Contradistinctive floral attributes, pollination guilds and their consequence on the outcrossing rate in two elevational morphs of Rhododendron arboreum Sm

Infraspecific floral trait variations may appear in response to elevational differences in alpine plant species. There is enormous information on the selection of such morphs mediated by biotic and/or abiotic variables. Whether such differences contribute to differences in reproductive strategy and mating outcomes is rarely investigated. We investigated these aspects in two distinct elevational floral morphs (Red and Pink) of Rhododendron arboreum Sm. in Western Himalaya. The red morphs occupy the lower elevations while pink morphs the higher elevations. The two morphs differ in floral traits like phenology, dimension, display, quality of floral rewards, and pollinators that happen to influence interaction with available pollinator pool at each elevation. The pink morph exhibits entomophily, while the red ones show ornithophily. Although experimental pollinations established that both the morphs are self-compatible, selfing results in significantly lower fruit-set than either cross- or open-pollinations. The outcrossing rate in the red morph, as determined by using simple sequence repeat (SSR) markers, was higher (tm=0.82) than that in the pink morph (tm=0.76), with a tendency of the latter to be shifting towards mixed-mating strategy. However, the extent of biparental inbreeding was comparable among the two morphs. It is inferred that the differences in the mating outcomes among the morphs in the tree species are linked to those emerging from floral traits and the pollination by different functional groups of floral visitors.

The complete chloroplast genome of Piptanthus nepalensis, a medicinal plant

Piptanthus nepalensis (Hooker) Sweet is a semi deciduous or deciduous shrub belonging to the genus Piptanthus, Leguminosae. P. nepalensis has been used as a folk medicinal herb in Nepal and was cultivated all over the world as an ornamental plant. In the present study, we sequenced the entire genome of the chloroplast of P. nepalensis. The total length of the chloroplast genome in P. nepalensis is 152,195 bp, including a large single-copy region of 82,048 bp, a small single-copy region of 17,675 bp, and a pair of inverted repeats regions of 26,236 bp. The overall guanine-cytosine (GC) content of the genome was 36.7%. There are 131 genes in the chloroplast genome of P. nepalensis, including 85 protein-coding genes, 8 rRNA genes and 38 tRNA genes. Phylogenetic analysis showed that P. nepalensis is closely related to Maackia floribunda.

Possible Synergistic Effects of Thymol and Nicotine Against Crithidia bombi Parasitism in Bumble Bees

Floral nectar contains secondary compounds with antimicrobial properties that can affect not only plant-pollinator interactions, but also interactions between pollinators and their parasites. Although recent work has shown that consumption of plant secondary compounds can reduce pollinator parasite loads, little is known about the effects of dosage or compound combinations. We used the generalist pollinator Bombus impatiens and its obligate gut parasite Crithidia bombi to study the effects of nectar chemistry on host-parasite interactions. In two experiments we tested (1) whether the secondary compounds thymol and nicotine act synergistically to reduce parasitism, and (2) whether dietary thymol concentration affects parasite resistance. In both experiments, uninfected Bombus impatiens were inoculated with Crithidia and then fed particular diet treatments for 7 days, after which infection levels were assessed. In the synergism experiment, thymol and nicotine alone and in combination did not significantly affect parasite load or host mortality. However, the thymol-nicotine combination treatment reduced log-transformed parasite counts by 30% relative to the control group (P = 0.08). For the experiment in which we manipulated thymol concentration, we found no significant effect of any thymol concentration on Crithidia load, but moderate (2 ppm) thymol concentrations incurred a near-significant increase in mortality (P = 0.054). Our results tentatively suggest the value of a mixed diet for host immunity, yet contrast with research on the antimicrobial activity of dietary thymol and nicotine in vertebrate and other invertebrate systems. We suggest that future research evaluate genetic variation in Crithidia virulence, multi-strain competition, and Crithidia interactions with the gut microbe community that may mediate antimicrobial activities of secondary compounds.

Antimicrobial nectar inhibits a florally transmitted pathogen of a wild Cucurbita pepo (Cucurbitaceae)

PREMISE OF THE STUDY

Floral nectars of many species contain antimicrobial chemicals, but their function in nectar is subject to debate. Previously, we have shown that Erwinia tracheiphila, the causative agent of bacterial wilt disease in cucurbits, can be transmitted via the floral nectaries. •

METHODS

We used a disk diffusion assay (DDA) to determine the antimicrobial effects of nectar from a wild gourd on lawns of Escherichia coli and Erwinia tracheiphila. We also used E. tracheiphila to inoculate flowers of wild gourd plants, with and without nectar. •

KEY RESULTS

The DDA showed that paper disks saturated with 10 μL of nectar inhibited the growth of E. coli on a larger area of the lawn than 40% glucose but a smaller area than 5% ampicillin for 12 h. On lawns of E. tracheiphila, nectar inhibited growth on a larger area than glucose for 24 h and there were no significant differences between ampicillin and nectar for12 h. A significantly larger proportion of the plants inoculated via flowers without nectar contracted wilt disease than plants with nectar. •

CONCLUSIONS

These findings indicate that nectar reduces transmission of E. tracheiphila via the nectaries and reveal the potential for florally transmitted pathogens to influence the evolution of floral traits.