A preliminary screening experiment was conducted to evaluate 47 cowpea [Vigna unguiculata (L.) Walp.] genotypes for use as a weed-suppressing cover crop. Of these, 11 were selected for further testing on the basis of vigorous growth and weed-suppressing ability. In a field experiment repeated over 4 years, the selected genotypes were not different from the leading cover crop cultivar `Iron Clay' in biomass production. Vigor ratings, vine growth ratings, and canopy widths of some genotypes exceeded those of `Iron Clay' Vigor ratings and canopy measurements were efficient selection criteria that could be useful for breeding cover crop cowpea cultivars. All except one selection were highly resistant to southern root knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood], and the selections varied in seed size, photoperiod, and response to foliar diseases.
Howard F. Harrison, Judy A. Thies, Richard L. Fery, and J. Powell Smith
Zhen-Xiang Lu, G.L. Reighard, W.V. Baird, A.G. Abbott, and S. Rajapakse
Eighteen peach rootstock cultivars, most of Prunus persica (L.) Batsch, were screened for diagnostic random amplified polymorphic DNA (RAPD) markers using synthetic decamer oligonucleotide primers. Twenty of the 80 primers were informative, and 40 amplified DNA bands from the informative primers were selected as RAPD markers. Based on combined banding patterns, all 18 rootstock cultivars were identified with only six of the 20 informative primers. Cluster analysis of the 18 peach rootstock cultivars using 40 RAPD markers produced a dendrogram of genetic relatedness in good agreement with their putative pedigrees. The first major bifurcation in the dendrogram divided these rootstock cultivars into two groups according to their resistance or susceptibility to root-knot nematodes [Meloidogyne incognita (Kofoid and White) Chitwood and M. javanica (Treub) Chitwood].
J.A. Thies, J.D. Mueller, and R.L. Fery
The southern root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] is a serious pest of pepper (Capsicum annuum L.). Currently, methyl bromide is used for nematode control, but the pending withdrawal of this fumigant from the United States market has resulted in a need for effective alternative root-knot nematode management measures. We evaluated the effectiveness of resistance of `Carolina Cayenne' relative to the susceptible genotypes `Early Calwonder' and PA-136 in greenhouse, microplot, and field studies. In all tests, `Carolina Cayenne' exhibited exceptionally high resistance (minimal galling, minimal nematode reproduction, and no yield reduction) to M. incognita; `Early Calwonder' and PA-136 were highly susceptible. In a test conducted in a heavily infested field, `Carolina Cayenne' outyielded PA-136 by 339%. The exceptionally high resistance exhibited by `Carolina Cayenne' provides an alternative to methyl bromide and other fumigant nematicides for managing root-knot nematodes in pepper.
Nancy Kokalis-Burelle, C.S. Vavrina, M.S. Reddy, and J.W. Kloepper
Greenhouse and field trials were performed on muskmelon (Cucumis melo) and watermelon (Citrullus lanatus) to evaluate the effects of six formulations of plant growth-promoting rhizobacteria (PGPR) that have previously been shown to increase seedling growth and induce disease resistance on other transplanted vegetables. Formulations of Gram-positive bacterial strains were added to a soilless, peat-based transplant medium before seeding. Several PGPR treatments significantly increased shoot weight, shoot length, and stem diameter of muskmelon and watermelon seedlings and transplants. Root weight of muskmelon seedlings was also increased by PGPR treatment. On watermelon, four PGPR treatments reduced angular leaf spot lesions caused by Pseudomonas syringae pv. lachrymans, and gummy stem blight, caused by Didymella bryoniae, compared to the nontreated and formulation carrier controls. One PGPR treatment reduced angular leaf spot lesions on muskmelon compared to the nontreated and carrier controls. On muskmelon in the field, one PGPR treatment reduced root-knot nematode (Meloidogyne incognita) disease severity compared to all control treatments.
Kathryn E. Brunson, Sharad C. Phatak, J. Danny Gay, and Donald R. Summer
Velvetbean (Mucuna deeringiana L.) was used in crop rotation to determine the influence on southern root-knot nematode (Meloidogyne incognita) in sustainable vegetable production. Replicated trials were conducted at four locations. Two cover crop treatments, crimson clover and subterranean clover, were used in the sustainable plots and rye was the plow-down cover crop for the conventional plots. Selected as the vegetable crops were tomato, pepper, and eggplant. Following the final harvest, velvetbean was planted into the sustainable plots and disked under after 90 days. Results from soil samples before and after velvetbean, indicated the sustainable plots had substantially reduced nematode densities, while most conventional plots showed increases. A correlation between location, treatment, root-gall indexes and nematode density occurred in all crops for 1992. In 1993 there was only a correlation between root-gall index and nematode density in pepper. However, root-gall indexes were significant for location and treatment in all crops.
