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Root extracts from Medicago truncatula effectively inhibit rice blast (Magnaporthe oryzae) disease

Kathryn Haydon: University of Arkansas

<div>Plants produce a range of secondary metabolites for defense against insects and pathogens. These include saponins, a structurally diverse group of compounds with varied pesticidal activities that are relatively non-toxic to humans, and therefore prime candidates as natural compounds to control plant disease. Rice blast, caused by the ascomycete <i>Magnaporthe oryzae</i>, is the most serious disease of rice (<i>Oryza sativa</i>), causing up to 30% of global yield losses every year. To determine the effect of natural plant compounds on rice blast development, saponins were extracted from the roots of hydroponically-grown <i>Medicago truncatula</i>. Either crude or C18 column-purified extracts were sprayed on three-week-old CO39 cultivar rice plants, both several hours before and three days after inoculation with a 10<sup>5</sup> spore/ml suspension of <i>M. oryzae </i>strain Guy11. Representative leaves were imaged seven days post inoculation and lesion number and diseased area were quantified. Spore suspensions were also applied to PDA plates containing root extract-soaked filter paper disks, and resulting zones of inhibition were measured. Both crude and enriched saponin extracts significantly decreased lesion number and area on plants, and produced measureable zones of clearing on <i>in vitro</i> cultures. Saponin-enriched extracts performed as well as the synthetic fungicide epoxiconazole. If produced on a large scale, root extracts can potentially be used as alternative means to manage rice blast disease.</div>