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Flowering of Crownvetch as Affected by Thermo-Inductive Treatment, Photoperiod, Plant Age, and Genotype¹

Since crownvetch (Coronilla varia L.) does not flower under conditions conducive to flowering in alfalfa, (Medicago sativa L.), red clover (Trifolium pratense L.), and birdfoot trefoil, (Lotus corniculatus L.), four hypotheses were developed concerning flowering in this species. These included: (i) crownvetch requires exposure to cool or cold conditions (thermo-induction) before flowering can occur; (ii) Thermo-induction can occur under either long or short photoperiods, but long photoperiods are subsequently required for the initiation and development of floral primordia; (iii) A certain plant age is required before thermo-induction can occur; and (iv) Crownvetch genotypes and cultivars differ in their need for thermoinduction. A series of field, greenhouse, and growth chamber studies indicated that all or nearly all 4- to 8-week-old plants of ‘Penngift’ crownvetch exposed to effective thermo-inductive treatment (minimum temperatures of 10 or less for 12 to 15 hr per day) subsequently flowered in 5 to 7 weeks when tested under warm conditions (20 C or above) and long photoperiods (16 hr or longer). Plants weeks old when subjected to thermo-inductive treatment required longer exposure (8 weeks) than 8-week-old plants, which required only 4 weeks of thermo-inductive treatment. In these studies thermo-induction occurred under both long (16- to 24-hr) and short (9- to 12-hr) photoperiods, but thermo-induced plants flowered only when subsequently exposed to photoperiods of 15 hr or more. Nearly all 5- to 8-week-old plants of the cultivar Penngift could be thermo-induced in 4 weeks. Plants of ‘Chemung’ and ‘Emerald’ cultivars needed to be both older (8 to 16 weeks) and thermo-induced at 10 C or below for longer periods (8 weeks or more) for a comparable response. addition, some genotypes within different cultivars differed somewhat in their response to thermo-inductive treatment. By using the above techniques, we were able to cause most plants of Penngift crownvetch to flower 13 to 16 weeks after seeding; plants of Emerald and Chemung, however, generally require 7 to 8 weeks longer.

Key Words: Coronilla varia L. • Thermo-induction • Photo-induction • Penngift • Emerald • Chemung

² Professor and Associate Professor, respectively, Department of Agronomy, The Pennsylvania State University, University Park, Pa. 16802.

³ Assistant Professor, Department of Plant and Soil Science, University of Maine, Orono, Me. 04473.

Received for publication March 10, 1971.