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Judy A. Thies and Richard L. Fery

Heat stability of the N gene that confers resistance to the southern root-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwood in pepper (Capsicum annuum L.), was determined at 24, 28, and 32°C. 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. Numbers of eggs/g fresh root, reproductive factor of M. incognita, numbers of second-stage juveniles in soil, egg mass production, and root galling increased (P < 0.05) for all cultivars as temperature increased. The response of the resistant cultivars to temperature increase was less dramatic than the response of the susceptible cultivars. Both `Charleston Belle' and `Carolina Wonder' exhibited a partial loss of resistance at 28 and 32 °C. Reproduction of M. incognita was minimal on the resistant cultivars at 24 °C, but increased at higher temperatures. However, at 32 °C reproduction of M. incognita on the resistant cultivars was only 20% of that on the susceptible cultivars and root gall indices were within the range considered moderately resistant. Unlike the susceptible cultivars, the shoot dry weights of the resistant cultivars were not suppressed at 32 °C. This suggests that `Charleston Belle' and `Carolina Wonder' may be somewhat tolerant to M. incognita at high soil temperatures. Although results indicate a partial loss of resistance occurred in `Charleston Belle' and `Carolina Wonder' under high soil temperatures, resistant cultivars may be a useful component of cropping systems designed to manage M. incognita in hot climates.

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Judy A. Thies and Richard L. Fery

Expression of the N gene, which confers resistance to southern root-knot nematode (Meloidogyne incognita Kofoid and White) in bell pepper [(Capsicum annuum L. var. annuum (Grossum Group)], is modified at high temperatures (28 °C and 32 °C), but its expression in the heterozygous condition (Nn) has not been documented at moderate or high temperatures. Responses of the near-isogenic bell pepper cultivars, Charleston Belle and Keystone Resistant Giant (differing at the N locus), and the F1 and reciprocal F1 crosses between these cultivars to M. incognita race 3 were determined at 24, 28, and 32 °C in growth chamber experiments. `Keystone Resistant Giant' (nn) was susceptible at 24, 28, and 32 °C. `Charleston Belle' (NN) exhibited high resistance at 24 °C and resistance was partially lost at 28 and 32 °C. However, at 32 °C root gall and egg mass severity indices for `Charleston Belle' were still in the resistant range, and the number of M. incognita eggs per gram fresh root and reproductive index were 97% and 90% less, respectively, than for `Keystone Resistant Giant'. Responses of the F1 and F1 reciprocal hybrid populations to M. incognita were similar to the response of the resistant parent at all temperatures. Root fresh weights and top dry weights indicated that both hybrid populations tolerated M. incognita infections at least as well as `Charleston Belle'. These findings indicate that i) only one of the parental inbred lines needs to be converted to the NN genotype to produce F1 hybrid cultivars with fully functional N-type resistance to M. incognita; and ii) cytoplasmic factors are not involved in expression of N-type resistance and the resistant parental inbred can used to equal advantage as either the paternal or the maternal parent.

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Richard L. Fery and Philip D. Dukes

Greenhouse experiments were conducted to determine the inheritance of the high level of southern root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] resistance exhibited by `Carolina Hot' cayenne pepper (Capsicum annuum L.) and to compare the genetic nature of this resistance to that exhibited by `Mississippi Nemaheart.' Evaluation of parental, F1, F2, and backcross generations of the cross `Mississippi Nemaheart' × `California Wonder' confirmed an earlier published report that the `Mississippi Nemaheart' resistance is conditioned by a single dominant gene. Evaluation of parental, F1, F2, and backcross generations of a cross between highly resistant and highly susceptible lines selected from a heterogeneous `Carolina Hot' population indicated that the resistance exhibited by `Carolina Hot' is conditioned by two genes, one dominant and one recessive. Evaluation of the parental and F2 populations of a cross between `Mississippi Nemaheart' and the highly resistant `Carolina Hot' line indicated that the dominant resistance gene in `Mississippi Nemaheart' is allelic to the dominant resistance gene in `Carolina Hot.' Comparison of the data that were collected on the parental lines in the latter cross demonstrated the superior nature of the resistance exhibited by `Carolina Hot.' The presence of the second resistance gene in `Carolina Hot' probably accounted for the higher level of resistance. The ease and reliability of evaluating plants for resistance to root-knot nematodes and the availability of a simply inherited source of resistance makes breeding for southern root-knot nematode resistance a viable objective in pepper breeding programs. This objective should be readily obtainable by the application of conventional plant breeding methodologies.

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Judy A. Thies and Richard L. Fery

Several species of root-knot nematodes [Meloidogyne incognita (Kofoid & White) Chitwood, M. arenaria (Neal) Chitwood, M. javanica (Treub) Chitwood, and M. hapla Chitwood] are major pests of peppers (Capsicum spp.) in the United States 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. Dept. 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 (most susceptible) accessions identified in these unreplicated tests were re-evaluated in a replicated greenhouse test. Seven of these 11 “best” accessions (PI 357613, PI 357503, PI 439381, PI 297493, PI 430490, PI 267729, and PI 441676) exhibited root gall severity indices <5.0 (1 = no galls; 9 = more than 80% of the 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 M. hapla eggs were extracted per gram of fresh root tissue and the reproductive index was >1.0 for each of these accessions. These observations suggest that the most resistant accessions tested are somewhat 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. Additionally, these results identify portions of the collection where future evaluations for M. hapla resistance should be focused. For example, the origin of the two most promising C. annuum accessions (PI 357613 and PI 357503) 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.

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Richard L. Fery and Judy A. Thies

conditioning a high level of resistance to the southern root-knot nematode [ Meloidogyne incognita (Chitwood) Kofoid and White], the peanut root-knot nematode [ M. arenaria (Neal) Chitwood], and the tropical root-knot nematode [ M. javanica (Treub) Chitwood

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Mary Ann D. Maquilan, Dominick C. Padilla, Donald W. Dickson, and Bala Rathinasabapathi

’, ‘Charleston Belle’, ‘Jalapeño’, and ‘UFRJ107(6)A3’ in decreasing order. Table 1. Reproductive potential of Meloidogyne incognita race 3 on six varieties of Capsicum species after 30 d from inoculation under two temperature regimes in the growth chamber

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Cody L. Smith, Joshua H. Freeman, Nancy Kokalis-Burelle, and William P. Wechter

watermelon cultivar ‘Royal Sweet’ was estimated with an initial population equal to 122 eggs/100 cm 3 of soil, 1.6 gal on bioassay roots/100 cm 3 of soil, or 3.6 J2/100 cm 3 of soil ( Xing and Westphal, 2012 ). Meloidogyne incognita is a common pest in

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Wenjing Guan, Xin Zhao, Donald W. Dickson, Maria L. Mendes, and Judy Thies

the southern United States and in other semitropical and tropical regions of the world. Meloidogyne incognita , M. javanica , and M. arenaria are the most widespread RKN species in the southeastern United States ( Zitter et al., 1996 ), and all of

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Howard F. Harrison Jr., D. Michael Jackson, Judy A. Thies, Richard L. Fery, and J. Powell Smith

produce seeds with impermeable seedcoats (hard seeds). The major attributes of lines US-1136, US-1137, and US-1138 have rapid growth, high biomass production, a long vegetative growth period, and southern root knot nematode [ Meloidogyne incognita

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Richard L. Fery and Judy A. Thies

dominant gene conditioning a high level of resistance to the southern root-knot nematode [ Meloidogyne incognita (Chitwood) Kofoid and White], the peanut root-knot nematode [ M. arenaria (Neal) Chitwood], and the tropical root-knot nematode [ M. javanica