Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2001
Publication Date: 5/1/2002
Interpretive Summary: Seedling root fluorescence (SRF) was first discovered as a difference between perennial and annual ryegrass in 1929 and implemented as a seed test in the U.S. in the early 1940s. It was never meant to be an infallible test of differences between the two grasses, but to be used as a guide for problems in questionable seed lots. Yet in 1991, SRF was implemented as a characteristic to describe ryegrass varieties (VFL) and has been regarded as an infallible difference since then. The Federal Seed Act mandates that any SRF above the VFL of a perennial ryegrass is automatically annual ryegrass. The fact is that biologically this is NOT true, but the requirement costs grass seed growers about $7 million in discounted seed sales. This research work on SRF at the National Forage Seed Production Research Center started in 1990 as part of Don Floyd's Ph.D. thesis for Oregon State University. This paper reports the first time that SRF expression is influenced by the conditions of the ryegrass plant when it is grown for seed production. While we did not determine the cause of the variation, the work is enough, along with other studies on the variability of SRF in the production environment, to demonstrate that the discounts for "other crop" applied to growers perennial ryegrass seed crops is not warranted.
Technical Abstract: Seedling root fluorescence (SRF) has been used since the early 1940s to discriminate Italian (annual) ryegrass (Lolium multiflorum Lam.) from perennial ryegrass (L. perenne L.). Generally, roots of Italian ryegrass fluoresce under ultraviolet light, while those of perennial ryegrass do not fluoresce, but the trait has readily introgressed from Italian to perennial. Breeders determine fluorescence levels of new ryegrass cultivars before they enter seed certification programs. The objective of this study was to ascertain genetic change for the expression of SRF during generations of seed multiplication. Four ryegrass populations, constructed to have low, medium, and high SRF levels, were increased independently for three generations at each of three Oregon locations (Aurora, Corvallis, and Madras). SRF was measured initially, and for each generation cycle at each location. There were significant differences in SRF among locations within populations and for seed production generation within locations. One population, for example, initially at 11% SRF increased to 36% over the three generations of seed multiplication at Corvallis, but decreased to 8 and 2% at the other two locations. The other three populations responded differently, showing large population X location and population X generation interactions for SRF expression. Location of increase and the seed production generation must be examined and carefully considered when describing fluorescence levels of cultivars for seed certification purposes. The large amount of variation associated with environmental influences indicates SRF is a poor characteristic to describe and predict ryegrass cultivar genetic purity.