Powdery scab management in South Africa

Transcription

1 Powdery scab management in South Africa Prof Jacquie van der Waals, University of Pretoria Spongospora subterranea f. sp. subterranea (Sss) is an increasingly important pathogen of potatoes globally. Infection of potatoes by Sss results in three diseases of the potato plant, namely, root infection and subsequent reduced nutrient and water uptake, root galling, and powdery scab lesions on tubers. The long-living resting spores of Sss contaminate soil, infect future potato crops and make control of this pathogen particularly difficult. There is currently no method or treatment available that is singly effective in controlling the pathogen; thus growers must implement an integrated disease management strategy to reduce losses. The decision making process in application of an integrated management strategy for powdery scab is summarised in the flow chart in Fig. (modified from Merz & Falloon, 207). Page 2 CHIPS Julie/Augustus 208

2 Tegniese Nuus Nuus Technical News News Field choice More than 5 years previously Previous potato or other host crop Less than 5 years previously Potato cultivar planted Pathogen present Tolerant Susceptible Plant tolerant cultivar NO YES Determination of soil contamination levels by qpcr testing 2 Medium / high risk Low risk Return to beginning for alternative field YES NO Alternative field available? Limit irrigation and N fertilisation during tuber initiation Avoid compacted or poorly drained fields Soil management Plant non-hosts or trap crops in rotation cycle Soil treatments, before planting or in season 4 CHIPS July/August 208 Page

3 . Cultivar susceptibility results from field trials conducted by van der Waals et al Challenger Markies Konsul Sifra Harmony Valor Mondial Nicola Fianna BP Savanna Almera Avalanche Nectar Kikko Electra Mean root galling DI scores Fig 2. Root gall disease indices for cultivars tested in four powdery scab field trials. Numbers above bars indicate the number of trials the cultivar was planted in out of the four. Powdery scab lesions DI scores Eos Konsul Fianna Lanorma Markies Valor Challenger Sifra Diva Synergy Marimba Mondial Harmony Avalanche Elmondo BP Nicola Savanna Kikko Nectar Electra Almera Triomf Fig.. Tuber lesion disease indices for cultivars tested in five powdery scab field trials. Numbers above bars indicate the number of trials the cultivar was planted in out of the five. Page 4 CHIPS Julie/Augustus 208

4 Tegniese Nuus Technical News Table : Host status of Spongospora subterranea f. sp. subterranea in some common weeds and crops planted in South Africa, conducted in pot trials in a greenhouse Botanical name Common English name Host type Advice to growers Acanthospermum hispidum Upright star bur Host Type 2 Eradicate Ageratum conyzoides Billy goat weed Host Type 2 Eradicate Allium cepa Onion Host Type 2 Avoid Avena sativa White oats Host Type 2 Avoid Avena strigosa Black oats Trapping crop Excellent rotation crop Bidens pilosa Black Jack Host Type 2 Eradicate Brassica oleracea Cabbage Non-host Good rotation crop Brassica juncea Indian mustard Host Type Avoid Cleome monophylla Spindlepod Host Type 2 Eradicate Datura stramonium Stinkblaar Host Type 2 Eradicate Daucus carota Carrot Non-host Good rotation crop Euphorbia heterophylla Wild poinsettia Host Type 2 Eradicate Galinsoga parviflora Gallant soldier Non-host No threat Glycine max Soybean Trapping crop Excellent rotation crop Ipomoea plebia Sabi morning glory Non-host No threat Nicandra physalodes Apple of Peru Host Type 2 Eradicate Oxalis latifolia Purple garden sorrel Host Type 2 Eradicate Physalis angulata Wild gooseberry Host Type 2 Eradicate Phaseolus vulgaris Green bean Host Type Avoid Raphanus raphanistrum Oilseed radish Non-host Good rotation crop Secale cereale Rye Non-host Good rotation crop Setaria pumila Annual Timothy grass Host Type Eradicate Setaria verticillata Burgrass Non-host No threat Solanum lycopersicum Tomato Host Type 2 Avoid Sorgum bicolor Grazing sorghum Non-host Good rotation crop Tagetes minuta Mexican marigold Host Type 2 Eradicate Triticum aestivum Wheat Host Type 2 Avoid Zea mays Maize Host Type 2 Avoid Note: This advice relates only to management of Spongospora subterranea f. sp. subterranea. Bear in mind that some of these excellent or good rotation crops may be hosts to other pathogens. CHIPS July/August 208 Page 5

5 Tegniese Nuus Technical News 2. Soil testing by means of conventional or quantitative PCR Conventional PCR can be used to determine the presence of presence of Spongospora subterranea f. sp. subterranea (Sss) in soil (or other media), but this technique is not very sensitive and can give false negatives. Quantitative PCR or ddpcr can be used to quantify amount of Sss in soil or other media. Please contact Prof van der Waals for more information Results from Van der Waals et al. on host range of Spongospora subterranea f. sp. subterranea 4. Soil treatments or amendments A number of pot and field trials have been conducted on the efficacy of various products in reducing final disease caused by Sss. One article has been published on results of pot trials: Simango, K. & van der Waals, J.E Effects of Different Soil Treatments on the Development of Spongospora subterranea f. sp. subterranea in Potato Roots and Tubers in the Greenhouse. Potato Research 60: Other results on the efficacy of calcium cyanamide were presented at the European Association of Potato Research Congress in 207: Van der Waals, J.E., Slabbert, C. & Simango, K Calcium Cyanamide: Potential for Management of Spongospora subterranea f. sp. subterranea? EAPR, Versailles, 7-4 July 207. The results of the most recent field trial, planted in KwaZulu-Natal in 207, cannot yet be made available. Two more field trials have recently been planted, one in Limpopo and the other in the Sandveld, to evaluate the efficacy of various soil amendments and biological control agents in reducing root galling and powdery scab. For more information on powdery scab management, please contact Jacquie van der Waals on , or Jacquie.vdwaals@up.ac.za C Page 6 CHIPS Julie/Augustus 208