Different pollination approaches to compare the seed set of diploid and tetraploid red clover Trifolium pratense L.

Abstract

In red clover seed production, low seed yield is limiting the commercial exploitation of tetraploid red clover. To explore if pollination is the limiting factor for the seed yield in tetraploid red clover, we investigated pollinator behaviour and plant reproductive success in diploid (2x) cultivar ‘Rajah' and tetraploid (4x) cultivar ‘Amos' using honey bee and hand pollination approaches. We measured the seed set at the flower head level with the increasing visitation rate of honey bees (one bee, two bees and open pollination) and pollen diversity (one and two pollen donors) of hand pollination. We found no difference in honey bee pollination behaviour (visitation rate) between the diploid and tetraploid red clover. Surprisingly, the seed set in two bees was significantly lower than that of one bee in ‘Rajah'. We suggest that honey bees prefer to visit already tripped florets or to visit fewer florets due to scent marks left by the previous honey bees. In open pollination, seed number per flower head in ‘Amos' (on average 11) was half of ‘Rajah' (on average 20). Seed set in ‘Amos' was lower than 50% of ‘Rajah' in honey bee (one bee treatment) and hand pollination (one and two pollen donors treatments). There were no differences in stigma receptivity whereas pollen viability in ‘Amos' was lower than ‘Rajah' after the peak pollen viability was reached (six days after the onset of flowering). We suggest that the fertility problems such as low pollen viability may be the reason for the low seed set in tetraploid red clover. This conclusion should be verified by investigating other fertility traits during the ovary, embryo and seed development with a broader range of diploid and tetraploid cultivars.

Seed Production of Red Clover (Trifolium pratense L.) under Danish Field Conditions

“…These findings are in line with seed production from western Oregon in the United States, where the typical red clover seed yields can reach 600 kg ha −1 and where over 1000 kg ha −1 were reported for some seed growers [31,32]. Remarkable is that the tetraploid cultivar 'Amos' obtained only around half of the seed yield of the two diploid cultivars in 2014 and 2015 (Figure 5), which is in agreement with previous studies [1,[33][34][35][36]. In agreement with our third hypothesis, the seed yield difference corresponds to a lower seed number per flower head and calculated seed set in 'Amos' (Figures 8-10).…”

“…Recent studies urged the importance of improving the fertility of red clover [30,48]. Studying meiotic aberrations and embryo abortion [30,49], and investigating the pollination process that directly linked to the seed setting process [36,47] may improve our understanding for future breeding activities.…”

Pollinators, pests and yield—Multiple trade‐offs from insecticide use in a mass‐flowering crop

“…High weevil density reduced the experimental yield of unsprayed clover (within treated sites) and, to a lesser extent, final yield in untreated relative to treated clover. This little difference in final yield may be because diploid cultivars, unique in our study to untreated, organically-managed sites, are more able to set seed than tetraploid cultivars (Boelt et al, 2015;Hederström et al, 2021;Jing et al, 2021;Vleugels et al, 2015) and thus able to compensate (to some extent) for pest damage. Fertile cultivars, also observed within oilseed rape (Lankinen et al, 2018), are important for farmers wishing to maximise their yields (Boelt et al, 2015;Knapp et al, 2016), and fertility should be considered as an additional trait alongside pest-resistance and pollinator-dependency/attraction within the IPPM framework (Egan et al, 2020;Lundin et al, 2021).…”

Improving pollen and nectar supply by identifying the red clover (Trifolium pratense) cultivars that attract most pollinators

“…We also examined which plant traits are associated with greater pollinator visitation. Previous work has examined interactions between red clover cultivars and pollinators in relation to seed production (Hederström et al, 2021; Jing et al, 2021; Vanommeslaeghe et al, 2018; Vleugels et al, 2015), but none have examined red clover cultivars from the perspective of floral resource provision. Here, we compared pollinator visitation and quantified plant traits that may affect attractiveness to pollinators (inflorescence density, florets per inflorescence, floret length and nectar sugar production) across 20 red clover accessions (12 cultivars and 8 breeding lines) grown under management typical for silage production in the UK (AHDB, 2021a).…”