Sources of Resistance to Zucchini Yellow Mosaic Virus in Lagenaria siceraria Germplasm

One-hundred ninety U.S. PIs of bottlegourd [Lagenaria siceraria (Mol.) Standl.] were evaluated for their resistance to the Florida strain of Zucchini yellow mosaic virus (ZYMV-FL). Seedlings in the first leaf stage were mechanically inoculated with freshly prepared ZYMV-FL tissue extract in a greenhouse. Four weeks postinoculation, plants were visually evaluated for symptom expression and tissue samples from upper noninoculated leaves were collected for serological analysis with enzyme-linked immunosorbent analysis (ELISA). A combination of symptom expression and ELISA value was considered in determining the resistance or susceptibility for each accession. Of the 190 L. siceraria PIs screened, 36 accessions were in complete resistance (no disease symptom with negative ELISA on all tested plants), 64 PIs showed partial resistance (some of the tested plants were resistant, whereas others were susceptible), and 90 PIs were susceptible (severe symptom and positive ELISA on all tested plants). The ZYMV-FL resistance exists mostly among L. siceraria PIs collected in India. Thirty-three of the 36 L. siceraria PIs showing ZYMV-FL resistance were collected in India, one in Indonesia, one in South Africa, and one in Zimbabwe. To rule out any potential escapes in the primary screening, a repeated test using representative accessions, including 10 susceptible, three partially resistant, and three completely resistant PIs, was done to confirm the ZYMV-FL resistance. Furthermore, the resistance to ZYMV-FL was shown to be heritable in progenies generated through self-pollination of single plants in each of five resistant PIs as well as in three F1 hybrids.