Impact of Rhizobium radiobacter Inoculation on Physiological Stresses and Nutrients of Grafted Rose (Rosa hybrida L.) Cultivars

The manifestation of physiological stresses can lead to a variety of unfavorable outcomes such as oxidative stress, imbalances in nutrient homeostasis, and in extreme scenarios, plant mortality. Rose is a popular ornamental plant that exhibits vulnerability to crown gall, a pathological condition primarily attributed to the presence of Rhizobium radiobacter (also known as Agrobacterium tumefaciens). In the present study, impacts of R. radiobacter inoculation on the graft strength, nutrient levels, and oxidative stress of two distinct rose cultivars ('Angelina' and 'Pearl') in relation to their sensitivity to R. radiobacter were investigated. Rhizobium radiobacter was inoculated at the grafting site, and the grafted plants were grown for a period of 90 days. The findings indicated that the presence of bacteria in the samples led to more robust graft unions, owing to the development of enlarged calluses (crown galls) that functioned as a potent inherent adhesive. The inoculation of R. radiobacter reduced shoot biomass, while promoted root biomass. The nutrient levels in the infected samples were higher than their levels in the non-infected samples. Consequently, the non-infected samples exhibited higher relative water content (RWC) than the RWC of infected samples. The infection caused by R. radiobacter-induced oxidative stress, as evidenced by the elevated levels of malondialdehyde and electrolyte leakage. Following to bacterial infection, decline in catalase (CAT) and increase in guaiacol peroxidase (GPX) activity were detected. The inoculation of R. radiobacter into the host plant altered the sink/source balance, leading to more accumulation of nutrients in the leaves. Occurrence of oxidative stress, reduction in leaf area, and shoot biomass in the inoculated 'Angelina' cultivar were indicative of higher susceptibility of this cultivar to R. radiobacter infection, while, 'Pearl' cultivar exhibited higher resistance to R. radiobacter infection, as evidenced by its higher: soluble carbohydrates, soluble protein, and proline contents, and GPX activity compared to 'Angelina' cultivar.

Automated summary

This study investigated the effects of Rhizobium radiobacter inoculation on graft strength, nutrient levels, and oxidative stress in two rose cultivars ('Angelina' and 'Pearl') in relation to their sensitivity to R. radiobacter. The findings showed that R. radiobacter inoculation led to stronger graft unions and higher nutrient levels but also caused oxidative stress. Additionally, the 'Pearl' cultivar exhibited higher resistance to R. radiobacter infection compared to the 'Angelina' cultivar.