Abstract
Plant reproduction in red clover requires cross-fertilization via insect pollination. However, the influences of visitation rate and timing on maximizing ovule utilization are yet to be determined. We aimed to study the influences of visitation rate, flowering stage, and self-incompatibility on reproductive success. We applied hand and honey bee pollination in the study of eight red clover cultivars with two ploidy levels released between 1964 and 2001. In hand pollination, increasing the visitation rates (from 10 to 80 pollinated florets per flower head) increased the seed number per flower head but reduced the seed number per pollinated floret. Different flowering stages (early, middle, and full flowering) did not influence the seed number per pollinated floret significantly. There was a marked difference in reproductive success depending on the ploidy level, with 0.52 seeds per pollinated floret in diploid and 0.16 in tetraploid cultivars. During the cultivar release history, seed number per pollinated floret seemed to decrease in diploid cultivars, whereas it increased in tetraploids. In honey bee pollination, diploid cultivars had more two-seeded florets than tetraploids. Different visitation rates and the stochastic nature of pollen transfer resulted in difficulties when the plant reproductive success between hand and bee pollination was compared. A maximum of 0.27 seeds per pollinated floret were produced in hand pollination compared to the 0.34 in honey bee pollination. In spite of this, hand pollination provided a valuable method for studying the pollination biology and reproduction of red clover. Future studies may employ hand pollination to unravel further aspects of the low reproductive success with the future perspective of improving seed number per pollinated floret in tetraploid red clover.
Highlights
The influence of pollinator performance on the plant reproductive success is of interest in the research fields of conservation biology, evolutionary ecology, breeding, and seed/fruit production in agriculture
We found a significant effect of visitation rate and ploidy on the seed number per flower head (Figure 2) and seed number per pollinated floret (Figure 3), while there was no significant effect of released year (Table 2)
Seed number per flower head in diploids [Estimated marginal means (EMMs) 7.76 with 95% CI (6.28, 9.59)] was significantly (P = 0.009) higher than that of tetraploid red clover [EMMs 4.83 with 95% CI (3.91, 5.95), Figure 2B]
Summary
The influence of pollinator performance on the plant reproductive success is of interest in the research fields of conservation biology, evolutionary ecology, breeding, and seed/fruit production in agriculture (reviewed in Mayer et al, 2011). Two Ploidy Levels Red Clover and rewards under natural conditions (Ne’eman et al, 2010). The recommendation for red clover seed production is using four to five honey bee (Apis mellifera L.) colonies per hectare (Brødsgaard and Hansen, 2002). There is a lack of direct measurements at the pollination level, such as the flower visitation rate to estimate pollinator performance in order to maximize the reproductive success of different crops (Garibaldi et al, 2020)
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