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Title: MODIFIED EXPRESSION OF THE N ROOT-KNOT NEMATODE RESISTANCE GENE IN PEPPER AT HIGH SOIL TEMPERATURES

Author
item Thies, Judy
item Fery, Richard

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: The southern root-knot nematode, Meloidogyne incognita, is a major pest in bell pepper growing areas of the U.S. and worldwide. The first root-knot nematode resistant bell pepper cultivars, Charleston Belle and Carolina Wonder, were developed and released by USDA, ARS, Charleston, S.C. in April 1997. Resistance to root-knot nematodes in tomato is ineffective when soil temperatures reach or exceed 83F; however, no information is available concerning effectiveness of root-knot nematode resistance in bell peppers grown in hot climates. We compared reactions of two resistant (Charleston Belle and Carolina Wonder) and two susceptible (Keystone Resistant Giant and Yolo Wonder) pepper cultivars to root-knot nematodes at temperatures of 75, 83, and 89F. Nematode reproduction and severity of root galling increased on both the resistant and susceptible cultivars as temperature increased. However, at the higher temperatures, the resistant cultivars supported only 20% as many nematodes as the susceptible cultivars; and roo galling on the resistant cultivars did not increase to a susceptible level. Plant top weights of the susceptible, but not the resistant cultivars, were reduced at high temperatures. Therefore, it appears that the resistant cultivars may withstand nematode attack under high soil temperatures, even though greater numbers of nematodes build-up on their roots.

Technical Abstract: Heat stability of the N gene that confers resistance to the southern root-knot nematode, Meloidogyne incognita, in pepper (Capsicum annuum L.), was determined. Responses of resistant bell pepper cultivars Charleston Belle and Carolina Wonder (homozygous for the N gene) and their respective susceptible recurrent backcross parents, Keystone Resistant Giant and Yolo Wonder B, to M. incognita were compared at 24, 28, and 32C. Nematode reproduction and root galling increased (P < 0.05) for all cultivars as temperature increased and temperature x cultivar interactions were significant (P < 0.01). The responses of the resistant cultivars to increased temperatures were less dramatic than the responses of the susceptible cultivars. Nematode reproduction was minimal on the resistant cultivars at 24C, but increased at higher temperatures. However, at 32C, nematode reproduction on the resistant cultivars was only 20% that of the susceptible cultivars and root gall indices were within the range considered moderately resistant. Unlike the susceptible cultivars, shoot dry weights of the resistant cultivars were not suppressed at 32C, suggesting that the resistant cultivars may be somewhat tolerant to M. incognita at high temperatures. Although a partial loss of resistance to M. incognita occurred in Charleston Belle and Carolina Wonder under high soil temperatures, root-knot nematode resistant bell pepper cultivars may be a useful component of cropping systems designed to manage M. incognita in hot climates.