Response of Some Watermelon Accessions to a Puerto Rico Strain of Zucchini yellow mosaic virus

Abstract

One of the most important members of the Potyviridae is Zucchini yellow mosaic virus (ZYMV). It affects watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] as well as other cucurbits in most parts of the world. Although several genotypes have been reported as having resistance to ZYMV, differential responses to ZYMV strains are known to occur. Using a Puerto Rico strain of ZYMV (ZYMV-PR, GenBank accession number MN422959), we tested the response of 11 genotypes [PIs from the U.S. Department of Agriculture (USDA) National Genetic Resources Program] previously reported as having resistance to this virus. In two greenhouse trials, the first three leaves of seedlings of each genotype were mechanically inoculated with ZYMV-PR. An enzyme-linked immunosorbent assay (ELISA) was done on each seedling’s fourth leaf and symptom severity was rated on the first, third, fifth, and seventh leaves. There were significant genotype × trial interactions for most variables, but some genotypes performed consistently in both trials. All seedlings of PI 537277 tested negative for ELISA (absorbance < 0.200) across both trials. PI 537277, PI 595200, PI 595201, and PI 595203 were generally among the accessions with the lowest symptom severity scores. Overall, symptom severity correlated poorly with ELISA readings. But all plants of PI 537277, and most plants of PI 595201 and PI 595203, had low ELISA readings and low severity scores. Despite having low severity scores, PI 595200 was among the genotypes with the highest ELISA readings in trial 2. For the plant breeder, the most useful genotypes are those that exhibit reduced severity as well as low ELISA. PI 537277, PI 595201, and PI 595203 met those criteria in this study. Of these three accessions, PI 595203 would be the most useful in a breeding program because it has shown resistance to the Puerto Rico, Florida, and China strains of ZYMV.