‘Guardians from the Grass’; Harnessing fungal endophytes to suppress plant parasitic nematodes of potatoes

Globally, ca.374 million tons of potatoes are produced per annum, providing a staple food that is rich in carbohydrate, protein, fibre and vitamin C (FAO, 2024). Several plant parasitic nematodes pose a threat to potato crops cultivated in the UK. Potato cyst nematodes (PCN; Globodera pallida and G. rostochiensis) are quarantine pests that prevent seed production in contaminated land and limit yields in susceptible ware crops. Stubby root nematodes (SRN; Trichodorus and Paratrichodorus spp.) are equally important, especially on lighter soils (80-90% sand fraction), where they are more prevalent. Root feeding by SRN can cause stunted growth and patchy emergence. Additionally, the nematodes can vector tobacco rattle virus (TRV), causing malformations and spraing (necrotic arcing in the flesh of tubers). Management of PCN and SRN typically requires nematicides, such as fosthiazate and fluopyram. While fosthiazate is registered until July 2029, there are concerns about its future in light of revocation of two similar compounds in the last 5 years (ethoprophos and oxamyl). Epichloë spp. are endophytic fungi, that form symbiotic relationships with grasses. The endophyte colonises the host apoplast, taking nutrition through cell walls. Grasses with Epichloë spp. benefit from physiological benefits (increased growth), antioxidant production, which minimises stress, and protection against pests and pathogens via secreted alkaloids e.g. lolines. Alkaloids secreted by Epichloë, accumulate in roots, shoots and seeds, and can be released through root exudates. These compounds have been recorded to be nematostatic and nematicidal to plant parasitic nematodes (Mwangi et al., 2024). Unpublished work from Harper Adams University (Nyambura Mwangi - PhD) revealed that extracts from Festulolium grass and seed infected with Epichloë increased the mortality of the SRN Trichodorus primitivus, under in-vitro conditions. Differences in mortality were observed with extracts collected from grasses at different periods after planting; 8-week-old plants gave the greatest effect (1250-5000 µg/ml resulted in ca.70-100% mortality). Similarly, grass that was mechanically bruised increased the degree of mortality. Furthermore, modest reductions (ca. 24% reduction) in PCN egg viability were observed where cysts were buried in potting medium where Epichloë infected grasses were cultivated and incorporated (Williams and Back, unpublished). Although these findings are encouraging, further work is required to validate the strategy under UK field conditions and determine its optimal application