UBC Theses and Dissertations
Do brassica cover crops influence soil fungal and nematode communities in a vineyard? O'Farrell, Corynne
Brassica plants with biofumigant properties have been used to mitigate soil borne pathogens for years. This is common in till systems where brassicas are incorporated into the soil. The effect of these crops as living mulch on soil microbes is not as well studied. This study compared the response of the soil microbial community to four brassica species, two commonly used in vineyards (Sinapis alba L. (white mustard) and Raphanus sativus (L.) Domin) and two native/naturalized to the Okanagan (Capsella bursa-pastoris (L.) Medik. And Boechera holboelli (Hornem.) Á.Löve & D.Löve (Holbøll’s rockcress)). These cover crops were grown in a vineyard for one growing season. Soil samples were taken at the end of the season for DNA and nematode extraction. The fungal community was analyzed by sequencing of the ITS2 sub-region. Species evenness was higher in brassicas compared to the control. I found no differences in community composition. Changes to the arbuscular mycorrhizal fungi (AMF) community were analyzed by spore count; I found no differences. The nematode community was analyzed by counting total, plant parasitic (PPN), and free-living nematodes (FLN). There were no differences in abundance of nematodes. I found the relative abundance of PPN to be significantly lower in the C. bursa-pastoris and S. alba treatments compared to the control. A greenhouse experiment was conducted to determine if any of the four brassicas act as hosts for fungal pathogen Ilyonectria liriodendri (PARC60 and PARC393), nematode pathogen Mesocriconema xenoplax, or AMF Rhizophagus irregularis. The same four cover crops as well as a grapevine control were grown in soil inoculated with the organism of interest for four months, at the end of which abundance of I. liriodendri and AMF in the roots was measured as well as M. xenoplax abundance in the soil. There were no differences in I. liriodendri colonization between cover crops, but all had some colonization suggesting they may be able to act as hosts. None of the brassicas were colonized by AMF, although B. holboelli was colonized by another fungal endophyte. Abundance of M. xenoplax in the soil was significantly lower in soil of all brassicas compared to the grapevine.
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