Grafted Watermelon Research Articles

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

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

Responses of Grafted Watermelon onto Cucurbita pepo Tiana F1 Hybrid to Boron Nutritional Disorders

Sensitivity to boron stress in growing media during the early seedlings stage could severely inhibit watermelon growth and development. The aim of this study was to test if watermelon (Citrullus lanatus cv. Mahbubi) performance can be improved under different boron concentrations (0, 46.31 and 935.11 µmol·L−1 H3BO3) by grafting watermelon plants onto Cucurbita pepo Tiana F1 hybrid rootstock. Shoot dry weight of grafted watermelon was significantly higher than those of non-grafted plants under boron stress conditions (0 and 935.11 µmol·L−1). Boron concentration of the aerial organs of the grafted plants was higher than in the non-grafted ones when treated with 0 µmol·L−1 H3BO3. However, with the application of boron (935.11 µmol·L−1 H3BO3), the aerial organs of grafted plants accumulated lower boron than non-grafted ones. The Cucurbita pepo rootstock also improved the absorption of several other nutrients and leaf chlorophyll content and the Fv/Fm ratio was also increased at high boron root concentration. Higher activities of several antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD) and peroxidase (POX) in grafted watermelons were associated with a significant reduction in H2O2 and malondialdehyde (MDA) generation when compared with those of non-grafted plants under boron stress conditions (0 and 935.11 µmol·L−1 H3BO3). Grafted plants reported improved growth, nutrient uptake and several other physiological parameters when compared to non-grafted watermelon plants under boron stress conditions.

Field and Greenhouse Evaluations of Cucurbit Rootstocks to Improve Verticillium Resistance for Grafted Watermelon

Grafting watermelon (Citrullus lanatus Thunb.) onto resistant rootstocks is used in many areas of the world to overcome soilborne disease losses including verticillium wilt caused by Verticillium dahliae Kleb. Currently, this disease poses a serious risk to watermelon growers in Washington State. To identify resistant rootstocks, the verticillium wilt reactions (chlorosis, necrosis, and wilting) of 14 nongrafted PI accessions including Benincasa hispida Thunb., Cucurbita moschata Duchesne ex Poir., and Lagenaria siceraria Molina Standl. from the U.S. Department of Agriculture National Plant Germplasm System (USDA NPGS); 11 nongrafted commercially available rootstocks; and, nongrafted ‘Sugar Baby’ watermelon (verticillium wilt–susceptible control) were visually assessed in a field naturally infested with V. dahliae at a rate of 17 colony-forming units (cfu) per gram of soil. Typical symptoms of verticillium wilt were observed on all entries. ‘Sugar Baby’ had the highest relative area under disease progress curve (RAUDPC) value (26.80), which was not significantly different from ‘64-19 RZ’, ‘Marvel’, PI 368638, PI 634982, and PI 642045 (average = 10.16). PI 419060 (1.46) had the lowest RAUDPC value, which was not significantly different from ‘Miniature Bottle Gourd’, PI 326320, PI 419016, PI 536494, PI 636137, ‘Strong Tosa’, ‘Strongtosa’, and ‘TZ 148’ (average = 3.36). The mean RAUDPC value of PI accessions (5.49) did not differ significantly from the mean value of the commercial rootstocks (5.68). Microsclerotia typical of Verticillium spp. were observed in the stems of all but one entry (PI 181913). In a greenhouse study, a subset of 12 entries were inoculated with V. dahliae, and by 22 days after inoculation (DAI), ‘Sugar Baby’ had a significantly higher disease rating than all entries except PI 419060, PI 438548, and ‘Titan’. A strong positive correlation was observed between the field and greenhouse studies. Results indicate that commercial rootstocks as well as PI accessions could be used to successfully manage verticillium wilt in Washington; however, grafting compatibility with watermelon must first be ascertained for the promising PI accessions. Although greenhouse-based verticillium wilt assays can be used to help predict rootstock performance in the field, accurate assessment may require manipulating environmental conditions (e.g., temperature and humidity) to approximate field conditions.

