Abstract
Abstract: The objective of this work was to purify and standardize the rue (Ruta graveolens) extract and evaluate its effect on Magnaporthe oryzae as an alternative to the integrated management of rice blast. The drug was characterized, the liquid extract was obtained, and the methodology for quantifying the standard markers psoralen and bergapten was validated. Rue extract and the markers, solely or in combination, were assayed in vitro, as well as in greenhouse conditions, for their ability to suppress leaf blast, by the evaluation of mycelial growth, conidial germination, and appressorium formation. Rue extract inhibited M. oryzae mycelial growth (100%), conidial germination (LD50=0.237 mg), and the appressorium formation (LD50=0.121 mg); besides, the extract reduced leaf blast severity by 80.84%. Fluorescence microscopy showed that rue extract did not damage M. oryzae cell wall and plasma membrane, indicating another mode of action. Rue extract has a great potential for controlling rice leaf blast.
Highlights
Rice blast is considered by plant pathologists as the most important disease caused by fungi (Dean et al, 2012) and result in up to 100% grain yield losses depending on weather conditions and on cultivar resistance (Prabhu et al, 2009)
The disease cycle begins when conidia contact the host and penetrate the leaf tissue by rupturing the cuticle via penetration peg of the appressorium, a specialised structure differentiated at the extremity of the germ tube (Wilson & Talbot, 2009)
The percolate flowed at 1 mL min‐1, and psoralen and bergapten contents were analysed by thin layer chromatography (TLC) until plant drugs were exhausted
Summary
Magnaporthe oryzae (Catt.) B.C. Couch (anamorph, Pyricularia oryzae Cav.) causes rice blast, a highly destructive disease which is spread worldwide (Ebbole, 2007). Rice blast is considered by plant pathologists as the most important disease caused by fungi (Dean et al, 2012) and result in up to 100% grain yield losses depending on weather conditions and on cultivar resistance (Prabhu et al, 2009). The initial leaf blast symptoms are characterized by small necrotic brown lesions, which later become elliptical with a grey or white centre. These lesions coalesce and cause partial or total death of the affected leaf (Prabhu & Filippi, 2006) in five days, while starting another disease cycle
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