Identification and Fungicides Screening of Lasiodiplodia theobromae Causing Leaf Spot of Agave sisalana

Objective Agave sisalana is an important hemp crop in China. A kind of leaf spot of sisal disease occurs in Zhanjiang area of Guangdong Province, which can lead to a large area of necrosis of sisal leaves and affect the yield. The identification and fungicide test of the pathogen causing leaf spot of sisal were conducted so as to control the disease effectively.

Method The fungi were isolated from diseased sisal on PDA medium by tissue isolation method, and the pathogen was obtained after the validation of Koch' s rule. The pathogen was identified with the morphological characteristics of the fungus and its ITS (internal transcribed spacer) sequence. Furthermore, the sensibilities of different fungicides to the pathogen were determined by mycelial growth rate method.

Result It was found that the conidia, isolated from the leaf spot of sisal in Zhangjiang area, were oval, single spore, dark brown, separated by a middle septum, which was similar to the combination of two cells, and the ITS sequence had more than 99% of homology with Lasiodiplodia theobromae. The fungicides results showed that chlorothalonil, hexaconazole, prochloraz, tebuconazole, difenoconazole, fipronamide and thiophanate methyl all had good inhibition effect on Lasiodiplodia theobromae, among which chlorothalonil had the best inhibition effect with EC₅₀ value of 0.000132 μg/mL.

Conclusion The pathogen isolated from leaf spot of sisal in Zhanjiang area was identified as L. theobromae, which was sensitive to chlorothalonil, hexazolol, imitamine, tebutazolol, benzoethycloazole, flupyramide and methyl thiobacillam.