[Objective]This study aimed to screen toxin mutant of Dickeya zeae(Erwinia chrysanthemi pv.zeae)and investigate its biological characters.[Method]We obtained a toxin mutant strain D.zeae Ech7-3-42 by using acridine orange as a mutagenic agent and compared their biological characteristics and virulence between the toxin mutant and wild strain.[Result]There was no significant difference in pectin lyase,protease,cellulase and the production of extracellular polysaccharide and lipopolysaccharide,but significant difference in toxin biological activities and virulence.Ech7-3-42 mutant did not produce toxin,as well as the loss of virulence on rice and HR on tobacco,but did not lose the ability to soft rot on potato.Mutant strain Ech7-3-42 can infect rice root and then enriched in the root neck and stalk,but it could not cause rice foot rot.Dickeya zeae(wild and mutant strain)could be detected by PCR in the root neck and below the 1-2 cm long stem area,but could not be detected in the leaves.[Conclusion]We believed that toxin may be one of the important factors for D.zeae virulence on rice.
