Seed Yield of Norwegian and Swedish Tetraploid Red Clover (Trifolium pratense L.) Populations

Abstract

While tetraploid plants of red clover are taller, have thicker stems, and have broader leaves that altogether result in a higher forage yield compared to diploids, they generally have substantially lower seed yields than diploid plants. Tetraploid red clover can be induced chemically by colchicine or nitrous oxide (N2O) and sexually by union of unreduced gametes. The average seed yield of tetraploid red clover in Norway is 60% of the diploid yield, while in Sweden it is 75%. One objective of this paper was to examine whether there is a difference in seed yield among chromosome doubled tetraploids and crossed tetraploids. A second objective was to investigate differences in seed yield and seed yield components in Norwegian and Swedish tetraploid populations. The third objective was to study which yield component most correlates with the seed yield per hectare. Seed production experiments were established at Landvik and Bjørke in Norway and Svalöv and Lännäs in Sweden. Populations made by crossings of tetraploids gave significantly greater yield (p < 0.001) compared to populations that were made by chromosome doubling. On average, Norwegian and Swedish varieties had equal yields in both experimental years. Norwegian and Swedish varieties differed mostly in earliness traits. Swedish populations began flowering on average 4 d earlier than Norwegian populations. Genotypic correlations showed that seed yield per flower head was the component with the highest correlation (r = 0.956 and r = 0.977) with yield per hectare in both experimental fields. Results from the second experimental year indicate a trend towards improved seed yield after several cycles of recurrent selection for higher seed yield per flower head.

Seed Yield Components in Single Plants of Diverse Scandinavian Tetraploid Red Clover Populations (Trifolium pratense L.)

“…Seed yield per flower head was also identified as the component most strongly correlated (r = 0.96 and 0.98) with seed yield per area in two multisite dense-stand seed production experiments with twelve tetraploid cultivars and breeding populations (Amdahl et al, 2016). Similarly, in the current study, SYFH was also identified to be the most strongly correlated (r = 0.91 and 0.68 in experiments one and two, respectively) with the SYP.…”

“…As evidenced in our dense plant canopy trials (Amdahl et al, 2016), differences in seed yield between tetraploid cultivars are likely to be more prominent under optimal weather conditions. In experiment two, SFH, SYFH and FERT showed a tendency of being higher in cultivars that gave the highest SYP; however, these differences were not significant.…”

“…Many breeders and researchers have used seed-yield components to measure, compare, and explain differences in seed yield between diploid and tetraploid red clover populations and cultivars ( Julén, 1954;Wexelsen and Vestad, 1954;Dennis, 1975;Vleugels et al, 2015bVleugels et al, , 2016Amdahl et al, 2016). Components that determine seed yield in red clover can be classified as primary components, i.e., the number of flower heads per unit area (sometimes recorded as number of flower heads plant −1 or shoot −1 ), the number of florets per flower head, the number of seeds floret −1 , and weight seed −1 (often recorded as thousand-seed weight).…”

“…1). Since we investigated the importance of different components for seed yield ha −1 of the same tetraploid cultivars and populations in a previous study (Amdahl et al, 2016), our objective was also to verify those findings on single plants. No significant difference (P = 0.243) in FFH were detected, and 'Tripo' and 'Lasang' did not differ significantly in either Corolla or SFH.…”

“…A description of all cultivars and their background is available in Amdahl et al (2016). Cultivars used in experiment one were 'Tripo' (4´), 'Lasang' (4´), and 'Lea' (2´).…”