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Publication #ENY-061

Susceptibility of Flowers and Bedding Plants to Root-Knot Nematodes1

Romy Krueger and Robert McSorley2

Introduction

Root-knot nematodes can cause serious problems on flowers and bedding plants. Root-knot, which is characterized by swelling of the root (Fig. 1), is caused by the feeding activities of root-knot nematodes (Meloidogyne spp.). Different species of root-knot nematodes may be present in the soil, and different races may occur within these species. These root-knot nematode races may differ in their ability to infect some plant species and cultivars. Different species or cultivars of flowers may have different susceptibilities to these species and/or races. Selecting the right flower or bedding plant for a site may help to prevent losses due to root-knot nematodes. This publication summarizes some recently published work on this subject and provides an overview of flower cultivars and their susceptibility to different species and races of root-knot nematodes, particularly M. incognita, M. javanica, and M. arenaria, all of which are common in Florida.

Figure 1. 

Root symptoms caused by root-knot nematodes


[Click thumbnail to enlarge.]

Selecting a bedding plant – Identifying a possible root-knot problem

Before selecting any bedding plant, it is beneficial to obtain a soil nematode sample to determine which nematodes are present in the soil. More information on how to take a soil nematode sample and where to submit it can be found here: http://edis.ifas.ufl.edu/sr011. However, identification of root-knot nematode species is difficult and often requires molecular techniques and is not performed on routine nematode samples. Submission of a soil sample will only help to clarify if root-knot nematodes are present in the soil. If root-knot nematodes were a problem in the site before, selecting the right plant may be easier, but it is still often based on trial and error, eliminating or selecting flower species and cultivars according to the degree of damage observed in the previous crop. Eventually it might be possible to identify which root-knot nematode is present or if there is a mixture of species and races. As techniques for root-knot nematode identification improve, new species and races might be found. For example, M. mayaguensis and M. floridensis have only recently been identified from Florida (Mendes et al. 2007, Stanley et al. 2006). Relatively little is known about the susceptibility of flowers and bedding plants to these species.

An important tool in managing root-knot nematodes is rotation of plants that are susceptible, but are desired plants, with plants that are resistant. Root-knot nematodes, which are plant parasites and require a host for long-term survival, will be either unable to reproduce on these resistant plants or may only produce relatively small numbers of offspring. As numbers of offspring decrease, so does the potential for damage to a following susceptible flower planted in the site. Once the susceptible flowers are planted, nematode numbers build up again. Successful use of rotation requires knowledge about the degree of susceptibility of different plants. Tables 2 and 3 below might be useful in making the decision about which bedding plant to select. It can also serve as a guideline for choosing more suitable plants for sites that are infested with root-knot nematodes.

How Tables 2 and 3 were prepared

These tables combine and summarize the research efforts of several researchers over a number of years (McSorley 1994, McSorley and Frederick 1994, McSorley and Frederick 2001, Mendes et al. 2007, Om et al. 2008, Wang and McSorley 2005, Wang et al. 2004). In all of these studies, the researchers used similar methods, so it is possible to compare results among the different studies. An older study from the 1930s used different methods, and the identification of the root-knot nematode species was not clear at that time. Crow (2007) gives a good summary of this older study as well as some other work: http://edis.ifas.ufl.edu/in470.

In the studies used to prepare Tables 2 and 3, all researchers used a root gall index to rate the severity of root-knot infestation on the roots of a plant. Several studies also reported the number of nematode eggs produced per plant, and/or numbers of hatched mobile juveniles (J2) that were produced per plant. We wanted to develop a rating scale for flower cultivars that included root gall indices as well as the numbers of eggs or juveniles produced per plant. Ratings were assigned based on the categories shown in Table 1. A rating was given in each category (gall index, eggs per plant produced, and J2 per plant) for each species/race of nematode and each plant cultivar. In most cases, ratings were identical or similar in all categories, so the corresponding descriptive term was used in Tables 2 and 3. If ratings were close they were averaged, but if they were far apart, the result was described as “variable." If a nematode has not been tested on a particular cultivar, then the result is listed as “unknown."

