Click here to download a PDF version of this spotlight.
» The guava root-knot nematode has become a major pathogen of vegetable crops, including tomatoes and peppers.
» The guava root-knot nematode has a very wide host range and can result in severe damage to host root systems and substantial yield losses.
» Tomato and pepper varieties with resistance to other species of root-knot nematode are likely susceptible to the guava rootknot nematode.
Root-knot of tomato is caused by several species of nematodes in the genus Meloidogyne. Infection of tomato roots by these nematodes often results in the formation of galls (swellings) that disrupt the ability of the plant to take up water and nutrients from the soil. The nematodes live in the galls and feed on root cells. The guava root-knot nematode (Meloidogyne enterolobii) was first detected in North America in 2004, and it has since spread to other states in the southeastern U.S. This species was first isolated and described in China in 1983, and it has become an important pathogen in tropical and subtropical regions of Asia, Africa, and Central and South America. The common name, guava root-knot nematode, came from severe damage to guava trees in Brazil caused by this species. It is feared that changing climates may allow M.enterolobii to expand its range into more northern areas.1,2,3,4
The species has also been found on greenhouse-grown tomatoes and cucumbers in Switzerland.5 The first U.S. detection of the guava root-knot nematode (GRKN) was in Florida in 2004.1 It has since been found in North Carolina, South Carolina, and Louisiana.2,4 GRKN has a host range of over 3,000 plant species, including crop, ornamental, and weed species. GRKN has been especially destructive on tomato, pepper, cotton, soybean, and sweet potato, in some cases resulting in complete crop loss.4 GRKN is now a major concern for agricultural production worldwide.1 Some have stated that it is the “most damaging root-knot nematode in the world” and that it is “the most threateningspecies to impact Florida tomatoes.”2,6 GRKN is now one of themost common species of root-knot nematode found in Florida.
SYMPTOMS
Infection by most species of root-knot nematodes results in similar symptoms, most notably the formation of galls on the roots of susceptible plants (Figure 1). The galls produced by GRKN are typically larger than those produced by other Meloidogyne species.1,2,4,6 However, this can be difficult to distinguish even with side-by-side comparisons. Because galls impair the roots’ ability to take up water and nutrients from the soil, infected plants can experience stunting, yellowing (chlorosis) of the foliage, and early wilting with moisture stress.Early infections can result in plant death, leading to reduced plant stands. A patchy distribution, with groups of affected plants in the field, is common for rootknot epidemics.1,2
GRKN has also been described as a more aggressive pathogen than other RKN species, causing more severe symptoms. The nematode is particularly damaging to tomato and sweet potato crops. Yield losses of up to 65%have been observedon some tomato crops.2,3
Distinguishing infections of GRKN from those of other RKN species can be difficult, even for experienced nematologists. Lab procedures using DNA identification tools are being developed but are not widely available. One indication that the pathogen is GRKN and not another RKN species is the development of symptoms on crop varieties with resistance genes for root-knot.4
LIFE CYCLE AND HOST RANGE
Like other root-knot nematode species, the guava root-knot nematode starts its life cycle as an egg in the soil. The first stage juvenile (larva) forms in the egg and molts to form the second stage juvenile (J2), which emerges from the egg and seeks out roots of susceptible plants. The J2 penetrates a susceptible root near the root tip and establishes a feeding site within the root where it feeds on nutrients from expanding root cells (Figure 2). Living in the gall tissue, the juvenile goes through two more stages, J3 and J4, before becoming a male or female adult. Female root-knot nematodes are globose in shape and stay within the gall, while the males retain their worm-shape form and exit the gall to find and mate with a female. The females produce eggs and deposit them outside of their bodies in an egg-mass. A female typically produces 400 to 600 eggs. The males can fertilize the eggs produced by females, but males are not required for the production of viable eggs. The GRNK lifecycle can be completed in as little as four weeks during warm conditions. The high rate of reproduction can lead to high populations of GRKN in the soil in a relatively short time. The nematodes can be spread within and between fields ininfested soil, crop debris, and other plant materials such assweet potato tubers and ornamental plants.1,4
