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United States Department of Agriculture

Agricultural Research Service


item Simon, Philipp
item Matthews, William
item Roberts, Philip

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Carrot production around the world is threatened by the attack of nematodes in the soil. Genetic resistance to nematodes is an excellent way to continue carrot production without pesticides, most of which will be outlawed within five years. We have found a naturally occurring source of genetic resistance in a Brazilian carrot, Brasilia, which resists one of the most economically important nematodes, Meloidogyne javanica, found in the southern U. S. and other warmer areas of the world. This paper documents the inheritance pattern of resistance as due to a single gene. This indicates that we can readily manipulate resistance in breeding programs of the vegetable see industry and in public programs.

Technical Abstract: Root-knot nematodes (Meloidogyne spp.) are serious pests of carrot (Daucus carota L.) worldwide. While soil treatment with nematicides is the primary means for managing nematodes in carrot, there is a need to identify and introduce host plant resistance for crop improvement. This study was conducted to determine the inheritance of resistance to root-galling and reproduction by M. javanica (Treub) Chitwood in a selection of carrot variety, Brasilia. F2, F3, F4, and BC1 progenies from the cross, BR1252 X B6274, (a susceptible inbred line) were screened in pot tests for reaction to M. javanica. The observed reactions based on galling and egg production on fibrous roots gave segregation patterns in all tests that were consistent with relatively simply inherited dominant resistance. Field testing in progress indicates that this resistance is very effective against both M. javanica and M. incognita. A single gene model fits the observed data acceptably well in F3 generations. The range of 3 percent to 51 percent susceptible plants in segregating F3 families and 1 percent to 47 percent in segregating F4 families is much wider than the 25 percent expected with a single gene model, and linked duplicate factors in the coupling phase could also explain the observed segregation patterns. Egg production data in the F2, F3, and F4 families provided evidence for slightly lower resistance expression in the heterozygous condition.

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