Explanation of different susceptibilities

A wide range in susceptibility is seen among the flower species and cultivars (Tables 2 and 3). Some of these results come from single tests while others were averaged across several studies. Snapdragon is consistently one of the most susceptible flower crops (Fig. 2). Marigolds (Fig. 3) generally show good levels of resistance. The use of resistant marigolds against root-knot nematodes is well known, and additional information can be found here: http://edis.ifas.ufl.edu/ng045. Cultivars designated as “high” or “susceptible” could be expected to develop problems if root-knot nematodes are present, but even cultivars designated as “intermediate” or “variable” should be used with much caution. Several different cultivars were classified as “variable," such as Periwinkle cultivars, Dianthus 'Baby Doll Mix', and 'Qis White' larkspur. 'Qis White' was inconsistent, making its responses difficult to predict. Because dianthus 'Baby Doll Mix' is technically a mixture of different cultivars, it also has a variety of susceptibilities, and, therefore, variable results are expected, unless all the cultivars contained in the mix respond similarly to root-knot nematodes. Periwinkle, which produces high galling indices, does not support a high degree of egg production. The same is true to some extent for 'Scarlet' Zinnia. This indicates that although the plant is subject to infection, it has some degree of tolerance to root-knot nematodes. It may initially produce galls but possibly will grow out of it because future egg production on that plant will be low.

On the other hand, a plant that has little galling, but high egg production, is not a good candidate for rotation. Even if this type of plant can tolerate some damage, it does not minimize nematode numbers in the soil, which is the purpose of a rotational plant. Nematode population density will continue to increase on this plant, and will threaten the next crop planted if that plant is susceptible. Ratings of Lisianthus in response to M. incognita are favorable but should be used with caution. Although it showed little galling in greenhouse tests, considerable galling can be observed in the field. It is possible that galling in the field resulted from another species of root-knot nematode that was not evaluated in those greenhouse tests. For example, M. mayaguensis is a relatively newly discovered species in Florida soils, as is M. floridensis. Recent work by Mendes et al. (2007) evaluated the susceptibility of many petunia cultivars to M. incognita race 4 and M. mayaguensis. All of the petunia cultivars in Table 3 received a rating of “high” for susceptibility to M. mayaguensis and all cultivars except for 'Supertunia Lavender Pink' were rated “high” for susceptibility to M. incognita race 4. 'Supertunia Lavender Pink' was rated “susceptible." From these findings it becomes clear that most petunia cultivars should be avoided if M. incognita race 4 or M. mayaguensis are present. Greenhouse pots from the tests summarized in Tables 2 and 3 were inoculated with reared root-knot nematodes whose identity was firmly established, and not with nematodes found in the soil of field plots or gardens. Nematodes found in the soil from a sampled site might not be accurately identified for root-knot nematode species or races, or could be a mixture of different species and races. For this reason, plant cultivars that show resistance to multiple types of root-knot nematodes are generally more useful than those showing resistance to only one species or race.

Figure 2. 

Snapdragon (Antirrhinum majus)


[Click thumbnail to enlarge.]

Figure 3. 

Marigold (Tagetes spp.)


[Click thumbnail to enlarge.]

Closing remarks

Because of the difficulties mentioned above in identifying root-knot nematodes, it is highly unlikely that anyone planting flowers or bedding plants will know which species they will have. Meloidogyne incognita is very common throughout Florida, but other species, even M. mayaguensis, could occur throughout the state as well. It is interesting that whenever more than one nematode species or race were tested, relatively similar results were obtained for the species and cultivars summarized in Table 2, rarely differing by more than one rating classification. It is hoped that the table will provide some general guidelines about which plants are typically quite susceptible to root-knot nematodes and which ones tend to show high levels of resistance. In practice, growers, landscapers, and home gardeners should carefully check to verify that these responses are consistent in their own sites, recognizing that in some cases results could be very different in the event of unusual responses to other root-knot nematode species.

