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Grafted processing tomato for the management of southern blight in California

Natalie Solares: University of California at Riverside

<div>Southern blight, caused by the soil borne fungus <em>Athelia rolfsii</em>, is a disease of many crops and is particularly difficult to manage in processing tomatoes. The objective of this research is to evaluate grafting for southern blight management in California processing tomatoes. Two cultivars H5608 and H8504 were evaluated as scions grafted to rootstock of Maxifort, a hybrid cultivar resistant to southern blight, or as non-grafted controls. Yield data was collected from a field trial conducted in soil with <em>A. rolfsii</em> that consisted of 165 m long plots arranged in a randomized complete block (RCB) with 7 replications. A greenhouse study was conducted to evaluate the performance of each treatment under 0, 5, 10, and 20 sclerotia per 100 cm<sup>3</sup> of soil. One-plant pots were arranged in a RCB with 8 replications, and disease severity was rated every 2 to 3 weeks. At 5 and 10 sclerotia per 100 cm<sup>3 </sup>of soil, disease severity in the greenhouse was statistically similar among grafted H5608, grafted H8504, and non-grafted H8504 on the final three rating dates, whereas disease caused by <em>A. rolfsii</em> was significantly more severe in non-grafted H5608 compared to the other three treatments. In the field, yield was not significantly influenced by cultivar, but was significantly higher in grafted plots (by 23% or 36%) compared to the non-grafted treatments. Our results suggest grafting susceptible cultivars to the resistant rootstock Maxifort can reduce southern blight and augment yield.</div>