2016 and 2018, plants of nongrafted cultivar Fascination and Fascination grafted onto Carolina Strongback and interspecific hybrid squash cultivar Carnivor were inoculated or not inoculated with M. incognita before transplanting into field plots infested or not infested with F. oxysporum f. sp. niveum race 2. Incidence of Fusarium wilt and area under the disease progress curve did not differ when hosts were inoculated with F. oxysporum f. sp. niveum alone or F. oxysporum f. sp. niveum and M. incognita together. Fusarium wilt was greater on nongrafted watermelon (78% mean incidence) than on both grafted rootstocks and lower on Carnivor (1% incidence) than on Carolina Strongback (12% incidence; P ≤ 0.01). Plants not inoculated with F. oxysporum f. sp. niveum did not wilt. At the end of the season, Carnivor had a greater percentage of the root system galled than the other two hosts, whereas galling did not differ on Fascination and Carolina Strongback. F. oxysporum f. sp. niveum reduced marketable weight of nongrafted Fascination with and without coinoculation with M. incognita. M. incognita reduced marketable weight of Fascination grafted onto Carnivor compared with noninoculated, nongrafted Fascination. In conclusion, cucurbit rootstocks that are susceptible and resistant to M. incognita retain resistance to F. oxysporum f. sp. niveum when they are coinfected with M. incognita.
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Seedcoat adherence to emerged cotyledons of seedless watermelons ( Citrullus lanatus (Thunb.) Matsum & Naki) results in distortion of seedlings that effectively restricts the number of productive plants in a planting. Significantly fewer seedcoats adhered to cotyledons when seeds were oriented with the radicle end up at a 45° or 90° angle than when seeds were oriented horizontally or with the radicle end down at a 45° or 90° angle. Emergence was not affected by seed orientation.
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Drought is one of the most prevalent limiting factors causing considerable losses in crop productivity, inflicting economic as well as nutritional insecurity. One of the greatest challenges faced by the scientific community in the next few years is to minimize the yield losses caused by drought. Drought resistance is a complex quantitative trait controlled by many genes. Thus, introgression of drought resistance traits into high yielding genotypes has been a challenge to plant breeders. Vegetable grafting using rootstocks has emerged as a rapid tool in tailoring plants to better adapt to suboptimal growing conditions. This has induced changes in shoot physiology. Grafting applications have expanded mainly in Solanaceous crops and cucurbits, which are commonly grown in arid and semi-arid areas characterized by long drought periods. The current review gives an overview of the recent scientific literature on root-shoot interaction and rootstock-driven alteration of growth, yield, and fruit quality in grafted vegetable plants under drought stress. Further, we elucidate the drought resistance mechanisms of grafted vegetables at the morpho-physiological, biochemical, and molecular levels.
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Two years of field trials conducted in a Meloidogyne incognita-infested field evaluated grafting and Paladin Pic-21 (dimethyl disulfide:chloropicrin [DMDS:Pic] 79:21) for root-knot nematode and weed control in tomato and melon. Tomato rootstocks evaluated were; 'TX301', 'Multifort', and 'Aloha'. 'Florida 47' was the scion and the nongrafted control. A double crop of melon was planted into existing beds following tomato harvest. Melon rootstocks, C. metulifer and 'Tetsukabuto', were evaluated with nongrafted 'Athena' in year 1. In year 2, watermelon followed tomato with scion variety 'Tri-X Palomar' as the control and also grafted onto 'Emphasis' and 'Strongtosa' rootstocks. Four soil treatments were applied in fall both years under Canslit metalized film; Paladin Pic- 21, methyl bromide:chloropicrin (MeBr:C33, 67:33), Midas (iodomethane:chloropicrin 50:50), and a herbicide-treated control. M. incognita J2 in soil were highest in herbicide control plots and nongrafted tomato. All soil treatments produced similar tomato growth, which was greater than the herbicide control. All treatments reduced M. incognita J2 in roots compared to the herbicide control. 'Multifort' rootstock produced the largest and healthiest roots; however, the number of M. incognita isolated from roots did not differ among the tomato rootstocks tested. Galling on tomato was highest in herbicide control plots and nongrafted plants. In melon, M. incognita J2 in soil did not differ among melon rootstocks, but numbers isolated from melon rootstocks increased in 'Tetsukabuto' compared with C. metuliferus. 'Tetsukabuto' were larger root systems than nongrafted 'Athena'. All fumigants provided protection for all melon rootstocks against galling by M. incognita compared to the herbicide control. Galling on C. metuliferus rootstock was less in all fumigant treatments compared with nongrafted 'Athena' and 'Tetsukabuto'. In watermelon, M. incognita in soil and roots did not differ among soil treatments or watermelon rootstocks, and yield was lower in both grafted rootstocks compared with the nongrafted control. All soil treatments increased average fruit weight of watermelon compared with the herbicide control, and provided effective weed control, keeping the most predominant weed, purple nutsedge (Cyperus rotundus L.), density at or below 1/m row. Grafting commercial scions onto M. incognita-resistant rootstocks has potential for nematode management combined with soil treatments or as a stand-alone component in crop production systems.
