This doctoral dissertation presents epidemiological studies on the stability and transmission of citrus bark cracking viroid (Cocadviroid rimocitri, CBCVd) via water, soil, and root intertwining. In the experiments investigating the stability and transmissibility of CBCVd in water, the viroid was confirmed to remain infectious even in 100-fold diluted contaminated plant sap. Furthermore, CBCVd was shown to persist in water, with viroid RNA detectable up to 16 weeks and infectivity confirmed up to the third week. The release of CBCVd from roots into the water and subsequent transmission from infected to healthy hop plants through a contaminated nutrient solution were also verified. In contrast, no transmission was observed in experiments where test plants were irrigated with diluted contaminated plant sap. In experiments involving artificially contaminated sterilized and non-sterilized soils, in which CBCVd-infected plants were initially cultivated, followed by soil sieving and the subsequent planting of healthy plants, as well as in assays using CBCVd-contaminated soils collected from hop fields in close proximity to the roots of infected plants, no evidence of viroid transmission was detected either in the sampled soils or in the test plants. However, in experiments where infected and healthy plants were co-cultivated in pairs, with physical contact restricted to the root zone, CBCVd transmission through root intertwining was confirmed, resulting in the infection of test plants. A correlation was established between the degree of root system intertwinement and the severity of plant infection. This study demonstrates the potential for CBCVd survival and transmission through water sources, contaminated soils, and root system interconnections.
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