References

Crow, W.T. 2007. Nematode management for bedding plants. ENY-052, Entomology & Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL. (http://edis.ifas.ufl.edu/in470 )

Crow, W.T., Woods, F.E. 2007. Nematode Assay Laboratory. ENY-027, Entomology & Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL (http://edis.ifas.ufl.edu/sr011 )

Krueger, R., Dover, K.E., McSorley, R. 2007. Marigold (Tagetes spp.) for nematode management, ENY-056 (NG045), Entomology & Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL. (http://edis.ifas.ufl.edu/ng045)

McSorley, R. 1994. Susceptibility of common bedding plants to root-knot nematodes. Proc. Fla. State Hort. Soc. 107: 430-432.

McSorley, R. Frederick, J.J. 1994. Response of some common annual bedding plants to three species of Meloidogyne. J. Nematol. 26: 773-777.

McSorley, R., Frederick, J.J. 2001. Host suitability of some vinca and salvia cultivars to two isolates of root-knot nematodes. Proc. Fla. State Hort. Soc. 114: 239-241.

Mendes, M.L., Dickson, D.W., Schoellhorn, R., Cetintas, R., Brito, J.A. 2007. Host status of petunia cultivars to root-knot nematodes. Nematol. Medit. 35: 91-94.

Om, N., McSorley, R., Frederick, J.J. 2008. Response of cut flowers and bedding plants to root-knot nematodes. Proc. Fla. State. Hort. Soc. 121: 370-373.

Stanley, J. Koklais-Burelle, N., Dickson, D. 2006. Host status of Meloidogyne floridensis on selected weeds and cover crops common to Florida. Nematropica 36:149.

Wang, K.-H., Dover, K., McSorley, R. 2004. Susceptibility of cultivars of Lisianthus, Eustoma grandiflorum to Meloidogyne incognita. Soil Crop Sci. Soc. Florida Proc. 64: 112-116.

Wang, K.-H., McSorley, R. 2005. Host status of several cut flower crops to the root-knot nematode, Meloidogyne incognita. Nematropica 35: 45-52.

Tables

Table 1. 

Rating numbers and descriptions used to summarize data for Tables 2 and 3.

Rating

Description

No. of eggs or J2

Root gall index

5

high susceptibility

> 10,000

> 4

4

susceptible

5,000-10,000

3-4

3

intermediate susceptibility

1,000- 4,999

2-3

2

low susceptibility

100- 999

1-2

1

resistant

>0- 99

>0-1

0

immune

0

0

Table 2. 

Bedding plant cultivars and their susceptibility to different species of root-knot nematodes.

Species

M.arenaria

M.incognita

M.javanica

race 1

race 1

race 2

 

Ageratum

-Blue Mink

resistant

immune

unknown

immune

Alyssum

-Rosie O'Day

resistant

unknown

unknown

immune

Blue Lace

-Madonna Blue

unknown

susceptible

high

unknown

Carnation

-Chabaud Giant

unknown

unknown

resistant

resistant

Celosia

-Century Mix

susceptible

susceptible

unknown

intermediate

Coleus

-Rainbow

susceptible

intermediate

unknown

intermediate

Delphinium

-Butterfly Blend

unknown

unknown

resistant

low

Dianthus

-Baby Doll Mix

variable

low

unknown

resistant

Gypsophila

-Covent Garden

susceptible

unknown

unknown

unknown

Larkspur

-Qis Dark Spur

unknown

intermediate

unknown

unknown

-Qis White

unknown

variable

intermediate

unknown

Lisianthus

-Avila Rose Rim

unknown

low

low

unknown

-Balboa Purple

unknown

resistant

unknown

unknown

-Balboa White

unknown

resistant

unknown

unknown

-Catalina White

unknown

resistant

unknown

unknown

-Echo Blue

unknown

resistant

unknown

unknown

-Echo Pink

unknown

intermediate

low

unknown

-Malibu Blue Blush

unknown

low

unknown

unknown

-Ventura Blue Rim

unknown

resistant

unknown

unknown

-Ventura Purple

unknown

resistant

unknown

unknown

-Laguna Pink Rim

unknown

resistant

unknown

unknown

Marigold

-Dwarf Primrose

resistant

immune

unknown

immune

-Snow Drift

unknown

unknown

resistant

resistant

-Petite

unknown

unknown

resistant

low

-Jaguar

unknown

unknown

resistant

resistant

Nasturtium

-Dwarf Jewel Blend

unknown

unknown

intermediate

low

Pansy

-Jolly Joker

susceptible

unknown

unknown

unknown

Periwinkle (Vinca)