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Verticillium wilt caused by Verticillium dahliae is a serious disease for watermelon growers in Washington State. Grafting represents a possible alternative disease management strategy, but little is known about rootstock resistance to verticillium wilt or the performance of grafted watermelon in the different production regions of the state. In this study, verticillium wilt severity, yield, and fruit quality were evaluated at three contrasting field sites in Washington using verticillium wilt-susceptible ‘Sugar Baby’ (diploid) watermelon grafted onto four commercial rootstock cultivars (Marvel, Rampart, Tetsukabuto, and Titan); nongrafted ‘Sugar Baby’ was included as the control. Verticillium dahliae soil densities varied at each site (<1.0, 5.7, and 18.0 colony-forming units (cfu)/g soil at Othello, Eltopia, and Mount Vernon, respectively). Area under disease progress curve (AUDPC) values differed significantly among treatments at Eltopia and Mount Vernon. Nongrafted ‘Sugar Baby’ had the highest AUDPC value at all three sites, while ‘Sugar Baby’ grafted onto ‘Tetsukabuto’ had the lowest AUDPC value at Eltopia and Mount Vernon. Nongrafted ‘Sugar Baby’ also had the lowest fruit weight per plant at all sites, but ‘Sugar Baby’ grafted onto ‘Tetsukabuto’ had the highest fruit weight per plant at Eltopia and Mount Vernon. Marketable fruit weight per plant did not differ among treatments at Othello. Yield was negatively correlated with AUDPC values at both Eltopia and Mount Vernon. Fruit number per plant was only significantly impacted at Eltopia, where ‘Sugar Baby’ grafted onto ‘Tetsukabuto’ had more fruit per plant than all other treatments except ‘Sugar Baby’ grafted onto ‘Rampart’. Fruit quality (flesh firmness, total soluble solids, and lycopene content) was unaffected by grafting at either Othello or Eltopia, except for increased flesh firmness for ‘Sugar Baby’ grafted onto ‘Marvel’ and ‘Titan’ as compared with nongrafted ‘Sugar Baby’ at Eltopia. At season’s end, plants were sampled from all treatments at Eltopia and Mount Vernon and assayed for V. dahliae. Microsclerotia typical of this organism were observed in all samples. Results from this study indicate that verticillium wilt of watermelon can be successfully managed by grafting when the V. dahliae soil density exceeds 5.0 cfu/g in Washington. In addition, grafting does not reduce fruit quality and using certain rootstocks can improve the quality of flesh firmness at certain locations. © 2015 American Society for Horticultural Science. All rights reserved.
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Grafting with resistant rootstocks is an effective strategy to manage a variety of soilborne diseases and root-knot nematodes in solanaceous and cucurbitaceous vegetables. In addition, improved resistance to some foliar diseases and viruses has also been reported in grafted plants. Hence, grafting technology is considered an important and innovative practice of integrated pest management and a promising alternative for soil fumigants in vegetable production. Inherent resistance within rootstocks and improved plant nutrient uptake are generally suggested as the main reasons for improved disease control in grafted vegetables.However, increasing evidence indicated that systemic defense mechanisms may also play an important role in plant defense as a result of grafting. This review analyzes current literature on the use of grafting techniques for disease management in vegetable crops, discusses potentialmechanisms associatedwith grafting-conferred plant defense, and identifies needs for future research to promote more effective and efficient use of grafting technology to support sustainable vegetable production.
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Limited water supply in the Mediterranean region is a major problem in irrigated agriculture. Grafting may enhance drought resistance, plant water use efficiency, and plant growth. An experiment was conducted in two consecutive growing seasons to determine yield, plant growth, fruit quality, leaf gas exchange, water relations, macroelements content in fruits and leaves, and water use efficiency of mini-watermelon plants [Citrullus lanatus (Thunb.) Matsum. and Nakai cv. Ingrid], either ungrafted or grafted onto the commercial rootstock 'PS 1313' (Cucurbita maxima Duchesne x Cucurbita moschata Duchesne), under open field conditions. Irrigation treatments were 1.0, 0.75, and 0.5 evapotranspiration rates. In both years (2006 and 2007), marketable yield decreased linearly in response to an increase in water stress. When averaged over year and irrigation rate, the total and marketable yields were higher by 115% and 61% in grafted than in ungrafted plants, respectively. The fruit quality parameters of grafted mini-watermelons such as fruit dry matter and total soluble solids content were similar in comparison with those of ungrafted plants, whereas titratable acidity, K, and Mg concentrations improved significantly. In both grafting combinations, yield water use efficiency (WUEy) increased under water stress conditions with higher WUE values recorded in grafted than ungrafted plants. The concentration of N, K, and Mg in leaves was higher by 7.4%, 25.6%, and 38.8%, respectively, in grafted than in ungrafted plants. The net assimilation of CO2, stomatal conductance, relative water content, leaf, and osmotic potential decreased under water stress conditions. The sensitivity to water stress was similar between grafted and ungrafted plants, and the higher marketable yield from grafted plants was mainly the result of an improvement in nutritional status and higher CO2 assimilation and water uptake from the soil.
