GRAFTED WATERMELON: TRANSPLANT, FRUIT PRODUCTION AND CONSUMER BENEFIT

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: TERMINATED
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1003428
• Project No.: SC-1700487
• Project Start Date: Oct 1, 2014
• Project End Date: Nov 1, 2016

Project Director
Hassell, R.

Recipient Organization
CLEMSON UNIVERSITY
(N/A)
CLEMSON,SC 29634

Performing Department
Agricultural & Environmental Sciences

Non Technical Summary
I graft a watermelon plant onto a disease-resistant plant to overcome these diseases. I study ways of improving the grafting process through grafting methods, rootstock treatment, and cultural practices. I'm trying to make the grafted plants more affordable and effective for growers by eliminating the regrowth from the rootstock plant. Controlling the regrowth is very expensive for growers and requires a lot of labor. I invented a treatment called 'blinding' that burns out the growing point of the rootstock before a watermelon plant is grafted onto it. Because blinding the rootstock removes the growing point, the rootstock seedling stores all the energy it would normally put to new growth. Then, when the rootstock is grafted, it's full of energy to heal the graft and give the new plant a head start. We have found that blinding the rootstocks and letting them store up energy gives a higher graft success and better transplant success in the field. We are also finding that grafted watermelon is sweeter and firmer, has more lycopene, and lasts longer after harvesting. Grafted watermelon plants are more vigorous and have higher yields, so the farmer doesn't have to plant as many plants to get the same amount of fruit. Grafting watermelon provides a lot of benefits, but it is expensive. Blinding the rootstocks make it more affordable for growers to buy grafted watermelon transplants, and could allow for better, more effective grafting methods. Consumers would benefit from the added nutritional components in grafted watermelon. Blinding rootstocks completely changes the way we look at grafting. Because the rootstocks store energy after blinding, new, grafting methods are possible, and need to be perfected. We also need to continue to study the blinding process and determine its effects on grafted transplants.

Animal Health Component

0%

Research Effort Categories

Basic

(N/A)

Applied

100%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
204	1429	1020	100%

Knowledge Area
204 - Plant Product Quality and Utility (Preharvest);

Subject Of Investigation
1429 - Cucurbits, other;

Field Of Science
1020 - Physiology;

Keywords

watermelon grafting

citrullus lanatus

regrowth control

grafting methods

cotyledon-free graft

Goals / Objectives
1: Disease Interactions: The interactions of the soilborne disease tolerance and root knot nematode susceptibility of rootstocks has not been investigated. Research is needed to ensure an understanding of impacts of using grafted plants on soil, and the tolerance of grafted plants to root knot nematode pressure.2: Growth and Fruit Quality Effects: Cultural practices using grafted plants need to be determined in order to increase adoption of grafted cucurbits in commercial production. Research is necessary to determine cultural practices such as spacing and fertilizer use. As new rootstock and scion cultivars are released, continued research on the rootstock-scion combination effects on fruit quality is also necessary.3: Develop and improve grafted transplant production and growing methods: As scion cultivars differ in growth and vigor, methods of improving graftability of seedless watermelon cultivars is important in improving graft success. Scion age and growing conditions will be studied to increase energy required for graft success. Fatty alcohol rootstock treatments can also increase the time in which rootstocks can be grafted, and can improve graft success of the new, hypocotyl-only grafting method. However, the rootstock treatment has not yet been tested using the hole-insertion method. Research on effects of application timing and rootstock age on graft survival is required.4: Determine if health properties of cucurbits are enhanced by specific rootstock/scion combinations. Changes in grafted cucurbit fruit quality appear to be both rootstock- and scion-dependent, causing contradictory reports in the literature. Texture, flavor, and sweetness are the variables most often noted to be negatively impacted in watermelon and melon (Davis et al., 2008). In melon, grafting was found to decrease ascorbic acid (Xu et al., 2006b), and fermentation occurred in fruit from scions grafted to vigorous interspecific squash rootstocks (Muramatsu, 1981; Chung, 1995). In contrast, carotenoid content increased in melons with certain rootstock and scion combinations (Alan et al., 2007; Alexopoulos et al., 2007). Grafting increased soluble solids content, lycopene, and some amino acids of watermelon fruit (Davis and Perkins-Veazie, 2005; Perkins-Veazie et al., 2013). Differences in experimental results among researchers may be caused by the variation in fruit sugar accumulation with rootstocks (Xu et al., 2006b).