The GRKN has a host range that is larger than most of the other root-knot species, and it can infect many agronomic,horticultural, ornamental, and wild (weed) plant species.Resistance genes for other root-knot species have been used to create resistant varieties of several crop species. However, these forms of resistance do not provide protection from infection by GRKN or the development of severe symptoms. The Mi1 genes in cotton, sweet potato, and tomato; the N and Tobasco genes in pepper; the Mh gene in potato; the Mir1 gene in soybean; and the Rk gene in cowpea that provide resistance against Meloidogyne incognita, M. javanica, and M. arenaria provide no resistance against GRKN, M. enterolobii.1,3,5
Some known weed hosts of GRKN include American nightshade, common purslane, ground cherry, hairy crabweed, morning glory, pokeweed, purple and yellow nutsedge, redrootand smooth pigweed, spiny amaranth, and wild mustard
MANAGEMENT
In some areas, extreme plant quarantine procedures have been enacted to help prevent the introduction or spread of the GRKN.1 Soil fumigation and the use of non-fumigant nematicides may provide some reduction of soilborne inoculum, but these measures have not been able to completely alleviate production problems caused by GRKN.1,2,3,6
Some resistance to GRKN has been found in a few tree fruit crops, and low nematode reproduction rates were observedon two carrot varieties. However, resistance genes effective against GRKN are not available in other annual crop species.3 Bacterial and fungal biological control agents are being evaluated for their effectiveness in managing GRKN. The egg parasitic fungi Pochonia chlamydosporia and Purpureocillium lilacinum are used as biological control agents for other RKN species. A 2017 study found that these agents were able to reduce the hatching of J2 GRKN larvae by 13 to 84% in some situations, and that they seemed to be most effective wheninfestation levels were low.7
Rotation to non-host or poor host crops can help lower population levels of the GRKN in the soil. However, with thewide host range, finding appropriate rotational crops can bea challenge. Planting non-host and poor host cover crops in the off-season may also contribute to a reduction in GRKN soil populations.1,6 A few crops that have been shown tobe non-hosts or poor hosts of GRKN include corn, peanut,garlic, grape, and strawberry.1,3 Some varieties of broccoli and cabbage appear to have some level of resistance to GRKN, but others are known to be susceptible. A list of plants that may be poor hosts or non-hosts includes carrot, leeks, lettuce, annual ryegrass, oats, radish, rice, rapeseed, rye, sorghum, sugarcane, and wheat.4
Soil and plant samples can be tested for the presence and population levels of RKN species, but these assays may not be able to be distinguish GRKN from other RKN species.8
SOURCES
1 Hayes, R. and Subbarao, K. 2011. Fifteen years of Verticillium wilt of lettuce in America’s salad bowl: a tale of immigration, subjugation, and abatement. Plant Disease 95:784-792.
3 Matheron, M. 2019.Comparison of two lettuce wil1 Liu, C., Grabau, Z., and Desaeger, J. 2022. Guava root-knot nematode or pacara earpodroot-knot nematode. Featured Creatures. University of Florida, Department of Entomology andNematology. Publication: EENY-793.
2 Hare, R. 2019. The guava root-knot nematode – a new pest in Louisiana. Louisiana State University Ag Center. https://www.lsuagcenter.com/profiles/coverstreet/articles/page1531770181050.
3 Castagnone-Sereno P. 2012. Meloidogyne enterolobii (= M. mayaguensis): profile of an emerging, highly pathogenic, root-knot nematode species. Nematology 14(2): 133-138.
4 Overstreet C, McGawley EC, Clark C, Rezende J, Smith T, Sistrunk M. 2018. Guava root knot nematode: A potentially serious new pest in Louisiana. Pub 3670. Baton Rouge: Louisiana State University AgCenter.
5 Kiewnick S. 2009. Effects of the Mi-1 and the N root-knot nematode-resistance gene on infection and reproduction of Meloidogyne enterolobii on tomato and pepper cultivars. Journal of Nematology 41(2): 134-139.
6 Thompson, C. 2021. Guava root-knot nematodes threat to Florida tomatoes. Specialty Crop Industry, September 21, 2023.
7 Silva S, Carneiro RMDG, Faria M, Souza DA, Monnerat RG, Lopez RB. 2017. Evaluation of Pochonia chlamydosporia and Purpureocillium lilacinum for suppression of Meloidogyne enterolobii on tomato and banana. Journal of Nematology, 49(1): 77-85.
8 Everts, K., Sardanelli, S., Kratochvil, R., and Gallagher, L. 2005. Cultural practices for rootknot and root-lesion nematode suppression in vegetable crop rotations: nematode sampling procedures. SARE Outreach. SARE Publication #06AGI2005.
Websites verified 10/16/2023 diseases.
ADDITIONAL INFORMATION
For additional agronomic information, please contact your local seed representative. Performance may vary, from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this article are based upon information obtained from the cited sources and should be used as a quick reference for informationabout vegetable production. The content of this article should not be substituted for the professional opinion of a producer, grower, agronomist, pathologist and similar professional dealing with vegetable crops.
BAYER GROUP DOES NOT WARRANT THE ACCURACY OF ANY INFORMATION OR TECHNICAL ADVICE PROVIDED HEREIN AND DISCLAIMS ALL LIABILITY FOR ANY CLAIM INVOLVING SUCH INFORMATION OR ADVICE.
5911_279851 Published 11/09/2023