Kittipat Ukoskit, Paul G. Thompson, Gary W. Lawrence, and Clarence E. Watson
The inheritance of root-knot nematode race 3 [Meloidogyne incognita (Kofoid & White) Chitwood] resistance was studied in 71 progenies of the F1 backcross population produced from the resistant parent `Regal' and the susceptible parent `Vardaman'. The distribution frequency of the progenies measured on total nematode number (eggs + juveniles) indicated a bimodal distribution with a ratio of 4 resistant: 1 susceptible. Based on this phenotypic ratio, the proposed genetic model was duplex polysomic inheritance (RRrrrr = resistant). Bulk segregant analysis in conjunction with the RAPD technique was employed to identify RAPD marker linked to the root knot nematode-resistant gene. Nine of 760 random decamer primers screened showed polymorphic bands. Primer OPI51500 produced a band in the resistant bulk, but not in the susceptible bulk. Estimated recombination frequency of 0.24 between the OPI51500 marker and the root-knot nematode-resistant gene indicated linkage.
F.A. Hammerschlag and R.N. Huettel
Five in vitro propagated peach scion cultivars (Suncrest, Rio Oso Gem, Compact Redhaven, Redhaven, Jerseyqueen) and two rootstock (Nemaguard and Lovell) were screened in vitro and in microplots for their susceptibility to the root-knot nematode, Meloidogyne incognita. Evaluations in tissue culture for galling were conducted at 5 wk. Trees in microplots were evaluated for 3 years for nematode populations, trunk diameter, and yield. Comparative results indicated that the number and size of galls observed at 5 wk in vitro is indicative of the response of peaches to nematodes under field conditions after three years. Cultivar Compact Redhaven was significantly more tolerant to root-knot than `Lovell' the most widely used peach rootstock. These results suggest that Compact Redhaven might be potentially useful as a rootstock in the Southeast where Nemaguard is used sparingly because of its lack of cold tolerance. In addition, these results indicate that in vitro screening holds promise as a rapid technique for evaluating root-knot nematode resistance.
Kathryn E. Brunson, Sharad C. Phatak, J. Danny Gay, and Donald R. Sumner
Velvetbean (Mucuna deeringiana L.) has been used as part of the crop rotation in low-input vegetable production in southern Georgia to help suppress populations of root-knot nematode (Meloidogyne incognita) for the past 2 years. Over-wintering cover crops of crimson and subterranean clovers were used the low-input plots and rye was the plow-down cover crop in the conventional plots. Tomatoes, peppers, and eggplant were the vegetable crops grown in these production systems. Following the final harvest in 1992, use of nematicides in the low-input plots was discontinued and velvetbean was then planted into the low-input plots and disked in after 90 days. Results from the 1993–94 soil samples taken before and after velvetbean showed a continuing trend of reduced nematode numbers where velvetbean had been, while most conventional plots that had nematicides applied resulted in increases in nematode populations.
P. D. Dukes and Janice R. Bohac
There are four known physiological races of the southern root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood]. Races are designated I through 4 and their identifications are based soley on differential hosts. These race problems as related to breeding sweetpotato for resistance to attack by all races are reviewed and discussed. Data are presented showing the reactions of selected cultivar and breeding clones of sweetpotato to all four races. The reactions of races 1 and 3 are generally well—known. Races 2 and 4 apparently are spreading and becoming more numerous in the southern states where soybean and tobacco are grown. Comparative disease indices are presented showing that generally sweetpotatoes were less susceptible to races 2 and 4. However, there were some notable exceptions, for example, `Sulfur' and `Beauregard' were equally susceptible to all races. High resistances to attack by races 2 and 4 were found in `Sumor', `Nemagold', `Excel', W-241 and others.
A.G. Hunter, O.L. Chambliss, and J.C. Williams
Four southernpea (cowpea) [Vigna unguiculata (L.) Walp.] cultivars representing various combinations of resistance and susceptibility to blackeye cowpea mosaic virus (BlCMV) and southern root-knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood] were used to determine effectiveness of simultaneous screening of plants for resistance to both pathogens. Plants were inoculated with both pathogens simultaneously, each pathogen separately, or left uninoculated as controls. The resistance classification of the cultivars based on treatments with only one pathogen was not different from that based on the treatment with both pathogens. Virus × nematode interaction was not a significant source of variation in BlCMV symptoms and root-knot nematode galls. Simultaneous screening for both pathogens in southernpeas appears to be a feasible option.