Project Methods
OBJECTIVE 1: Eight experiments with FON and Meloidogyne incognita will be done in the greenhouse (a growth chamber will be used in July and August). In each experiment, plants will be non-grafted or grafted, inoculated with FON race 1 or race 2. Each experiment will be repeated in year 2. Host cultivars. One cultivar of each rootstock species, interspecific hybrid squash, bottle gourd, and citron, will be used in each experiment. Seedless watermelon cultivars Tri-X 313 and Fascination will be used in experiments with FON races 1 and 2, respectively.OBJECTIVE 2: For both watermelon and melon, we propose to obtain different species of rootstocks, Cucurbita maxima x Cucurbita moschata (interspecific squash hybrids), Cucurbita moschata (pumpkin), Cucurbita ficola (figleaf gourd), Lagenaria sp. (bottle gourd), Citrullus citroides (wild watermelon), and Cucumis melo (melon) to obtain cultivars within each rootstock type. We plant to take this diverse group of rootstocks and evaluate them this new HoRhizotron tool for root growth/"vigor" over a few week period.OBJECTIVE 3: We propose a series of experiments to determine the optimal rootstock and scion ages for success using different grafting methods, as well as the application of rootstock fatty alcohol treatments on the hole-insertion graft method. Furthermore, the optimal scion growing conditions and healing chamber conditions (i.e. light, humidity, and the timing of change of the two factors) will be evaluated.Because production with grafted transplants requires different cultural practices in the field, we propose a within-row spacing field trial to determine the optimal spacing of grafted watermelon and melon plants. Effects of transplant spacing on yield, fruit quality, number of harvests, and fruit ripening will be determined.OBJECTIVE 4: Watermelon fruit quality consists of 3 parts: external appearance (shape, rind firmness, rind color), internal appearance (firm flesh, pink to bright red color of flesh, no hollow heart, cracks, or water soaking), and consumer appeal (texture, sweetness, health attributes). In this proposed research, plots will be sampled in the field at locations using a standardized protocol for cutting, firmness readings, and sampling. About 200 g of watermelon flesh will be removed from the heart (center) of each fruit, placed in plastic bags, and frozen at -20 °C. Frozen samples will be sent by overnight and analyzed at North Carolina Research Center for sweetness, acidity, lycopene and carotenoid profiles, and amino acids (citrulline, arginine, etc.). Frozen samples will be partially thawed and pureed. Soluble solids content of the puree will be measured with digital refractometers and acidity determined with 0.01N NaOH to pH 8.1 using a pH meter. Total lycopene will be determined on each sample via transmission of the puree using a Hunter Ultra Pro Xenon colorimeter (Davis et al., 2003). Carotenoid profiles will be determined on selected replicates of the samples by micro extraction with hexane:acetone:ethanol followed by HPLC separation of carotenoids (Perkins-Veazie et al., 2006). Citrulline content will be determined from purees using HPLC (Jayaprakasha et al., 2011).

Progress 10/01/14 to 11/01/16

Outputs
Target Audience:Watermelon growers and Cucurbit grafters both in the USA and other countries Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Grafting workshops for growers and transplant producers were conducted on a yearly basis. How have the results been disseminated to communities of interest?Workshops, publications, handouts, web page, magazines What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? 1: Desease Interactions: Developed a rootstock 'Bulldog" that has resistance to Fusarium Wilt and tolerance to root knot nematodes 2: Growth and Fruit Quality Effects: Grafted plants can be planted at 32 square feet instead of the standard 24 square feet. Fruit from grafted plants once mature can remain in the field for up to 3 weeks without decay. However fruit from non-grafted plants hold up only a few days. 3: Develop and improve grafted transplants: Grafted transplants are now grafted without any chance of re-growth. 4: Determine health properties: Studies have not been carried out in a replicated manner.

