Using cover crops to mitigate vine decline and reduce pathogens in vineyard soils

Wine grape production is an important economic asset in many nations, however a significant proportion of vines succumb to soil-borne pathogens, reducing yields and causing economic losses. Young vine decline (YVD) occurs when grapevines experience stunted growth, reduced yield, delayed fruiting, and root necrosis, often leading to dieback in vineyards worldwide. These symptoms are largely due to soil-borne fungal pathogens including Ilyonectria species which may be present in the soil or brought to the area by contaminated nursery plants. Restrictions in fungicide use and high-density planting regimes have exacerbated the incidence of YVD in vineyards. Public demand for low-impact sustainable agriculture has encouraged researchers to test alternative approaches to combat soil-borne diseases. Cover crops are plants that are grown alongside main crops or during non-production seasons in order to maintain and enhance soil composition. These plants provide several well known benefits and also may serve as a line of defense against soil-borne fungal pathogens by producing volatile root exudates and/or harbouring suppressive microbes. I tested whether cover crop diversity and provenance affect the persistence and infectivity of YVD pathogens in agricultural soil. In a greenhouse experiment, I inoculated soil with a 106 conidia spore suspension of Ilyonectria liriodendri and then conditioned soil with cover crops for several months to investigate changes in pathogen abundance and fungal communities via Illumina sequencing. After removal of cover crops, Chardonnay cuttings were introduced and grown for a short period to analyse growth responses and disease symptoms. When grown alone, white mustard was the only cover crop associated with reductions in necrotic root damage and abundance of Ilyonectria in Chardonnay roots. The suppressive effects of white mustard largely disappeared when paired with other plants or when grown with all other plants in the high diversity treatment. Soil fungal communities under white mustard were similar to buckwheat and wheat but not clover. These results highlight the suppressive potential of white mustard and its value as a biofumigant cover crop in vineyards.Arts and Sciences, Irving K. Barber School of (Okanagan)Biology, Department of (Okanagan)Graduat