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In a recent issue of Nature, Huang et al. identify and show how to overcome the barriers to successful pollen germination after interspecific crosses. 1 Their findings answer a long-standing question about reproductive barriers in flowering plants and open the door to harnessing genetic diversity of distant relatives for crop improvement., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Hybridisation between individuals of different species can lead to maladapted or inviable progeny due to genetic incompatibilities between diverging species. On the other hand, mating with close relatives, or self-fertilisation may lead to inbreeding depression. Thus, both too much or too little divergence may lead to problems and the organisms have to carefully choose mating partners to avoid both of these pitfalls. In plants this choice occurs at many stages during reproduction, but pollen-pistil interactions play a particularly important role in avoiding inbreeding and hybridisation with other species. Interestingly, the mechanisms involved in avoidance of selfing and interspecific hybridisation may work via shared molecular pathways, as self-incompatible species tend to be more 'choosy' with heterospecific pollen compared to self-compatible ones. This review discusses various prezygotic post-pollination barriers to interspecific hybridisation, with a focus on the mechanisms of pollen-pistil interactions and their role in the maintenance of species integrity. [ABSTRACT FROM AUTHOR]

Background. Fig/wasp pollination mutualisms are extreme examples of speciesspecific plant-insect symbioses, but incomplete specificity occurs, with potentially important evolutionary consequences. Why pollinators enter alternative hosts, and the fates of pollinators and the figs they enter, are unknown. Methods. We studied the pollinating fig wasp, Ceratosolen emarginatus, which concurrently interacts with its typical host Ficus auriculata and the locally sympatric alternative host F. hainanensis, recording frequencies of the wasp in figs of the alternative hosts. We measured ovipositor lengths of pollinators and style lengths in female and male figs in the two host species. Volatile organic compounds (VOCs) emitted by receptive figs of each species were identified using GC-MS. We tested the attraction of wasps to floral scents in choice experiments, and detected electrophysiologically active compounds by GC-EAD. We introduced C. emarginatus foundresses into figs of both species to reveal the consequences of entry into the alternative host. Results. C. emarginatus entered a low proportion of figs of the alternative host, and produced offspring in a small proportion of them. Despite differences in the VOC profiles of the two fig species, they included shared semiochemicals. Although C. emarginatus females prefer receptive figs of F. auriculata, they are also attracted to those of F. hainanensis. C. emarginatus that entered male figs of F. hainanensis produced offspring, as their ovipositors were long enough to reach the bottom of the style; however, broods were larger and offspring smaller than in the typical host. Female figs of F. hainanensis failed to produce seeds when visited by C. emarginatus. These findings advance our current understanding of how these species-specific mutualisms usually remain stable and the conditions that allow their diversification. [ABSTRACT FROM AUTHOR]

Information on reproductive biology and pollination ecology studies of threatened plants are essential to develop strategies for their sustainable utilization and effective conservation. As such, these studies were conducted on Rheum webbianum , a high-value "vulnerable" medicinal herb of the north-western Himalaya. This species presents a unique mode of reproductive behavior through the involvement of different floral events, including the movement of reproductive organs. The plants survive extremely cold conditions through underground perennating rhizomes that sprout into juvenile shoots with the onset of the favorable climatic conditions. The peduncle arises from the axils of the radical leaves, bearing a globular collection of densely arranged hermaphrodite flowers with temporally separated male and female phases; the male phase precedes the female phase (protandry). Anther dehiscence and stigma receptivity is post-anthesis. Anthers dehisce longitudinally along margins, liberating a large mass of spherical and tricolpate pollen with spinulose exine. Pollen viability decreased to < 10% on day 9. Pistil is tristylous, with each style terminating into a fan-shaped stigma lobe. The pollen receptive surface of each stigmatic lobe remains incurved at an angle of 360° and shows upward movement after anthesis, forming a funnel-like structure at an angle of 180° with respect to the ovary. Pollination syndrome is ambophilous. Spontaneous autogamy or geitonogamy to a certain extent is achieved in this species due to the arrangement of flowers in the inflorescence and overlapping of male and female reproductive phases among them. Incurved stigmatic lobes and outward movement of stamens too facilitate outcrossing. Pollen/ovule ratio estimates, results of pollination experiments on breeding behavior, outcrossing, and self-compatibility indices demonstrated that plants are self-compatible and cross-fertile. [ABSTRACT FROM AUTHOR]