Publications

Progress 10/01/14 to 09/30/15

Outputs
Target Audience:As methyl bromide has been phased out, grafting cucurbits onto disease-resistant rootstocks is the only option for growing watermelon in fields with Fusarium wilt. Because the rootstocks are not hosts for the disease, grafting onto these rootstocks protects the crop from soil-borne diseases and brings other benefits as well. The robust rootstock also provides enough nutrients to the watermelon scion to increase fruit number, size, and nutritional value. Grafted watermelon lasts longer in the field without going over-ripe, so a grower can hold his crop until the price is high without losing fruit quality. However, producing grafted plants can be very costly, especially in labor required to control regrowth from the rootstock. Regrowth from the rootstock plant competes with the watermelon scion for light and nutrients. If regrowth occurs early, the graft will be lost, and if it occurs later in the field, yields will suffer. Our target audience is aimed toward improving the watermelon grafting process by overcoming the challenge of rootstock regrowth to make grafting cheaper and more efficient. We are researching a compound that burns out just the squash meristem, and leaves the squash plant ready for grafting, without any regrowth. When we treat the plants with this compound and then leave them in the greenhouse over time, the rootstocks store up carbohydrates that can be used for energy. The more energy a rootstock has, the better the graft heals and the faster the rootstock re-roots. The treatment also increases the grafting window of these rootstocks from just a few days to 3 weeks. One of the most exciting aspects that we are researching is a new, more efficient grafting method that is possible as a result of the accumulated carbohydrates. A rootstock's cotyledons are a lot like human kidneys: we can still live if we lose one, but not both. In the same way, the rootstock must have at least one cotyledon remaining when it is grafted, to provide the energy to heal the graft. After the treatment, the rootstocks store so much energy that they no longer rely on the energy provided by the cotyledons, and can be grafted without them. This is a much easier and more efficient grafting method because it completely eliminates suckering, requires less space, and is more cost-effective. The rootstock treatment and grafting procedure we have developed will make the grafting process more efficient and effective and, ultimately, more beneficial to South Carolina watermelon growers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?In Sept (2014) I was asked to visit Australia and to demonstrate the new method of vegetable grafting. I was gone for two weeks. I worked with two greenhouse operations and instructed them in grafting of vegetables. I conducted two hands-on grafting workshops. One in December of 2014 and the other on April of 2015. There were over 200 participants learning the art of grafting cucurbits Supplied grafted plants for demonstrations in four states at 1 acre sites, Florida, Georgia, North Carolina, and Indiana. How have the results been disseminated to communities of interest?Edisto Feild Day: Gilbert Miller organized this Field Day, (July 2014) and asked that I take some time to educate the growers on my grafting work with watermelons 25th Annual Southeast Vegetable & Fruit Expo, Myrtle Beach, South Carolina, November 27 and 28 2014 Co-chair of the educational session. This involvedgrowers from three states. The educational program involvedtwo days of intense educational programs that ran all day. This involved planning and organizing 12 sessions involving four speakers per session. I also gave three talks on grafting, specialty potatoes, sweet corn cultivars. Grafting Workshop to demonstrate manual and robotic grafting methods, February 2015, at USDA Vegetable Laboratory, Charleston, SC. Grafting Workshop to demonstrate manual and robotic grafting methods, Dec 2014, at Southeast Vegetable and Fruit Expo, Myrtle Beach, SC. What do you plan to do during the next reporting period to accomplish the goals? We would like to develop a rootstock vigor assay that can be conducted under controlled growing conditions in the greenhouse or phytotron, and then to translate these results to the field. We plan to document root growth and/or vegetative growth and resulting yields in the field to better understand the rootstock-scion relationship. We propose a series of experiments to determine the optimal rootstock and scion ages for success using different grafting methods, as well as the application of rootstock fatty alcohol treatments on the hole-insertion graft method. Furthermore, the optimal scion growing conditions and healing chamber conditions (i.e. light, humidity, and the timing of change of the two factors) will be evaluated. Because production with grafted transplants requires different cultural practices in the field, we propose a within-row spacing field trial to determine the optimal spacing of grafted watermelon and melon plants. Effects of transplant spacing on yield, fruit quality, number of harvests, and fruit ripening will be determined.