Control of Fusarium Wilt of Watermelon by Grafting onto Bottlegourd or Interspecific Hybrid Squash Despite Colonization of Rootstocks by Fusarium

Grafting watermelon (Citrullus lanatus var. lanatus) onto rootstocks of interspecific hybrid squash (Cucurbita moschata × 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 F. 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 F. 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, F. 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 F. 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 F. oxysporum and isolates of F. oxysporum f. sp. niveum colonized interspecific hybrid squash, bottlegourd, and grafted watermelon. The rootstocks evaluated, however, restricted movement of F. oxysporum f. sp. niveum into the watermelon scion, suppressed wilt symptoms, and increased fruit yields in an infested field.

Susceptibility of Cucurbit Rootstocks to Didymella bryoniae and Control of Gummy Stem Blight on Grafted Watermelon Seedlings with Fungicides

Seedlings of watermelon are susceptible to Didymella bryoniae, the cucurbit pathogen that causes gummy stem blight, particularly when they are grown in the greenhouse for use as transplants. Seedlings of bottle gourd (Lagenaria siceraria) and interspecific hybrid squash (Cucurbita moschata × C. maxima) that are used as rootstocks for grafting watermelon are susceptible to gummy stem blight when wounded. Nonwounded rootstock seedlings of both genera were as susceptible to gummy stem blight as seedless watermelon. Because grafted plants must be misted or held at high relative humidity for 1 week so the graft union will heal, fungicides may be necessary to manage gummy stem blight under these disease-conducive environmental conditions. Nine fungicides were applied as foliar treatments at labeled rates per 467 liters/ha water to nongrafted seedlings of watermelon and five rootstock cultivars. Fluopyram + tebuconazole injured all five bottle gourd and hybrid squash cultivars and stunted watermelon and hybrid squash seedlings. Cyprodinil + difenoconazole injured all five rootstock cultivars and watermelon. Tebuconazole stunted bottle gourd and watermelon seedlings. Four of the five fungicides that were not phytotoxic reduced incidence and severity of gummy stem blight on seedless watermelon grafted onto bottle gourd Emphasis and hybrid squash Strong Tosa. Difenoconazole and cyprodinil were more effective than mancozeb or cyprodinil + fludioxonil, which were more effective than thiophanate-methyl, which was not significantly different from the water control (P = 0.01). Nongrafted watermelon seedlings and watermelon seedlings grafted onto watermelon as the rootstock were as susceptible to gummy stem blight as watermelon seedlings grafted onto cucurbits. Although difenoconazole and cyprodinil are not registered currently on cucurbits, transplant growers can apply mancozeb or cyprodinil + fludioxonil to manage gummy stem blight on watermelon and rootstock seedlings during greenhouse production.

Plant Growth, Fruit Yield and Quality, and Tolerance to Verticillium Wilt of Grafted Watermelon and Tomato in Field Production in the Pacific Northwest

