| Ralstonia solanacearum(Rs) is a soil-borne disease and silicon can induce resistance in tomato against R. solanacearum. However, most studies focus on pathogen resistance mechanism mediated by silicon from aboveground persperctive. In this study, two tomato cultivars, HYT(susceptible) and H7996(resistant), were chosen to investigate the underground mechanism of silicon-induced resistance in tomato against Ralstonia solanacearum thought hydroponics and organic acid or SA addition experiments.The results showed that disease incidence of R. solanacearumwas reduced by 37.5% and disease severity by 25.0% in 2 m M silicon treatment for HYT, but no effects for H7996. The amout of R. solanacearumin roots and stems was reduced after silicon supply, but this effect was not significant. The amount of Rs in stems were the highest, which reached 107~108 cfu·g-1. The concentration of Si in roots, stems and leaves were increased in Si pre-treated group. In addition, silicon mainly accumulated in roots. Moreover, silicon concentration significantly increased in roots after R. solanacearum inoculation.Ten days after inoculation, root growth and photosynthesis of plants were severely inhibited but improved by silicon addition. Silicontreatments increased root surface area by 51.6%, average root diammer by 22.8%, root volume by 46.8%, net photosyntheticrate by 65.9%, intercellular CO2 concentration by 30.6% and transpiration rate by 208% t for HYT variety.Under Rs stress, the secretion of citric acid in roots was increased for HYT, but reduced in silicon pre-treated group. The concentration of citric acid in roots reduced by 51.1%~231% and the secretion of citric acid reduced 6~16 times in Rs+Si treatment compared with Rs treatment. One day after Rs inoculation, the concentration of organic acids in Rs treatment was higher than that of Rs+Si treatment for H7996, but this change was opposite after 4 and 7 days inoculation. Moreover, the activities of three organic acids metabolize related enzyme were increased in Rs+Si treatment in comparison with Rs treatment for H7996.Seven days after inoculation, total amino acids in roots were increased by 9.9% in Rs+Si treatment compared with Rs treatment for HYT. In addition, Rs+Si treatment increased lysine content by 97.2~248% and phenylalanine by 12.8%~38.3% in roots while Rs treatment resulted in 77.5%~78.5% increase of valinecompared with Si treatment.Organic acid and salicylic acid(SA) addition experiment showed that, the disease incidence of R. solanacearum was higher after citric acid(CA) and malic acid(MA) addition compared with Rs treatment, but reduced by 18.1%~29.7% and 17.4%~28.6% aftersalicylic acidand silicon treatmen. Meanwhile, the amount of R. solanacearumin tomato stems was significantly reduced by 62.5% after salicylic acid addition compared with Rs treatment. In addition, dry weight and fresh weight of tomto were reduced after malic acid addition. Moreover, root surface area and volume were increased in Rs+SA+Si treatment and Rs+CA treatment compared with CK. After 7 days inoculation, net photosynthetic rate, stoma conduction, intercellular CO2 concentration and transpiration rate in leaves were significantly reduced in Rs treatment and Rs+CA treatment compared with CK. For H7996, all organic acid or SA addition treatments could reduce the disease incidence, and Rs+MA treatment and Rs+SA+Si had the best effects, which was 25% lower than that of Rs treatment. However, the fresh weight of shoots and leaves in Rs+MA treatment was lower and the dry weight of shoots and leaves of all addition treatments was lower compared with CK. Additionally, root morphological parameters in all addition treatments were reduced, especially in Rs treatment and Rs+MA treatment. |
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