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Impact of Grafting on Watermelon Growth, Fruit Yield and Quality Grafting is an alternative approach to reduce crop damage resulting from soil-borne pathogens and increases plant abiotic stress tolerance, which in turn increases crop production. The purpose of this study was to determine whether grafting could improve plant growth and fruit quality of watermelon through monitoring the changes induced by different rootstock-scion combinations. Watermelon ( Citrullus lanatus ) cv. Aswan F 1 was grafted into five rootstocks (Nun 6001 F 1 , Strongtosa F 1 , Tetsukabuto F 1 , Ferro F 1 and Shintoza F 1 ) hybrids between Cucurbita maxima and Cucurbita moschata. Highest vegetative growth and fruit yield were obtained by ‘Nun 6001 F 1 ’ as a rootstock using the tongue approach method. Grafting reduced significantly sex ratio by reducing the number of male flowers. Grafting increased significantly lycopene content in fruit flesh by 57% over the control treatment, but did not affect soluble solids content (SSC). One third of the control non-grafted plants died and Fusarium oxysporum was isolated as the responsible pathogen. These results indicate that grafting watermelon onto specific rootstock influences growth, productivity, and quality of the fruit as well as disease resistance. Grafting can be suggested as an alternative method to control of Fusarium wilt in watermelon production.
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The objective of this study was to examine the effects of grafting and kinds of rootstocks on yield that are economically feasible for the watermelon producer. Fruit characteristics and quality attributes of grafted plants in open field conditions were also analyzed. The tongue approach grafting method was adopted. Three Watermelon cultivars of ‘Crimson Tide’, ‘Dumara’, and ‘Farao’ were used as the scion. Three hybrid squashes of ‘Dynamo’, ‘RS-841’, and ‘Shintosa’ were used as rootstocks. Results showed that some fruit quality indicators such as dry matter, total soluble solids, total sugar and titratable acid contents were lower in grafted plants while lycopene contents remained unchanged. The pH was slightly altered by grafting. Use of rootstock did not show advantages at comparable fruit quality indicators. Results also showed that fruit shape index, rind thickness, fruit weight, total yield and marketable yield were significantly influenced by grafting. Use of rootstocks significantly increased previously mentioned values which is related with yield, as compared to the non-grafted plant. Analyses proved the use of rootstocks as economically feasible and an advantageous alternative in watermelon production.
Article
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The potential of grafted watermelon for resistance toFusarium oxysporum f.sp.niveum on some Curcurbitaceae,Lagenaria, Luffa, Benincasa and commercial rootstocks was evaluated. Effects of grafting on yield and quality of diseased plants were evaluated. All grafted plants and rootstocks were resistant to the three known races (0, 1, and 2) ofF. oxysporum f.sp.niveum except watermelon cv. ‘Crimson Tide’, which was susceptible to race 2. Fruit yield was positively (21–112%) affected byLagenaria rootstocks but negatively affected (200–267%) byCucurbita rootstocks when compared with the control. While only minor differences in fruit quality were determined in control and grafted plants onLagenaria rootstocks, the quality parameters for watermelon grafted ontoCucurbita rootstocks were lower than in the control. The reasons for low yield and quality might be due to an incompatibility betweenCucurbita rootstocks and watermelon. These results showed that rootstock influence on disease resistance as well as yield and quality of scion fruit is important in determining the potential use of grafting applications in watermelon.
Article
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Research on grafted watermelon at the Lane Agricultural Research and Extension Center in Lane, Oklahoma provided data for the cost benefit analyses performed in this work. Grafting of watermelon onto resistant rootstock was found to provide effective resistance to Fusarium wilt but at an increased cost of $1,743 per hectare. The resistance of these plants to multiple soil-borne diseases provides the farmer a viable risk management strategy and an alternative to methyl bromide for disease control. Soil-borne diseases such as Fusarium wilt continue to plague watermelon growers in intensive production areas where land resources are scarce and rotation of various crops is limited. Fusarium wilt is generally observed in farmers' fields during the latter stages of production when most of the costs have been incurred. Risk management alternatives available to the farmer have been reduced by the loss of soil fumigation chemicals such as methyl bromide. Currently, most seedless cultivars are susceptible to Fusarium wilt. It would appear that many of the present-day triploids have a similar genetic background. With triploids commanding almost 75% of the watermelon market in 2006, Fusarium wilt resistance has become a major emphasis for seed companies. A farmer planning for yields of 40,000 kg/ha would have to receive a price of $0.19/kg to breakeven with grafted plants while non-grafted plants would breakeven at $0.13/kg with the same yield. In the case where a field is known to have a history of Fusarium wilt, the probability of losing most or all of the crop after the majority of production costs have been expended forces the farmer to evaluate best alternative decisions based on costs versus probable revenues.
