Effect of grafting on the control of gummy stem blight in muskmelons

Abstract

Gummy stem blight, caused by Didymella bryoniae, is the most important fungal diseases of muskmelons cultivated in protected environments in Brazil. Fungicides are used to control this disease, and little is known about the effectiveness of alternative control methods. The aim of this study was to evaluate the effect of grafting on the control of gummy stem blight in four muskmelon hybrids. The hybrids Bonus II, Sunrise, Louis and Prince hakusho were grafted onto the squash hybrid Shelper, which is immune to D. bryoniae. Two experiments were conducted, one in greenhouse with artificial inoculation of the pathogen and the other in protected environment using crop residues and soil infected with the pathogen. Under greenhouse conditions, mycelial discs of the pathogen were inoculated onto the hypocotyl or at the union graft/rootstock region of the grafted plants and onto ungrafted plants of each hybrid. By growing these four melon hybrids in a protected environment, the effect of grafting on the control of gummy stem blight could be studied. When these melons were grown in the greenhouse or in a protected environment, grafting significantly reduced the growth of gummy stem blight in all four melon hybrids. For grafted hybrid plants inoculated at the hypocotyl, the disease severity decreased by 34.1%, 33.8%, 51.1% and 48.0% for Sunrise, Bonus II, Louis and Prince hakusho, respectively, compared to ungrafted plants. For grafted plants inoculated at the union graft/rootstock region, the disease severity decreased by 54.3%, 57.3%, 54.1% and 44.6%, respectively. For melons grown in protected environments, grafting reduced the severity of gummy stem blight in the four melon hybrids by 34.3%, 34.8%, 45.8% and 49.6%, respectively. Thus, grafting onto immune rootstocks significantly reduced the severity of D. bryoniae in the four muskmelon hybrids grown under greenhouse and protected environment conditions.