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PLANT GENETIC RESOURCES

Birdsfoot Trefoil Flowering Response to Photoperiod Length

National Forage Seed Production Res. Cntr., USDA-ARS, 3450 SW Campus Way, Corvallis, OR 97331

* Corresponding author (steinerj{at}ucs.orst.edu)

Birdsfoot trefoil (Lotus corniculatus L.) is an indeterminate Old World perennial forage legume that is widely adapted to environments ranging from Scandinavia in the north to highlands near the equator in the south. Because of poor root and crown rot resistance, natural reseeding in pastures is desired. Therefore, birdsfoot trefoil genotypes that flower and set seeds at lower latitudes would be desirable to aid persistence and thus improve pasture forage quality. The purpose of this research was to determine the effects of photoperiod length and collecting site ecogeography on flowering of 68 birdsfoot trefoil accessions from the USDA-ARS National Plant Germplasm System (NPGS) collection. The flowering response index (FRI) described accession flowering in 10-, 13-, 16-, and 19-h photoperiod lengths. As photoperiod length increased from 13 to 19 h, the percentage of accession clones that flowered increased. Photoperiod lengths equal to 16 h were too long to differentiate germplasm differences, and thus are not suited as a selection criterion for flowering at low latitudes. Under 13-h photoperiod length, as collecting site latitude increased, the FRI and percentage of clones in an accession that flowered decreased. Only an induced mutant flowered in the 10-h photoperiod length treatment. Since wild accessions were collected from habitats as little as 7° N latitude, a new natural minimal critical photoperiod requirement at 12.5 h was inferred. When selecting genotypes for use in low latitude pastures, the flowering response at 13-h photoperiod length should be considered if reseeding is desired.

Abbreviations: FRI, flowering response index • FRI_Comp, composite flowering response index • HU, heat units • HU_Ave, average number of HU for an accession to flower • HU_Max, heat unit cut-off threshold • NPGS, USDA-ARS, National Plant Germplasm System • POP, percentage of population that flowered