Impacts
What was accomplished under these goals? I am successfully leading a grafting team of scientists that consists of the following people: Dr Shaker Kousik (USDA, Charleston SC), Dr. Amnon Levi (USDA, Charleston SC), Dr. Kai-shu Ling (USDA, Charleston SC), Dr. Judy Theis (USDA, Charleston SC), Dr. Tony Keinath (Clemson, Charleston SC), Gilbert Miller (Clemson, Blackville SC), Dr. Josh Freeman (University of Florida Quincy Fl), Dr. Jonathan Schulthesis (NC State, Raleigh NC), Dr, and Dr. Penelope Perkins-Veazie (NC State, Raleigh NC). The purpose of this teamis to cover all aspects of grafting from methods (myself), disease tolerance (Dr. Kousik, Dr. Keinath), virus resistance (Dr. Ling), breading material (Dr. Levi), nematode resistance (Dr. Ties), field elevations (Dr. Schulthesis, Dr. Freeman, Mr. Miller, and myself) and post-harvest (Dr. Perkins). The overall objective of this team is to work together as one unit and come up with material that works best for the grafting procedure in the United States. Syngenta Vegetable seeds provided us with grafting material, seeds, and other equipment amounting in gifts of $30,000. They also provided a grant to work on the grafting methods in the amount of $80,000. Rootstock material was also provided from the following seed companies: Zeraim Gedera, Seminis, Harris Moran, Sakata, and USDA. We had 32 rootstock lines that we evaluated in our specialty areas. It was my job to coordinate this effort. I did all the grafting and delivered all plants for each test. This past year was excellent. Progress has been made toward recommendations for the Southeast. We have published 5 scientific papers that were peer reviewed in 2014-2015. This is the only team that I am aware of that is working together to cover all aspects of grafting. We have developed a new grafting method that has gained national and international interest as a method that could greatly improve the efficiency of grafting throughout the world. Gave four out of state invited presentations: Ohio, Utah, North Carolina, Florida and twointernational trips: Australia (ISHS Meeting). China ( International Grafting Symposium)

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Mahmud, I., Kousik, C.S., Hassell, R., Chowdhury, K., Boroujerdi, A. 2015. NMR Spectroscopy Identifies Metabolites Translocated from Powdery Mildew Resistant Rootstocks to Susceptible Watermelon Scions. J. Agric. Food Chem., DOI: 10.1021/acs.jafc.5b02108.
• Type: Journal Articles Status: Published Year Published: 2014 Citation: Daley, S.L., J. Adelberg, and R. L. Hassell. 2014. Improvement of grafted watermelon transplant survival as a result of size and starch increased over time caused by rootstock fatty alcohol treatment: part 1. HortTechnology 24(3):343-349.
• Type: Journal Articles Status: Published Year Published: 2014 Citation: Daley, S.L., W. P. Wechter, and R. L. Hassell. 2014. Improvement of grafted transplant survival as a result of size and starch increase over time caused by rootstock fatty alcohol treatment: part ll. HortTechnology 24(3): 350-354.
• Type: Journal Articles Status: Published Year Published: 2014 Citation: Daley, S.L. and R. L. Hassell. 2014. Fatty alcohol application to control meristematic regrowth in bottle gourd and interspecific hybrid squash rootstocks used for grafting watermelon. HortScience 49(3):206-264.