Growth, fruit yield and quality, and potential tolerance to verticillium wilt (Verticillium dahliae) were compared among non-grafted, self-grafted, and grafted triploid watermelon (Citrullus lanatus Thunb., ‘Crisp’n Sweet’) and heirloom tomato (Solanum lycopersicum, ‘Cherokee Purple’). Rootstocks for watermelon were ‘Emphasis’ bottle gourd (Lagenaria sicerarea) and ‘Strong Tosa’ interspecific squash hybrid (Cucurbita maxima × Cucurbita moschata), and rootstocks for tomato were ‘Beaufort’ and ‘Maxifort’ interspecific tomato (Solanum lycopersicum × Solanum habrochaites). Field trials were carried out in 2010 and 2011 at Hermiston and Eltopia (eastern Oregon and Washington, respectively) and Mount Vernon (western Washington). Grafted watermelon had significantly larger stem diameter than non-grafted and self-grafted plants both years at Mount Vernon, whereas there were no differences at Hermiston or Eltopia. Grafted tomato in 2011 had significantly larger stem diameter than non-grafted and self-grafted plants at Eltopia and Mount Vernon, and ‘Beaufort’-grafted plants were significantly taller than other treatments at Mount Vernon. Grafting did not impact watermelon or tomato fruit yield or quality at any location either year. Foliar symptoms of verticillium were not observed on ‘Crisp’n Sweet’ watermelon at the eastern locations either year; however, at Mount Vernon, ‘Emphasis’ and ‘Strong Tosa’-grafted plants had significantly lower verticillium wilt severity than non-grafted and self-grafted plants both years. Microsclerotia were observed in all recovered watermelon stems sampled at Eltopia and Mount Vernon. V. dahliae was isolated from non-grafted and ‘Emphasis’-grafted ‘Crisp’n Sweet’ stems at Eltopia and non-grafted, self-grafted, and ‘Strong Tosa’-grafted stems at Mount Vernon. Foliar symptoms of verticillium wilt and microsclerotia in stems were not observed on ‘Cherokee Purple’ plants at either location both years despite site histories of the disease. Grafting with ‘Emphasis’ and ‘Strong Tosa’ rootstocks may be an effective strategy for managing verticillium wilt on watermelon in western Washington; however, grafting ‘Cherokee Purple’ onto ‘Beaufort’ and ‘Maxifort’ did not provide any advantages for tomato under the field conditions of this study.

Root exudates from grafted-root watermelon showed a certain contribution in inhibiting Fusarium oxysporum f. sp. niveum.

Grafting watermelon onto bottle gourd rootstock is commonly used method to generate resistance to Fusarium oxysporum f. sp. niveum (FON), but knowledge of the effect of the root exudates of grafted watermelon on this soil-borne pathogen in rhizosphere remains limited. To investigate the root exudate profiles of the own-root bottle gourd, grafted-root watermelon and own-root watermelon, recirculating hydroponic culture system was developed to continuously trap these root exudates. Both conidial germination and growth of FON were significantly decreased in the presence of root exudates from the grafted-root watermelon compared with the own-root watermelon. HPLC analysis revealed that the composition of the root exudates released by the grafted-root watermelon differed not only from the own-root watermelon but also from the bottle gourd rootstock plants. We identified salicylic acid in all 3 root exudates, chlorogenic acid and caffeic acid in root exudates from own-root bottle gourd and grafted-root watermelon but not own-root watermelon, and abundant cinnamic acid only in own-root watermelon root exudates. The chlorogenic and caffeic acid were candidates for potentiating the enhanced resistance of the grafted watermelon to FON, therefore we tested the effects of the two compounds on the conidial germination and growth of FON. Both phenolic acids inhibited FON conidial germination and growth in a dose-dependent manner, and FON was much more susceptible to chlorogenic acid than to caffeic acid. In conclusion, the key factor in attaining the resistance to Fusarium wilt is grafting on the non-host root stock, however, the root exudates profile also showed some contribution in inhibiting FON. These results will help to better clarify the disease resistance mechanisms of grafted-root watermelon based on plant-microbe communication and will guide the improvement of strategies against Fusarium-mediated wilt of watermelon plants.

Grafting watermelon seedling production management system based on process control strategy

Greenhouse environmental management, seedling bed scheduling, and fertilizer and water management are the core technologies of seedling nursery. Precision management and control of the whole production process guarantees high grated seedling quality. In order to improve management efficiency of grafted watermelon seedling production and seedling quality, this paper designs and develops a grafted watermelon seedling production management system based on process control methods by process control strategy, seedling bed planning design, and handheld device technology.

