The effects of commercial seaweed extracts on disease resistance and crop yield

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Philip, Benjamin Ross
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University College Cork
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In the face of climate change, crop production faces many challenges, such as increased productivity per unit land area under increasingly harsh climatic conditions, with far less dependence on fossil fuel-based aids such as fungicides. Seaweeds are a sustainable resource which have shown potential in crop production, but there is a shortage of independent research on commercial seaweed extracts. The research described in this thesis investigated the effects of three seaweed extracts (SWEs), Algita 50, Super 50 (both from Ascophyllum nodosum) and Nematec (from Laminaria digitata) on oilseed rape. Under greenhouse conditions, Super 50 and Nematec induced both local and systemic resistance to the generalist necrotroph Sclerotinia sclerotiorum and the generalist hemibiotroph Rhizoctonia solani, but only local resistance to the specialist necrotroph Alternaria brassicicola, whereas Algita 50 induced resistance to only R. solani. Both root drench or foliar application of the SWEs resulted in similar chlorophyll content on local and systemic leaves after inoculation with R. solani. In a separate study, root drench application of the SWEs resulted in significantly lower potato tuber black-scurf compared to a foliar application. The level of resistance to R. solani in oilseed rape induced by foliar application of any of the three SWEs prevented death of the plant, whereas none of the SWEs induced resistance against this pathogen in potato. Under field conditions, Super 50 treatment resulted in reduced infection by A. brassicicola in both the leaves (scored 12 d after inoculation) and pods (scored 28 d after inoculation), suggesting a long-lived effect. One foliar spray application of Algita 50 resulted in an increase in net profit of €716 ha-1 in the absence of disease and a break-even yield the presence of disease. Different SWEs used different routes to achieve increased yield, including delayed senescence (Nematec), reduced pod shattering (Super 50) and reduced abiotic stress. Foliar treatment with Algita 50 resulted in significantly greater seed yield, seeds m-2, thousand-seed weight and seed oil content compared to the control. Overall, it was clear that different extraction methods and different seaweed species produced SWEs with different crop characteristics, so that farmers could use specific SWEs to target particular desirable traits, although a down-side was that there were significant differences in efficacy between batches of the same SWE.
Ascophyllum nodosum , Laminaria digitata , Sclerotinia sclerotiorum , Rizoctonia solani , Alternaria brassicicola , Seaweed , Extract , Disease , Yield
Philip, B. R. 2017. The effects of commercial seaweed extracts on disease resistance and crop yield. PhD Thesis, University College Cork.