Thirteen sweetpotato (Ipomoea batatas) genotypes were characterized for resistance to Meloidogyne incognita, M. javanica, M. hapla, and M. arenaria races 1 and 2 in greenhouse tests. The following sweetpotato genotypes representing a range of reactions to M. incognita were evaluated: U.S. Plant Introduction (PI) 399163 (highly resistant = HR), Sumor (HR), Nemagold (HR), Excel (HR), Tinian (HR), Hernandez (resistant = R), Jewel (R), Regal (R), Porto Rico (intermediate = I), Centennial (susceptible = S), Georgia Jet (S), Sulfur (S), and Beauregard (S). Meloidogyne incognita was most pathogenic to sweetpotato of the four Meloidogyne spp. evaluated in these studies. The U.S. Plant Introduction (PI) 399163 and Sumor were resistant to M. incognita in all tests. Only two genotypes, Beauregard and Porto Rico, were susceptible to M. javanica. All genotypes evaluated were resistant to M. hapla, M. arenaria race 1, and M. arenaria race 2. Sumor, U.S. PI 399163, and Nemagold appear to provide the highest levels of resistance against the four Meloidogyne spp. used in these studies. Since M. incognita is the most commonly occurring root-knot nematode species in sweetpotato growing areas of the southern U.S. and is pathogenic to most of the commonly grown sweetpotato cultivars, efforts to develop resistant cultivars that have desirable horticultural characteristics for the U.S. market should be directed toward this root-knot nematode species.
J. A. Thies and A. Levi
Root-knot nematodes (Meloidogyne incognita, M. arenaria, and M. javanica) cause severe damage to watermelon and resistance has not been identified in any watermelon cultivar. In greenhouse tests, we evaluated 265 U.S. plant introductions (PIs) for nematode resistance (based on root galling and nematode reproduction), and identified 22 PIs of Citrullus lanatus var. citroides as moderately resistant to M. arenaria race 1. In subsequent tests, these 22 PIs exhibited low to moderate resistance to M. incognita race 3 and M. arenaria race 2. Three watermelon (C. lanatus var. lanatus) cultivars (Charleston Gray, Crimson Sweet, and Dixie Lee), three C. colocynthis PIs, and four C. lanatus var. citroides PIs, all previously shown to be susceptible to M. arenaria race 1, were susceptible to M. incognita race 3 and M. arenaria race 2. The C. lanatus var. citroides PIs that are most resistant to both M. incognita and M. arenaria should be useful sources of resistance for developing root-knot nematode resistant watermelon cultivars.
R.L. Fery and J.A. Thies
The development of southernpea cultivars with a persistent green seed color has been the subject of much interest in the U.S. horticultural industry for more than two decades because seeds of such cultivars can be harvested at the dry seed stage of maturity without loss of their fresh green color. Two genes, gt (green testa) and gc (green cotyledon), are known that condition a persistent green seed color in southernpea. The gt gene was identified more than 25 years ago, but cultivars containing this gene have not been well-accepted by the industry because of the frequent occurrence of discolored (brown stains) seeds. Cultivars containing the more recently discovered gc gene, however, do not produce the discolored seeds and are used extensively in the frozen food industry. Efforts to develop cream-, blackeye-, and pinkeye-types of cultivars containing both the gt and gc genes are nearing completion. The dry seeds harvested from candidate cultivars homozygous for both the gt and gc genes are stain free and exhibit a deeper and more uniform green color than seeds harvested from cultivars homozygous for just one of the genes. It is anticipated that newer cultivars containing both of the genes that condition a persistent green seed color will not only have an enhanced value to the frozen food industry, but will also have great potential for use in the dry pack industry.
R.L. Fery and J.A. Thies
The peanut root-knot nematode (Meloidogyne arenaria race 1) is potentially a major pest of pepper cultivars belonging to the species Capsicum chinense. Greenhouse tests were conducted to: 1) compare the level of resistance to the peanut root-knot nematode exhibited by the recently released C. chinense germplasm line PA-353 to that exhibited by the C. annuum cv. Carolina Cayenne; 2) to determine the inheritance of the resistance in the C. chinense germplasm line PA-353; and 3) to determine the genetic relationship between the resistance exhibited by the C. chinense germplasm line PA-353 and that exhibited by the C. annuum cv. Carolina Cayenne. The level of resistance exhibited by the C. chinense germplasm line PA-353 was equal to the high level of resistance of the C. annuum cv. Carolina Cayenne. Evaluation of parental, F1, F2, and backcross populations of the cross between the resistant C. chinense germplasm line PA-353 and the susceptible C. chinense accession PA-350 indicated that the resistance in C. chinense is conditioned by a single dominant gene. The F2 population of the interspecific cross between the resistant C. chinense germplasm line PA-353 and the resistant C. annuum cv. Carolina Cayenne did not segregate for resistance, indicating that the dominant resistance gene in C. chinense is likely allelic to or closely linked to a gene conditioning resistance in C. annuum. The availability of a simply inherited source of outstanding resistance makes breeding for peanut root-knot nematode resistance a viable objective in C. chinense breeding programs.
