Breaking-bud pollination: a new pollination process in partially opened flowers by small bees

Abstract

Plant-pollinator interactions have usually been researched in flowers that have fully opened. However, some pollinators can visit flowers before full opening and contribute to fruit and seed sets. In this paper, we researched the pollination biology of flowers just starting to open in four field experiments. We observed the insect visitors to Lycoris sanguinea var. sanguinea for 3 years at five sites. These observations revealed that only small bees, Lasioglossum japonicum, often entered through tiny spaces between the tepals of 'breaking buds' (i.e. partially opened flowers) and collected pollen. We hypothesized that they can pollinate this species at the breaking-bud stage, when the stigma is located near the anthers. To measure the pollination effect of small bees at the breaking-bud stage, we bagged several breaking buds after small bees had visited them and examined whether these buds were pollinated. In bagging experiments, 30% of the breaking buds set fruit and seeds. Fruit-set ratios of the breaking buds did not differ significantly from those of the fully opened flowers, which had been visited by several insect species. We also counted the pollen grain numbers on the body of L. japonicum and on the anthers of randomly-selected and manipulated flowers. These experiments revealed that all of the captured bees had some pollen of target plants and that L. japonicum collected most of the pollen grains at the breaking-bud stage. Our results showed that the new pollination process, breaking-bud pollination, happened in breaking buds by L. japonicum, although there is no evidence to reveal that this is the most effective pollination method for L. sanguinea var. sanguinea. In principle, this new pollination process can occur in other flowering plants and our results are a major contribution to studies of plant-pollinator interactions.

Plant-pollinator interactions in East Asia: a review

“…Bees of the Andrenidae, Colletidae, and Halictidae visit flowers with short-tubed and exposed nectaries (Osada et al 2003;Matsuyama et al 2009;Tian & Ren 2019). Pollen-collecting small bees sometimes act as important pollinators of long-tubed flowers that lack longtongued pollinators, suggesting their compensatory role as pollinators of such flowers (Zhang et al 2011a;Guo & Wang 2014;Yamaji & Ohsawa 2015;Zhu et al 2017). Small bees act as the main pollinators of some plants, including species of Liliaceae (e.g., Fritillaria (Naruhashi et al 2006)), Berberidaceae (e.g., Epimedium (Suzuki 1984)), Orchidaceae (e.g., Cypripedium and Gastrodia (Bänziger et al 2005(Bänziger et al , 2008Sugiura 2017)), and Theaceae (e.g., Camellia (Deng et al 2010)).…”

Mutant selection in the self-incompatible plant radish (<i>Raphanus sativus</i> L. <i>var. sativus</i>) using two-step TILLING

“…1D and 1E show a fruit that was successfully produced and a pistil that failed to be fertilized, respectively. To obtain BC 1 M 2 seeds, flowers with petals that slightly protruded from sepals were used for bud pollination (Yamaji and Ohsawa 2015). Petals, sepals, and stamens were removed from the flowers with tweezers, and stamens with pollen from the same mutated flower were attached to carpels to produce self-crossed BC 1 M 2 plants (Fig.…”