Variable pollen viability and effects of pollen load size on components of seed set in cultivars and feral populations of oilseed rape

Abstract

Pollination success is important for crop yield, but may be cultivar dependent. Less is known about which floral traits influence pollination success. Floral traits, e.g. traits related to attraction and reward, can also contribute to gene flow via pollen, the latter being of particular importance in oilseed rape (Brassica napus) where gene flow occurs between plants of crop, volunteer and feral origin as well as related taxa. We investigated the relationship between pollen load size and seed set in winter oilseed rape. We compared variability in pollen-viability traits, flower production (flowers from the main raceme times number of branches) and seed number and weight per siliqua among cultivars and feral populations (growing outside of agricultural fields) under controlled conditions. Both seed number and weight were saturated at relatively low pollen loads in the tested cultivar. Pollen viability and estimated flower production differed among cultivars, indicating that these traits could contribute to yield variability. Seed weight per siliqua, but not pollen traits or flower production, was lower in ferals compared to cultivars. Thus, while the probability of establishment may be reduced in ferals (due to lower seed weight per siliqua) this will not necessarily impact their contribution to gene flow via pollen. In oilseed rape a relatively low pollen load may be sufficient for full seed set in some cultivars, suggesting less dependence on insect pollination for high yield than generally expected. Our results also showed that previously less investigated floral traits, such as pollen viability, pollen tube growth rate and flower number, can differ between cultivars. Studies of these traits may provide targets for increasing crop yield and provide general knowledge about gene flow between cultivated, feral and related wild populations.

Escaped oilseed rape: Occurrence in the agricultural landscape and potential pollen-mediated gene flow from crop oilseed rape

“…In a previous study on pollen germination rate and pollen tube growth rate, Lankinen et al (2018) found larger variation within five feral populations and seven cultivars of OSR than between these two groups. They demonstrated that only one cultivar showed significantly higher pollen performance than one feral population.…”

“…Feral oilseed rape may also need to allocate resources to other functions than pollen since they grow in less favorable conditions than the crop plants. However, when crop cultivars and ferals were compared, there was no difference in pollen viability (Lankinen et al 2018).…”

“…We used pollen from six to eight plants per locality, depending on how many usable flowers that were available (Alnarp and Kyrkheddinge N = 8, Dalby N = 7 and Marieholm N = 6). Pollen germination rate and pollen tube growth rate was assessed following germination in vitro in Hoeksta medium (Hoekstra & Bruinsma 1975), modified as described in Lankinen et al (2018). We germinated pollen from two flowers from each plant in a drop of the medium on a microscopic slide that was placed in the dark, at a constant temperature of 22C for three hours.…”

Chromosome instabilities in resynthesized Brassica napus revealed by FISH

“…Fujii and Ohmido ( 2011 ) reported that RS plants with low pollen fertility contain aberrant chromosome fragments in somatic cells. Evaluation of pollen viability is an important characteristic of the genotype because the ability to pollinate is one of the basic selection features in plant breeding processes (Lankinen et al 2018 ). RS plants originating from interspecific crosses between B. rapa and B. oleracea are usually self-incompatible, a feature transferred from the parental species.…”

Fruit Set in Avocado: Pollen Limitation, Pollen Load Size, and Selective Fruit Abortion

“…When pollen grains land on the stigma, another factor that plays an important role in fertilization is the genotype of the pollen donor. Evidences are accumulating, suggesting that fertilization is not always a random process [34] and that mate choice occurs in numerous plant species [35][36][37][38][39][40][41][42][43][44][45][46]. Pollen competition is estimated to be higher in outcrossing than in selfing plants because pollen load in outcrossers is expected to be genetically more diverse [47].…”