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Mini-watermelon [Citrullus lanatus (Thunb.)] cultivars Valdoria and Vanessa were evaluated at 20, 30, 40, or 50 days after anthesis to determine maturity at harvest. Fruit circumference, weight, ground spot color, and number of senescent tendrils were measured as external indicators for each watermelon. Soluble solids content (SS), pH, and SS:total acid ratio (SS:TA) of each watermelon were determined to provide an indication of internal maturity. Regression and Akaike Information Criterion fit statistics analyses were performed to determine significant relationships and best predictors for external indicators of internal maturity factors. In this study, external predictors were most closely linked to fruit pH rather than to SS or SS/TA. Of the external indicators tested, fruit weight, circumference, number of senescent tendrils, and International Commission on Illumination (CIE) b* color coordinate values of the ground spot were best related to fruit pH. According to the regression models, two completely senesced tendrils, a circumference of 53 cm, weight of 3 kg, and CIE b* coordinate ground spot value of 40 are each sufficient to predict maturity when pH is used as the internal indicator of maturity under the conditions of this experiment.
Article
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Vegetable grafting began in the 1920s using resistant rootstock to control soilborne diseases. This process is now common in Asia, parts of Europe, and the Middle East. In Japan and Korea, most of the cucurbits and tomatoes (Lycopersicon esculentum Mill.) grown are grafted. This practice is rare in the United States, and there have been few experiments to determine optimal grafting production practices for different geographical and climatic regions in America. This is beginning to change as a result of the phase out of methyl bromide. The U.S. cucurbit and tomato industries are evaluating grafting as a viable option for disease control. Because reports indicate that type of rootstock alters yield and quality attributes of the scion fruit, some seed companies are investigating grafting as a means to improve quality. It has been reported that pH, flavor, sugar, color, carotenoid content, and texture can be affected by grafting and the type of rootstock used. Reports vary on whether grafting effects are advantageous or deleterious, but it is usually agreed that the rootstock/scion combination must be carefully chosen for optimal fruit quality. Additionally, it is important to study rootstock/scion combinations under multiple climatic and geographic conditions because many rootstocks have optimal temperature and moisture ranges. This report gives an overview of the effect of grafting on vegetable quality.
Article
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Grafting of vegetable seedlings is a unique horticultural technology practiced for many years in East Asia to overcome issues associated with intensive cultivation using limited arable land. This technology was introduced to Europe and other countries in the late 20th century along with improved grafting methods suitable for commercial production of grafted vegetable seedlings. Later, grafting was introduced to North America from Europe and it is now attracting growing interest, both from greenhouse growers and organic producers. Grafting onto specific rootstocks generally provides resistance to soilborne diseases and nematodes and increases yield. Grafting is an effective technology for use in combination with more sustainable crop production practices, including reduced rates and overall use of soil fumigants in many other countries. Currently, over 40 million grafted tomato seedlings are estimated to be used annually in North American greenhouses, and several commercial trials have been conducted for promoting use of grafted melon seedlings in open fields. Nevertheless, there are issues identified that currently limit adoption of grafted seedlings in North America. One issue unique to North America is the large number of seedlings needed in a single shipment for large-scale, open-field production systems. Semi- or fully-automated grafting robots were invented by several agricultural machine industries in the 1990s, yet the available models are limited. The lack of flexibility of the existing robots also limits their wider use. Strategies to resolve these issues are discussed, including the use of a highly controlled environment to promote the standardized seedlings suitable for automation and better storage techniques. To use this technology widely in North American fresh vegetable production, more information and locally collected scientific and technical data are needed.
Article
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Due to limited availability of arable land and high market demand for off-season vegetables, cucurbits (plants in the family Cucurbitaceae) are continuously cultivated under unfavorable conditions in some countries. These conditions include environments that are too cold, wet, or dry, or are cool low-light winter greenhouses. Successive cropping can increase salinity, the incidence of cucurbit pests, and soilborne diseases like fusarium wilt caused by Fusarium spp. These conditions cause various physiological and pathological disorders leading to severe crop loss. Chemical pest control is expensive, not always effective, and can harm the environment. Grafting can overcome many of these problems. In fact, in many parts of the world, grafting is a routine technique in continuous cropping systems. It was first commonly used in Japan during the late 1920s by grafting watermelon [Citrullus lanatus (Thunb.) Matsum. and Nakai] onto pumpkin [Cucurbita moschata Duchesne ex. Poir] rootstocks. Soon after, watermelons were grafted onto bottle gourd [Lagenaria siceraria (Molina) Standl.] rootstocks. This practice helped control declining yield due to soilborne diseases. China produces more than half the world's watermelons and cucumbers (Cucumis sativus L.), and approximately 20% of these are grafted. Use of rootstocks can enhance plant vigor through vigorous attainment of soil nutrients, avoidance of soil pathogens and tolerance of low soil temperatures, salinity, and wet-soil conditions. The type of rootstock affects cucurbit plant growth, yield, and fruit quality. Cucurbit grafting is rare in the United States, but with continued loss of quality disease-free farmland along with the phase-out of methyl bromide, the U.S. cucurbit industry sees grafting as an attractive option. Some seed companies now offer watermelon transplants grafted onto squash or bottle gourd rootstocks, and some transplant facilities offer grafting services. There have been thorough analyses of cucurbit grafting in other countries, but the literature in English is limited. This review summarizes the state of the cucurbit grafting industry on a global level, translating work published in many languages.
