Identification and Management of Crown Gall Disease (Rhizobium sp.) of kiwifruit Actinidia deliciosa Liang and Ferguson) in Dolakha, Nepal

The crown gall disease of kiwifruit, caused by the bacterium Rhizobium (formerly Agrobacterium), is a significant plant disease that affects the roots and stems, leading to tumor-like growths. In June 2022, a survey of kiwifruit nurseries was conducted in Boch, Bhimeshwar, Dolakha. The survey covered 20 nurseries from three farms to observe the incidence of crown gall disease in the area. Subsequently, samples were collected and analyzed at the laboratory. The findings reveal that the isolated bacteria produced distinct creamy white colonies on PDA and exhibited a positive KOH test and Gram-negative staining. Pathogenicity tests confirmed the presence of crown gall symptoms in carrot disks and tomato seedlings. Hence, the bacterium was found to be crown gall disease of kiwi caused by Rhizobium sp. Then, field research was conducted in a two-factorial randomized complete block design with three replications at the Temperate Fruits Rootstock Development Centre at Boch, Dolakha to find out the effective control measures for crown gall disease (Rhizobium sp.) management in Kiwifruit nursery. The first factor included six treatments (Kasu B, Hydrogen peroxide, Cuprex, Streptocycline, Kasu B + Streptocycline and untreated control). The second factor included three varieties of Kiwifruit (Hayward, Monty and Allison). In the field experiment, observations were taken on plant height, root length, colony count before and after the treatments, number of galls, and size of galls. The interaction of varieties and treatments on the disease management was significant (p<0.05). The highest bacterial population reduction (100%) was found in the plots of Allison treated with Streptocycline + Kasu B followed by Streptocycline-treated plots of Hayward. The Streptocycline showed the lowest gall numbers (2.67 ± 0.69) in Allison followed by Kasu B (6.76 ± 0.78). The Cuprex-treated Allison variety showed the smallest gall size (0.23 ± 0.40 cm) which was at par with Cuprex-treated Hayward (0.29 ± 0.50 cm) and Monty (0.32 ± 0.56 cm) varieties. In overall, Allison variety was found comparatively less susceptible to crown gall disease and Streptocycline was found to be effective in mitigating crown gall disease in Kiwifruit compared to other treatments.