Inheritance of Resistance to Gummy Stem Blight in Watermelon

Abstract

Gummy stem blight (GSB), caused by three related species of Stagonosporopsis [Stagonosporopsis cucurbitacearum (syn. Didymella bryoniae), Stagonosporopsis citrulli, and Stagonosporopsis caricae], is a major disease of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] in most production areas of the United States. We studied the inheritance of resistance to GSB using three PI accessions of watermelon. Four families of six progenies (Pr, Ps, F1, F2, BC1Pr, and BC1Ps) were developed from four crosses of resistant PI accessions by susceptible cultivars. Each family was tested in 2002 and 2003 in North Carolina under field and greenhouse conditions for resistance to GSB. Artificial inoculation was used to induce uniform and strong epidemics. The effect of the Mendelian gene for resistance, db, was tested. Partial failure of the data to fit the single-gene inheritance suggested that resistance to GSB of PI 482283 and PI 526233 may be under the control of a more complex genetic system.