Potato Review

52 POTATO REVIEW NOVEMBER/DECEMBER 2019 FOCUS: Rhizoctonia solani R hizoctonia solani – which causes yield-sapping stem and stolon canker and tuber skin blemishes such as black scurf – is now seen as one of the diseases most in need of consideration for potato producers in fresh, seed and processing sectors. While many are all too familiar with the disease and its e ect, a timely reminder of just how damaging it can be to growers if it’s not given attention at the right time, is always worth taking into account. It’s worth taking an in-depth look at the epidemiology and control of this damaging pathogen to maximise output and produce a bright and clean skin nish. Rhizoctonia solani is a pathogen belonging to a large group of fungi known as the basidiomycetes, which also include cereal diseases such as the smuts, bunts and Harper Adams potato expert Dr Matthew Back o ers an in-depth look at the epidemiology and control of Rhizoctonia solani rusts. It has an extremely large host range and causes economically important diseases in countless arable crops around the world, including cereals, oilseed rape, pulses, sugar beet as well as potatoes. Is all R. solani the same? e pathogen species is made up of a number of sub-groups, known as anastomosis groups (AG). e AG often dictates which host or hosts it favours and, in some cases, even the symptoms caused. In the eld, belonging to the same AG means hyphae – the branches of a growing fungus – from each organism are able to fuse together, share resources and help the pathogen thrive. Some AGs are more damaging to potatoes than others. For example, AG 2-1, AG 3 and AG 5 are important for potatoes in the UK. AG 8 has been detected in soil, but not on daughter tubers. ere is variation in symptoms, depending on the AG group or groups present. AG 3 is the most common and causes typical stem and stolon canker and black scurf on tubers later in the season. AG 2.1 causes mainly stem and stolon canker, with less black scurf. AG 8 only a ects roots and might not be picked up by agronomists. What is its lifecycle? e pathogen is one of the great survivors amongst plant diseases. It is a saprophyte, so can rest on decaying organic matter, which allows it to survive on senesced crop and other debris through the winter. In addition, sclerotia – resting structures in the form of a compact mass of mycelium – are formed at the end of the growing season and remain in the soil for a period of time until a suitable host is found. Additional sources of inoculum for following crops include infected seed, volunteer potatoes or groundkeepers and a number of weed hosts. Rhizoctonia solani: An expert recap MATTHEW BACK Researcher at Harper Adams University, specialising in potatoes. Matthew supervises several PhD projects looking at the biology and management techniques of plant parasitic nematodes. He also speaks regularly to the potato industry and at academic conferences. Black scurf caused by Rhizoctonia solani - copyright Blackthorn Arable