Submitted to: Seed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2008
Publication Date: 10/26/2008
Citation: Clement, S.L., Martin, R.C., Dombrowski, J.E., Elberson, L.R., Kynaston, M., Azevedo, M.D. 2008. Neotyphodium endophytes in tall fescue seed: infection frequencies after seed production and prolonged cold storage. Seed Science and Technology 36:710-720. Interpretive Summary: The USDA-ARS seedbank at Pullman, Washington is one of the world's largest, maintaining over 17,000 accessions of temperate grasses for U.S. and world agriculture. Seeds of these grass accessions are routinely acquired by American and foreign scientists to develop new cultivars. Additionally, these public and industry scientists acquire this material to retrieve seed fungi in the form of diverse fungal endophytes (called Neotyphodium fungi). While some grass-endophyte associations produce alkaloid chemicals that are toxic to grazing animals like cattle and sheep, some endophyte strains in grass hosts do not produce toxic alkaloids. These 'non-toxic' endophyte strains have been deliberately sought by scientist to resolve mammalian toxicity problems, and they have found these strains in grass collections at the Pullman seedbank. Curators at the Pullman seedbank must preserve this important microbial germplasm (Neotyphodium endophytes). This cooperative research between USDA-ARS scientists in Pullman and Corvallis, Oregon, determined that seed-regeneration activities and procedures at the Pullman seedbank are optimal for preserving viable endophytes. Another aspect of this multi-year study documented the presence of viable endophytes in seed of 20 Mediterranean tall fescue accessions stored for four to ten years in the Pullman seedbank. However, the results also suggested a decline in endophyte viability in some accessions during seed storage. This research is important because it demonstrates that stakeholders seeking diverse endophytes strains from the Pullman seedbank can have increased confidence that regenerated tall fescue seeds contain viable endophytes. On the other hand, the apparent loss of endophtye viability in some accessions indicate that additional research is required to identify optimal storage conditions for maintaining endophytes in seed from diverse accessions.
Technical Abstract: This research quantified frequencies of Neotyphodium-infected (E+) tillers and mature seed from E+ plants of two wild tall fescue (Lolium arundinaceum (Schreb.) S.J. Darbyshire (= Festuca arundinacea Schreb) accessions from the Mediterranean basin, and stored in the seed bank at the USDA, ARS Western Regional Plant Introduction (PI) Station, Pullman, Washington USA. Tiller infection rates were high on glasshouse (>97%) and field (100%) plants of each accession and over 99% of the seed from E+ plants of both accessions harbored viable Neotyphodium endophyte. Seed germination was either slightly improved (Morocco accession) or not affected (Italy) by endophyte infection. A wide range of temperatures (-27°–37°C) did not adversely impact endophyte transmission rates in the field plants. These results indicate that E+ wild tall fescue plants are capable of near perfect vertical transmission of viable endophyte into seed. They also suggest that viable endophyte is retained with current seed-regeneration practices at the Pullman PI Station. This study also documented viable Neotyphodium infection frequencies (16–100%) in plants grown from seed of 20 Mediterranean tall fescue accessions stored for four to ten years in the Pullman seed bank. However, low post-storage infection frequencies, in comparison with their high initial viability levels, suggested a decline in endophyte viability for some accessions during seed storage. Additional evidence for diminishing endophyte viability levels in some accessions was provided by Polymerase Chain Reaction (PCR), immunoblot, and microscopic seed assays, the results of which suggested the presence of high amounts of nonviable endophyte in their seed.