Assessment of host specificity among different species of glyphosate synergistic Pythium
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| Authors: | Descalzo, RC; Punja, ZK; Levesque, CA; Rahe, JE |
| Year: | 1996 |
| Journal: | Mycological Research 100: 1445-1453 |
| Title: | Assessment of host specificity among different species of glyphosate synergistic Pythium |
| Abstract: | A total of 39 Pythium isolates representing 14 species of Pythium was assessed for host specificity as glyphosate synergists. This was done using three groups of Pythium isolates from roots of glyphosate-treated bean (PBI), wheat (PWI), and isolates from various glyphosate-untreated hosts. PBI consisted of 15 isolates and included P. ultimum, P. sylvaticum, P. coloratum, P. irregulare and P. group 'HS'. PWI consisted of 14 isolates representing the first four of these species. Pythium from glyphosate-untreated hosts included single isolates representing P. aphanidermatum, P. spinosum, P. paroecandrum, P. hypogynum, P. splendens, P, sulcatum, P. vanterpooli, P. acanthicum, P. arrhenomanes and P. coloratum. The glyphosate synergistic potential of the Pythium isolates was determined by treating a-week-old seedlings growing in soil infested with individual isolates of Pythium with different doses of glyphosate. LD(50) values associated with each isolate were estimated by logistic regression analysis of plant mortalities recorded 4 wk after treatment with glyphosate, and compared with LD(50) values for plants grown in the absence of Pythium. Host specificity was assessed by comparing the glyphosate synergistic potential of PBI on bean and PWI on wheat seedlings, with the potential of these same isolates of PBI on wheat and PWI on bean seedlings. Glyphosate synergistic potential of PBI was also estimated on sunflower and pepper, to test whether PBI were capable of glyphosate synergistic interaction (GSI) on other unrelated dicot yledonous species. Pythium isolates from glyphosate-untreated hosts were tested on bean to determine if Pythium species not represented in the PBI and PWI groups were capable of GSI. The glyphosate synergistic potentials of the PBI and PWI on wheat seedlings were low and inconsistent compared to those observed on dicot plants. AU PWI and 12 of the 15 PBI were glyphosate synergists on beans, and all the PBI were glyphosate synergistic on sunflower and pepper seedlings. All Pythium isolates from glyphosate-untreated sources tested were also glyphosate synergists on bean seedlings. These various tests of glyphosate synergistic potential of Pythium isolates from diverse sources on various plant species revealed no evidence of host specificity among the isolates and species tested. |
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