Integrated management of agrobacterium tumefasciens cavara; the causal agent of crown gall disease in roses (rosa hybrida)

Abstract

Crown gall caused by Agrobacterium tumefasciens is one of the major diseases currently threatening the flower industry in Kenya. The disease significantly reduces production of roses by 50 – 100 % on susceptible rose varieties. Currently, there is limited understanding on the effectiveness of various cultural, biological and chemical control measures used by the flower growers in Kenya. The main objective of this study was to contribute to the increased productivity and quality of marketable roses through integrated management of A. tumefasciens. The specific objectives were to test the effect of various biostimulants such as foltron, biozyme, alexin, hicure and codamine radicular through spray or drench in suppressing A. tumefasciens in roses. The effect of sterilizing agents such as Dettol 0.5 ml / L, 1.0 ml / L and hydrogen peroxide1.0 ml / L, agrowipe (botanic neem extract) undiluted and vegetable oil (fresh fri) undiluted were tested in suppressing crown gall growths. Biological agents: Trichoderma asperellum 0.25 Kg / Ha and 0.5 Kg / Ha and Bacillus subtilis 0.2 L / Ha and 0.4 L / Ha were also tested in suppressing A. tumefasciens in roses. The effect of selected pesticides at various rates as control agents of A. tumefasciens in roses was also tested. Experiments were conducted at James Finlay Kenya LTD Tarakwet farm Kericho County in greenhouse F36 planted with rose variety tropical amazon. Ten galls located 15 cm above the growing media – pumice, were tagged on each treatment replicate and the initial gall diameter measured using a Vanier caliper. The galls were cut using a sterilized roll cut, treatments applied, and the new crown galls growths were measured once a week for twelve months, then cut and weighed using servo weighing balance. The number of fresh crown gall growths on each plot were counted, removed and the diameter measured once a month for twelve months. The number of marketable stems was counted daily from each treatment replicate for a period of twelve months to determine the yield. The quality of stems was determined by sampling 30 stems once a week from each treatment replicate and stem length, weight, and head size measured. Similar experiments were also conducted in pots under controlled environment. Results showed that the various biostimulants increased yield and quality of roses. Botanic neem extract and vegetable oil suppressed crown gall growths and had a higher yield and quality of roses than copper oxychloride. Previcur energy and enrich BM did not suppress A. tumefasciens. Bacillus subtilis and T. asperellum suppressed crown gall growth under controlled environment. It was concluded that integrated management of A. tumefasciens using biologicals, biostimulants and plant extracts increased yield and quality of roses and therefore recommended for use in the flower industry.