Abstract
ABSTRACT Plants synthesize specialized metabolites to defend themselves against pathogens. These active compounds, when isolated and identified, can be used as template for fungicide development. Based on field observations, Heteranthera reniformis (kidney leaf mudplantain) could potentially synthesize compounds with antifungal activity. The goal of this study was to evaluate the fungicidal activity of H. reniformis leaf extracts on Bipolaris oryzae development. The activities of hexane, ethyl acetate, and methanol extracts of H. reniformis leaves were tested on mycelial growth, sporulation, and colony morphology. Due to the highest inhibition of B. oryzae sporulation, methanol extract was chosen for concentration tests. The effect of methanol extract on B. oryzae spore length and germination was also evaluated. Methanolic extract was the most active in inhibiting B. oryzae sporulation. The morphology of the colonies is altered when the fungus grows in medium containing H. reniformis leaf extracts. Higher concentration of methanol extract stimulates mycelial growth and suppresses B. oryzae sporulation. There are reductions in length and number of germinated B. oryzae spores caused by methanol extract of H. reniformis leaves. Methanolic extract has compounds with antifungal activity and should be subjected to bioassay-guided isolation for purification and identification of these active compounds.
Highlights
Irrigated rice cultivation in the 2019/20 harvest in Brazil occupied a total area of 1,286 thousand hectares, where 9,744.5 thousand tons of grains were produced, resulting in an average yield of 7,530 kg ha-1 (CONAB, 2020)
In experiment 1, the mycelial growth index (MGI) was higher when the fungus grew in media containing H. reniformis extracts than in the media without the extract and was totally inhibited by the fungicide (Table 3)
Among the three H. reniformis extracts, the highest mycelial growth was observed in the ethyl acetate treatment, which differed from the others
Summary
Irrigated rice cultivation in the 2019/20 harvest in Brazil occupied a total area of 1,286 thousand hectares (ha), where 9,744.5 thousand tons of grains were produced, resulting in an average yield of 7,530 kg ha-1 (CONAB, 2020). Brown spot caused by the etiological agent Bipolaris oryzae (Breda de Haan) Shoem stands out as one of the main fungal diseases in rice causing relevant economic impact (ROSSMAN; MANAMGODA; HYDE, 2013). This disease affects seed germination, emergence of rice seedlings, reduces photosynthetic rate due to leaf lesions, causes sterility of spikelets, and leads to stained grains, causing losses in yield and in grain quality (BEDENDO; PRABHU, 2016). Chemical control, using fungicides, corresponds to one of B. oryzae management strategies, but there is need for new compounds with different modes of action to fight the increase of plant pathogens’ resistance to currently available fungicides. The importance of discovering new active molecules against plant pathogens is emphasized (KUCK; LEADBEATER; GISI, 2012)
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