Grafting Tomatoes for Disease Resistance and Improved Yield

Grafting Tomatoes for Disease Resistance and Improved Yield

A few weeks ago I was lucky enough to attend North Carolina State’s Tomato Field Day, at the Mountain Horticultural Crops Research and Extension Center in Mills River, NC.  Every summer crowds flock from all over the Southeast to learn what’s new in the world of tomatoes.  Since it’s not always convenient for you to drop what you’re doing to make a road trip to North Carolina, I’ll highlight something I learned from the field day.

Jonathan Kressin, a PhD candidate in Plant Pathology at NC State, is researching the effects of grafted tomatoes on bacterial wilt management.  Jonathan is not only researching rootstock varieties, he is also looking at cultural practice impacts on bacterial wilt.

Grafted Tomato Transplant

A recently transplanted grafted tomato plant. Photo Credit: Josh Freeman, University of Florida/IFAS

Materials and Methods

Jonathan selected 12 rootstock varieties for trials at the 3 tomato growing regions in North Carolina (Mountains, Piedmont, and Coastal Plains).  The cultural practice he is studying is transplant depth.  He wants to determine if burying the graft union has any effect on bacterial wilt tolerance in grafted plants.

Bacterial Wilt in a Tomato Field

A tomato field in Florida with severe incidence of bacterial wilt. Photo credit: Mathews Paret, University of Florida/IFAS

Results

  • Several of the tested rootstocks performed equally well across the 3 regions.  To help with disease resistance, it is important to rotate rootstock varieties and suppliers.
  • The rootstock variety ‘Shield’ displayed the least bacterial wilt resistance overall.
  • The rootstock variety ‘CRA66’ is recommended for open-pollinated varieties.
  • Transplant depth (burying plants below the graft union compared to above the union) did not have any effect on bacterial wilt occurrence.
  • Grafted plants have the potential to increase yield and average fruit size.

Future Research

  • Studies will be conducted to validate and understand the effect of transplant depth on bacterial wilt occurrence.
  • Genetic testing will be conducted to help develop rootstock rotation recommendations.

Grafted transplants significantly increase the cost of production, but as agricultural automation becomes more prevalent, transplant costs should come down.  Grafted tomatoes have the potential to increase yields and reduce inputs.  It’s exciting to see what the future holds for the ever adapting business of tomato farming.  More details on NC State’s tomato research can be found at the Mountain Horticultural Crops Research and Extension Center’s Tomato Production website.

Southern Blight Found in Holmes County Tomatoes

Southern Blight Found in Holmes County Tomatoes

Photo 1 – Southern Blight Foliage Wilt is Similar to Bacterial Wilt.  Credit Shep Eubanks

Photo 1 – Southern Blight foliage wilt looks similar to Bacterial Wilt. Photo credit Shep Eubanks

Southern blight (caused by Sclerotium rolfsii Sacc.) was found at two different tomato farms in Holmes County this week. Southern Blight is a serious fungal disease affecting diverse crops grown around the world, especially in tropical and subtropical regions. The disease is called “white mold” in peanuts and is a major disease across the Southeast. Since the phasing out of methyl bromide (EPA 2009) and the adoption of organic and other low-input production strategies, outbreaks of southern blight in tomatoes is becoming more common.

Early symptoms of southern blight begin with a discrete light brown, water-soaked lesion at the crown of the plant, near the soil line.   As the disease progresses a wilt develops and the wilted leaves of affected plants generally remain green and hang on the plant ( photo 1).  These symptoms can initially be confused with bacterial wilt caused by Ralstonia spp.

The disease is often not recognized in the field until the plant begins to wilt. Often the wilting is diurnal (during the daytime), with plants recovering at night. Under favorable weather conditions, however, the wilting can progress rapidly, become irreversible, and ultimately lead to plant death.

Unlike bacterial wilt, white mycelia can be seen near the soil line, often forming a mat around affected plant parts and serving as a clear sign of the pathogen (photo 2).

Photo 2 - Southern Blight on Tomato - photo courtesy of Shep Eubanks

Photo 2 – Southern Blight on Tomato.  Unlike bacterial wilt, white mycelia can be seen near the soil line. Photo credit: Shep Eubanks

In addition, numerous tan, round, or irregular mustard-seed-sized sclerotia are produced on affected plant parts and the surrounding soil surface shortly after mycelial growth is observed (Photo 3).

