Management of crown gall disease of roses using agrobacterium radiobacter, corn oil and copper hydroxide and oxychloride in Kenya
Murugi, Gitari Judith
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The cut-flower industry is one of the fastest growing sub-sectors of the horticultural industry contributing significantly to the continued growth of Kenyan economy. Roses are the most popular cut-flowers world-wide. Rose flower production in Kenya faces significant challenges particularly with regard to pests and diseases. Crown gall disease caused by A. tumefaciens is one of the limiting factors in the production of roses. The disease is widespread in rose flower farms and nurseries in Kenya causing a substantial loss of yield and therefore there is an urgent need to manage it. The study aimed at evaluating the antagonistic activity of naturally occurring A. radiobacter isolates from different flower farms in four ecological regions notably Nanyuki, Naivasha, Murang‟a and Timau against A. tumefaciens. In addition, Elianto oil, copper hydroxide (kocide 2000) and copper oxychloride were evaluated as chemical control agents Field survey was conducted over the period between August, 2012 and October, 2012. Gall and soil samples were collected during the period between November, 2012 and December, 2012. Laboratory work was conducted at Kenyatta University, Microbiology Department Laboratory while greenhouse experiments were carried out at Branan farm (Muranga County). The gall and soil samples were isolated on Yeast Extract Mannitol Agar supplemented with Congo red and Yeast Extract Peptone media. Colony morphology and standard biochemical tests including: Gram staining, catalase test, urease test, salt tolerance test, 3-ketolactose test, motility test and H2S production were performed for identification and confirmation of the isolates based on their Gram staining and cultural characteristics. Kirby-Bauer disc diffusion technique was used to determine antimicrobial sensitivity patterns of bacteria to antibiotics. Carrot disc assay test was conducted on A. tumefaciens for pathogenicity test while in vitro antagonistic test was done on A. radiobacter. In the greenhouse experiments, pathogenecity test was carried out using A. radiobacter and A. tumefaciens isolates on four varieties of rose plants. Minimum incidence (6%) of crown gall was observed on Topsun, Fuschiana and H3O rose varieties when A. radiobacter isolates were applied compared to 54% in the control. In Furiosa variety, there was minimal incidence of crown gall disease on treated plants and in control. There was no significant differences (P>0.05) in the interaction between rose flower variety and treatments on the number of plants with galls. In chemical control, there was no significant difference (P>0.05) in the interaction between treatment and variety with regard to number of plants with galls. The study confirmed that A. radiobacter had the potential in the management of crown gall disease on rose flower plants. Therefore, the study recommends the use of A. radiobacter (biological control agent) and chemical control methods to minimize spread of the disease.