Host ResistanceSouthern root-knot nematodeMeloidogyne incognita

Economic importance

• Major species of root-knot nematodes: M. Aenaria, M. hapla, M. incognita, and M. Javanica

• About 2000 plants are susceptible to infection by root-knot nematodes and they cause approximately $173 billion global and $13 billion of crop losses within U.S

• Root-knot nematode damage results in poor growth, a decline in quality and yield of the crop and reduced resistance to other stresses

Sasser, J.N., Carter, C.C. R. Overview of the International Meloidogyne Project 1975–1984. In An Advanced Treatise on Meloidogyne. North Carolina State University Graphics; 1985:19-24

Elling, A. A. 2013. Major emerging problems with minor Meloidogyne species. Phytopathology 103:1092-1102.

Wordwide distribution of M. incognita

CABI/EPPO, 2002. Meloidogyne incognita. Distribuiton Maps of Plant Diseases, No. 854, Wallingford, UK: CAB international

• M. hapla is the most common species in the northern eastern

• M. incognita has been reported in Delaware, Maryland, New Jersey, New York, Pennsylvania, Connecticut, and West Virginia.

• M. incognita occurs in every state in the southern region, whereas M. hapla, M. arenaria, and M. javanica occur sporadically in each state.

• M. incognita has also been reported in Arizona, Arkansas, California, Illinois, Hawaii, Indiana, New Mexico, North Carolina, South Carolina, Oregon, Texas, Utah, Virginia, Washington

CABI/EPPO, 2002. Meloidogyne incognita. Distribuiton Maps of Plant Diseases, No. 854, Wallingford, UK: CAB international

Waters, S. A., and Barker, K. R. 1994. Current Distribution of Five Major Meloidogyne Species in the United States. Plant Disease. 78:772-774.

In United States

Reminders• Root-knot nematode infect plant roots, causing the development of root-knot

galls that drain the plant's photosynthate and nutrients.

• The degree of root galling: nematode population density, Meloidogyne species and "race," and host plant species and even cultivar.

• Early-season infection leads to worse damage

• Root-knot nematodes are spread primarily by water or by soil clinging to farm equipment or on infected propagating stock transported into uninfested areas.

Agrios, G.N. 2005, Plant pathology, 5th edn, Elsevier Academic Press, Burlington, Mass

Mitkowski, N.A. and Abawi,G.S. 2003. Root-knot nematodes. The Plant Health Instructor. DOI:10.1094/PHI-I-2003-0917-01 Revised 2011

Female laying eggs into a gelatinous matrix outside the root. . At 16.2 and 30.0°C, life cycle takes respectively 63 and 20 days to complete

J2-J3 entering into feeding site. Galling starts occurring as a response parasitism. Crotalaria spp. are used as trap cropping for nematodes, permitting invasion and development, but not to complete its life cycle.

J2 infective stage attracted by root exudates. Motility of juveniles and subsequent root penetration decrease at soil temperatures below 18°C .

Egg stage of M. incognita. Molting from J1 to J2 occurs before hatching. Hatch decreases with decrease in moisture.

Carrot root heavily infected by M. incognita. Temperature limit for life cycle completion lies between 30 and 35.4°C

Disease cycle of Root-Knot Nematode

Close up on stylet structure, it acts injecting secretions and ingesting nutrients from host plant cells

Author: Vinicius Garnica

Losses are typically higher in sandy soils. Either by nutrient deficiency or weakened antagonist activity. Some evidence for the presence of biological suppressiveness in soils rich in organic matter.

(Courtesy N.A. Mitkowski)

Mechanisms of resistance to nematodes (Hendratno, 1976)

• Failure of the larvae to enter the roots

• Entry of reduced numbers with little or no development

• Entry of large number of juveniles with varying degrees of development ranging from none to few individuals reaching maturity

• Hypersensitive reactions form necrotic cells walling off parasite in theirs feeding-site.

MATEILLE Thierry : Research Program

Hendratno. Induced Variability of Resistance to Root-Knot Nematodes (Meloidogyne incognita) in Soybeans (Glycine max). Master's Thesis, University of Tennessee, 1976. http://trace.tennessee.edu/utk_gradthes/3001

1. Passive or pre-infectional resistance conditioned by anatomical, physio logical, chemical barriers, which may make the invasion of the nema tode difficult or disturb its behavior.