-Grape Cooler

unknown

resistant

unknown

resistant

-Blush Cooler

unknown

variable

unknown

variable

-Little Bright Eyes

intermediate

variable

unknown

variable

-Little Mixed Colors

immune

high

unknown

variable

-Peppermint Cooler

unknown

low

unknown

resistant

Petunia

-Dwarf Bedding

intermediate

low

unknown

low

-Fire Chief

variable

low

unknown

resistant

Poppy

-Oriental Red Perennial

susceptible

unknown

unknown

unknown

Salvia

-Sea Breeze

unknown

resistant

unknown

resistant

-Oxford Blue

unknown

susceptible

unknown

susceptible

-Flare

unknown

resistant

unknown

resistant

-Lady in Red

unknown

immune

unknown

resistant

-Victoria

unknown

immune

unknown

resistant

-Blue Bedder

unknown

unknown

resistant

resistant

-Bonfire

unknown

resistant

unknown

low

Shasta Daisy

-Alaska

intermediate

unknown

unknown

unknown

-Silver Princess

unknown

low

susceptible

susceptible

Snapdragon

-Dwarf Magic Carpet

unknown

unknown

susceptible

intermediate

-First Ladies

high

high

unknown

high

-Potomac Rose

unknown

susceptible

unknown

unknown

-Potomac Pink

unknown

high

susceptible

susceptible

-Potomac Royal

unknown

susceptible

susceptible

unknown

Verbena

-Florist

high

low

unknown

high

White Dill

-Green Mist

unknown

high

high

unknown

-Queen of Africa

unknown

high

high

unknown

Zinnia

-Scarlet

resistant

low

unknown

intermediate

-Thumbelina

unknown

unknown

resistant

resistant

-Envy

unknown

unknown

immune

resistant

Table 3. 

Susceptibility of selected Petunia cultivars to M. incognita race 4 and M. mayaguensis.

Species

M.incognita

M.mayaguensis

race 4

 

Petunia

-Easy Wave Red

high

high

-Easy Wave Rose Down

high

high

-Easy Wave White

high

high

-Madness Midnight 288

high

high

-Milliflora Prostrate

high

high

-Miniflora Prostrate

high

high

-Petunia Mini Blue

high

high

-Petunia Suncatcher

high

high

-Petunia Pink Vein (Florida)

high

high

-Suncatcher Dark Lavender

high

high

-Suncatcher Saphire

high

high

-Supertunia Blushing Princess

high

high

-Supertunia Lavender Morn

high

high

-Supertunia Lavender Pink

susceptible

high

-Supertunia Lemon Plume

high

high

-Supertunia Mini (Blue Veined)

high

high

-Supertunia Mini (Bright Pink)

high

high

-Supertunia Mini (Pastel Pink)

high

high

-Supertunia Mini Purple

high

high

-Supertunia Mystic Pink

high

high

-Supertunia Red

high

high

-Surfinia Baby Compact

high

high

-Surfinia Red Petunia

high

high

-Surfinia Sugar Plum

high

high

-Sweet Sunshine 5

high

high

-Tidal Wave Silver

high

high

Footnotes

1.

This document is ENY-061, one of a series of the Entomology and Nematology Department, UF/IFAS Extension. Original publication date May 2010. Reviewed April 2016. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Romy Krueger, graduate assistant, and Robert McSorley, retired professor, Entomology and Nematology Department, UF/IFAS Extension, Gainesville, FL, 32611.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.