Study On Etiology Of Glycyrrhiza Uralensis Roor Rot And Screening Of Fungicides

Liquorice (root of Glycyrrhiza uralensis), the king of Chinese traditional medicine usedfor the treatment of gastric or duodenal ulcers, hepatitis, sore throats, coughs, bronchitis,arthritis, allergies, and cardiovascular disease, was largely dependent on wild resources beforedomestic cultivation establishment in the late1990s. From2002, serious outbreaks of root rotoccurring on cultivated G. uralensis plants in Ningxia, China, have severely affected the yieldand quality of liquorice and been considered as a major threat to commercial production ofliquorice in this area. Therefore, we carried out the research on isolating and identifying thepathogens of G. uralensis root rot. Meanwhile, we screened the control fungicides.The diseased roots of G. uralensis with root rot symptom were sampled in Ningxia,China. Seventy eight fungal isolates were finally isolated from the materials and classifiedinto three categories. The pathogens were identified according to Koch’s postulate. G013andFLR were found to be pathogenic to G. uralensis plants. Based on the morphologicalcharacteristics and sequence analysis of ITS and EF-1α, the representative isolates G013andFLR were identified as Fusarium solani and F. oxysporum, respectively. The host range testshowed that the two pathogens could also infect potato (Solanum tuberosum) and Soybean(Glycine max), but not Wheat (Triticum aestivum Linn.), Cowpea (Vigna unguiculata), Alfalfa(Medicago sativa), Kidney bean (Phaseolus vulgaris), Cucumber (Cucumis sativus Linn.),Eggplant (Solanum melongena L.), Pepper (Capsicum frutescens), Tomato (Solanumlycopersicum), Corn (Zea mays L.) and Cotton (Gossypium spp.). This is the first report of rootrot caused by F. solani and F. oxysporum on G. uralensis in China.Toxicity of five fungicides to F. solani and F. oxysporum causing root rot of G. uralensiswas tested by means of mycelial growth and spore germination in the laboratory. The resultsof mycelial growth showed that the toxicity of the5fungicides to F. solani could be arrangedin descending order: fludioxonil, carbendazim, daconil, thiophanate-methyl, metalaxylmancozeb. The toxicity of the5fungicides to F. oxysporum could be arranged in descendingorder: fludioxonil, carbendazim, metalaxyl mancozeb, daconil, thiophanate-methyl. Theinhibitory effect of fludioxonil was the strongest among the fungicides tested. The results of spore germination indicated that the toxicity of the5fungicides to F. solani could be arrangedin descending order: metalaxyl mancozeb, carbendazim, fludioxonil, daconil,thiophanate-methyl. The toxicity of the5fungicides to F. oxysporum could be arranged fromin descending order: metalaxyl mancozeb, carbendazim, daconil, thiophanate-methyl,fludioxonil. The inhibitory effect of metalaxyl mancozeb was the strongest among thefungicides tested.