Cold tolerance and flowering in rose clover (Trifolium hirtum All.)

Abstract

Rose clover (Trifolium hirtum All.) is a winter annual legume with potential for increased use as a forage crop in Texas, Oklahoma and the U.S. southern region. There is a need for rose clover cultivars are needed with improved winter growth, extended seasonal forage production and improved winter survival. The objectives of the study were to: 1) develop screening methods to measure freezing stress resistance; 2) determine stress resistance in selected germplasm; 3) evaluate variation for flowering date in the U.S. Plant Introduction Collection; and 4) evaluate the inheritance of flowering date. A modified electrolyte leakage assay capable of detecting rose clover acclimation, deacclimation and freezing tolerance was developed. Freezing tolerance was measured as percent electrolyte leakage after a 60 min exposure to -14 °C and a 24 h thaw at 4 °C. Rose clover germplasm with superior freezing tolerance was identified . Other rose clovers were observed with a range of deacclimation and acclimation rates. Seed dormancy, low temperature growth and date of flowering were all good predictors of tolerance to freezing in rose clover. Flowering traits were recorded for fifty six plant introductions, six breeding lines and four cultivars of rose clover. A 40 d difference in days post-planting to full bloom was noted among rose clover entries. The inheritance of rose clover flowering could not be determined from the F2 populations, due to lack of difference in flowering date of parental lines. The flowering dates of parental lines used in these crosses were less than 7 d apart.