Article
Background: The market demand for seedless watermelon has been continuously increasing because of consumer preference. Grafting is a useful tool to manage soil-borne diseases in watermelon production, but the use of squash rootstocks may negatively affect watermelon fruit quality. Currently, most research has focused on seeded cultivars while grafting effects on seedless watermelons remain largely unknown. This multi-season study was conducted to assess the effects of squash rootstocks, including both Cucurbita maxima ? C. moschata and C. moschata cultivars, with intact or excised and regenerated roots, on fruit quality of seedless watermelon 'Melody' using both instrumental and sensory measurements under different production scenarios. The grafted watermelon plants were also challenged by field inoculation with Fusarium oxysporum f.sp. niveum (FON). Results: A combination of instrumental measurements and consumer sensory analyses suggested that fruit quality of the seedless watermelon 'Melody' was not impacted by the use of the squash rootstocks used in this study, which included soluble solids content, titratable acidity, pH, and most fruit sensory properties. Watermelon flesh firmness was increased by grafting while the grafting effect on lycopene content was inconclusive. Root excision and regeneration did not influence the grafting effect, while the grafting effect on flesh firmness varied among the rootstocks under FON inoculation. Conclusion: Overall, grafting with squash rootstocks did not reduce fruit quality attributes of 'Melody' while improving texture. Our results support incorporating grafting into integrated management programs for seedless watermelon production.
Article
Grafting of seedlings is a technique used for watermelon (Citrullus lanatus) production in many countries. Because of higher costs involved, the use of grafted seedlings can only be recommended if it provides clear biological and economic benefits. Since rootstock performance is influenced by compatibility with the cultivar, the existing disease pressure, and climatic conditions, it is necessary to evaluate rootstocks with current cultivars to appraise possible benefits in a given area. Two experiments were carried out in two consecutive seasons with the objective of evaluating the benefits of grafting under Chilean conditions. The rootstocks used were ‘Marathon’ (Cucurbita maxima × Cucurbita moschata) and ‘Macis’ (Lagenaria siceraria) with different scions, including some seedless cultivars. In both experiments, grafted plants increased their yield compared with nongrafted plants (136% and 159% in Expts. 1 and 2, respectively). This effect was due to an increased number of fruit per plant (P < 0.01), and the weight gain of the fruit (P < 0.01). Plants presented with fusarium wilt [Fusarium oxysporum f. sp. niveum (FON)] in both experiments, which seemed to be the main limitation for nongrafted plant production. In the evaluation of quality attributes [soluble solid concentration (SCC), firmness, color, polar diameter, equatorial diameter, and rind thickness], positive effects were observed in the fruit of grafted plants. For the conditions of these experiments, the increase in yield of grafted plants would be associated with an economic benefit that exceeds its additional cost. © 2016, American Society for Horticultural Science. All rights reserved.
Article
Vegetable grafting is most common in European and Asian countries where crop rotation is no longer an option and available land is under intense use. Grafting is an alternative approach to reduce crop damage resulting from soilborne pathogens and increase plant abiotic stress tolerance, which increases crop production. We discuss and outline four grafting methods that are available for vegetable production in cucurbits: tongue approach grafting, hole insertion grafting, one cotyledon grafting, and side grafting.
Article
An experiment was conducted during 2005 and 2006 in Kinston, NC, with the objective of maximizing triploid watermelon [Citrullus lanatus (Thunb.) Matsum. and Nak.] fruit yield and quality by optimizing the choice and use of pollenizers. Treatments were pollenizer cultivars planted singly ['Companion', 'Super Pollenizer 1' ('SP1'), 'Summer Flavor 800' ('SF800'), and 'Mickylee'] or in pairs ('Companion' + 'SP1', 'Companion' + 'SF800', and 'SP1' + 'SF800'). All pollenizers from these seven treatments were interplanted with the triploid cultivar Tri-X-313. Planting arrangement was compared by establishing 'SF800' in a hill versus an interplanted field arrangement. Effect of pollenizer establishment timing on triploid fruit yields and quality was evaluated by establishing 'SP1' 3 weeks after planting and comparing it with the establishment of 'SP1' at the time of triploid plant establishment. Finally, a triploid planting with no pollenizer (control) was included to determine pollen movement. Fruit yield from the control was 22% or less of yield of the other treatments containing a pollenizer and less than 10% in the initial or early harvests. Pollen movement was minimal among plots and differences in yield and fruit quality could be attributed to pollenizer treatment. In 2005, the use of 'Companion', 'SP1', or 'Mickylee' as pollenizers produced similar total yields, whereas 'SF800' produced the lowest yield. In 2005, 'Companion' produced more large fruit than the other individual pollenizer treatments. Combining the pollenizers generally did not enhance triploid yields or quality. Interplanting of pollenizers consistently resulted in greater yield compared with the hill system. Late planting of 'SP1' increased the incidence of hollow heart in the marketable fruit and decreased yield compared with simultaneously planting 'SP1' and triploid plants. Thus, selection of pollenizer, planting arrangement, and time of pollenizer establishment are all important considerations to optimizing triploid yield and quality.
