The water uptake by the seed in arid and semi-arid ecosystems may not be continuous, but may occur in hydration and dehydration cycles (HD). In order to investigate the benefits of discontinuous hydration on seed germination of Pilosocereus catingicola subsp. salvadorensis subjected to environmental stresses, an imbibition curve was determined and times X, Y and Z selected, corresponding to 25, 50 and 75% of the first phase of imbibition, respectively. Seeds of two populations (Caatinga and Restinga) were subjected to 0, 1, 2 and 3 HD cycles, with 48 h of dehydration. Water and saline stress responses were tested at five osmotic potentials (0.0, –0.1, –0.3, –0.6 and –0.9 MPa). Discontinuous hydration provided greater tolerance to water and saline stress in the seeds from the Caatinga region. When the seeds were subjected to water stress, the reduction of the mean germination time (MGT) provided by HD cycles decreased with increasing concentration of the solution. In saline stress, the reduction of MGT was greater in the solutions with the highest concentrations. We conclude that the seeds of the same species collected from populations located in different ecosystems have different germination responses after passage through discontinuous hydration and HD cycles. This provides greater tolerance to environmental stresses but with different responses among populations.

Observations in a citrus grove indicated that hairy beggarticks numbers were higher in plots receiving thiazopyr alone or thiazopyr with oxyfluorfen than in nontreated plots. At 120 days after treatment (DAT), approximately 90% more hairy beggarticks plants had emerged in plots receiving thiazopyr at 0.56 kg ai/ha than in nontreated plots. A tank mix of thiazopyr plus oxyfluorfen, each at 0.56 kg/ha, resulted in a 55% increase in hairy beggarticks number at 120 DAT. Greenhouse studies using seeds collected from sites with or without herbicide history produced similar results. Oxyfluorfen at 0.28 kg/ha stimulated seed germination but injured seedlings by 47% or more at 36 DAT when applied at higher rates. Thiazopyr applied at 0.56 kg/ha antagonized the preemergence activity of oxyfluorfen at 0.28 or 0.56 kg/ha. Thiazopyr at 1.12 kg/ha stimulated hairy beggarticks germination by 37% compared with nontreated containers.

Sweet corn is seeded under a wide range of population densities; however, the extent to which variable population density influences weed suppression is unknown. Therefore, field studies were undertaken to quantify the influence of sweet corn seeding level on growth, seed production, and post-harvest seed germination of wild-proso millet, one of the most problematic weeds in the crop. As crop seeding level increased, path analysis results indicated the crop canopy became taller and thicker, resulting in less wild-proso millet biomass, seed production, and germinability. However, at the level of individual fields, reductions in wild-proso millet growth and seed production were modest, at best, between a crop population currently used by growers and a higher crop population known to optimize yield of certain hybrids. These results indicate near-future increases in sweet corn seeding levels may play a minor role in improving weed management in individual sweet corn fields. Nonetheless, a reduction in crop populations, via weather- or management-driven phenomenon, increases risk of greater wild-proso millet seed production.

Modification of the cropping environment to make weed seed more susceptible to fatal germination or decay processes is based, in part, on the premise that seed longevity is affected by the crop-influenced environment in which seed is produced, hereafter, called the maternal crop environment. The objective of this investigation was to determine the influence of maternal crop environment on wild-proso millet seed production, germinability, and seed coat tone (i.e., lightness), a trait previously associated with seed longevity in wild-proso millet. Maternal corn environments were established by growing wild-proso millet plants in four morphologically different sweet corn hybrids in four replicates over 2 yr. Wild-proso millet seed was collected at sweet corn harvest, enumerated, characterized for seed coat tone, and tested for germination. Principal component factor analysis reduced six sweet corn traits measured between silking and harvest into a single maternal corn environment factor that accounted for 84% of the variation among crop canopies. Functional relationships between maternal corn environment factor scores and wild-proso millet seed characteristics were clarified by fitting linear models. For each unit decrease in maternal environment factor score, wild-proso millet seed production increased 1,535 seed m−2, germination increased 2.2%, and seed coat tone was 1.8% lighter. These results show the size and germinability of wild-proso millet seed was highest in less-competitive maternal corn environments characterized by a short time to crop maturity and a small crop-canopy size.

