Virulence development and genetic polymorphism in Meloidogyne incognita (Kofoid & White) Chitwood after prolonged exposure to sublethal concentrations of nematicides and continuous growing of resistant tomato cultivars.
BACKGROUND
The root-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwood, is an important plant pathogen damaging to tomato. Continuous use of resistant tomato cultivars and nematicides for its effective management might lead to resistance break-up or nematicide failure. Genetic variability and virulence in M. incognita on susceptible Pusa Ruby tomato were analysed by bioassay, esterase and DNA polymorphism after a 5 year weekly exposure to carbofuran, carbosulfan, cadusafos and triazophos at 0.0125, 0.0250 and 0.0500 microg g(-1). Virulence in M. incognita after a 5 year multiplication on resistant tomatoes was assessed.


RESULTS
The nematicidal treatments resulted in the development of virulent M. incognita populations. Their invasion potential increased significantly after continuous exposure to low concentrations of the nematicides. Also, growing resistant tomato cultivars for ten successive seasons resulted in a 6.6% increase in the invasion potential. These virulent populations exhibited 1-3 additional esterase and DNA bands compared with untreated populations.


CONCLUSIONS
A 5 year exposure of M. incognita to sublethal concentrations of nematicides or resistant tomato cultivars exerted enough selection pressure to cause genomic alterations for virulence development. Isozyme markers can be used for rapid and precise diagnostics of field populations by advisory services, enabling judicious remedial management decisions.
Meher
Hari C
HC
Indian Agricultural Research Institute, New Delhi, India. hcm_nema@yahoo.com
Gajbhiye
Vijay T
VT
Chawla
Gautam
G
Singh
Ghanendra
G
D000818:Animals; D006790:Host-Parasite Interactions; D007113:Immunity, Innate; D018551:Solanum lycopersicum / Q000276:immunology / Q000469:parasitology*; D010575:Pesticides / Q000494:pharmacology*; D010935:Plant Diseases / Q000276:immunology / Q000469:parasitology*; D011110:Polymorphism, Genetic; D014431:Tylenchoidea / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity*; D014774:Virulence
D010575:Pesticides