Optimizing Watermelon Grafting Techniques

Abigail Attavar, MS StudentPinki Devi, PhD Student

Dr. Carol Miles, ProfessorDepartment of Horticulture

Problem: Verticillium Wilt

• Caused by Verticillium dahliae (Vd)

• Symptoms are chlorosis, necrosis and wilting

• Management is difficult because:• Persistent in soil for up to 14 years (in the

form of microsclerotia)

• Wide host range of about 400 plant species

• Soil fumigation with methyl bromide in the past but new fumigants are less efficient

• Soil solarization has moderate efficiency

Verticillium wilt disease progress

Grafted watermelon Non-grafted watermelon

WSU NWREC Mount Vernon, September, 2017

Grafting as a biological disease management strategy

Grafting – A propagation technique

Grafting is a technique that joins together two plants through their stem vascular tissues in order to take advantage of their combined characteristics.

Graft union

Scion

Rootstock

Splice grafting

1 2 3 4

Step 1. Cut the rootstock at 45° angle, under the cotyledon leavesStep 2. Cut the scion at 45° angle, ensuring the diameter is the same as the rootstockStep 3. Place a grafting clip onto the rootstock, rootstocks should occupy half the length of the clipStep 4. Place the scion into the grafting clip

One cotyledon grafting method

1 2 3 4

Step 1. Cut the rootstock at a 60° angle with one cotyledon remaining on the plantStep 2. Cut the scion at a 60° angle below the cotyledons, where its diameter matches that of the rootstockStep 3. Join the two cut stems togetherStep 4. Secure with a grafting clip.

Graft the plants

Place grafted plants in healing chamber

Monitor the healing process daily

Gradually reintroduce grafted plants to greenhouse environment conditions

Acclimate plants to natural environmental conditions

Seed scion and rootstock

Transplanting to Field

Plant the graft union well above the soil line

Efficiency of grafting as a disease management strategy

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21-Jul 26-Jul 31-Jul 5-Aug 10-Aug 15-Aug 20-Aug 25-Aug 30-Aug 4-Sep 9-Sep

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Non-graftedSelf-graftedStrong TosaEmphasis

Watermelon 2010 & 2011

Buller, S., Inglis, D. and Miles, C., 2013. Plant growth, fruit yield and quality, and tolerance to verticillium wilt of grafted watermelon and tomato in field production in the Pacific Northwest. HortScience, 48(8), pp.1003-1009.

Soil infestation of Verticillium dahliae: 18.0 cfu·g–1 at Mount Vernon, WA

Verticillium Wilt Progress

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42 60 70 83

Eltopia

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Eltopia

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42 60 70 83

Othello

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42 60 70 83

Othello

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45 52 59 72 89

Mount Vernon

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45 52 59 72 89

Mount Vernon

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Black plastic mulch Clear plastic mulch

Days after transplanting

Dabirian, S., Inglis, D. and Miles, C.A., 2017. Grafting watermelon and using plastic mulch to control verticillium wilt caused by Verticillium dahliae in Washington. HortScience, 52(3), pp.349-356.

Fruit Yield

Yield per plant (kg)

Treatment Eltopia Othello Mount Vernon

TriX Palomar (non-grafted) 14.7 30.4 7.4 b

TriX (Super Shintosa) 12.2 28.1 14.6 a

TriX (Tetsukabuto) 11.0 28.7 11.8 a

TriX (Just) 11.1 23.4 12.7 a

P-value 0.37 0.17 0.009

Soil infestation with Verticillium dahliae: <1 cfu g-1 at Eltopia, 2.6 cfu g-1 at Othello, and 27 cfu g-1 at Mount Vernon

Fruit Quality

Firmness (N)

Lycopene

(𝜇g.g-1) TSS %

Treatment

Eltopia 2.20 b 38.58 a 10.28

Othello 2.44 b 36.54 a 10.51

Mount Vernon 3.00 a 27.85 b 10.54

P-value < 0.0001 < 0.0001 0.22

Current research on watermelon grafting at WSU

Problem: Availability of Rootstocks

• Grafting onto a resistant rootstock can help manage the disease for watermelon• BUT resistant rootstocks are not

easily available

Solution: Screening germplasm for resistance

• Germplasm in USDA National Germplasm System is collected from all over the world• Potential sources of resistant rootstock

