Jointed goatgrass and downy brome continue to plague winter wheat producers in the western United States. Because there are no effective herbicides for in-crop control of these weeds, producers are seeking cultural practices that stimulate seed germination and deplete the soil seed bank. We determined the effect of limited tillage and crop canopy on seedling emergence of these grasses. One tillage operation with a sweep plow increased jointed goatgrass seedling emergence 74% in the first year but did not affect emergence in later years. Downy brome emergence was not affected by tillage. Jointed goatgrass seedlings emerged over 5 yr, whereas downy brome did not emerge after 3 yr. Seedling emergence of both species was two times greater in corn and barley than in proso millet. Producers will accrue more benefit for seedbank management with cultural strategies such as alternative rotations and competitive wheat canopies than with limited tillage using a sweep plow.

Garden huckleberry, a member of the Solanaceae family and a close relative of black nightshade, is an exotic plant introduced from Africa. Information on garden huckleberry response to a new environment and to herbicides is useful for determining the potential of this species to become an invasive weed, predicting the potential range of this species in the United States, and developing an optimum garden huckleberry management program. Germination and survival of garden huckleberry seed, as affected by environmental factors, were studied under greenhouse and controlled-environment growth chamber conditions. Garden huckleberry seed became viable between 2 and 3 wk after anthesis and was nondormant when separated from fresh berries. Garden huckleberry seed was not photoblastic and germinated equally well under both a 14-h photoperiod and continuous darkness. Seed germinated at constant temperatures from 17 to 35 C, with optimum germination between 22 and 30 C. Germination of garden huckleberry seed markedly declined as the osmotic potential of the germination medium decreased. The optimum pH for germination of garden huckleberry was between 5 and 9. Paraquat, dicamba, and bromoxynil provided excellent garden huckleberry control (95 to 100%); atrazine and glyphosate were more phytotoxic (90%) than imazamox (80%); and acifluorfen and foramsulfuron gave inadequate control.

Wild oat is the most important weed in Argentine barley and one of the worst weeds in wheat and barley worldwide. During 1997 and 1998, field experiments were performed to determine the response of wild oat to N fertilizer at planting and at early tillering at 55 kg ha−1 with and without the use of diclofop-methyl. Seedling emergence and survival rate, individual fecundity, and preharvest seed dispersal rate of wild oat were assessed. The effect on the individual growth of wild oat was also studied. N fertilizer increased both wild oat seedling survival rate and fecundity, especially when it was applied at early tillering. However, the effect of N fertilization was negligible with diclofop-methyl treatment. In addition, the application of N fertilizer reduced the seed dispersal rate immediately before crop harvest. Quantification of the effects of each agronomic practice, such as N fertilization, is useful to develop simulation models that predict the population dynamics. When N was applied at sowing, the annual growth rate of the wild oat population was almost 25% lower than when applied at early tillering.

There was fruiting of the dipterocarps of Pantai Aceh Forest Reserve, Penang, Peninsular Malaysia in September 1986. The opportunity was taken to investigate the establishment and seedling survival of Shorea curtisii, Shorea multiflora and Shorea pauciflora over the subsequent year. The germination and seedling survival of Shorea curtisii was compared between canopy gaps and forest understorey sites.

Under the shaded conditions none of the species grew beyond the two leaf stage over their first year. Shorea multiflora seedlings suffered a 72% mortality, significantly lower than that of Shorea pauciflora (89%) and Shorea curtisii (93%). The major cause of mortality appeared to be drought, though Shorea curtisii was also prone to predation by small mammals.

In a gap, Shorea curtisii seeds probably germinated less well but seedling survival (28% versus 7%) and growth was better than canopy-shaded conspecifics. Seedlings in gaps escaped small mammal predation.

Field experiments and survival analysis were used to test whether the Janzen-Connell model operated for two common Amazonian tree species in Peru: the midstorey palm, Astrocaryum murumuru, and the canopy-emergent legume, Dipteryx micrantha. Seed and seedling survival patterns of these species partially supported the model, depending on tree species, type of predator, spatial scale and the particular year. At a small scale of a 2.5-ha plot, Astrocaryum seed predation by insects and mammals was density-dependent. At a larger scale of 100 ha, Dipteryx seed survival increased with distance from conspecific adults, but for Astrocaryum seeds there was no distance dependence. At the scale of 200–400 ha Dipteryx seed survival was negatively related to the number of individuals present in groups of conspecific adult trees. In 1992 a higher proportion of Astrocaryum seedlings survived far from, compared with close to, conspecific adult trees, whilst in 1993 more Dipteryx seedlings survived beneath conspecific adult trees than farther away.

