Previous studies indicated that seeds of Viburnum odoratissimum had only physiological dormancy (PD), but no measurements of embryos were made during the dormancy-break treatments. Thus, we investigated embryo growth and radicle and cotyledon emergence over a range of temperatures. Seeds have underdeveloped embryos, and their length increased about 300% before radicle emergence. Embryos also had PD, as evidenced by delays in beginning of embryo growth (2–3 weeks) and of germination after embryos were elongated (4 weeks). After radicle emergence, epicotyl emergence was delayed 1–8 weeks, depending on incubation temperature, but cold stratification was not required to break PD of the epicotyl. Unlike seeds of many previously studied Viburnum spp., epicotyls of V. odoratissimum have non-deep, rather than deep, PD. Hence, a new level of MPD called non-deep, simple, epicotyl MPD has been identified.

Community composition and ecosystem processes during succession may be driven partly by traits of plant species that attain dominance. Here, we addressed the hypothesis that Stipa pulcherrima, the dominant grass of abandoned continental grasslands, controls seedling recruitment of co-occurring species through chemical effects of its litter. Eight species with successful and unsuccessful recruitment under field conditions were selected (four familial pairs) to study experimentally the effects of leaf leachate under four temperature regimes. Since fungi developed in leachate-treated Petri dishes, in another experiment seeds were surface sterilized to remove confounding effects of fungi on recruitment. Leachate affected various stages of seedling recruitment: it significantly reduced seed germination (by 33–94%) and radicle elongation, and it delayed germination of seedlings of all species. In two families, species with unsuccessful field recruitment were more negatively affected than the successful ones. In a third family, the species with successful recruitment was more negatively affected, and in the fourth there were no differences. Similar germination responses after exclusion of fungi through seed-surface sterilization suggested that leachate was responsible for the observed effects on recruitment. Besides other traits and physical/microclimatic effects of accumulating litter, S. pulcherrima influences plant community dynamics and may potentially affect ecosystem processes through its secondary compounds.

Recent concern about gene flow from transgenic plants to weedy species has attracted much research on the fitness of their hybrids. However, no studies have been reported on the very early effects of the seed size of hybrids compared with parental plants for germination, seedling establishment and plant growth. We produced hybrids between male sterile Brassica napus L. (oilseed rape) and five weedy relatives, including Brassica juncea (L.) Czern, B. nigra (L.) Koch, B. rapa L., Hirschfeldia incana (L.) Lagrèze-Fossat and Raphanus raphanistrum L. The hybrid seeds formed between B. napus and B. rapa varied in size, while all the hybrid seeds formed with the other species were small. In a direct-seeded field experiment, small seeds of both parents and hybrids had a lower frequency of emergence and a lower seedling survival rate than large seeds, and resulted in later flowering with less biomass. However, no difference was recorded in a transplant experiment, indicating that growth in the juvenile period was sensitive to the small seed class in field conditions only. The optimum environmental conditions in the greenhouse probably homogenized the developmental differences observed at the early stage, and thus reduced the variation during subsequent growth in the field. This point has not been, but should be, considered in risk assessment of transgenic plants. The lower seedling establishment of small-seeded hybrids could hamper further gene flow.

We report the determination of abscisic acid (ABA) and its metabolites, phaseic acid (PA), dihydrophaseic acid (DPA) and ABA glucose ester (ABA-GE), in non-dormant dry and imbibed seeds of tomato (Solanum lycopersicum Mill.) cv. Moneymaker (wild type), and its tss1, tss2 and tos1 mutants. High ABA in dry seeds may originate from ABA accumulation in the sheath tissue, which was in contact with an ABA-containing medium, the endocarpus. The highest germination percentages at 72 h, observed in tss1 and tss2, coincided with minimal ABA content. Wild-type and mutant seeds showed different ABA and catabolic patterns, and these were correlated with their sensitivity to abiotic stress. Whereas dry seeds showed a high basal ABA, imbibed seeds showed higher ABA metabolite content, particularly DPA. The dramatic decrease of ABA following seed imbibition suggests an activation of ABA catabolism during the early stages of the germination process. The observed variation of ABA metabolites among dry and imbibed seeds of Solanum lycopersicum cv. Moneymaker and its tss1, tss2 and tos1 mutants shows that ABA metabolism is differentially regulated in these genotypes.

In vitro techniques are essential for Striga research and the development of appropriate control methods. In the laboratory, pre-screening of non-host or false-host plants of Striga for trap cropping or the screening of hosts for resistance involves visual evaluation of Striga seed germination that may be stimulated by plant parts or root exudates. This technique is presently laborious because the small Striga radicles are colourless. A number of solutions were evaluated to visualize the radicles of Striga hermonthica to obtain a reliable, simple and fast staining method yielding good contrast for visual observation, with readily available, inexpensive and minimally toxic dyes and staining solutions. The inks Brilliant Blue (Pelikan), Blue (Geha) and Brilliant Green (Pelikan), in either vinegar or lactic acid, produced radicles with excellent contrast, whereas radicles stained with Brilliant Red (Pelikan), Black (Sheaffer), Brilliant Black (Pelikan) gave good contrast. Striga radicles stained with Aniline Blue in vinegar or lactic acid, or Coomassie Brilliant Blue R250 in lactic acid, showed excellent contrast. Radicles stained with Ink Black (Sheaffer), Cotton Brown, or Rubin S in either vinegar or lactic acid also showed good contrast. With water as the diluent, only Lactophenol Blue showed excellent contrast. For health, safety and environmental concerns, availability and staining time, Blue ink in household vinegar (5% acetic acid) appears to be an excellent dye for Striga radicles and could be used in routine Striga germination assays.