• Screened 56 germplasm accessions from 4 different rootstock species for resistance to Verticillium wilt

• 16 resistant accessions were used as rootstock for watermelon grafting and we assessed:• Yield• Fruit number• Fruit quality

Study conducted in 2017 at Mount Vernon, WA

Problem: Rootstock Regrowth

The meristem tissue below the axillary bud

Squash leaves

• Scouting plants in the greenhouse• Removing rootstock regrowth in the field

• Time consuming• Labor intensive

• Competition with scion for light, space, and water and nutrient uptake

• Decreases graft success• Death of scion

Possible solution

Splice grafting can be more efficient and cost effective grafting method

➢ Eliminate rootstock regrowth➢ 2-3 times faster than other

available techniques➢ Less labor cost

Limitation:• Low carbohydrate level• Dessication of the grafted seedling

during healing• Low survival rate

Past research

Gra

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0% Sucrose 1% Sucrose 2% Sucrose 3% Sucrose

Days after grafting

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Repeat 1

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Repeat 2

Dabirian, S. and Miles, C.A., 2017. Antitranspirant Application Increases Grafting Success of Watermelon. HortTechnology, 27(4), pp.494-501.

Ongoing research

Greenhouse studies: To increase survival of splice-grafted watermelonStudy 1. Effect of antitranspirant applied prior to graftingStudy 2. Effect of sucrose in combination with antitranspirant

applied prior to grafting

Field Study: Effect of grafting method on fruit maturity and quality as compared to non-grafted watermelon

• Emergence of female flower• Harvest date• Hollow heart and hard seed formation • Quality: fruit firmness, total soluble solids, lycopene content

Rootstock Species Cultivar Company Website

Interspecific

squash hybrid

Cucurbita maxima x

C. moschata

Carnivor, Super Shintosa,

Strong Tosa

Syngenta http://www.syngenta-us.com/crops/vegetables

Shintosa camelforce,

Ercole

Nunhems http://www.nunhemsusa.com/www/NunhemsInternet.nsf/

id/US_EN_WatermelonCobalt, Ferro Rijkzwaan https://www.rijkzwaanusa.com/crop/rootstockJust, Tetsukabuto, Titan,

Keystone

Takii seeds http://www.takiiseed.com/

Flexifort Enza Zaden http://www.enzazaden.us/Rootpower Sakata http://sakata.co.za/product/rootpower/RS 841 Seminis https://www.ahernseeds.com/products/rs841/?lang=en

Samura Genome seeds http://www.genomeseeds.com/prodect/rootstock/cucurbit-

rootstock/502Bass BS-1, AQ Origene seeds http://www.origeneseeds.comKardosa Aruba seed https://www.arubaseed.com/rootstocks

Calabash gourd Lagenaria siceraria Pelop Rijkzwaan https://www.rijkzwaanusa.com/crop/rootstock

Bingo, Valett F1, Savor Takii seeds http://www.takiiseed.com/Emphasis Syngenta http://www.syngenta-us.com/crops/vegetablesMacis Nunhems http://www.nunhemsusa.com/www/NunhemsInternet.nsf/id/US_EN_

HomeRS 3532 Aruba seed https://www.arubaseed.com/rootstocks/

Wax gourd Benincasa hispida Round, Oblong Kitazawa seeds https://www.kitazawaseed.com/seeds_winter_melon.htmlCitroides Citrullus lanatus Carolina Strongback Syngenta http://www.syngenta-us.com/crops/vegetables

Watermelon Citrullus lanatus Yokozuna F1 Takii http://www.takiiseed.com/goods_list/goods_list_2.php?called=catego

ry&vctg_no=29

Commercially Available Rootstocks

www.vegetablegrafting.org

Acknowledgements

• WSU Mount Vernon NWREC Vegetable Horticulture Staff• WSU Mount Vernon NWREC Plant Pathology Department• Funding provided by:

• Washington State Department of Agriculture• United State Department of Agriculture

SCRI No. 2011- 51181- 30963 and 2016-51181-25404• Northwestern Agricultural Research Foundation

• Seed companies:

Thank you.

Questions?

For more information on vegetable grafting, visit www.vegetablegrafting.org