The southern root-knot nematode, Meloidogyne incognita [(Kofoid & White) Chitwood], causes serious economic losses to melon (Cucumis melo L.) production in the United States. The present study was conducted to determine if separable differences in nematode resistance of Cucumis melo could be found at some inoculum level. Five C. melo lines were compared with Cucumis metuliferus Naud. (C701A), a highly resistant species, for root necrosis, galling, egg mass production, and reproduction when inoculated at 0, 500, 1000, 2000, or 5000 nematode eggs per plant. Using these criteria, melon line C880 inoculated with 1000 eggs per plant was highly susceptible, while PI140471, PI 183311, and the cultivars Chilton, Georgia 47, Gulf Coast, Planters Jumbo, and Southland were less susceptible. In greenhouse tests with an inoculum level of 1000 eggs per plant, low levels of resistance were evident. A thorough screening of the available germplasm against M. incognita may identify higher levels of root-knot nematode resistance for incorporation into improved melon cultivars.
Perry E. Nugent and P.D. Dukes
Richard L. Fery and Judy A. Thies
Scotch Bonnet and Habanero peppers, extremely pungent cultivar classes of Capsicum chinense Jacq., are increasing in popularity in the United States. Because the southern root-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwood, is a major pest of many C. annuum cultivars, a series of greenhouse and field experiments was conducted to determine if Scotch Bonnet and Habanero peppers from available commercial and private sources also are vulnerable to the pest. In an initial greenhouse test, a collection of 59 C. chinense cultigens was evaluated for reaction to M. incognita race 3. All cultigens obtained from commercial sources were moderately susceptible or susceptible. However, four accessions obtained through Seed Savers Exchange listings exhibited high levels of resistance. Three of these cultigens (PA-353, PA-398, and PA-426) were studied in subsequent greenhouse and field plantings, and each was confirmed to have a level of resistance similar to that available in C. annuum. All three of the resistant cultigens are well-adapted and each is potentially useful in commercial production without further development. None of the Habanero cultigens was resistant to the southern root-knot nematode. The resistant Scotch Bonnet cultigens may serve as sources of resistance for development of root-knot nematode—resistant Habanero peppers.
Richard L. Fery and Judy A. Thies
Greenhouse experiments determined the inheritance of resistance to the peanut root-knot nematode [Meloidogyne arenaria (Neal) Chitwood race 1] in Capsicum chinense Jacq. germplasm lines PA-353 and PA-426. Evaluation of parental, F1, F2, and backcross populations of the crosses PA-353 × PA-350 and PA-426 × PA-350 (PA-350 is a susceptible cultigen) indicated that resistance in both C. chinense germplasm lines was conditioned by a single dominant gene. Evaluation of the F1 × resistant parent backcross populations in the cytoplasm of their respective resistant and susceptible parents indicated that the cytoplasm of the resistant parent is not needed for full expression of resistance. Allelism tests indicated that the dominant resistance gene in both PA-353 and PA-426 is allelic to a resistance gene in C. annuum L. `Carolina Cayenne'. However, these allelism tests did not demonstrate conclusively that the M. arenaria race 1 resistance gene in C. chinense is the N gene that conditions resistance to the southern root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] in C. annuum. The ease and reliability of evaluating plants for resistance to root-knot nematodes and the availability of simply inherited sources of resistance makes breeding for peanut root-knot nematode resistance a viable objective in C. chinense breeding programs.
Peter Cousins and M. Andrew Walker
The grape Vitis champinii Planchon is one source of nematode resistance in grape rootstocks. Several selections valued for their resistance to the root-knot nematode (Meloidogyne incognita), a serious pest of grape production, are used as rootstocks and in rootstock variety development. However, V. champinii-based rootstock varieties are faulted for their excess vigor and susceptibility to other root pests. Root-knot nematode populations with the ability to damage important V. champinii-based rootstocks have been identified and may become more common. Other V. champinii accessions might be sources of nematode resistance genes with different specificities or might have more suitable horticultural characteristics than V. champinii varieties in commercial use. Nine V. champinii accessions from the National Clonal Germplasm Repository, Davis, Calif., and a V. champinii rootstock variety were screened for resistance to M. incognita. Resistance was assessed by counting eggs produced per root system. Eight of ten V. champinii accessions did not support nematode reproduction. Susceptible accessions supported lower nematode reproduction than susceptible V. vinifera control varieties. Progeny testing from crosses of resistant and susceptible accessions suggests that a dominant and a recessive gene may condition root-knot nematode resistance.
W. R. Maluf, S. M. Azevedo, and V.P. Campos
Heritabilities for resistance to root knot nematodes (Meloidogyne javanica and Meloidogyne incognita races 1, 2, 3, and 4) were studied in a population of 226 sweetpotato clones of diverse origin. For each nematode isolate tested, 128-cell speedling trays were filled with previously inoculated substrate (30000 eggs/1000 mL substrate). Sweetpotato clones suitably tagged and identified were randomly planted in the cells (one plant/cell), with a total of four plants per clone per isolate. Ninety days after inoculation, sweetpotato plants had their roots washed for substrate removal, and treated with 150 mg·L–1 Phloxine B to stain nematode egg masses. The number of egg masses per root was recorded, and plants were accordingly assigned scores from 0 (highly resistant) to 5 (highly susceptible). Broad-sense heritability estimates were 0.87, 0.91, 0.81, 0.95, and 0.93 respectively for resistance to M. javanica and races 1, 2, 3, and 4 of M. incognita. The frequencies of resistant genotypes were higher for M. javanica and lower for M. incognita race 2. Genotypic correlations (rG) among the resistances to the various Meloidogyne isolates utilized were weak, ranging from 0.11 to 0.57, suggesting independent genetic controls. Clones could be selected, however, with high levels of resistance to all nematode isolates tested. (This work was supported by CNPq, CAPES, FAPEMIG, and FAEPE/UFLA.)
