Evaluation of rootstocks for grafted plants as a strategy to manage Southern Blight in tomato (Solanum Lycopersicum)

Abstract

Sclerotium rolfsii is a soil-borne fungus responsible for the disease Southern blight. With few effective chemical controls, this disease is a continuing problem in the southeastern U.S. Vegetable grafting has gained momentum as a method to manage soil-borne diseases. An experiment was conducted to evaluate 6 lines of tomato (Solanum lycopersicum) and two near relatives (Solanum pimpinellifolium) for varying levels of resistance to S. rolfsii. The intraspecific rootstocks Multifort and Maxifort were also analyze for Southern blight resistance. These six lines are processing tomatoes from Texas A&M University: 5635M, 5707M, 5719M, 5737M, 5876M, 5913M with reported resistance to S. rolfsii. In 1992, Leeper and others released six processing tomato breeding lines with resistance to S. rolfsii (Leeper et al., 1992). Leeper (1992) specifically states that there are 2 PI’s (S. pimpinellifolium) with noted resistance, however, they were not specifically used in the breeding program. The original source of resistance was unknown but following research from Mohr (1955) was shown that the method of incurred resistance was cited as secondary stem thickening as the plant matured which provided a greater barrier against the pathogen. To evaluate disease resistance, plants were grown under greenhouse conditions in Auburn, AL. These eight lines plus two susceptible controls were organized in a RCBD with two plants of each line per block with four replicates repeated 3 times in Aug, Sept, and Oct 2016. One isolate of S. rolfsii was used to inoculate half of the plants in each block when the plants were 8-weeks-old. The plants were evaluated and graded on a 0-5 scale over the next 7-10 days. All plants displayed signs of infection three to four days after inoculation. Greenhouse screening resulted in 100% disease pressure in an environment that favored the disease. Statistical evaluation using R software showed that although the disease progressed differently among the eight lines and controls, the results were the same for each line. No significant difference in resistance was observed among the lines screened. 5635M, 5876M, PI 126432, 5635M, 5719M performed significantly worse than the interspecific rootstocks Maxifort and Multifort, which had the overall lowest disease rating. The intraspecific rootstocks showed the greatest resistance to the greenhouse screening. Additional research should be conducted under field conditions to evaluate disease progression as past research with these six lines showed resistance to Southern blight under field conditions.