Fig. 1.

Experimental design and the influence of soil nutrient properties on disease incidence. A Schematic of the field trial design, with each treatment comprising three replication plots, each containing 40 tomato plants. B The relationship between standardized nutrient properties and disease incidence (DI) caused by pathogen R. solanacearum, using multiple linear regression analysis. C The influence of soil nutrient properties on DI, predicted by random forest method. D Relationship between soil available phosphorus and DI, using unary linear regression analysis. E Schematic of the pot experiment design. Six replicates, each containing three tomato plants, were employed during seasons 1 (2020 October 22-2021 January 13) and 2 (2021 March 21-2021 June 12). Three replicates, each containing two tomato plants, were employed during season 3 (2022 September 15-2022 November 28). Seasons 1 and 2 corresponded to trials 1 through 4, while season 3 was dedicated to the 5th trial. All treatments depicted in this figure received equivalent nitrogen and potassium fertilization. The CK control, without any fertilization or pathogen inoculation, is not shown. Treatments include AP, soil applied with calcium superphosphate as relatively available phosphorus; UP, soil applied with calcium phosphate as relatively unavailable phosphorus with equivalent amount phosphorus to AP treatment; −P, soil with no phosphorus supply. Phosphorus stress gradually increased in the order of AP, UP, and −P. +RS groups were inoculated with pathogen at 1 × 10⁷ colony-forming units g⁻¹ soil. RS denotes R. solanacearum; P denotes phosphorus. Significance levels are denoted as follows: “ns,” not significant, “.”P < 0.1, “*”P < 0.05, “**”P < 0.01, and “***”P < 0.001