Article
Application of fatty alcohol compounds to rootstock meristems can control rootstock meristematic regrowth, thus decreasing the cost of producing grafted watermelon transplants by reducing the labor. Eight rates of Fair 85® and Off-Shoot T®, two commercially available fatty alcohol compounds, were applied to the meristem region of bottle gourd (Lagenaria sicereria cv. Emphasis) and interspecific hybrid squash (Cucurbita maxima × Cucurbita moschata cv. Carnivor) rootstocks to determine the optimal application rate to control regrowth without damaging the remaining plant parts. A water-only control treatment was also included. Rootstock seedlings were rated for damage and regrowth on Days 1, 7, 14, and 21 after treatment. Damage increased and regrowth decreased with increasing rates of fatty alcohol compound. In addition, a significant compound-by-rate interaction indicated that inert ingredients in the fatty alcohol formulation have an effect on both damage and regrowth. The optimal treatment rate, e.g., providing at least 95% control of regrowth with less than 10% damage, was found to be between a 5% (Off-Shoot T®) and 6.25% (Fair 85®) fatty alcohol application. At the optimal treatment rate, no adverse effects to grafting success were observed in the grafting procedure.
Article
Delineating the depth and extent of the watermelon [Citrullus lanatus (Thumb.) Matsum. & Nak.] root zone assists with proper irrigation management and minimizes nutrient leaching. The objective of this 3-year field study was to measure root distribution and root length density of watermelon (cv. Wrigley) grafted on two different rootstocks (Lagenaria siceraria cv. 'FR Strong' and Cucurbita moschata 3 Cucurbita maxima cv. Chilsung Shintoza) and grown under three soil moisture treatments. Irrigation treatments tested were: no irrigation (NI), briefly irrigated for fertigation and earlyseason plant establishment; minimally irrigated (MI), irrigated when soil moisture in top 0.30 m of soil fell below 50% available water capacity (AWC); well irrigated (WI), irrigated when soil moisture in top 0.30 m of soil fell below 15% (AWC). Root length density (RLD) was measured from 75-cm-deep soil cores at two locations three times per growing season and a third location at the end of the season. Cores 1 and 2 sample locations were 15 cm to the side of each plant: Core 1 on the same side as the drip tape and Core 2 on the opposite side. At the end of the season, Core 3 was taken 15 cmoutside of the bed in bare ground. RLD was significantly greater in the 0- to 30-cm soil depth and dropped dramatically below 30 cm; it was not significantly affected by irrigation treatment or rootstock. Core 1, next to the drip tape, had greater RLD than Core 2, 30 cm from drip tape, but only at the later sampling dates. Roots were found in Core 3 at all depths, but the RLD was significantly less than that measured in Cores 1 and 2. These findings suggest that the effective root zone depth for watermelon is 0 to 30 cmand that the particular scion/rootstock combinations tested in this study do not differ in root systemsize or location.
Article
Research on vegetable grafting and the spread of methods for this in Japan began around 1920 with a study on watermelon. Cucurbita moschata was initially used as a rootstock with watermelon to prevent fusarium wilt. In the 1930s, watermelon cultivation using rootstocks from bottle gourd or wax gourd, especially bottle gourd, was rapidly adopted after suitable rootstock species and accessions had been selected and a stable grafting method using cotyledonary-stage seedlings had been developed. From the 1950s through to the 1970s, sudden wilt of bottle-gourd-grafted watermelon caused by the pathogens Fusarium oxysporum f. sp. lagenariae and/or Pythium spp. or by physiological disorders spread, and rootstocks to replace that of bottle gourd were sought. Based on the results of various trials, mainly on Cucurbita spp., the fusarium-wilt-resistant (f. sp. lagenariae) bottle gourd variety 'Renshi' was eventually released in the 1980s. Since then, fusarium-wilt-resistant bottle gourd rootstocks have been the main rootstocks used in Japan. The best choice for a root-stock cultivar is dependent on the production area, and many different rootstock species and cultivars are used for various conditions. The state of grafting of cucurbitaceous vegetables in Japan is briefly surveyed.
