PHYSIOLOGICAL RESPONSES OF WATERMELON GRAFTED ONTO BOTTLE GOURD TO FUSARIUM OXYSPORUM F. SP. NIVEUM INFECTION

Abstract

To explore the physiological bases of the resistance of grafted watermelon to Fusarium wilt, watermelon ‘Sumi 1’ (SM1) was grafted onto bottle gourd rootstock ‘Chaofengkangshengwang’ (CFKSW) using the hole insertion grafting method. Grafted watermelon (SM1/CFKSW) and non-grafted plants were planted in soil infested with Fusarium oxysporum f. sp. niveum race 1 (FON 1). Resistance of grafted and non-grafted watermelon and rootstock against Fusarium wilt was evaluated, and the activities of plant defense enzymes, contents of malondialdehyde (MDA), along with activities of pathogenesis related proteases were determined. Results showed that grafted plants (2.3% disease incidence) were more resistant to FON 1 compared to non-grafted ones (95.7% disease incidence). Phenylalanine ammonia lyase (PAL) activity increased in all analyzed plants, but was higher in grafted plants and rootstock than in non-grafted plants up to 120 h after inoculation (HAI). The activities of the antioxidants peroxidase (POD) and polypheno1 oxidase (PPO) significantly increased in all plants within 12 HAI, and activities in grafted plants and rootstock remained at higher levels up to 120 HAI, whereas the level in SM1 gradually decreased. Content of malondialdehyde (MDA) in grafted plants and rootstock gradually decreased after 12 HAI and reached the lowest level at 120 HAI, while in SM1 the MDA content increased since FON 1 inoculation and was much higher than the other two samples at 120 HAI. By 24 HAI and 48 HAI, higher levels of I²-1,3-glucanase and chitinase accumulated in the grafted plants and rootstock, respectively. The grafted watermelon provided an intermediated resistant response to FON 1 under the experimental conditions of this study. These findings suggested that the resistance of grafted watermelon is associated with the high levels of defense enzymes and PR proteases in grafted plants.