Sources of resistance to the watermelon strain of papaya ringspot virus (PRSV-W) have been identified within the watermelon (Citrullus lanatus) germplasm collection. Inheritance of resistance to papaya ringspot virus-watermelon strain was studied in three C. lanatus var. citroides accessions: PI 244017, PI 244019, and PI 485583. The susceptible parent lines `Allsweet', `Calhoun Gray', and `New Hampshire Midget' were crossed with resistant accessions to develop F1, F2, and BC1 generations for six families. A single recessive gene was found to control resistance to PRSV-W. The gene symbol `prv' is proposed for PRSV-W resistance in watermelon. Additional work is needed to determine whether the genes in PI 244017, PI 244019, and PI 485583 are allelic for resistance to PRSV-W.
Nihat Guner*, Zvezdana Pesic-VanEsbroeck and Todd Wehner
Nihat Guner, Zvezdana Pesic-VanEsbroeck, Luis A. Rivera-Burgos and Todd C. Wehner
Sources of resistance to the watermelon strain of papaya ringspot virus-watermelon strain (PRSV-W) have been identified within the watermelon (Citrullus lanatus) germplasm collection. Inheritance of the resistance to PRSV-W was studied in three Citrullus amarus (formerly C. lanatus var. citroides) PI accessions: PI 244017, PI 244019, and PI 485583. Three susceptible parent lines, ‘Allsweet’, ‘Calhoun Gray’, and ‘New Hampshire Midget’, were crossed with resistant PI accessions to develop F1, F2, and BC1 progenies in six families. A single recessive gene was found to control the resistance to PRSV-W in all three resistant PI accessions. Allelism tests indicated that the three PI accessions carry the same resistance allele to PRSV-W. The gene symbol ‘prv’ is proposed for PRSV-W resistance in PI 244017, PI 244019, and PI 485583 in watermelon.
Nihat Guner, Zvezdana Pesic-VanEsbroeck, Luis A. Rivera-Burgos and Todd C. Wehner
The Florida strain of Zucchini yellow mosaic virus (ZYMV-FL) is one of the major viral diseases of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai]. Although some screening has been performed for ZYMV resistance in watermelon, the germplasm collection has not been screened extensively for resistance. The objectives of this study were to screen the U.S. Department of Agriculture (USDA) watermelon germplasm collection for ZYMV resistance and to verify the disease rating for the most resistant and most susceptible accessions. We used a randomized complete block with four replications, 1613 PI accessions, and 41 cultivars. ‘Charleston Gray’ and ‘Crimson Sweet’ susceptible controls were used to verify that the ZYMV inoculum was virulent. After the last rating, an enzyme-linked immunosorbent assay (ELISA) was performed to determine the presence of a virus in the plant tissue. The PI accessions with high resistance to ZYMV-FL that also exhibited resistance to other watermelon viruses were PI 595203, PI 386015, PI 386016, PI 386024, PI 386025, PI 386026, PI 244018, PI 244019, PI 485583, PI 494528, and PI 494529. The ZYMV-FL retest of the most resistant 46 PI accessions showed that there were some escapes. Sixteen resistant PI accessions had a rating of 3.0 or less for the average and maximum ratings: PI 595203, PI 537277, PI 560016, PI 386016, PI 386019, PI 485580, PI 494529, PI 595200, PI 494528, PI 595201, PI 386025, PI 494530, PI 386015, PI 386021, PI 386026, and PI 596662. Overall, PI 595203 had the highest resistance according to both the germplasm screening and the retest studies.