The Influence of Rootstock Selection on Fruit Quality Attributes of Watermelon

Grafting watermelon (Citrullus lanatus) to control Fusarium wilt has been practiced in Europe, the Middle East, and the Far East for decades. Until recently, grafting watermelon has not been practiced in the United States due to labor costs and land availability. There is some disagreement in the literature as to the effects that grafting has on water- melon fruit quality. This study was designed to determine the effects of grafted watermelon on fruit firmness, lycopene content, and total soluble solids (TSS) using five different rootstocks. When using Cucurbita ficifolia or Cucurbita maxima x Cucurbita moschata hybrid as the rootstock, watermelon fruit consistently had higher fruit firmness values. Other C. maxima x C. moschata hybrids or Lagenaria siceraria rootstocks generally produced lower or more varied fruit firmness values. Grafting increased fruit firmness by as much as 25% in some cases, but field and year effects were ob- served. In addition, grafting had no effect on lycopene content or TSS. Furthermore, no off-flavors were detected in fruit from grafted plants, but there was a 5- to 7 day delay in fruit maturity compared to their non-grafted counterpart. Although environment can have a major influence on fruit quality attributes, rootstock selection may be equally important in achieving the desired outcome.

COST BENEFIT ANALYSES OF USING GRAFTED WATERMELON TRANSPLANTS FOR FUSARIUM WILT DISEASE CONTROL

ISHS IV International Symposium on Seed, Transplant and Stand Establishment of Horticultural Crops; Translating Seed and Seedling Physiology into Technology COST BENEFIT ANALYSES OF USING GRAFTED WATERMELON TRANSPLANTS FOR FUSARIUM WILT DISEASE CONTROL

ECONOMICS OF GRAFTED VS CONVENTIONAL WATERMELON PLANTS

Grafting of watermelons has been used in many countries to provide control of, or resistance to, certain soil borne diseases such as Fusarium wilt. The impact of grafting on postharvest quality has not been thoroughly examined. This report deals with the comparison of the costs of production between grafted versus conventional watermelons and the potential net revenue of the two. A 2-year study was conducted on the effects of grafting watermelon (Citrullus lanatus) onto rootstocks of squash and gourd at Lane, Okla., in both 2004 and 2005. Details of the research methodology are outlined in “Year Two: Effects of Grafting on Watermelon Yield and Quality” by Roberts et al. Costs of using grafted transplants increased the costs of production from $1,209 to $1,914 or $705/acre at 1,500 plants/acre. Results of the 2-year study indicated grafted watermelons had slightly lower yields per acre, similar sugar in some grafted combinations the first year but slightly lower the second year, similar lycopene content, and much higher firmness. Results of a 10-day storage study indicated that firmness of fresh-cut flesh for all watermelons declined after ten days on the shelf. However, the grafted watermelon flesh was firmer after ten days than the nongrafted fruit at the beginning of the ten days. This improved shelf life should interest the cut-fruit industry and should lead to contract price enhancement for the growers. A market price of $0.02/lb for grafted watermelons above the market price of nongrafted watermelons would be needed to provide similar net revenues at the same yield per acre.

INFLUENCE OF PLUG CELL SIZE FOR ROOT VIGOR AND SEEDLING QUALITY ON GRAFT WATERMELON SEEDLING

INFLUENCE OF PLUG CELL SIZE FOR ROOT VIGOR AND SEEDLING QUALITY ON GRAFT WATERMELON SEEDLING

Fusarium solani f. sp. cucurbitae race 1, a potential pathogen of grafted watermelon production in Spain*

A crown, root and fruit rot of squash (Cucurbita maxima and Cucurbita moschata) has been observed in eastern provinces of Spain over the past 4 years. Isolations from the crown of symptomatic plants and fruits yielded primarily a Fusarium solani that was identified as F. solani f. sp. cucurbitae race 1 on the basis of pathogenicity tests and disease symptoms in the field. In Spain, more than 90% of watermelon plants are grafted, using different Cucurbita hybrids (C. maxima × C. moschata) as rootstocks. In 1998, some grafted watermelon plants were first found to be affected by F. s. cucurbitae race 1. The purpose of this study was to evaluate the pathogenicity of this fungus on several rootstocks commonly used for grafting watermelon (Brava, Titan, Shintoza, RS‐841, TZ‐148 and TW‐1) in order to prevent a possible spread of this fungus that could cause serious economic losses in watermelon production. None of them proved to be resistant.