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Abstract

Potato cyst nematodes are responsible for ca.26-50 million pounds of losses to the UK potato industry each year. With few chemical control options remaining, it is imperative that sustainable crop protection methods are identifyed and developed to ensure food security, whilst minimizing impact on soil health. Use of chitinous amendments for PCN management aligns to Sainsbury’s Net Zero target through using by-products from various industries and their interests in sustainable systems, IPM and soil health. Chitin by-products come from a variety of streams.

Description

Potato crops are subject to a range of pests and diseases, but none are more damaging than potato cyst nematodes (PCN) (Globodera spp.), which occupy around 48% of the potato growing area in England and Wales (AHDB, 2019) and 13.2% of production land in Scotland (Pickup et al., 2019). There are many concerns associated with PCN, including their long-term survival in soil (20+ years), severe yield loss in unprotected crops (up to 80%), the legislation surrounding seed production and diminishing chemical control options. Globodera pallida, the dominant PCN species, is more challenging to manage, due to fewer commercially acceptable resistant varieties and its tendency to hatch over a longer period than its sibling species G. rostochiensis, thus escaping the activity of nematicides applied at planting. Since 2007, three granular and two fumigant nematicides have been banned from use, whilst the remaining granular product may be lost in 2023. Various alternative crop protection options are being investigated including brassica biofumigants and trap crops. A further option in PCN management is the addition of chitinous amendments to soil. These types of approaches are regarded as ecological and should be given greater priority than chemical interventions according to the IPM pyramid.

Chitin is the second most abundant polysaccharide in the world and is present in a range of industry by-products including shellfish waste composed of crustaceans such as langoustines, crabs and lobsters, spent mushroom compost (SMC) and the frass and pupal cases associated with black soldier fly (BSF) production. The benefits of applying chitin, chitosan and chitin rich organic products to soil are discussed and evaluated in a recently completed AHDB/BBSRC report by Back & Evans (2022). In particular, soil-borne pests and pathogens can be reduced with chitin including fungi, oomycetes, protists and nematodes. Chitin and chitosan (the deacetylated form of chitin) are thought to suppress pathogens by 1. Increasing populations of microbes that secrete chitinase; fungi and nematodes contain chitin in their cell walls and eggshells respectively, 2. Causing the release of ammonia, which is toxic to pests and pathogens, 3. Enhancing the activity of antagonists such as Bacillus subtilis, which secrete chitinase, 4. Inducing plant resistance by acting as a plant defense elicitor. Unpublished work by HAU (Adekoya, 2020) identified that 64% of 107 experimental observations on chitin and plant parasitic nematodes were conducted on root knot nematodes, with a further 15% on cyst nematodes. Of the few studies conducted on PCN, Ebrahimi et al. (2016) recorded reductions in egg numbers and further reductions in the viability of the encysted eggs following applications of crab shell compost. Whilst this study used field soil, it was conducted under controlled conditions.  Angus Horticulture Ltd., a company based in Angus, Scotland, producing compost from a mixture of wood chip and shellfish waste, has independent field data from different sources, demonstrating soil benefits including pest and pathogen reductions. Indeed, known soil benefits include increased organic matter, plant growth stimulation and promotion of mycorrhizal activity (Sharp, 2013; De Corato, 2021).

Objectives & approaches: 1. Evaluate the ability of chitinous soil amendments to suppress PCN populations in controlled conditions and within potato rotations:  Glasshouse and field experiments will compare pure chitin and chitosan amendments against organic by-products. We will assess changes in PCN populations by determining egg number and through measurement of trehalose content in the egg shells. Trehalose is a sugar found in the perivitelline layer of egg shells of PCN; loss of trehalose is indicative of egg mortality. Analysis will include assessing the impact of chitin on the performance of the potato crop through measuring ground cover and yield. Variables to be assessed will include timing and quantity of amendments.  2. Develop and optimise the method for evaluating chitinase activity E.g. using colorimetry such as that detailed in Ferrari et al., (2013). 3. Investigate mechanisms of PCN suppression using the chitinase assay discussed above and/or measurement of ammonia E.g. Martins et al. (2021). 4. Develop methods for optimising and combing the use of chitinous soil amendments with other non-chemical methods, including applications with biopesticides such as Bacillus subtilis or mycorrhiza and cover crop species. 5. Evaluate, the impact of organic soil amendments on soil health using bioindicators such as collembola and/or earthworms.