Floral biology and late-acting self-incompatibility in Jacaranda racemosa (Bignoniaceae)

Abstract

Breeding-system studies have been conducted with 38 of the approximately800 species of Bignoniaceae, and self-incompatibility was found in 31 of these. In species for which the site of self-incompatibility barrier was studied, self-pollinated flowers consistently failed to develop into fruits, even though pollen tubes grew down to the ovary and penetrated most of the ovules. In this study, we have investigated the floral biology and the breeding system in Jacaranda racemosa Chamisso, with hand-pollination experiments and the histology of post-pollination events. Flower anthesis lasted 1–3 days, and although the frequency of flower visitation was extremely low, natural pollination seemed to be effected mainly by medium-sized bees. Because the conspicuous staminodium favours eventual pollination by small bees, a possible role of the staminodium in the increase of potential pollinators is suggested. Hand-pollinations indicated that J. racemosa is a self-sterile species. Histological analysis of post-pollination events indicated the occurrence of a kind of late-acting self-incompatibility in which the processes of ovule penetration, fertilisation and endosperm initiation were slower in selfed than in crossed pistils. Until the time of self-pollinated pistil abscission, no signs of endosperm malfunction or proembryo development were observed in selfed pistils. Therefore, inbreeding depression is an unlikely explanation for self-sterility in J. racemosa.

Pollination biology in Jacaranda copaia (Aubl.) D. Don. (Bignoniaceae) at the "Floresta Nacional do Tapajós", Central Amazon, Brazil

“…The position of the anthers and stigma inside the petal hood promoted the pollen deposition on the upper head and thorax of the pollinators. The basal constriction of the corolla tube was compatible with long-tongued bees, such as Euglossa, as reported also by Bittencourt Júnior & Semir (2006). The same foraging behavior of these agents was registered in the pollination biology of Arrabidaea conjugata (Vell.)…”

“…It has been also suggested that the staminode may be used as a bridge by halictid bees to reach the anthers, eventually touching the stigma (Gottsberger & SilberbauerGottsberger 2006). It also retains pollen grains on the glandular hairs (trichomes), which are collected by bees (Morawetz 1982 apud Gottsberger & SilberbauerGottsberger 2006), and diminishes the space inside the corolla chamber, thus promoting better contact of the pollinators with the reproductive organs (Bittencourt Júnior & Semir 2006). In J. copaia, all those functions can be assumed.…”

“…The staminode function has been comprehensively discussed (Bittencourt Júnior & Semir 2006, Gottsberger & Silberbauer-Gottsberger 2006. Vieira et al (1992) suggested that this structure had three different functions in Jacaranda caroba (Vell.)…”

“…(Bittencourt Júnior & Semir 2006). These studies showed clear evidences of self-incompatibility (SI) (Bittencourt 1981) and ovarian or late-acting self-incompatibility (LSI) (Vieira et al 1992, Bittencourt Júnior & Semir 2006. Gottsberger & Silberbauer-Gottsberger (2006) discuss about the superimposed pollination system of this genus, where three layered types of pollination coexist.…”

“…(Vieira et al 1992) and J. racemosa Cham. (Bittencourt Júnior & Semir 2006). These studies showed clear evidences of self-incompatibility (SI) (Bittencourt 1981) and ovarian or late-acting self-incompatibility (LSI) (Vieira et al 1992, Bittencourt Júnior & Semir 2006.…”