Article
Grafting watermelon (Citrullus lanatus var. lanatus) onto rootstocks of interspecific hybrid squash (Cucurbita moschata x C. maxima), bottle gourd (Lagenaria siceraria), or citron (Citrullus lanatus var. citroides) has been used in Asia and Israel to mange Fusarium wilt of watermelon caused by Fusarium oxysporum f. sp. niveum. The objectives of this study were to determine the frequency of infection of six rootstocks by E oxysporum f. sp. niveum races 1 and 2 and the field performance of grafted rootstocks in Charleston, SC. Grafted and nongrafted watermelon and rootstock plants were inoculated in the greenhouse with race 1, race 2, or water (the control treatment). With both races, the frequency of recovery of E oxysporum from scion and rootstock portions of inoculated watermelon plants grafted onto 'Ojakkyo' citron was greater than from watermelon plants grafted onto 'Shintosa Camel' and 'Strong Tosa' interspecific hybrid squash, and from plants grafted onto 'Emphasis', 'Macis', and 'WMXP 3945' bottlegourd. For nongrafted plants inoculated with race 1, percent recovery also was greater from Ojakkyo than from interspecific hybrid squash and bottlegourd. For nongrafted plants inoculated with race 2, E oxysporum was recovered from the base of >= 79% of all inoculated plants. More than two-thirds (15) of 21 isolates recovered from the tops or scions of inoculated plants were pathogenic on watermelon. In spring 2010 and 2011, the six rootstocks were grafted with seedless watermelon 'Tri-X 313', which is susceptible to both races, and transplanted in a field infested with races 1 and 2 of E oxysporum f. sp. niveum. Disease incidence for nongrafted and self-grafted Tri-X 313 (the control treatments) and Tri-X 313 grafted onto Ojakkyo citron did not differ significantly. Grafted watermelon plants produced greater weights and numbers of fruit than plants of the two control treatments. Nonpathogenic isolates of E oxysporum and isolates of E oxysporum f. sp. niveum colonized interspecific hybrid squash, bottlegourd, and grafted watermelon. The rootstocks evaluated, however, restricted movement of E oxysporum f. sp. niveum into the watermelon scion, suppressed wilt symptoms, and increased fruit yields in an infested field.
Article
Grafting on disease-resistant rootstocks is a growing practice in watermelon cultivation worldwide. Reports on effects of grafting on watermelon fruit postharvest performance are scarce. The current work examined postharvest performance at 25C of four diploid cultivars grown nongrafted or grafted onto three Cucurbita maxima × C. moschata rootstocks. Despite sucrose accumulation throughout storage at the expense of fructose and glucose, total soluble carbohydrates and soluble solids content declined. Lycopene content peaked 7 days postharvest and intensity of flesh color increased concomitantly; yellowing of flesh was detected at 14 days. Rootstocks reduced soluble solids content only in the second year of experiments by 0.8–1.0°Brix. Rootstocks improved postharvest flesh firmness and lycopene content and enhanced flesh color. Rind was minimally thickened by rootstocks and declined with storage. Grafting diploid cultivars on interspecific rootstocks improved fruit quality and storability. Potential reduction in soluble solids content in response to grafting is limited and not detrimental to fruit quality.
Article
Yield and fruit characteristics of grafted plants of the ‘Reina de Corazones’ watermelon cultivar (Citrullus lanatus (Thunb.) Matsum and Nakai), grown in Fusarium-infestated soils, were determined in a series of experiments performed in the 8-year period 1993–2000. The experiments were performed in the coastal area south Valencia, Spain, in soils with a clay content ranging from 16 to 38%. Plant survival and yield were the highest in plants grafted onto several Cucurbita maxima × Cucurbita moschata hybrids and onto ‘Jover’ and ‘Bodi 1’ C. moschata cultivars. The survival ratio of the plants grafted onto ‘Shintoza’ rootstock (C. maxima × C. moschata) was 93%, while the mean yield in an early production cycle with harvests extending from the end of June to mid-August was 89,000kgha−1. The ‘Shintoza’ rootstock increased fruit size compared to the non-grafted plants, and improved yield stability by decreasing the coefficient of variation to 20%. The use of ‘Shintoza’ rootstock had no effect on the soluble solids concentration of the central endocarp, and did not increase the development of yellowish bands in the flesh or the internal breakdown of the endocarp. The use of this rootstock is an advantageous alternative to soil fumigation by methyl bromide for the control of Fusarium wilt in watermelon production, as it is cheaper and safer, and the yields are higher and more reliable.
