Controlling Of Rice Blast Disease By A Plant-derived Natural Compound Thymol

Rice is one of the important crops in China.The rapid increase in population requires greater demand for rice.However,a serious agricultural problem emerges with the increase in the plant area of rice.Rice blast disease is a kind of destructive disease caused by Magnaporthe oryzae.Rice can be infected by this fungus during the entire growth stage(e.g.seedling blasts,leaf blasts,spike blasts,and neck blasts),resulting in dramatic decrease,even nothing return,in rice production.Chemical fungicides(e.g.tricyclazole and orazamide)have been widely used for the control of rice blast disease since 1960s.However,the application of chemical fungicides always leads to fungal resistant problem,environmental pollution,and food safety problem.Therefore,it is necessary to develop novel fungicide with low-toxicity and high efficiency for to prevent rice blast disease.Thymol,a plant-derived natural compound,is main constitute of essential oil from Thymus species.Thymol is an environmental-friendly compound with wide-spread anti-fungal properties.Previous work from our lab suggested that thymol showed strong fungicidal activity for agricultural pathogens.In this study,the effect of thymol on the growth of M.oryzae and the control of rice blast disease was investigated as follows,1.Thymol pronouncedly inhibited the growth of M.oryzae in vitro.Several experiments were performed to test the fungicidal activity against M oryzae in vitro by investigating the changes of hyphal growth and a serious of physiological parameters.The results showed that thymol significantly inhibited the growth of M.oryzae in a dose-dependent manner with EC50 at 27.1 ?g/mL.Compared to the control group,treatment with thymol(at EC50 concentration)resulted in remarkable increases in relative conductivity,glycerol content,MDA content,and pyruvate content in hyphae.The content of ergosterol significantly decreased in thymol-treated hyphae than that of control.These results suggested that thymol was able inhibit the growth of M oryzae by disrupting the integrity of cell membrane and impacting cell metabolism.2.Thymol showed activity of M.oryzae in rice leaves.Tricyclazole is one of most frequently-used fungicides for the control of rice blast disease.The effect of thymol on the pathogenicity of M oryzae in rice leaves was tested in a green-house study.Fresh rice leaves were treated with sterilized water(control),thymol,and tricyclazole,respectively,followed by inoculation with same amount of spores of M.oryzae.Compared to severe disease symptom of blast disease in control group,leaves pretreated with either thymol or tricyclazole showed slight disease symptoms.And thymol showed a little bit better effect on preventing the infection of M.oryzae.The expression of rice defensive genes was further detected.It was shown that thymol,but not tricyclazole,significantly upregulated the expression of PR1 and PR10 in rice leaves.These results suggested that thymol was able to prevent infection of M.oryzae on rice leaves by probably inhibiting the growth of M.oryzae and activating rice defensive responses.3.Thymol(5%)EW(Emulsion in Water)showed high efficiency in the control of rice blast disease in field test.This experiment investigated the controlling effect of thymol(5%)EW(previously developed by our lab)on rice blast disease in field.Rice filed was sprayed with 300×,600×,and 1200× of thymol(5%)EW.Water and 1000× of tricyclazole wettable powder(75%)were sprayed as negative and positive control,respectively.Disease indexes were collected before and after sprayings for the calculation of controlling efficiency.The results indicated that the controlling effect of thymol(5%)EW at 300× was 85.9%,which was similar to that of tricyclazole(82.85%).Thymol(5%)EW at 600× and 1200x showed decreased controlling efficiency as compared to 300×.These results suggested that thymol could be applied in the controlling of rice blast disease with low eco-toxicity.