News
Ralstonia solanacearum
14 Jan 2016
Solanum dulcamara, a wild plant that can be infected
Ralstonia solanacearum, the causal agent of brown rot of potatoes, is a regulated pathogen with serious implications for potato production in the EU. A number of races and biovars of R. solanacearum exist. Race 3 Biovar 2 affects potatoes. It also affects a number of solanaceous plants, including weedy species. It is tuber-borne in potatoes and is also water-borne. Symptom development is favoured by warm temperatures and moist soils. Affected plants wilt in the field at the top leaflets and as the disease progresses plants become stunted, yellowed, severely wilted and will eventually die. In tubers, the typical symptom is a brown discolouration of the vascular ring. This eventually rots, and a white slime may appear outside the tuber. The organism can also cause latent infections in tubers, and if these are planted, the disease will transmit to growing plants. The bacteria can spread on machinery and in irrigation water.
Some weedy species, particularly Solanum dulcamara (common name of ‘woody nightshade’ in the UK), are significant for the spread of disease as they can harbour the organism without showing symptoms, and can release it into watercourses, from which there may be abstraction for irrigation. Watercourses may also become infected by discharge of untreated contaminated wash water or waste from imported and infected ware potatoes. Groundkeepers are a potential source of infection. R. solanacearum is a regulated organism in the EU, and control is through inspection and prevention of infected seed stocks entering individual countries. This has been an effective policy, with the discovery of the diseased in seed stocks gradually decreasing in the EU.
A Pocketdiagnostic™ lateral flow device is available for rapid on-site diagnosis of suspected outbreaks, so that appropriate action can be taken to prevent further spread and contamination of water.
Solanum dulcamara, a host plant
Ralstonia solanacearum infecting a potato
A culture of the bacterium Ralstonia solanacearum
Ralstonia solanacearum
Ralstonia solanacearum infecting a potato
Ralstonia solanacearum damaging a tomato crop
New diagnostic developments
20 Apr 2015
Seed and soil-borne downy mildews
A new project at NIAB is focused on the development of molecular diagnostic tests for a number of downy mildew pathogens in seed and soil. Detection of resting spores (oospores) of downy mildew in fields destined for pulse (pea and bean) crops would provide growers with an estimate of field risk of these diseases. Once the level of field risk is known, growers can plan rotations, select cultivars, and decide on seed treatment options to minimise the threat of downy mildew development in the crop. Both pea (Pisum sativum) and faba bean (Vicia faba) are susceptible to distinct downy mildew species. The diseases are difficult and expensive to control with foliar sprays, and avoiding severely infected soils offers a means of avoiding high disease pressure occurring in the crops. The tests may be particularly valuable to vining pea producers, where downy mildew can cause significant loss in produce quality. New “greening” policies in the EU, which will encourage the planting of pulse crops, will increase the need for informed integrated disease management options, so the new diagnostic tests are well timed.
Seed transmitted downy mildew remains unproven in pulse crops, but is thought to be a means of transmission of other downy mildews. The project is thus also exploring detection of Peronospora belbahrii in basil seed lots, and Hyaloperonospora parasitica in salad rocket seed. In each case seed has been suspected as the cause of introduction of downy mildew into production systems.
Unusual seed-borne disease records
20 Apr 2015
Cochliobolus on barley seeds
A higher than usual proportion of barley seed lots tested at NIAB in the UK have been infected with Cochliobolus sativus, the causal agent of a foot root and leaf spot in cereals. The fungus can infect wheat as well, but barley seed lots seem particularly prone, with approximately one third of samples tested in 2014 having the disease. Levels of infection have generally been low, but a few samples have had very high levels, including one where over 70% of seeds were infected in a 200 seed test. At the same time, one or two samples of barley seedlings were submitted to NIAB’s Plant Clinic last autumn with evidence of Cochliobolus infection, including stunting and discolouration at the stem base (foot rot). It is not possible to link the infected seed lots with field outbreaks at this stage. The pathogen may also be soil-borne, on plant debris. Cochliobolus is rare in the UK, and is normally regarded as a disease of warmer countries, but the recent outbreaks may herald a more significant emerging threat, possibly associated with above average autumn temperatures.
Flag or stripe smut on winter rye
A single sample of rye seed tested at NIAB in 2014 was severely contaminated with flag smut (Urocystis occulta) spores. This comparatively rare disease in the UK produces striking symptoms on the plant, with leaves and stems showing long yellowish stripes which burst open to reveal a mass of black spore balls containing teliospores. These are wind-blown, and will adhere to other seeds at harvest, as well as contaminating soil. The spores germinate in the autumn to infect the developing seedling, and the fungus grows systemically within the plant before breaking out from the stripes again as the plant matures. U. occulta only infects rye, and is distinct from the flag smut infecting wheat (Urocystis agropyri). Rye is grown on a comparatively small area in the UK, but is a high value crop with specialist milling markets. Control of stripe smut is important, and seed treatments should be used if seed is contaminated. It is important to identify fields where infected crops have been grown, since the spore balls can persist for several years, and subsequent crops in the rotation should have seed treatment to guard against infection from the soil.
UK Government publishes its forward vision for animal and plant health
18 Dec 2014
This report sets out the findings of a study to determine how the UK can improve its capability in animal and plant health science over the next 10 to 15 years.
This study was undertaken by the Government Chief Scientific Adviser, Sir Mark Walport, and Defra’s Chief Scientific Adviser, Professor Ian Boyd. It was guided by a steering group of experts from the UK government, the devolved administrations, the research councils, industry and academia.
Orobanche crenata (Bean Broomrape) in the UK
12 Sep 2014
In the last weeks we have confirmed the occurrence of an infestation of Bean Broomrape (Orobanche crenata) on a single farm over number fields of field bean in South East England. There's absolutely no reason at this stage to believe that this species will go on to become a major pest in the UK. However it is very important to step-up vigilance and to increase awareness of this pest among farmers and advisors across the UK. This is the second confirmed infestation in two years (these two infestations are currently thought to be unconnected). While there have been sporadic reports of this pest since 1974 in the UK, until now these have all been very localised, occurring in one specific area in the South East. The timing of this situation is very unfortunate since legumes including field beans are likely to become more important in UK rotations as a result of EU 'Greening' legislation.