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UBC Theses and Dissertations

The effect of soil moisture stress on allelopathic influence of hound's-tongue (Cynoglossum officinale L.) Momayyezi, Mina


Little information on the effect of environmental stressors on hound’s-tongue interaction with associated herbivores and grasses is available. This study investigated the effect of soil moisture stress (SMS) on allelopathic influence of hound’s-tongue on a) feeding preference and growth of grasshopper (Melanoplus sanguinipes Fab.) and b) seed germination and seedling growth of Idaho fescue (Festuca idahoensis Elmer), bluebunch wheatgrass (Agropyron spicatum (Pursh) Scribn. and J. G. Sm.), and hound’s-tongue (Cynoglossum officinale L.). Hound’s-tongue plants were grown under four SMS levels [100, 80, 60, and 40% field capacity (FC)] in a greenhouse. On intact hound’s-tongue, grasshoppers preferred mid-aged leaves of plants at 40% FC; whereas there was no consistent relationship between the leaf age and the area consumed for plants at 100% FC. Grasshoppers showed no statistically significant preference for discs excised from old leaves at 100 vs. 80, 60, or 40% FC. However, analyses of pooled results showed their preference for discs from old leaves at 60 and 40% over 100% FC. In bioassays employing discs from young leaves, grasshoppers significantly preferred young leaves at 40 compared to 100% FC. In disc choices between young and old leaves of plants at the same SMS, grasshoppers preferred young over old leaves at 40% FC. The greater preference and higher growth of grasshoppers on younger leaves of plants grown under higher SMS could increase our understanding of the effect of insects’ herbivory on hound’s-tongue under various SMS in rangelands. Inhibitory effects of hound’s-tongue leaf leachate on germination of hound’s-tongue and bluebunch wheatgrass and seedling growth of grasses increased with SMS only in one Petri dish experiment. In soil, hound’s-tongue leaf leachate and leaf residue from plants grown under SMS had either no or inconsistent allelopathic effects on seedling growth of grasses. Hound’s-tongue root elongation was inhibited in soil covered with residue from 40 compared to 80% FC plants. This study suggests that SMS could increase the inhibitory effect of hound’s-tongue mother plants on growth of its seedlings, but it may not have any ecologically significant effect on the allelopathic influence of hound’s-tongue on germination and seedling growth of neighboring grasses in nature.

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