Papaya Ringspot Virus Watermelon Strain and Zucchini Yellow Mosaic Virus Resistance in Watermelon

GUNER, NIHAT. Papaya Ringspot Virus Watermelon Strain and Zucchini Yellow Mosaic Virus Resistance in Watermelon. (under the direction of Dr. Todd C. Wehner) Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is a major crop in the southern United States. Papaya ringspot virus-watermelon strain (PRSV-W, formerly Watermelon mosaic virus-1) and Zucchini yellow mosaic virus (ZYMV) affect all agricultural species of the Cucurbitaceae and are of great economic importance because of their destructiveness. Watermelon has not been screened extensively for resistance to PRSV-W. Although there is a resistance source for ZYMV resistance, the identification of additional sources of resistance to ZYMV would be highly desirable since the initial sources of resistance are temperature dependent, or not resistant to some of the more severe strains of the virus. The objectives of this study were 1) to screen the USDA watermelon germplasm collection along with available watermelon cultivars for PRSV-W resistance; 2) to verify the disease rating for the most resistant and most susceptible accessions; 3) to determine the genetic control of PRSV-W resistance; and 4) to screen the U.S.D.A. watermelon germplasm collection along with available watermelon cultivars to identify additional sources of resistance to ZYMV. A total of 1275 plant introduction accessions and 44 watermelon cultivars were screened for PRSV-W resistance. The experiment was a randomized complete block with five replications. Enzyme-linked immunosorbent assay (ELISA) was performed after the last rating to determine whether the virus was in the plant tissue. After the germplasm screening, the most resistant and most susceptible cultigens were retested to verify their reactions. Of the 60 resistant PI accessions in the final retest, eight had resistance with a rating of 3.6 or less for the best, average and maximum ratings: PI 244017, PI 244019, PI 482342, PI 482318, PI 485583, PI 482379, PI 595203, and PI 244018. None of the watermelon cultivars tested exhibited resistance to PRSV-W. Inheritance of PRSVW resistance was studied in three C. lanatus var. citroides accessions: PI 244017, PI 244019, and PI 485583. Three 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 in all three resistant PI accessions. A test of allelism indicated that resistance to PRSV-W in the three PI accessions was due to the same gene. Therefore, the gene symbol 'prv' is proposed for PRSV-W resistance in PI 244017, PI 244019, and PI 485583 in watermelon. The USDA germplasm collection of 1613 introduction accessions, as well as 41 watermelon cultivars, was screened for resistance to the Florida strain of Zucchini yellow mosaic virus (ZYMV-FL). The experiment was a randomized complete block with four replications. A retest study was conducted after the germplasm screening to verify the reaction of the most resistant and susceptible accessions. The PI accessions with the highest resistance to ZYMV were PI 595203, PI 537277, PI 560016, PI 386016, PI 386019, PI 485580, PI 494529, and PI 595200. PI 595203 was the most resistant accession based on both the germplasm screening and the retest study. PI accessions with the highest resistance to ZYMV-FL that also had resistance to other watermelon viruses PRSV-W and WMV (Watermelon mosaic virus, formerly Watermelon mosaic virus-2) were PI 595203, PI 386015, PI 386016, PI 386024, PI 386025, PI 386026, PI 244018, PI 244019, PI 485583, and PI 494528, PI 494529. Papaya Ringspot Virus Watermelon Strain and Zucchini Yellow Mosaic Virus Resistance