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Title: EVALUATION OF A CORE OF THE U.S. CAPSICUM GERMPLASM COLLECTION FOR REACTION TO THE NORTHERN ROOT-KNOT NEMATODE (MELOIDOGYNE HAPLA)

Author
item Thies, Judy
item Fery, Richard

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2001
Publication Date: 3/15/2002
Citation: THIES, J.A., FERY, R.L. EVALUATION OF A CORE OF THE U.S. CAPSICUM GERMPLASM COLLECTION FOR REACTION TO THE NORTHERN ROOT-KNOT NEMATODE (MELOIDOGYNE HAPLA). HORTSCIENCE. 2002. v.37(5). p.805-810.

Interpretive Summary: Several species of the root-knot nematodes (Meloidogyne spp.) are major pests of peppers (Capsicum spp.) in the U.S. and worldwide. Resistance to Meloidogyne incognita, M. arenaria, and M. javanica has been identified in several pepper accessions, but there are few reports of resistance to the northern root-knot nematode, M. hapla. Therefore, we selected a 10% core set (440 accessions) of the 14 available Capsicum spp. in the Capsicum germplasm collection (3,731 accessions) maintained by the USDA, and evaluated this core for resistance to M. hapla in greenhouse tests. The 11 "best" of the 440 accessions appeared to have very low resistance to M. hapla. Seven of these 11 "best" accessions exhibited root gall severity indices <5.0 (1 = no galls; 9 = > 81% root system covered with galls) and each of these indices was significantly lower than the indices of the "worst" accessions and susceptible controls. Although a gall index <5.0 indicates a moderate level of resistance, more than 3000 eggs were extracted per g of fresh root tissue, which suggests that they are relatively susceptible. This study demonstrates clearly that there is significant genetic variability within the entire USDA Capsicum germplasm collection for M. hapla resistance. These results identify portions of the collection where future evaluation emphasis should be focused. For example, the origin of the two most promising C. annuum accessions in the core was Yugoslavia. Thus, additional accessions from this temperate region of the world should receive priority attention in any effort to identify better sources of resistance in C. annuum to M. hapla.

Technical Abstract: Several species of the root-knot nematodes (Meloidogyne spp.) are major pests of peppers (Capsicum spp.) in the U.S. and worldwide. Resistance to M. incognita, M. arenaria, and M. javanica has been identified in several Capsicum accessions, but there are few reports of resistance to M. hapla. Therefore, we selected a 10% core (440 accessions) of the 14 available Capsicum spp. in the Capsicum germplasm collection (3,731 accessions) maintained by the U. S. Department of Agriculture (USDA), and evaluated this core for resistance to M. hapla in unreplicated greenhouse tests. The 11 best (most resistant) and the 3 worst (least resistant) accessions identified in these unreplicated tests were re-evaluated in a replicated greenhouse test. Seven of these 11 "best" accessions exhibited root gall severity indices <5.0 (1 = no galls; 9 = > 81% root system covered with galls) in the replicated test, and each of these indices was significantly lower than the indices of the "worst" accessions and susceptible controls. Although a gall index <5.0 indicates a moderate level of resistance, more than 3000 eggs were extracted per g of fresh root tissue and the reproductive index was greater than 1.0 for each of these accessions suggesting that they are relatively susceptible to M. hapla. The results of our evaluation of a core of the USDA Capsicum germplasm collection demonstrates clearly that there is significant genetic variability within the overall collection for M. hapla resistance.