The dynamics of early life-history stages are important for understanding regional diversity patterns in tropical trees. In this study, patterns of seed removal, seedling survival and ectomycorrhizal (ECM) colonization in monodominant and mixed tropical rain forests in Guyana were investigated during a masting event of an ECM monodominant tree, Dicymbe corymbosa. Two seed densities (1 m−2 and 6 m−2) were tested in two forest types (monodominant versus mixed) with 10 plots per treatment (40 plots total). Germination success, seed and seedling survival after 1 y were measured for the monodominant tree, and four non-dominant canopy tree species found in both forest types (Eschweilera sagotiana, Licania laxiflora, Chrysophyllum sanguinolentum and Carapa guianensis). A significant effect of forest type was detected for seed removal and seedling survival. In the mixed forest, seed removal was higher for all species, with 27% average removal compared with 7% average seed removal in the monodominant forest. Germination success was significantly lower for all but one species in the mixed forest, with average germination of 41% compared with 78% germination in the monodominant forest. Seed and seedling survival of the monodominant tree was greatest within the monodominant forest with 93% of seeds germinating and 85% of seedlings surviving after 1 y compared with 65% germination and 15% seedling survival in the mixed forest. Per cent ectomycorrhizal colonization of Dicymbe corymbosa was near 100% in the monodominant forest, but significantly lower (14%) in the mixed forest. These results suggest that seedling survival patterns, rather than seed survival, are more important for recruitment success in this system and that ectomycorrhizal inoculum may limit establishment of Dicymbe corymbosa in the mixed forest.

Desiccation-tolerant organisms, or life-cycle stages of particular taxa, occur among animals, higher and lower plants, terrestrial micro-algae, lichens and bacteria. Recent investigations have revealed that a number of mechanisms conferring desiccation tolerance appear to be common to the diversity of life forms able to survive extreme dehydration. In particular, parallel processes involving late embryogenic abundant (LEA) or LEA-like proteins, accumulation of sugars, aspects of active oxygen species (AOS) and non-enzymic and enzymic antioxidants have been the recent focus of attention, some across a diversity of organisms. The present contribution considers advances made from the study of these processes, particularly in enhancing current understanding of the composition of, and protection afforded by, the glassy state in desiccated organisms. Strong evidence that proteins, particularly LEAs, are implicated in glass formation is reviewed, and behaviour of such proteins upon dehydration is discussed in this context. The question of the ability of cells to survive complete water removal is considered in the context that it is unlikely, and that the basis of the deterioration of very dry seeds results from abstraction of water necessary to maintain the integrity of the intracellular glassy state. Finally, the revelation that desiccated seeds deteriorate with time, even under extremely good genebanking conditions, is discussed.

In a field experiment with a susceptible population of annual wild carrot (Daucus carota) from Iran, artificial inoculations with the fungal pathogen A. dauci led to a strong and very significant increase of the diseased leaf area. The pathogen caused a very significant decrease in fecundity and seed survival of the host. This considerable fitness reduction by A. dauci would suggest that introgression of disease resistance from cultivated (transgenic) carrot cultivars into wild carrot populations could strongly increase the fitness of wild carrot. In spite of the potential ability of A. dauci to lower the fitness of the host considerably, wild carrot is very common in The Netherlands. Disease levels of wild carrot were estimated in 26 natural populations in 1998. No A. dauci could be detected on the leaves, and only 0.4% of the seeds were contaminated with A. dauci, in spite of the conducive weather for A. dauci. Resistance tests showed that all 26 monitored populations were highly resistant to A. dauci strains from The Netherlands. It is probable that the strong potential fitness reduction by A. dauci led to a high selection pressure towards resistance in The Netherlands. In conclusion, our results suggest that transgenic resistance to A. dauci would not be beneficial to wild carrot populations in The Netherlands because they are already resistant to this pathogen.

Palm seeds of the genus Astrocaryum are known to attract a wide range of seed predators, including insects, rodents and peccaries. We investigated the removal of seeds of Astrocaryum murumuru var. macrocalyx in dense groves and under solitary palms, both within and outside of peccary exclosures. We set out arrays of 40 seeds at each of 40 sites representing four treatments: in the open and in peccary exclosures, in groves and under solitary palms. Seed removal from each site was monitored daily for 55 d. Infra-red-triggered cameras were installed to identify the species that removed seeds. From the known and hypothesized behaviour of vertebrate seed predators under various circumstances, we predicted that (1) overall seed loss should be higher under solitary trees, (2) peccaries should forage preferentially in groves, (3) the variance in the rate of seed removal should be higher in groves, (4) a greater fraction of the seeds removed from solitary palms should be scatterhoarded, and consequently, (5) greater numbers of seedlings should recruit near solitary palms than in groves. The first four of these predictions were confirmed and the last was rejected by the results. Peccaries preferred to forage in groves, and small rodents preferred to forage under solitary palms. Whether in groves or under solitary palms, peccaries preferentially removed seeds from large arrays (21–40 seeds), and mostly ignored small arrays (≤ 20 seeds). Camera trapping demonstrated that the most frequent visitors to seed arrays were Myoprocta pratti and Proechimys spp. There was no significant difference in the numbers of seedlings around trees in groves versus solitary trees.