Floral longevity, nectar production, pollen release, and stigma receptivity in Haskap (Lonicera caerulea)

Abstract

Haskap (Lonicera caerulea L.) is a temperate fruiting shrub grown commercially in northern regions of Europe, Asia, and North America. Haskap is self-incompatible and requires insect pollinators in order to set fruit; however, very little is currently known about its floral biology or pollinator specializations, particularly in North American cultivars. Here, we examine floral longevity, nectar dynamics, the timing of anther dehiscence, and stigma receptivity in flowers of greenhouse-grown ‘Tundra’, a Haskap cultivar developed and grown in Saskatchewan, Canada. Anthesis lasted 83.3 ± 25.9 hours (mean ± SD) in un-pollinated flowers; pollination caused early senescence within 34.3 ± 15.2 hours after pollination. Nectar was present from the onset of anthesis, and nectar volume peaked at 9-16 hours after opening. Nectar volume was maintained throughout anthesis and was not resorbed prior to abscission of the corolla from the ovary, and nectar removed during anthesis was replenished to the original volume. The stigma showed a reaction to hydrogen peroxide while still in the bud stage, suggesting it is receptive even before the flower opens. Early stigma receptivity, nectar production, and anther dehiscence maximize opportunities to be successfully pollinated, along with high floral longevity and pollination-triggered senescence. These results suggest that Haskap flowers utilize a generalist, rather than a specialized, pollination strategy. Observations that some flowers open in the evening or were already open in the morning suggest that nocturnal pollinators such as moths may be important, in addition to known diurnal pollinators.