With increased restrictions on pesticides, the lack of new active ingredients coming onto the market and increased pesticide resistance, finding ways to reduce treatment applications can save time and money for farmers but also minimises selection pressure on the pathogens. Fera has been working to develop a suite of direct soil tests that will allow farmers to understand the levels and distribution of pathogens in the field and anticipate the risk of disease before planting the next crop. This can help with selection of the most suitable crop and variety for the available land and conditions as well as minimising the need for pesticides, potentially reducing costs and increasing yield. Soil testing enables more precision farming practices to be delivered and it helps farmers and agronomists to understand the biological diversity of soils in relation to both plant health and productivity. By using this approach farmers and growers can demonstrate to their communities their environmental responsibility in creating a sustainable environment.
AHDB–Potatoes estimate that avoidable waste results in an average annual post-harvest loss to the British potato industry of 1 million tonnes due to disease, damage, and failure to meet market specifications. This represents an estimated annual cost of £30m. Using DNA-based monitoring of soil borne pathogens and the latest predictive modelling, the levels of DNA found in fields can be related to the risk of disease development, enabling farmers to more selectively choose the crops and varieties they plant. An increasing range of pathogens that can be identified directly from soil DNA will help with selection of the best management practices to minimise disease risk by helping us help farmers understand the biological diversity of soils in relation to plant health and productivity. Tuber skin blemish diseases are a major cause of wastage in washed ware potatoes due to the high quality requirements of the pre-pack market. Soil-borne diseases can also directly reduce yield in the field. Additional losses result from failure to meet disease tolerances during seed potato certification, influencing demand in national and overseas markets.
Improvements in our methods to extract DNA from the soil means we can now handle larger, more representative, sample volumes up to 500g. This increases the accuracy of detection of soil borne pathogens, many of which can be widely distributed in low populations in the soil prior to planting.
Currently available direct soil tests are usually performed on small samples (<10g) or involve bioassays which are laborious and time consuming to perform. Improvements in our methods used to extract DNA from soil now allow us to significantly increase sample sizes to handle volumes of up to 500g. This allows us to pool representative samples from a given area to increase the accuracy of soil tests where a simple presence/absence answer is required, increasing the likelihood of detection from a single test when populations are in low numbers or clustered, yet still present a significant infection risk.
Sampling for soil-borne pathogens has historically employed a W-shape sampling pattern. This can bean effective sampling strategy when aiming to detect pathogens where the distribution is even across the field such as for black dot (Colletotrichum coccodes). However when the distribution is more clustered in the field such as is the case with Verticium dahliae or Rhizoctonia solani,employing a grid pattern for sampling and testing samples individually can be more effective to understand the risk of disease development in the field.
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