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.
J.A. Thies, J.D. Mueller, and R.L. Fery
A 3-year field study was conducted at Blackville, S.C., to evaluate the potential of using resistant pepper (Capsicum annuum L.) cultivars as a rotation crop for managing the southern root-knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood]. The experiment was a split-plot with main plots arranged in a randomized complete-block design. In 1993, the entire experimental site was infested with M. incognita by inoculating a planting of susceptible PA-136 cayenne pepper with eggs of M. incognita race 3. In 1994, the main plots were planted to either highly resistant `Carolina Cayenne' or its susceptible sibling line PA-136. In 1995, `Carolina Cayenne' and the susceptible bell cultivars California Wonder and Keystone Resistant Giant were grown as subplots in each of the original main plots. `Carolina Cayenne' plants were unaffected by the previous crop. Previous cropping history, however, had a significant impact on the performance of the bell cultivars; the mean galling response was less (P < 0.01) and the yield was 2.8 times greater (P < 0.01) in the main plots previously cropped with `Carolina Cayenne' than in those previously cropped with PA-136. These results suggest that resistant pepper cultivars have considerable merit as a rotation crop for managing M. incognita infestations in soils used for growing high-value vegetables.
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.
J. A. Thies, P. A. Berland, and R. L. Fery
Rhizoctonia solani is an important pathogen of cowpea (Vigna unguiculata) in the southern U.S. and is the primary cause of seedling diseases in this crop. Stand losses caused by R. solani are especially severe when cowpea is planted in cold, spring soils. Three cowpea cultivars (Coronet, Knuckle Purple Hull, and Mississippi Silver) were evaluated in R. solani-inoculated field tests at four planting dates in Charleston, SC during 2005. The tests were planted on 25 Apr., 9 May, 27 May, and 13 June. The experimental design for each test was a split-plot with six replicates. Whole plots were cultivars, and sub-plots were inoculated with R. solani and an uninoculated control. Rhizoctonia solani caused significant seedling losses in all cultivars planted on the first three planting dates. Seed weight and seed numbers were reduced for `Mississippi Silver' in inoculated plots for all planting dates. In general, `Mississippi Silver' and `Coronet' had higher stand counts and heavier seed yields than `Knuckle Purple Hull', but all three cultivars were susceptible to R. solani. The development of resistant cowpea cultivars would reduce stand losses due to R. solani and improve seed yields of cowpea planted in cold, spring soils.
J. A. Thies, P. A. Berland, and R. L. Fery
Rhizoctonia solani is an important pathogen of cowpea (Vigna unguiculata) in the southern U.S. and worldwide. Cowpeas are especially susceptible to seedling diseases caused by R. solani when planted in cold, moist, spring soils. Nine cowpea cultivars were evaluated in inoculated field tests at six planting dates in Charleston, S.C., during 2004. The cowpea cultivars evaluated were Bettergro Blackeye, Knuckle Purple Hull, Mississippi Silver, Colossus-80, Charleston Nemagreen, Texas Cream-40, White Acre, Coronet, and Charleston Greenpack. The tests were planted on 20 Apr., 29 Apr., 11 May, 19 May, 27 May, and 8 June. The experimental design for each test was a split-plot with six replicates. Whole plots were cultivars, and sub-plots were inoculation with R. solani and an uninoculated control. Rhizoctonia solani caused significant seedling losses in all cultivars evaluated during mid-April to early June and seed yields were reduced in the 11 May planting. In general, standard cowpea cultivars (Mississippi Silver, Colossus-80, and Coronet) had higher stand counts and produced heavier seed yields than other cowpea cultivars, although these standard cultivars were not resistant to R. solani. Resistant cowpea cultivars are needed to allow earlier planting of the crop in cold soils, which would extend the growing season and allow more efficient use of harvesting equipment and processing facilities.
R.L. Fery, P.D. Dukes Sr., and J.A. Thies
The southern root-knot nematode (Meloidogyne incognita) is a major pest of bell peppers (Capsicum annuum) in the United States. Since none of the leading bell pepper cultivars grown in the U.S. exhibit adequate levels of resistance, a breeding program was initiated to incorporate the N root-knot nematode resistance gene into commercial bell pepper germplasm. A backcross breeding procedure was used. The donor parent of the N gene was the open-pollinated, pimiento pepper cultivar Mississippi Nemaheart, and the recurrent parents were the open-pollinated bell pepper cultivars Keystone Resistant Giant and Yolo Wonder. A large number of homozygous resistant BC6 populations were evaluated in field tests in 1995, and two lines (PA-440, an isoline of `Keystone Resistant Giant', and PA-453, an isoline of `Yolo Wonder') were selected for further field evaluation and seed multiplication in 1996. Results of replicated field and greenhouse tests conducted in 1996 indicate that root-knot nematode resistance has been incorporated successfully in `Keystone Resistant Giant' and `Yolo Wonder' backgrounds.