Screening for resistance to blackeye cowpea mosaic virus (BlCMV) and rootknot nematode on the same plant is possible if the two pathogens do not interact significantly. To determine if such interactions were present four cultivars were planted in 72-cell styrofoam flats, with a combination of BlCMV and nematode inoculations (--, -+, +-, and ++). `Freezegreen' is known to be susceptible to both pathogens, `Mississippi Silver' is resistant to both, `California Blackeye #5' is susceptible to BlCMV, and `Worthmore' is resistant to BlCMV. Nematode treated seeds were inoculated at planting with 2,000 eggs of (Meloidogyne incognita Race 3); BlCMV was inoculated on primary leaves a week later. Plants were visually rated for symptoms: either negative or positive for BlCMV and 1-5, no galls and heavily galled respectively, for rootknot. Analyses of variance using percentage of plants negative for virus symptoms or average nematode score as the dependent variable, resulted in non-significant virus × nematode interactions. Results by cultivar indicated simultaneous screening did not change their resistance/susceptible classifications.
A. G. Hunter and O. L. Chambliss
A.G. Hunter, O.L. Chambliss, and L.O. Wells
Nine southernpeas, varying in their resistance to cowpea curculio, and the susceptible California Blackeye # 5 (CBE) were tested with six treatments: methyl parathion and endosulfan at recommended and one-quarter rate, a control with tractor traffic, and one without traffic. CBE had 42.7% curculio-damaged seeds over all treatment, while resistant entries ranged from 3.7% to 9.5%. Over all entries, methyl parathion at the recommended rate resulted in the lowest percentage of curculio-damaged seed (7.3%); endosulfan at the recommended rate was next with 9.1%. The percentage of damaged seed was not significantly different for the methyl parathion and endosulfan treatments using one-quarter recommended rates, the control with traffic, and the control without traffic—10.8%, 11.2%, 12.6%, and 11.7%, respectively. `Carolina Cream' (3.7% damaged seed over all treatments) and methyl parathion at the recommended rate resulted in the lowest percentage of curculio damaged seed: 1.3%.
Oyette L. Chambliss, Arthur G. Hunter, and Richard O. Hampton
Germplasm accessions and advanced lines were evaluated for seed transmission of the seed borne viruses, cucumber mosaic (CMV), cowpea severe mosaic (CSMV), and blackeye cowpea mosaic (B1CMV). Seed samples from 822 field plots (274 out of 300 accessions in 3 replications) which had been evaluated for insect resistance in 1992 were planted in the greenhouse. Mosaic virus symptoms had been apparent throughout the 1992 field planting. Evaluation for mosaic symptoms was done at the seedling stage in the greenhouse and 89 entries exhibited seed borne virus symptoms in one or more plants. Of these, 78 were shown by ELISA (enzyme linked immunosorbant assay, direct antigen coating method) to contain at least one of the seed borne viruses for which we were evaluating.
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.
A.G. Hunter, G.E. Boyhan, E.H. Simonne, and O.L. Chambliss
Seed harvested from 41 entries in the 1994 southernpea variety trial was grown in a greenhouse for evaluation of seedborne mosaic viruses. When second trifoliate leaves were fully expanded, 100 plants per plot per block (4) were evaluated for blackeye cowpea mosaic virus (B1CMV), cucumber mosaic virus (CMV), cowpea severe mosaic virus (CSMV), and southern bean mosaic virus (SBMV). The average number of plants with virus symptoms ranged from 2% (Pinkeye Pinkpod) to 44% (Bettergreen). Plants with symptoms were assayed using enzyme-linked immunosorbent assay (ELISA). At least one virus was detected with ELISA in all entries, except for `Zipper Cream' in which none were evident. All viruses were detected in seven entries. B1CMV and CMV were present in 13. CMV was present in all but `Zipper Cream', `Mississippi Cream', and `Texas Pinkeye'. Symptomatology was poorly correlated to ELISA results: six entries having all four viruses had symptoms on less than 13% of their plants.
A.G. Gillaspie, O.L. Chambliss, R.L. Fery, A.E. Hall, J.C. Miller Jr., and T.E. Morelock
The Vigna Crop Germplasm Committee has established a core subset for the USDA cowpea germplasm collection. The subset consists of 9.3% (700 accessions) of the 7525 accessions currently contained in the collection. The subset was selected on the basis of country of origin, taxonomic characteristics, and known disease and pest resistance characteristics. Theoretically, the lines in the subset represent the genetic diversity present in the entire collection. A listing of the accessions in the subset is available from the Vigna germplasm curator (A.G. Gillaspie). The listing can also be accessed through the USDA's Germplasm Resources Information Network (GRIN).