Chen Jiang, Penelope Perkins-Veazie, Sylvia M. Blankenship, Michael D. Boyette, Zvezdana Pesic-VanEsbroeck, Katherine M. Jennings and Jonathan R. Schultheis
A series of studies were conducted to better understand the occurrence and causes of internal necrosis (IN) in ‘Covington’ sweetpotato (Ipomoea batatas). Assessment of the problem among the industry was done for 2 years and revealed that IN was widespread in commercial storage facilities throughout the state of North Carolina; both incidence and severity were generally low (<10% incidence with minimal severity of symptoms). A few storage rooms had a high percentage of IN with severe storage root symptoms but results were inconsistent across years and among rooms. Preharvest studies with commercially used insecticides did not induce IN, but the harvest aid ethephon consistently induced IN with an incidence higher than 50%. Internal necrosis symptoms were not detectable at harvest, and earliest consistent incidence was observed 6 days after harvest (DAH) during the curing phase. Symptoms became more prevalent and severe at 30 DAH. However, in commercial storage rooms, no relationship was found between IN incidence and postcuring storage temperature or relative humidity (RH) conditions. Sweetpotato storage roots stored in air-tight barrels and exposed to 100 ppm ethylene after curing showed no relationship between the presence of ethylene gas in storage and incidence of IN. Our results indicate that IN incidence of ‘Covington’ is erratic with no obvious cause among storage rooms and that initiation of IN may occur most frequently during the first week following harvest.
G. Craig Yencho, Kenneth V. Pecota, Jonathan R. Schultheis, Zvezdana-Pesic VanEsbroeck, Gerald J. Holmes, Billy E. Little, Allan C. Thornton and Van-Den Truong
‘Covington’ is an orange-fleshed, smooth-skinned, rose-colored, table-stock sweetpotato [Ipomoea batatas (L.) Lam.] developed by North Carolina State University (NCSU). ‘Covington’, named after the late Henry M. Covington, an esteemed sweetpotato scientist at North Carolina State, was evaluated as NC98-608 in multiple state and regional yield trials during 2001 to 2006. ‘Covington’ produces yields equal to ‘Beauregard’, a dominant sweetpotato variety produced in the United States, but it is typically 5 to 10 days later in maturity. ‘Covington’ typically sizes its storage roots more evenly than ‘Beauregard’ resulting in fewer jumbo class roots and a higher percentage of number one roots. Total yields are similar for the two clones with the dry matter content of ‘Covington’ storage roots typically being 1 to 2 points higher than that of ‘Beauregard’. ‘Covington’ is resistant to fusarium wilt [Fusarium oxysporum Schlect. f.sp. batatas (Wollenw.) Snyd. & Hans.], southern root-knot nematode [Meloidogyne incognita (Kofoid & White 1919) Chitwood 1949 race 3], and moderately resistant to streptomyces soil rot [Streptomyces ipomoeae (Person & W.J. Martin) Wakswan & Henrici]. Symptoms of the russet crack strain of Sweet Potato Feathery Mottle Virus have not been observed in ‘Covington’. The flavor of the baked storage roots of ‘Covington’ has been rated as very good by standardized and informal taste panels and typically scores as well or better in this regard when compared with ‘Beauregard’.
Christopher A. Clark, Washington L. da Silva, Ramón A. Arancibia, Jeff L. Main, Jonathan R. Schultheis, Zvezdana Pesic van-Esbroeck, Chen Jiang and Joy Smith
Two distinct syndromes have emerged in some production areas that have caused losses of sweetpotato (Ipomoea batatas) storage roots during postharvest storage: a complex of fungal rots (end rots) progressing from either end of storage roots and a necrotic reaction (internal necrosis) progressing internally from the proximal end of storage roots. This study was conducted in multiple environments to evaluate whether the use of preharvest ethephon application and storage with or without curing after harvest could be used to screen sweetpotato breeding lines for susceptibility/resistance to these two disorders. Treating vines with ethephon 2 weeks before harvest and placing harvested roots directly into storage at 60 °F without curing resulted in the greatest incidence of end rots in each state and there were significant differences in incidence among the sweetpotato genotypes evaluated. However, when ethephon was not used and roots were cured immediately after harvest, the incidence of end rots was low in all the genotypes evaluated except for one breeding line. Incidence and severity of internal necrosis were greatest when ethephon was applied preharvest and roots were cured immediately after harvest, but two cultivars, Hatteras and Covington, had significantly more internal necrosis than all others.