Miconia chartacea is a widely distributed tree in Brazil, occurring at altitudes ranging from 300 m to 1900 m in the Caatinga, Cerrado and Atlantic Forest biomes. In this work we attempted to classify M. chartacea seeds regarding their behaviour during storage and their germination syndrome and to determine, from a storage test in Cerrado soil and laboratory conditions in situ and ex situ, the longevity of seeds, as well as the capacity of the species to form a soil seed bank. The results suggested that M. chartacea seeds form a transient soil seed bank in the Cerrado and can be classified as orthodox in terms of storage behaviour, although the seeds are dispersed with a relatively high water content. The life span of seeds was favoured in soil-stored seeds in comparison with dry storage at 25°C, whereas storage at low temperatures prevented a decrease of the seed's germinability with storage time (330 d). M. chartacea seeds are dispersed during the dry season and germinate during the next rainy season, which can be classified as an intermediate–dry germination syndrome. Seeds of this species are dispersed in the Cerrado when temperatures and soil moisture are relatively low, which favours the formation of a soil seed bank, considering that the seeds tolerate desiccation and their longevity is favoured by low temperatures. A transient seed bank type is favoured by the loss of viability in storage at warm temperatures linked to the rainy season, and the predictable seasonal variations in climate in the region, with germination being restricted to the beginning of the rainy season.

Some of the seed-evolved volatiles, which were mainly composed of methanol, acetaldehyde, ethanol and acetone, caused the loss of seed germinability during storage. In general, the deleterious effects of the volatiles increased with increasing RH and temperature during storage. Acetaldehyde had the strongest deleterious effect regardless of RH and temperature, while ethanol caused seed deterioration only at high RHs. Acetone was slightly deleterious to some species, while methanol was almost inert in most seeds. Various aldehydes applied during storage showed some toxicity to seed germinability, which decreased, except for 3-methylbutanal, with increasing molecular size, suggesting that the endogenous volatile compounds with an aldehyde group cause seed deterioration. On the other hand, the contents of volatile compounds in seeds were higher when they were stored at 44% RH (water sorption zone 2), than when stored at 12% RH (water sorption zone 1). Acetaldehyde, the most deleterious volatile, was more abundantly accumulated within the seeds stored at −3.5°C than at 23°C. Based on these facts, it is suggested that endogenous volatiles, especially acetaldehyde, may be an important factor that accelerates seed deterioration which often occurs under lower RHs and/or temperatures throughout long-term storage.

Germinability and the rate of germination were related to seed mass in Lithospermum arvense L. and Anchusa arvensis (L.) Bieb. Prior to germination experiments, seeds from two populations of each species had been sorted into nine similarly sized groups according to their seed mass. Germinability varied greatly among the different seed-mass fractions in L. arvense, while differences were smaller in A. arvensis. Germination rate varied with seed mass in some cases. However, in many cases where clear patterns in the relationship between germination characteristics and seed mass were found, these patterns differed both between species and between populations. Furthermore, the character of the relationship varied depending on the experimental conditions used. It is hard to identify the cause of these relations since within- and between-plant variability can affect both seed mass and germination characteristics independently. It is concluded that the results of a germination test can differ depending on the seed mass fractions used, but that the magnitude and direction of such differences are difficult to foresee. Therefore, seed batches should be prepared with care, and experiments designed with awareness of the importance of the germination conditions chosen.

Development of the highly desiccation-sensitive (recalcitrant) seeds of primarily one species, Avicennia marina, is reviewed and compared with the ontogeny of desiccation-tolerant (orthodox) seeds. A. marina seeds undergo no maturation drying and remain metabolically active throughout development, which grades almost imperceptibly into germination. While PGR control of histodifferentiation is essentially similar to that characterizing desiccation-tolerant seeds, the phase of growth and reserve deposition is characterized by exceedingly high cytokinin levels which, it is proposed, promote a sink for assimilate import. While some starch accumulation does occur, the predominant reserves are soluble sugars which are readily available for the immediate onset of seedling establishment upon shedding. ABA levels are negligible in the embryo tissues during seed maturation, but increase in the pericarp, which imposes a constraint upon germination until these outer coverings are sloughed or otherwise removed. The pattern of proteins synthesized remains qualitatively similar throughout seed development in A. marina, and no LEA proteins are produced. This suggests both that seedling establishment is independent of maturation proteins and that the absence of LEAs and desiccation sensitivity might be causally related. The study on A. marina reveals that for this recalcitrant seed-type, germination per se cannot be defined: rather, it is considered as the continuation of development temporarily constrained by the pericarp ABA levels. This leads to a reexamination of the role of rehydration as key event sensu stricto, in the germination processes in desiccation-tolerant (orthodox) seeds.

