Germination of horsenettle (Solanum carolinense L.) seeds was inhibited by horsenettle root, stem and leaf material incorporated into soil in in vitro tests. Leaf material had the strongest effect, producing statistically significant inhibition when 2 g were added to 100 g soil mixture. The addition of microbial inhibitors along with horsenettle leaf material did not prevent the inhibition of horsenettle seeds, indicating that inhibition was not caused by microbial decomposition of leaf carbohydrates. Moreover, the addition of carbohydrate in the form of dried lettuce leaves did not inhibit horsenettle seed germination. Inhibition also was apparent in a more natural setting: Germination of horsenettle seeds planted in an experimental plot in the absence of horsenettle was 20 % greater than in a plot where horsenettle had grown for less than 1 year. In the laboratory, the potency of the inhibitor decayed after several weeks of moist storage. Inhibition could be reversed by washing inhibited seeds and replanting them in fresh soil. The decay and reversibility results are consistent with the hypothesis that autoallelopathy in this species functions to maintain a viable seed bank while reducing intraspecific competition between seedlings and adults.
Sexual expression and maternal investment were investigated in the herbaceous perennial Solanum carolinense (Solanaceae). Field censuses, pollen germination studies, and the results of hand—pollination experiments in a greenhouse revealed that there are three flower types. Morphological males (M) are found near the tip of the inflorescence and have short styles; these flowers did not set fruit when pollinated. All other flowers have long styles and are morphological hermaphrodites (H); among these, those near the base of an inflorescence set fruit when pollinated (fruiting hermaphrodites, FH) while those in intermediate positions did not (functional males, FM). No morphological differences were apparent between FH and FM flowers. Male function of M and H flowers was indistinguishable in terms of pollen germination and quantity and quality of seed produced. The proportions of FM flowers decreased with later inflorescences, but the proportion of FM flowers increased correspondingly. Thus, the morphological sex ratio, M/(M + H), decreased with plant size, while the functional sex ratio, (M + FM)/(M + FM + FH) did not vary. These data do not support evolutionary theories that predict increased allocation to female versus male function with increasing plant size. In addition, experimental manipulations were performed on greenhouse plants. Morphological sex ratio changed in response to various plant hormones, which suggests hormone involvement. Sex ratio increased in response to increased shade and water stress, which supports those evolutionary theories that predict a shift to maleness in response to stress. However, increasing levels of fertilizer also increased the morphological sex ratio Pollination did not influence the morphological sex of subsequent flowers; rather, regulation of fruit—set after pollination occurred via changes in the proportion of H flowers that did (FH) or did not (FM) set fruit. The results are discussed in terms of three stages at which maternal investment can be regulated: flower initiation, flower maturation, and fruit maturation.
Ovipositing females of the host—specific herbivorous moth Frumenta nundinella Zeller discriminated among horsenettle (Solanum carolinense L.) plants in the laboratory and at five field populations. In laboratory experiments, the number of larvae that developed in high—density plant groups was not significnatly greater than the number that developed in low—density groups. Consequently, individual plants in low—density groups were disproportionately affected; twice as many larvae developed on them as on individual plants in high—density groups. Moths also discriminated between groups of pure horsenettle (high relative abundance) and groups of horsenettle plus another naturally co—occurring species (low relative abundance). Individual plants in high relative abundance groups had a tenfold greater infestation than did plants in low relative abundance groups. Natural horsenettle populations varied in density, relative abundance, plant size, and fruit production. Plant size, fruit production, and population density were all positively correlated, so the populations with the greatest density had the largest plants, which produced the most fruits. Despite differences in these plant parameters among sites, the extent of infestation differed little, except for one site that lacked parasitoids that attack F. nundinella. Infestation within field sites was heterogeneous among plants. Virtually all large plants (those with @> 15 fruits), but only about half the small plants (those with < 15 fruits), became infested (one or more infested fruit per plant). However, a greater proportion of the fruit crop was infested on small plants than on large plants. Large plants remained in flower an average 2.5 wk longer than did small plants, so a smaller proportion of their flowers was available during the short period of high oviposition risk. Because of the short oviposition period, plants that flowered earlier or later than the mean flowering time of their populations appeared to have lower infestations than did plants that flowered close to the population means.
Abstract The electrochemical properties of carbon film based ring‐disk and split‐disk electrodes in small active volume (0.24–2μL) radial flow cells were studied in order to employ them in conjunction with microbore liquid chromatography (LC) for determining catecholamines. The high conversion of dopamine (DA) at the disk of a ring‐disk electrode makes the DA limiting current lower than the theoretical value at a low flow rate. The collection efficiency (CE) increases with decreasing flow rate and cell thickness, which is different from previously reported results. A high CE of 0.96 was achieved because of the narrow gap of 5 μm. On the other hand, a higher limiting current was observed with the split‐disk than with a commercially available dual‐disk electrode because of its efficient geometry for analyte collection. The cross talk of the DA after reacting at one of the electrode is only 2%. The ring‐disk and split‐disk electrodes were suitable as series and parallel electrochemical detectors for small bore LC. A detection limit of 103 fg was obtained for DA at the disk of the ring‐disk because of the high signal in the thin‐layer radial flow cell and the low noise level of the carbon film. In contrast, very slight interference was observed from neighboring electrodes when determining catecholamines at the split‐disk.