R.L. Fery and J.A. Thies
Scotch Bonnet and Habanero peppers, extremely pungent cultivar classes of Capsicum chinense, are becoming popular in the United States. Since the southern root-knot nematode (Meloidogyne incognita) is a major pest of many C. annuum cultivars commonly grown in the United States, a series of greenhouse and field studies was conducted to determine whether Scotch Bonnet and Habanero peppers also are vulnerable to the pest. An effort was made to collect Scotch Bonnet and Habanero seeds from all available commercial and private sources. In an initial greenhouse test, a collection of 59 C. chinense accessions was evaluated for reaction to M. incognita (race 3). All accessions obtained from commercial sources were moderately susceptible or susceptible. However, four accessions obtained via Seed Savers Exchange listings exhibited high levels of resistance. Three of these accessions (identified by the seed sources as Yellow Scotch Bonnet, Jamaica Scotch Bonnet, and Red Habanero) were studied in subsequent greenhouse and field plantings, and each was confirmed to have a level of resistance similar to the level of resistance exhibited by the C. annuum cv. Mississippi Nemaheart. Each of the resistant lines has good fruit and yield characteristics. The two Scotch Bonnet accessions produce yellow, bonnet-shaped fruit. The Red Habanero accession does not produce the lantern-shaped fruit typical of Habanero cultivars; the fruit have a bonnet shape.
Richard L. Fery and Judy A. Thies
Greenhouse tests were conducted to compare the levels of resistance to the southern root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] exhibited by recently released Capsicum chinense Jacq. Scotch Bonnet-type germplasm lines PA-353, PA-398, and PA-426 to the levels of resistance exhibited by C. annuum L. `Carolina Cayenne' and `Mississippi Nemaheart'; to determine the inheritance of the resistance in C. chinense germplasm line PA-426; and to determine the genetic relationship between the resistances exhibited by C. chinense germplasm line PA-426 and C. annuum `Carolina Cayenne'. The results of a replicated test indicated that the level of resistances exhibited by the resistant released C. chinense germplasm lines is equal to the level of resistances exhibited by the resistant C. annuum cultivars. Evaluation of parental, F1, F2, and backcross populations of the cross PA-426 × PA-350 (a susceptible Habanero-type C. chinense cultigen) indicated that the resistance in C. chinense is conditioned by a single dominant gene. The results of an allelism test indicated that this dominant gene is allelic to the dominant gene that conditions much of the southern root-knot nematode resistance in the C. annuum `Carolina Cayenne'. The ease and reliability of evaluating plants for resistance to root-knot nematode and the availability of a simply inherited source of outstanding resistance makes breeding for southern root-knot nematode resistance a viable objective in C. chinense breeding programs.
Anne M. Gillen and Fred A. Bliss
An F2 population from a single F1 plant from the cross of peach [Prunus persica (L.) Batsch] rootstock cultivars Harrow Blood (HB) × Okinawa (Oki) was used to locate the Mi locus, which conditions resistance to Meloidogyne incognita (race 1) (Kofoid and White) Chitwood. These data and comparison of common markers among published genetic linkage maps placed the Mi locus on Prunus L. linkage group 2. Two restriction fragment length polymorphisms (RFLPs) [linked at 4.8 and 6.8 centimorgan (cM), repulsion phase] and one random amplified polymorphic DNA (RAPD) marker (linked at 9.5 cM, coupling phase) were linked to Mi. The RAPD marker was cloned, sequenced, and converted to a polymerase chain reaction (PCR)-based cleaved amplified polymorphic sequence (CAPs) marker. Clones of resistance gene analogs (RGA) developed from Oki were highly polymorphic when used as RFLP probes. The RGA's mapped to four linkage groups but clustered on two of the four linkage groups, providing limited coverage of the genome. Even so, they may be useful as markers for disease resistance genes that occur in other populations. The linkage maps of the HB × Oki F2 population and a peach × almond (Prunus amygdalus Batsch) F2 population were colinear in certain regions, however, a significant number of markers mapped to different linkage groups among the two populations. The locus for the blood-flesh trait (red-violet mesocarp) mapped to the top of linkage group 4.
Susan L.F. Meyer, Inga A. Zasada, Mario Tenuta, and Daniel P. Roberts
The biosolid soil amendment N-Viro Soil (NVS) and a Streptomyces isolate (S 99-60) were tested for effects on root-knot nematode [RKN (Meloidogyne incognita)] egg populations on cantaloupe (Cucumis melo). Application of 3% NVS (dry weight amendment/dry weight soil) in the soil mixture resulted in significant (P ≤ 0.01) suppression of RKN egg numbers on cantaloupe roots compared to all other treatments, including 1% NVS and untreated controls. Ammonia accumulation was higher with the 3% NVS amendment than with any other treatment. Adjustment of soil pH with calcium hydroxide [Ca(OH)2] to the same levels that resulted from NVS amendment did not suppress nematode populations. When cultured in yeast-malt extract broth and particularly in nutrient broth, S 99-60 was capable of producing a compound(s) that reduced RKN egg hatch and activity of second-stage juveniles. However, when this isolate was applied to soil and to seedling roots, no suppression of RKN egg populations was observed on cantaloupe roots. Combining S 99-60 with NVS or Ca(OH)2 did not result in enhanced nematode suppression compared to treatments applied individually. The results indicated that NVS application was effective at suppressing RKN populations through the accumulation of ammonia to levels lethal to the nematode in soil.
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.