Response of US Cucumis melo Plant Introductions to Phytophthora capsici

Phytophthora capsici is distributed worldwide, and is an aggressive pathogen with a broad host range infecting solanaceous, leguminaceous, and cucurbitaceous crops. Over the past two decades, increased incidence of Phytophthora blight, particularly in eastern states, has threatened production of many vegetable crops. Cucumis melo (honeydew and cantaloupe), while especially susceptible to fruit rot, is also susceptible to crown/root rot. Currently, little is known about host resistance to P. capsici in C. melo. To assess resistance in C. melo seedlings, 318 Cucumis melo US Plant Introductions (PIs) from diverse geographic locations and two commercial hybrid cultivars (Athena and Dinero) were grown under greenhouse conditions. At the three to four leaf stage, seedlings were inoculated with a five isolate zoospore suspension (1.0 x 10 super(4)) at the crown and monitored for six weeks. All the susceptible checks ('Athena' and 'Dinero') died within seven days post inoculation. Several PIs (PI 181748, PI 182964, and PI 273438) succumbed earlier than Athena and Dinero due to crown rot. Eighty seven PIs (27%) appeared to have some degree of tolerance to P. capsici. The level of resistance to P. capsici within individual PIs was variable. The 87 PIs selected from the primary screen are currently being re-screened and the results of this study will be presented.