Article
Two experiments were conducted to study the effect of grafting on nitrogen-use efficiency (NUE) in mini-watermelon plants. In the first study, mini-watermelon plants (Citrullus lanatus [Thumb.] Matsum. and Nakai cv. Minirossa) either ungrafted or grafted onto Macis, Vita (Lagenaria siceraria [Mol.] Standl.), PS1313, and RP15 (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne) rootstocks grown in hydroponics were compared in terms of shoot dry biomass, leaf area, root-to-shoot ratio, SPAD index, shoot N uptake, and nitrate reductase (NR) activity 40 d after transplantation in response to nitrate concentration in the nutrient solution (0.5, 2.5, 5, 10, 15, or 20 mM of NO). In the second experiment, the suitability of a selected rootstock with high NUE (Vita) to improve crop performance and NUE of grafted mini-watermelon plants was evaluated under field conditions. In the hydroponic experiment mini-watermelon grafted onto Vita rootstock needed the lowest nitrate concentration (1.31 mM of NO3) in the nutrient solution to reach half maximum shoot dry weight. Total leaf area, SPAD index, and shoot N uptake increased in response to an increase of N concentration in the nutrient solution. At 2.5 mM NO, mini-watermelon grafted on either Vita or RP15 had the highest NR activity whereas no significant difference was observed at 10 mM NO. The open-field study indicated that increasing N-fertilization rates from 0 to 100 kg ha–1 improved total and marketable yields of mini-watermelon plants while decreasing NUE. When averaged over N levels, the marketable yield, NUE, N-uptake efficiency, and N-utilization efficiency were significantly higher by 39%, 38%, 21%, and 17%, respectively, in Minirossa grafted onto Vita compared to ungrafted Minirossa plants. Therefore, grafting mini-watermelon plants onto selected rootstocks can be used as a quick and effective method for improving productivity and NUE.
Article
Lycopene is a red carotenoid with antioxidant properties and potential health benefits. Current methods to assay lycopene content are time-consuming and require organic solvents. This report discusses a rapid and reliable light-absorption method to assay watermelon lycopene content that uses no organic solvents. Light absorption of 152 watermelon flesh purees was measured with a xenon flash colorimeter/spectrophotometer that can measure actual light absorption from opaque samples; results were compared with a hexane extraction method. The puree absorbance method gave a precise linear relationship (R2= 0.98) to lycopene content and was independent of lycopene concentrations or watermelon variety within the lycopene concentration measured (24 mg/g to 88 mg/g fresh weight).
Article
Grafting is an important integrated pest management strategy to manage soilborne pathogens and other pests of solanaceous and cucurbitaceous crops. Important diseases managed by grafting are caused by fungal pathogens such as Verticillium, Fusarium, Pyrenochaeta and Monosporascus; oomycete pathogens like Phytophthora; bacterial pathogens, particularly Ralstonia; root knot nematodes and several soil-borne virus pathogens. Rootstocks can include intraspecific selections that utilize specific major resistance genes and interspecific and intergeneric selections that exploit non-host resistance mechanisms or multigenic resistance. Rootstock selection has also been documented to impact foliar pests including pathogens, arthropods and viruses. Over-reliance on specific rootstocks in production systems has led to the emergence of new pathogens or shifts in the host specificity of the pathogen population, emphasizing the need for multi-tactic approaches to manage soilborne pathogens. One advantage and associated challenge of grafting is that rootstock selection for disease management is site specific depending on the presence, population structure and dynamics of the pathogen, as well as edaphic, environmental and anthropogenic factors. The use of grafting as an Integrated pest management tool to manage biotic stress will be most successful when carried out with increasing knowledge about the biology, diversity, and population dynamics of the pathogen or other pests and when complemented with sustainable farming system practices. This review highlights major uses of grafting to manage soilborne pathogens, provides some novel information on managing foliar or other soilborne pests (insects, mites, weeds) and offers discussion on future research and applications.
Influence of grafting on the critical period for weed control in grafted watermelon
  • M B Bertucci
  • K Jennings
  • D Monks
  • D Jordan
  • F Louws
  • J R Schultheis
  • S Smith
  • N T Basinger
  • M Waldschmidt
Bertucci, M.B., K. Jennings, D. Monks, D. Jordan, F. Louws, J.R. Schultheis, S. Smith, N.T. Basinger, and M. Waldschmidt. 2017. Influence of grafting on the critical period for weed control in grafted watermelon. HortScience 52:S74 (abstr.).
Trial report: Seedless watermelon variety evaluation
  • T Coolong
Coolong, T. 2015. Trial report: Seedless watermelon variety evaluation. 5 May 2018. <http://blog.extension.uga.edu/ colquittag/files/2016/01/2015-UGA-Tifton-Watermelon-Variety-Trial-Results.pdf>.
Common cucurbit diseases and pests and susceptibility characteristics
  • M D Kleinhenz
Kleinhenz, M.D. 2015. Description of commercial cucurbit rootstocks. Common cucurbit diseases and pests and susceptibility characteristics. 5 Feb. 2015. <http://www.vegetablegrafting.org/ wp/wp-content/uploads/2015/02/ usda-scri-cucurbit-rootstock-table-feb-15.pdf>.
Grafting of herbaceous vegetable and ornamental crops
  • J Lee
  • M Oda
Lee, J. and M. Oda. 2003. Grafting of herbaceous vegetable and ornamental crops. Hort. Rev. 28:61-124.
Grafting watermelon onto pumpkin
  • K Tateishi
Tateishi, K. 1927. Grafting watermelon onto pumpkin. J. Jpn. Hort. (Nihon-Engei Zasshi) 39:5-8.
Grafting replaces methyl bromide
  • E Zagheni
Zagheni, E. 2003. Grafting replaces methyl bromide. Appropriate Technol. 30(4):10-11.