Photo 3 Closeup of mycelia and Sclerotia of Southern Blight - photo courtesy of Shep Eubanks

Photo 3 Closeup of mycelia and Sclerotia of Southern Blight.  Photo credit: Shep Eubanks

At this point in the growing season control of Southern Blight is very difficult.  The use of commercially available strobilurin fungicides (azoxystrobin, pyraclostrobin, and fluoxastrobin) are labeled for the control of southern blight on certain vegetables and may provide some relief, though control is difficult.

This disease requires an integrated approach for management including crop rotation, burial of crop residue and inoculum through deep plowing, use of pre-plant fungicides, and using healthy, disease free transplants.

For more information, download:
Integrated Management of Southern Blight in Vegetable Production

 

Spotted Wilt Virus in Tomato

Spotted Wilt Virus in Tomato

Tomato exhibiting signs of tomato wilted virus

Tomato exhibiting signs of tomato spotted wilt virus

Tomatoes, though a  joy to eat, are not the easiest crop to grow.  An Escambia County grower recently brought in a sample showing unusual patterns on the green fruit.  When he cut the fruit open, he noticed discoloration on the inside.  The issue was visually diagnosed as tomato spotted wilt virus. This problematic virus is transmitted from plant to plant by thrips (insects in the Order Thysanoptera.

Thrips at different stages of the life cycle

Thrips at different stages of their life cycle

This grower only has one plant showing symptoms in the fruit.  Thus far, the leaves still look healthy, but a virus is systemic.  Once a plant has a virus, there are no remedies.  UF/ IFAS Extension agents generally recommend growers plant resistant varieties.  The producer is growing two varieties: “Bella Rosa,” which is supposed to have resistance to fusarium wilt (races 1 and 2), tomato spotted wilt virus, and verticillium wilt, and “Amelia,” which is supposed to have resistance to fusarium wilt (races 1, 2, and 3), tomato spotted wilt virus, and verticillium wilt.  Information on disease resistance of several popular varieties and yield comparison can be found in the Spring 2009 and 2010 Commercial Fruit and Vegetable Variety Trials.

Inside of the diseased fruit exhibiting symptons.

Inside of the diseased fruit exhibiting symptoms.

Tomato spotted wilt virus is only one of many problems tomato growers can encounter.  For a handy little electronic diagnostic key, check out this Florida Tomato Scouting Guide.  If you can’t figure out what is plaguing your tomatoes, you can always contact your local county Extension agent.

 

Scouting Northwest Florida Tomatoes

Blossom End Rot

Identification of pests affecting crops is the first part of designing an Integrated Pest Management (IPM) program.  Scouting is an important part of any IPM program.  Once you identify problem pests, management decisions can be made such as changing cultural practices, using biological control methods or by applying pesticides.  By scouting and targeting problem pests, producers can reduce pesticide costs, reduce crop damage, and reduce pesticide resistance in pest populations.  Scouting is simple.  Here are 5 easy steps:
  1. Place yellow sticky traps (for whiteflies, leafminers, and aphids) and pheromone traps (for pepper weevils, tomato pinworms, tomato fruitworms and beet armyworms) around the field perimeter and check twice weekly.
  2. Map field into 2 acre grids.
  3. Select 6-10 plants in each grid twice weekly.
  4. Observe selected plants for flying insects as you approach.
  5. Inspect selected plants for caterpillars, true bugs and predators.

For North Florida, focus on scouting for Florida flower thrips, western flower thrips, stink bugs, spider mites, tomato pinworms, tomato fruitworms, leaffooted bugs, and whiteflies for the months of May and June.

You can also look for diseases and disorders in your tomatoes while you scout for insects.  Common diseases for May and June are Bacterial Wilt, Fusarium Wilt, Southern Blight and Tomato Spotted Wilt.  Disorders include Blossom End Rot, Catfacing and Sunscald.

For helping identifying insects, diseases and disorders, the Florida Tomato Scouting Guide can be found online at http://erec.ifas.ufl.edu/tomato-scouting-guide/.  The guide was developed by Dr. Ken Pernezny. The website contains identification keys for insects and diseases as well as good descriptions and color images of insects and diseases in tomatoes.

Search the leaves, fruit and stem for insects, diseases and disorders.