Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/11/2000
Publication Date: N/A
Citation: Interpretive Summary: Russian wildrye grass germplasm holds much promise as a species adapted to the 13 to 20 inch precipitation zone of central and northern Great Plains and Great Basin areas of North America. Early reports of high K/(Mg+Ca) in this forage suggested a high potential risk of causing grass tetany in grazing ruminants. This multi-regional study found considerable variability in the K/(Mg+Ca) and a reducing tetany potential (RTP) measured in the broad based germplasm of this species. Based on these findings, breeding and selection will now proceed while simultaneously including the RTP as one of the selection criterion.
Technical Abstract: Grass tetany or hypomagnesemic tetany in cattle results in reduced production or even death in cattle and sheep. Caused by an imbalance in dietary K, Ca, and Mg, the risk is best predicted by elevation of forage K/(Mg+Ca) greater than 2.2 (as chemical equivalents). Russian wildrye (Psathyrostachys juncea (Fisch.) Nevski has been reported to have ratios well above this level. Our objective was to determine the mineral concentration and ratio values for 65 accessions of Russian wildrye to select germplasm sources for low tetany risk and to determine the effects of year, location, and stage of harvest and their interactions with accessions on the mineral concentrations and ratios observed. Seedlings were established in space plant nurseries at Logan, UT, Mandan, ND, and Swift Current Saskatchewan, Canada. Samples were collected at V4 and E2 stages for two years at each site and analyzed for K, Mg, Ca, and P content. There were significant 4-way interactions for both the K/(Mg+Ca) ratio and RTP index. Selection for these traits in Russian wildrye germplasm will require multiple years and locations to adequately characterize accessions, breeding lines, or synthetics. The average K/(Mg+Ca) of individual accessions ranged from 2.17 to 3.02 verifying previous suppositions. Three tetraploid accessions were among the four highest ratio values. Evaluation of simple correlation statistics led to the suggestion that selection for reduced grass tetany risk among Russian wildrye genetic material should be based on the RTP rather than K/(Mg+Ca) index.