Findings from farm visits in the Eastern African Region Presenter - Eunice Mutitu Team; Gladys Maina -Team Leader Eunice Mutitu Paul Ngaruiya
Status of crown gall in the farms visited Crown gall was present in all the farms visited without exception. The farms visited represented most of the flower growing regions in the different countries. In Ethiopia the farms represented the low altitude areas of Debre Zeit at 1900 m asl, medium altitude of Sebeta at 2100 m asl and high altitude areas of Holeta at 2300 m asl. In Kenya the areas visited were Naivasha,Thika, and Nanyuki near Mt Kenya representing the high altitude growing areas. In Tanzania, roses are grown in Arusha and four out of the six farms in the area were visited.
One of the farm visits in Arusha Tanzania
Agrobacterium team members during one of the farm visits
Cont d The severity of crown gall varied from farm to farm severity was influenced by the intensity of control by cultural practices Farms that pruned or removed galls when they appeared and disinfected the tools continually and treated the wounds after removal fared better than those who did little or nothing. Susceptible varieties in the farms where rigorous control hygiene and sanitation practices were not followed, infection was not only found at or near soil level but also up some stems and even on small branches on the bending branches.
Cont d Galls appeared on wounded parts of the plant at the graft union, at the bending points of the rose branches, pruned areas and on top of stumps where harvesting has taken place and on any area bruised and even on natural openings The galls were of different sizes ranging from one cm diameter to as big as 5-6cm.Colours ranged from creamish with a spongy look of the young growing galls to blackish colour with cracked rough surface. The shapes were near spherical.
Young creamish to light yellowish smalll galls
Old,black and cracked gall
Losses due to crown gall Crown gall contributes to economic losses of the rose flower in many ways as follows; Reduced marketable stems Reduced stem lengths Reduced number of flushes per year Shortened lifecycle that averages three years instead of seven years Extra labour to carry out gall removal and control practices Expenditure on many test products for control
Loss due to reduced marketable stems. This is the most widespread loss caused by crown gall. To illustrate this a healthy rose plant has about three growing points each producing 7 stems per year. When crown gall infects the plant one or two of the growing points is blinded thus producing only a fraction of what is expected. Depending on the susceptibility of the variety the loss of stems ranged from about 5 to 50%
Multiple galls with one formed on top of a cut stem thus blinding it Cut stem blinded by a gall
Loss Cont d If a variety produces 200 stems per metre square with 20% stem loss due to the disease then 40 stems are lost which translates to 400,000 stems per ha per year. One stem sells at 20 euro cents which gives a loss of 80,000 euro. If the loss is double that it comes to a loss of 1,600,000 euro per year. This is a great loss in the long term and if the stem length factor is added,the losses are higher.
Shortened lifecycle This is another serious loss where the cycle of the severely infected rose crop is shortened by half. It costs about 50,000 euro to buy new plants and another 50,000 to pay for breeders rights giving a total of 100,000 euro. This cost is exclusive of fertilizers labour and all other production costs incurred to establish the crop before it comes into economic production Such losses can bring an otherwise profitable enterprise down and should not be taken lightly.
Management practices reported by growers The growers reported many and varied management practices that they practice. These can be broadly categorized in four groups namely; Cultural, biological, chemical and resistant varieties
Cultural Removal of galls Pruning of diseased branches Rouging diseased plants especially at early stages Disinfection of pruning knives and working benches Field hygiene. Pruned materials and galls are put in disposable bags and burnt or composted Treatment of recycled water with chlorine or UV Controlling workers in infected houses from moving to work in clean houses
Biological The main biological product cited by growers is the treatment of planting materials with Dygall It is the nonpathogenic antibiotic producing strain of Agrobacterium radiobacter (K84 ). Users were farms that produced their own planting materials and those with commercial nurseries. Being an unregistered product it was difficult to establish where it came from but one farm that also has a commercial nursery in Ethiopia had been allowed to import for own use after trials by the Ethiopian Research Division established that it works on nursery plants. It was reported that drenching regularly with Trichorderma had positive effect on crown gall but this could not be verified because crown gall was still present where the reports were made.
Chemical and related products Chemicals reported by growers included; Kocide or copper oxychloride used as paste on the gall or on the wound AB gel Agrospray Calcium hypochlorite Caustic soda Alliete spray on the galls Previcur drench Olive oil Vegetable oil Chemical products were tried in different farms but the galls would appear in other parts of the plant as the bacteria moved within the plant to other areas especially where there were wounds or in times of stress.
Copper pasted plants
Resistant varieties Most growers reported that some varieties were very susceptible while others were resistant or tolerant to crown gall. Most growers however concurred that most of the varieties grown had some level of crown gall and none was completely resistant. A number of growers reported that they uprooted the susceptible crop prematurely after about three to four years as the crop had become uneconomical due to the high level of infection by Agrobacterium. A number of growers felt that the breeders should take more responsibility in making sure that the varieties they produce are tolerant to Agrobacterium. The nurseries on the other hand should ensure that they only sell clean planting materials treated with Dygall to ensure the disease is not present.
Conclusions Agrobacterium infection on roses is widespread in the Eastern African region where roses are grown Losses range from farm to farm and region to region and are moderate to serious Resistant/tolerant varieties were reported by most of the growers Growers reported use of many products but they were not very effective Copper paste Kocide, was the most widely reported with some success Use of Dygall was constantly reported by those propagating their own materials but growers were vague about the source of the product Growers were keen on getting effective control of the disease and were willing to participate in trials in their farms Growers blamed propagators who sold them infected planting materials for disease in their farms Our report is being eargerly awaited by the farmers
Rose varieties for niche markets
Thank you for listening