1 Introduction Gummy stem blight (GSB), also known as vine decline or black rot, is a devastating fungal disease that affects a wide range of cucurbit crops including watermelon and has been reported across Central and South America, the Caribbean, Asia, Africa, Europe and Oceania. Since the late 20th century, changes in cultivation practices have made GSB a major constraint for both open-field and protected cultivation, with yield losses ranging from 30% to 100% in epidemic years (Seblani et al.