Meloidogyne incognita
Contents
Rev 09/27/2008
Meloidogyne incognita |
Contents |
Rev 09/27/2008 |
||
| Cotton Root-knot Nematode |
|
Classification |
|
Hosts |
|
|
|
Morphology and Anatomy |
|
Life Cycle |
| Return to Meloidogyne Menu |
|
Economic Importance |
|
Damage |
|
|
|
Distribution |
|
Management |
| Return to Heteroderidae Menu |
|
Feeding |
|
References |
| Go to Nemaplex Home Page |
Tylenchida
Tylenchina
Tylenchoidea
Heteroderidae
Meloidogyninae
Meloidogyne incognita
|
Major significance in tropics and warmer regions.
C-rated pests in California.
Feeding site establishment and development typical of genus.
 |
Sedentary endoparasites, giant cells. |
Vegetables, cereals, ornamentals, pasture, trees and shrubs, sugarcane, tobacco, cotton, potatoes, etc.
Meloidogyne incognita is involved in many disease interactions, eg blackshank of tobacco (Phytophthora parasitica var nicotianae), Granville wilt (Pseudomonas solanacearum) - resistant plants predisposed by M. incognita. Field trials with combined inoculations reduced tobacco crop values by $800/acre over the nematode alone. Resistance to M. incognita has been a very important solution to these complexes.
The tobacco industry in some counties of NC was saved by incorporating M. incognita resistance into the genome (NC95 the resistant variety). These interactions are especially important because of the research effort and consequent understanding. N.T. Powell was a pioneer in this area. He also showed that plants infected 4 weeks previously by M. incognita were susceptible to infection and decay by Pythium and Rhizoctonia, which are usually only important in seedling diseases.
Powell also showed that "non-pathogens" of tobacco, including Curvularia, Botrytis, Aspergillus, Penicillium and even Trichoderma can invade the altered root system and cause extensive decay.
The biopredisposition is thought to be more through physiological rather than mechanical effects.
The cotton cultivar Acala SJ2 is predisposed to Fusarium wilt by M. incognita, requiring nematode control where both pathogens occur in the southern San Joaquin valley of California. Acala SJ5 is tolerant to Verticillium wilt, but that cultivar is also predisposed by M. incognita.
|
|
Disruption of the vascular system. Abnormal partitioning of photosynthates to the feeding site of the nematode. Direct reduction of yield in many crops.
|
|
Quality and marketability loss through
distortion of root crops. |
|
|
|
Nematicides:
Nematicides have been very important. They may, however, be less effective when nematodes are embedded in plant tissue. For example, tuber viability of yellow nutsedge (Cyperus esculentus) and purple nutsedge (Cyperus rotundus), and survival of M. incognita harbored within them were unaffected by 1,3-D treatment (Thomas et al, 2004).
Host Plant Resistance:
Sources of host-plant resistance to M. incognita occur in several plant genera, including clovers, cotton, peach (e.g. Nemaguard), peanut, pineapple, corn, sweetpotato, tobacco and tomatoes.
Use of tobacco cultivars resistant to M. incognita in North Carolina, based on the resistance gene first introduced into cultivar NC95, has resulted in selection for the more virulent (to tobacco) M. arenaria and M. javanica..
The Mi gene of tomato is a single dominant gene that confers resistance to M. incognita, M. javanica and M. arenaria. It is located near the centromere of chromosome 6. The gene was first introduced into Lycopersicon esculentum from L. peruvianum in the 1940s by Dr. Charles Rick at UC Davis. Due to reproductive incompatibilities between the two plant species, embryo rescue techniques were used to dissect embryos from seed and culture them axenically. The gene has been cloned and sequenced in the laboratory of Dr. Valerie Williamson at UC Davis. Using Agrobacterium as a carrier, the resistance gene has been transferred to a susceptible tomato cultivar, which expresses the resistance. Plants grown from seeds of the transgenic plant are also resistant to M. incognita. However, after the second generation of plant offspring, the expression of resistance is progressively reduced in seed batches from some plants but not from others. In both cases, the gene is still present and is still coding for RNA (Goggin et al, 2004).
The resistance conferred by the Mi gene breaks down at soil temperatures >28C.
With repeated use of the single source of resistance in California tomato production, aggressive strains of the nematode are being selected (Kaloshian et al. 1996).
In the early 1990s, farm advisors and entomologist Dr. Harry Lange noticed that tomatoes with the Mi gene appeared to be also resistant to the potato aphid, Macrosiphum euphorbiae. Initial determination was that a gene tightly linked to Mi and designated Meu1 was responsible for the potato aphid resistance. Current research indicates, however, that the two genes are identical and that Mi confers resistance to both root-knot nematodes and the potato aphid. A more recent development is the discovery that the Mi gene also confers resistance against the white fly Bemisia tabaci (Nombela et al., 2003). The gene is located near the centromere of tomato chromosome #6.
As with the resistance to M. incognita, the resistance to the potato aphid is also progressively reduced after the the second generation of plant progeny (Goggin et al, 2004).
Kaloshian, I., V.M. Williamson, G. Miyao, D.A. Lawn and B.B. Westerdahl. 1996. "Resistance-breaking" nematodes identified in California tomatoes. California Agriculture 50(6):18-19.
Nombela, G., V. M. Williamson, and M. Muniz. 2003. The root-knot nematode resistance gene
Mi-1.2 of tomato is responsible for resistance against the whitefly Bemisia tabaci. Mol. Plant Microbe Int. 16:645-649.Thomas SH, Schroeder J, Murray LW. 2004. Cyperus tubers protect Meloidogyne incognita from 1,3-dichloropropene. J. Nematology 36: 131-136.
