Abstract Detail

Poster Session

Shymanovich, Tatsiana [1], Saari, Susanna [2], Charlton, Nikki D. [3], Young, Carolyn A. [3], Cech, Nadja [4], Faeth, Stanley H.  [1].

Alkaloid variation among epichloid endophytes of sleepygrass (Achnatherum robustum): Consequences insect herbivore resistance .

Epichloid endophytes are well known symbionts of many cool-season grasses that may buffer their hosts from environmental stress.  For example, endophytes may reduce herbivory by production of alkaloids toxic to invertebrates or vertebrates, or they may enhance host drought resistance.  Achnaterum robustum is a grass native to high elevations in the southwestern USA. Its common name, sleepygrass, is derived from the narcotic effects of endophytic ergot alkaloids on livestock. We observed differences in the alkaloids produced in two plant populations, Cloudcroft and Weed, located about 22 km apart in the Lincoln National Forest, NM.  We suspected two different endophyte species in these populations. Genetic analyses revealed major differences in alkaloid genotypes, which were supported by LC-MS chemical analyses. The Weed endophyte produced peramine, chanoclavine, several indole-diterpene alkaloids, and is thus likely Epichloë funkii. However, the Cloudcroft endophyte produced a very different array of alkaloids including the ergot alkaloids ergonovine and lysergic acid amide, and the indole-diterpene, paspaline, and appears to be an undescribed species. In biological assays using the bird cherry-oat aphid, Rhopalosiphum padi, far fewer aphids survived on infected Cloudcroft grasses compared with infected Weed grasses. Based on the difference in chemoprofiles for two endophytes and aphid performance, we hypothesized that the ergot alkaloid ergonovine is responsible for aphid mortality and therefore tested the direct effect of this compound on aphid survival. Oat seedlings free of alkaloids   were cut and placed in an aqueous ergonovine solution.  R. padi aphids were placed on individual leaves for 4 days. Ergonovine concentrations in the leaves were measured after the experiment. Aphid numbers on ergonovine treated leaves were reduced compared to control plants, thus supporting the hypothesis that ergonovine is insecticidal. This is the first study able to show not only feeding inhibition but strong insecticidal effects of ergonovine. Our results show that sleepygrass harbors different endophytes that produce widely varying alkaloid profiles that change susceptibility to insect herbivores. This variation in endophyte genotype and chemical profiles is common within and among host grass populations and species.

1 - University of NC at Greensboro, Biology, 321 McIver St.,, 312 Eberhart Bldg., Greensboro, NC, 27412, USA
2 - University of Copenhagen, Department of Plant and Environmental Sciences, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark
3 - Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK, 73401, USA
4 - University of NC at Greensboro, Chemistry and Biochemistry, 435 Patricia A. Sullivan Science Building, PO Box 26170, Greensboro, NC, 27412, USA

Keywords:
Achnatherum robustum
sleepygrass
endophyte
alkaloids
ergonovine
insecticidal.

Presentation Type: Offered Paper - Poster
Session: P6
Location: Lincoln Room/Kellogg Hotel and Conference Center
Date: Tuesday, June 10th, 2014
Time: 8:00 PM
Number: P6006
Abstract ID:31
Candidate for Awards:None