Effects Of Three Rhododendron Petals Media On Nonspecific Toxin Of Alternaria Tenuissima

The Baili Rhododendron Nature Reserve of Guizhou province is the largest native Rhododendron forest identified in China and the only nature reserve in China that protects Alpine Rhododendrons,known as the "Kingdom of Rhododendrons and the Earth’s Color Belt." However,in recent years,with climate change and increasing human activities,Rhododendron diseases often occur in the park.Rhododendron petal blight is the most infected and damaging disease in the nature reserve,which seriously reduces the flowers’ ornamental value and reproductive capacity.In this study,we used MR-9,the Alternaria tenuissima isolated from Rhododendron delavayi petal blight,as the experimental material and ensured the consistency of the strains before and after the isolation of single spores by microbial single spore isolation and phylogenetic analysis.PDA was used as a control group to determine the contents of Alternariol(AOH),Alternariol monomethyl ether(AME),Tenuazonic acid(Te A),and Altenuene(ALT),and to determine the total antioxidant capacity(T-AOC),superoxide dismutase(SOD)and catalase(CAT)activities in the bacteria.Referring to the results,200 g petals potato glucose agar medium was selected as the treatment group and ordinary PDA medium as the control group.In addition,the expression of genes in the metabolic action pathway of Cytochrome P450 on exogenous substances and some related genes,such as toxin synthesis,were determined using quantitative fluorescence PCR and provided the scientific basis for the prevention and control of A.tenuissima disease.1.The MR-9 strain isolated from the Rhododendron petal blight was inoculated in 16 kinds of Rhododendron petals medium including PDA,and the effect of the medium on the growth of the strain was observed,and its biomass was measured.The results showed that,compared with the control group,with the increase of Rhododendron petals addition,the growth rate of MR-9 was gradually accelerated and the colony diameter was gradually increased;the edge of the colony was gradually loosened and radiated;the diameter of mycelium in the insert treatment was gradually smaller and the mycelium was gradually thinned;the biomass was gradually increased.It was shown that the components of Rhododendron petals promoted the growth of strain MR-9 but inhibited the increase in mycelial diameter and mycelial number.2.MR-9 was incubated in 16 media including PDA,and its toxicity production in 16 different colors and ratios of petals was determined by high performance liquid chromatography(HPLC).The results showed that compared with the control group,the ALT,AOH and AME of MR-9 under petal-PDA culture decreased with the increase of petal addition,Te A increased with the increase of petal addition,and all four toxins of MR-9under pure petal culture decreased to zero.It showed that the quality of the addition of Rhododendron petals had an inconsistent effect on the toxin.3.Total antioxidant capacity(T-AOC),superoxide dismutase(SOD)and catalase(CAT)activities were measured in MR-9 bacterial bodies cultured in 16 species of Rhododendron petals medium.The results showed that the T-AOC and SOD activities in MR-9 bacterial bodies increased with the addition of Rhododendron petals compared with the control;CAT in MR-9 bacterial bodies showed a trend of increasing and then decreasing with the addition of Rhododendron petals.It showed that the oxidative stress of MR-9 was caused by three kinds of Rhododendron petals,and the stress gradually increased with the increase of petal addition.4.Based on the previous data on the content of MR-9 toxin and the activity of enzymes related to oxidative metabolism,200 g R.agastum +PDA(200 g MR + PDA),200 g R.irroratum subsp.pogonostylum + PDA(200 g HHLZ + PDA)and 200 g R.irroratum + PDA(200 g LZ + PDA)were selected as the control group for fluorescence quantitative PCR was performed to determine the expression of related genes.The results showed that compared with the control group,some genes of MR-9 in the metabolic pathway of P450 exogenous substances(SFA1、TRX1、Mgst1、hmg X、adh)were significantly changed,and the expression of toxin synthesisrelated genes(TAS1、TES1、TES、AKT7、afl V、orf6)were significantly down-regulated.This indicates that Rhododendron petals can inhibit the expression of streptavidin synthesis genes and thus reduce the toxicity production of streptavidin.