Introduction. Canarium schweinfurthii, a tree species in the rainforest of Nigeria whose fruits are intensively gathered and eaten, is seriously endangered because of poor seed germinability and usage. Our study examined the pattern of seed distribution of C. schweinfurthii in the soil from the stem base of the parent plant and through the soil profile, and it assessed the seed level of germinability. Materials and methods. Four stands of C. schweinfurthii were selected from a study area in Southeastern Nigeria. Soils were collected from six distances from each trunk base (1 m, 5 m, 10 m, 15 m, 20 m and 25 m) and at four soil depths (0–5 cm, 5–10 cm, 10–20 cm and 20–30 cm); then seeds of C. schweinfurthii were isolated from the cores. Moreover, the percentage of viability and germinability of the seeds collected from each distance and depth were determined. Results. The maximum number of seeds occurred at 1 m from the trunk base (82.3 seeds·30 cm–2), which was 55% of the total collected seeds, and no seed occurred beyond 20 m from the trunk base. The mean number of C. schweinfurthii seeds occurring at 0–5 cm soil depth was 51.3 seeds·30 cm–2, which was the highest from any profile. No seeds occurred below 20 cm. Sixty-seven percent of the total 148 seeds collected were considered viable, with about 80% of them occurring at the 0–5 cm soil depth. Even with the pre-sowing treatment (cutting the hard endocarp), only 30.8% of viable seeds collected from 0–5 cm soil depth were able to germinate, while 10% of those collected from 5–10 cm depth germinated. Conclusion. The localization of over 80% of C. schweinfurthii seeds within a 5-m radius from the stem base and 65% within 0–5 cm soil depth encourages easy fruit gathering by local sellers and leads to depletion of the seed bank. Seedling multiplication, protection of stands and domestication need to be initiated to lift C. schweinfurthii out of endangered status, considering the demand for the fruit and poor seed germination due to the hard endocarp.

Introduction.Garcinia kola, a multi-purpose fruit tree, produces fruit, seeds, roots and stem which are extensively used in Nigeria, Ghana and other West African countries for dental care. Cultivation of this fruit tree is limited because of poor seed germination. Our study therefore aimed at improving seed germination properties which will promote cultivation of G. kola by rural farmers. Materials and methods. Seeds taken from a single tree of G. kola were treated with cold water (22 °C), hot water (60 °C) and gibberelic acid (0.5 g × L-1) for various lengths of time. They were then put to incubate in sterilized river sand or a thick transparent polyethylene bag to evaluate the capacities of seed to be germinated under such conditions. In addition, the seed moisture content at harvest was also reduced to various levels before incubation in polyethylene bags to determine the critical moisture rate necessary for seeds to germinate. Results. The seeds incubated in the river sand without any treatment before sowing had an average time of germination of 71.2 d and a total percentage of germination of 28% whereas those incubated in polyethylene bags had an average time of germination of 25.8 d and a total percentage of germination of 62% . The cold water treatment, irrespective of the incubation method, did not significantly affect either the mean germination time or the total germination percentage. However, it significantly reduced the spreading out of the seed germination to 5.4 d. The seed pretreatment with gibberelic acid prolonged at the same time the average time of germination and the spreading out of the germination. The seed water content at harvest (50.4%) allowed the best rate of seed germination and the shortest spreading out of the germination period. Conclusion. The pretreatment of freshly harvested seeds with cold water followed by an incubation in a thick transparent polyethylene bag proved most effective in enhancing the germination of G. kola seeds. This procedure has to be recommended to promote the cultivation of this species.

Introduction. Des géniteurs d'amandiers autocompatibles ont souvent été utilisés pour introduire le caractère d'autocompatibilité dans leur descendance. Cependant, lors de tels programmes de création variétale, des problèmes de germination des graines obtenues et des difficultés de survie des jeunes plants ont été mis en évidence. L'objectif des travaux réalisés a été de quantifier les effets de la consanguinité sur certaines caractéristiques du développement des semences issues de tels géniteurs. Matériel et méthodes. Les descendances de la variété autocompatible Tuono autofécondée ou croisée avec des géniteurs mâles génétiquement éloignés ont été suivies et comparées, de la germination à l'âge de 3 ans. Les taux de germination, de levée et la vitesse de levée ont été évalués. Puis la croissance des plants a été étudiée à partir de la mesure régulière du diamètre de l'axe et de la hauteur des plants. Le nombre de nœuds, d'entre-nœuds, de rameaux anticipés et le taux de mortalité des plantules ont également été notés. Résultats. Par rapport aux semences issues d'allopollinisation, les graines issues d'autofécondation ont présenté un taux de germination moyen inférieur (61 % contre 81 %) ; la vigueur de leurs plantules, leur croissance radiale et apicale et le nombre de rameaux anticipés formés ont été plus faibles ; leur taux de mortalité a été supérieur (28 % contre 0,6 %). Discussion et conclusion. Les anomalies mises en évidence au cours de ces travaux seraient dues à l'endogamie et liées à l'accumulation de gènes défavorables dans la descendance consanguine.