Resistance to African black beetle (Heteronychus arator) in perennial ryegrass (Lolium perenne L.) infected with AR1 endophyte
Ross, K. M. (2016). Resistance to African black beetle (Heteronychus arator) in perennial ryegrass (Lolium perenne L.) infected with AR1 endophyte (Thesis, Doctor of Philosophy (PhD)). University of Waikato, Hamilton, New Zealand. Retrieved from http://hdl.handle.net/10289/9928
Permanent Research Commons link: http://hdl.handle.net/10289/9928
The insect pest, African black beetle (Heteronychus arator (Fabricus, 1775)) is of considerable economic cost to the New Zealand agricultural industry, in regions where the insect is established and regular outbreaks are now occurring. Selection for Epichloë festucae var. lolii (Latch, M.J. Chr. & Samuels) C. W. Bacon & Schardl, stat. nov. et comb. nov. endophyte-perennial ryegrass (Lolium perenne L.) associations which do not cause toxicity to livestock and with strong resistance to African black beetle (H. arator), would be of significant value to farmers in regions where this pest is a problem. Epichloë festucae var. lolii strain AR1 endophyte does not produce ergovaline, the alkaloid known to deter African black beetle (H. arator), yet pastures infected with this endophyte have moderate resistance to adult African black beetle (H. arator). Research into AR1 is of importance, as to date there have been no reports of toxicity in livestock brought about by consumption of from AR1-infected pastures and in the absence of African black beetle (H. arator) this ‘novel’ endophyte can provide highly productive pastures. AR1 endophyte produces secondary metabolites that are simple indole diterpenes, including paxilline and paxilline-like compounds. The numerous paxilline-like compounds produced by AR1 are detected by a paxilline ELISA (enzyme linked immunosorbant assay) and quantified collectively as paxilline immunoreactive equivalents. Earlier work suggested that these paxilline-like compounds could be the bioactive, or linked-marker associated with the bioactive compound(s), that provide some resistance to adult African black beetle (H. arator) feeding. The overall aim of this research was to determine if increased concentration of paxilline immunoreactivity was associated with a reduction in feeding damage using a series of adult African black beetle (H. arator) feeding trials on closely related AR1-infected perennial ryegrasses (L. perenne). A negative relationship was established between feeding damage from adult African black beetle (H. arator) and plant pseudostem paxilline immunoreactivity in AR1-infected perennial ryegrass (L. perenne) post exposure to beetles. However, it was not a simple relationship being complicated by: i) paxilline immunoreactivity ￼not reflecting endophyte concentrations; ii) the influence of cultivar on the expression levels of paxilline immunoreactivity; iii) the effect of African black beetle (H. arator) presence on expression levels of paxilline immunoreactivity; and iv) the paxilline ELISA quantifying the complete complex of paxilline-like compounds and not simply those that are bioactive. The highest concentrations of paxilline immunoreactivity were found in plant undamaged pseudostem and were not strongly correlated with the lower concentrations found in herbage. Therefore undamaged pseudostem is recommended as the section sampled if the entire plant pseudostem was not available. Low levels of feeding from adult African black beetle (H. arator) accentuated plant tiller production. However, the negative effects of high feeding pressure still affected plants four weeks post-exposure to beetles, with reduced paxilline immunoreactivity production and plant tiller numbers. Adult African black beetle (H. arator) were able to compensate the deterrent effects of AR1 once an endophyte-free food source was available. Results from this research contribute towards further understanding the bioactivity of AR1 endophyte against adult African black beetle (H. arator) and will underpin further research into the chemical basis for this resistance. The paxilline ELISA could potentially be used for screening E. festucae endophyte ryegrass associations that produce unknown compounds which deter African black beetle (H. arator) and which do not cause toxicity to livestock.
University of Waikato
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