• The plant may produce toxins that kill the nematodes. (e.g.: gossypol, cotton)

• Resistance may depend upon the fact that not every plant contains substances necessary for the development and reproduction of a certain nematode species, or contains them in an insufficient amount. (e.g.: essential aminoacids for galling production)

Mechanisms of resistance to nematodes (Giebel, 1982)

Giebel, J. 1982. Mechanism Of Resistance To Plant Nematodes . Annu. Rev. Phytopathology, 20:257-79

Mechanisms of resistance to nematodes (Giebel, 1982)

2. Active or post-infectional resistance operates in host plants due to contact with parasites, based on plant tissue hypersensitivity to nematode infection

• The hydrolytic nematode enzymes that destroy host cells may activate plant endohydrolases.

Photo by William Wergin & Richard Sayre

Giebel, J. 1982. Mechanism Of Resistance To Plant Nematodes . Annu. Rev. Phytopathology, 20:257-79

• The Mi gene of tomato is currently one of the best characterized nematode-resistance genes in plants.

• Single gene confers resistance through hypersensitive response (killing the feeding-site)

• Possibility that this gene could be transferred to plant species on which root-knot nematodes are a serious problem but for which no resistance is currently available

• Gene expression is both temperature- and plant developmental stage-dependent

Mi genes in tomato

Dropkin VH. 1969. The necrotic reaction of tomatoes and other hosts resistant to Meloidogyne: reversal by temperature . Phytopathology, 59:1632–37

Roberts. P. A. 1995. Conceptual and Pratical Aspects of Variability in Rool-Knot Nematodes Related to Host Plant Resistance. Annu. Rev. Phytopathology, 36:277-93

Williamson, V. M. 1998. Root-knot Nematode Resistance Genes In Tomato And Their Potential For Future Use. Annu. Rev. Phytopathology, 36:277-93

Root-knot Genetic Resistance in Soybeans

Image from Plant Health Progress article: Incidence of Meloidogyne incognita and Development of Resistant Soybean Germplasm in Illinois

Greenhouse bioassay, Uni. of Georgia, 2013

Further information and complete variety list athttp://www.swvt.uga.edu/2013/sysr13/AP103-5-nematode.pdf

Georgia 2013 Soybean, Sorghum Grain and Silage, and Summer Annual Forages Performance Trials - Annual Publication 103-5, pg. 41-44 December 2013

2014 Georgia Soybean Production Guide – Retrieved from http://www.caes.uga.edu/commodities/fieldcrops/soybeans/documents/2014GeorgiaSoybeanProductionGuide.pdf

North Carolina Soybean Variety Program

Available at http://soyvar.ncsu.edu/

• Effectiveness of resistant varieties can decrease over time if continually grown in nematode infested fields. Example from SCN:

The key is to rotate the sources of resistance, reduce pressure of selection for long-term effectiveness in minimizing the impact of SCN on soybean yields

• Year 1 – non-host crop • Year 2 – resistant soybean variety I• Year 3 – non-host crop• Year 4 – resistant soybean variety II• Year 5 – …

Preserving resistant cultivars

T. Kirkpatrick. Root-knot Nematodes: A Threat to Southern Soybean Production. http://www.plantmanagementnetwork.org/edcenter/seminars/soybean/RootKnotNematodes/

References• http://www.apsnet.org/edcenter/intropp/lessons/Nematodes/Pages/RootknotNematode.aspx• http://www.sciencedirect.com/science/article/pii/S0261219407000385• Nematodes in Root (http://www.optimara.com/doctoroptimara/diagnosis/rootnematodes.html)• Eggs (

http://coursewares.mju.ac.th:81/e-learning47/PP300/0016sugarteam1014/5605nematode/004%20under%20microscope/page_01.htm)

• Carriots(http://www.imagejuicy.com/images/plants/c/cyperus/20/)• Nematode colonizing root (Photo by William Wergin and Richard Sayre. Colorized by Stephen

Ausmus. U.S. Department of Agriculture)• Information (

http://www.apsnet.org/edcenter/intropp/lessons/Nematodes/Pages/RootknotNematode.aspx)• Stylet (

http://www.apsnet.org/edcenter/intropp/lessons/Nematodes/Pages/RootknotNematode.aspx)• Soybean field (http://www.plantmanagementnetwork.org/pub/php/research/2007/rootknot