Taxonomic And Biological Characterization Of Phoma-related Fungi On Thlaspis Arvense

Thlaspi arvense(Thlaspi arvense L.)is an annual herbaceous plant in the cruciferous family.It is widely distributed in various oilseed rape production areas in China as a weed in fields of oilseed rape.In survey of blackleg of oilseed rape samples in Linzhi of Tibet,and Datong county of Qinghai province,a kind of disease with similar symptoms of blackleg of oilseed rape(caused mainly by Leptosphaeria biglobosa ‘brassicae’和 L.biglobosa ‘canadensis’)was found in T.arvense.It was suspected to be caused by Leptosphaeria biglobosa ‘thlaspii’.In order to clarify the pathogens of the blackleg-like disease on T.arvense and to evaluate its risk to cause blackleg of oilseed rape,we carried out a study to taxonomically and biologically characterize the fungi isolated from T.arvense.The research results obtained are as follows:1.Identity of the fungi from diseased plants of T.arvense was clarifiedA total of 19 fungal isolates were obtained from 26 diseased samples of T.arvense.Morphological and molecular identifications(ITS,LSU,rpb2,tub2)showed that 17 isolates belong to Didymella macropodii,accounting for 89.48%.The remaining two isolates belong to Boeremia exigua,accounting for 5.26%,and Didymella glomerata,accounting for 5.26%.In addition,35 fungal isolates were obtained from 48 diseased samples of oilseed rape showing the blackleg symptoms.Morphological and molecular identifications showed that 30 fungi belong to L.biglobosa ‘brassicae’ and the remaining 5 fungi belong to L.biglobosa ‘canadensis’.2.Basic biological characteristics of the three fungi from T.arvense were determined.D.macropodii showed growth at 5℃ to 28℃ and the optimum temperature was20℃,under which it grew at 3.39 mm/d.Soluble starch and peptone were the most appropriate carbon and nitrogen sources for this fungus growth,respectively.The optimum p H was 7 for its mycelial growth.D.macropodii did not show any antagonistic ability to L.biglobosa.B.exigua showed growth within the temperature range from 5℃ to 30℃ and the optimum temperature was 28℃,under which it grew at 1.51 mm/d.Glucose and sorbitol were the most appropriate carbon source,and peptone was the most appropriate nitrogen source.The optimum p H was 7 for its mycelial growth.Moreover,B.exigua showed a strong antagonistic ability to Sclerotinia sclerotiorum,Botrytis cinerea and L.biglobosa.D.glomerata showed growth within the temperature range from 5℃ to 30℃ and the optimum temperature was 20℃,under which it grewat 3.39 mm/d.Maltose and peptone are the most appropriate carbon and nitrogen sources for mycelial growth,respectively.The optimum p H was 6 for its mycelial growth.Moreover,D.glomerata showed no antagonistic interaction with L.biglobosa.3.Virulence of the the three fungi from T.arvense was determined on oilseed rape.D.macropodii could cause disease on the true leaves and stems of oilseed rape Stem inoculation produced lesions with similar size to that caused by L.biglobosa with production of pycnidia on the surface of lesions.The remaining two fungi(B.exigua and D.glomerata)could hardly cause disease on oilseed rape.These results are helpful for understanding of the fungi related to L.biglobosa on oilseed rape and ultimately useful for monitoring of the pathogens of the blackleg diseases of oilseed rape.