Grafting Tomato to Manage Southern Blight, Prevent Yield Loss, and Increase Crop Value.

Abstract

Southern blight, caused by the soilborne fungus Athelia rolfsii, has increased in frequency and severity in the southern United States since the use of methyl bromide fumigation ceased. The objective of this study was to evaluate three cultivars of sticky nightshade (Solanum sisymbriifolium), previously used as tomato rootstocks because of resistance to root-knot nematode, for resistance to southern blight. Field experiments in infested soil were done in Georgia in 2020 and 2021 and in South Carolina in 2021. Tomato cultivar Roadster was used as the scion. Control treatments included non-grafted Roadster in all experiments and self-grafted Roadster in Georgia. In all three experiments, all rootstocks significantly reduced incidence of southern blight and increased vigor ratings compared to control treatments (P ≤ 0.007). The rootstocks Maxifort, White Star, and SisSynII, but not Diamond, significantly increased marketable weight (P ≤ 0.02) and crop value (P < 0.05) compared to control treatments. In South Carolina only, because of greater yields than in Georgia, net returns with Maxifort and White Star were significantly greater than net return with non-grafted Roadster (P = 0.004). When the wholesale price for fresh market tomato is ≥$13/box, grafting may be an effective and economical management for southern blight.