Screening and biological characteristics of metalaxyl-resistant isolates of Phytophthora sojae

To understand the characteristics of metalaxyl- resistant strain of Phytophthora sojae,metalaxyl-resistant( Mtr) isolates were obtained by chemical taming from wild- type parent isolate Pmg1. The investigated biological characteristics included resistance level,stability of resistance in the growth of hyphae,colony growth rate and morphology,production capability of zoosporangium and oospores. Morphology of hyphae,zoosporangium and oospores were also observed under optical microscope. Results showed that the resistance levels of Mtrisolates were 3 793. 7,5 581. 7,5 773. 9,4 409. 3 and 5 476. 0 folds of wild- type parent respectively,and the resistance were stably inherited during hyphae growth stage. Compared with wild- type parent Pmg1,Mtrisolates colony growth reduced. The morphology of hyphae,zoosporangium and oospores had no significant differences from those of wild- type parent,but zoosporangium and oospores production decreased significantly. The result indicated that it was easy for P. sojae to produce resistance to metalaxyl,and the resistance of Mtrisolates could remain in hyphae growth stage without metalaxyl. The resistance of Mtrisolates was increased and the production capability of zoosporangium and oospores was decreased,other biological characteristics had no significant change.