Pollen limitation and its effect on seed germination

Abstract

In nature, fruit and seed production in many plants have been shown to be pollen limited. Pollen limitation is demonstrated when open-pollinated plants that are hand-supplemented (Ps) with outcross pollen produce more fruits and/or seeds than open-pollinated controls that are not hand-pollinated (Po). There are three categories of results in such studies: Ps> Po, Ps= Poand Ps< Po, in which case pollen limitation indices are positive, zero and negative, respectively. In an index widely used to calculate pollen limitation, 1 – (Po/Ps), the bounds for Ps≥ Poare 0 to + 1, whereas the bounds for Ps< Poare 0 to –∞. The first aim of this review was to show how the pollen limitation index can be modified so that the bounds of Ps< Poare 0 and –1, whereupon the index gives equal weight to the best performer (Psor Po) and worst performer (Psor Po). In addition to seed quantity, pollen supplementation can affect seed quality, including germinability. Thus, our second aim was to summarize the results of studies that have also tested the effect of pollen limitation on seed germination. In short, the 30 case studies in 15 families, 16 genera and 18 species that we identified show that seed germination percentage increased, was not affected or decreased by pollen supplementation in 12, 11 and seven cases, respectively. The effect of pollen limitation on seed germination, which can be quite large, has not been considered in developing population growth models to determine the effect of pollen limitation on λ.

How much influence does the paternal parent have on seed germination?

“…Only a small percentage of the numerous studies on pollen limitation have measured the germination responses of seeds from treatment vs control, and some of them showed that pollen supplementation increased seed germination percentage. Of 30 cases (18 species) reviewed by Baskin and Baskin (2018) that compared germination of seeds produced by P s and P o plants, P s > P o in 12, P s = P o in 11 and P s < P o in 7. Thus, based on relative performance (see Appendix), in 40% of the cases pollen supplementation enhanced germination percentages/rate (speed).…”

Are Reproductive Traits Related to Pollen Limitation in Plants? A Case Study from a Central European Meadow

“…We calculated the pollen limitation index (PL) as PL = (P s − P o )/P max (P s or P o ) [48], where P s is the number of seeds from pollen-supplemented flowers, P o is the number of seeds from open-pollinated flowers, and P max is the larger of the two values (P s or P o ). For all subsequent analyses, similarly to Larson and Barrett [11], we established zero as the lower boundary of the PL, because any negative indices likely resulted from a potential experimental error [49], and therefore are not meaningful in the context of our study.…”

Reproductive biology, ecological life history/demography and genetic diversity of the megagenus Astragalus (Fabaceae, Papilionoideae)

“…The closer PL is to 1, the greater the benefit of pollen supplementation, and the closer PL is to -1 the greater the benefit of open pollination without pollen supplementation. Follwing Baskin and Baskin (2018): (1) when PL is ≥0.10, the plant is pollen limited (P s > P o ), (2) when PL is ≤ -0.10, open pollination is superior to pollen supplementation (P s < P o ) and (3) when PL is between -0.10 and 0.10, they are equal (P s = P o ). PL was 0.23 (A. utahensis), 0.29 (A. scaphoides), 0.33 (A. tragacantha), 0.40 (A. exscapus), 0.41 (A. peckii) and 0.46 (A. brauntonii) for fruit set, which means all six species were pollen limited, i.e.…”