Jerry M. Baskin’s research while affiliated with University of Kentucky and other places

Hordeum spontaneum is a winter annual weed that reduces crop yields in Iran. The aim of this study was to quantitatively analyze the effects of burial on seed longevity and germinability and of water potential and temperature on germination. Seeds were placed in nylon‐mesh bags and buried in soil in a semi‐arid region on 1 July 2018 and exposed to natural temperature regimes. After 2 months of burial, seed viability started to decline with a slope of 0.0169%, and after 9 months all seeds were nonviable. Fresh seeds were dormant, but became non‐dormant during summer via dry after‐ripening. Thus, by late autumn (December) the seeds germinated to 100% in dark at 5 and 15°C. The base, optimum, and ceiling temperatures were 0.27, 17.5, and 25°C, respectively, at a water potential of 0 MPa. The hydrotime constant was 50.6–426.9 MPa h, base water potential −1.23 to −0.333 MPa and hydrothermal constant 1350.5 MPa °C h. These results can be used to predict timing and extent of weed emergence of H. spontaneum in crops and in planning for sustainable management strategies.

Background and aims Seed heteromorphism is a plant strategy that an individual plant produces two or more distinct types of diaspores, which have diverse morphology, dispersal ability, ecological functions and different effects on plant life history traits. The aim of this study was to test the effects of seasonal soil salinity and burial depth on the dynamics of dormancy/germination and persistence/depletion of buried trimorphic diaspores of a desert annual halophyte Atriplex centralasiatica. Methods We investigated the effects of salinity and seasonal fluctuations of temperature on germination, recovery of germination and mortality of types A, B, C diaspores of A. centralasiatica in the laboratory and buried diaspores in situ at four soil salinities and three depths. Diaspores were collected monthly from the seedbank from December 2016 to November 2018, and the number of viable diaspores remaining (not depleted) and their germinability were determined. Results Non-dormant type A diaspores were depleted in the low salinity “window” in the first year. Dormant diaspore types B and C germinated to high percentages at 0.3 and 0.1 mol L⁻¹ soil salinity, respectively. High salinity and shallow burial delayed depletion of diaspore types B and C. High salinity delayed depletion time of the three diaspore types and delayed dormancy release of types B and C diaspores from autumn to spring. Soil salinity modified the response of diaspores in the seedbank by delaying seed dormancy release in autum and winter and by providing a low-salt concentration window for germination of non-dormant diaspores in spring and early summer. Conclusions Buried trimorphic diaspores of annual desert halophyte A. centralasiatica exhibited diverse dormancy/germination behavior in respond to seasonal soil salinity fluctuation. Prolonging persistence of the seedbank and delaying depletion of diaspores under salt stress in situ primarily is due to inhibition of dormancy-break. The differences in dormancy/germination and seed persistence in the soil seedbank may be a bet-hadging strategy adapted to stressful temporal and spatial heterogeneity, and allows A. centralasiatica to persist in the unpredictable cold desert enevironment.

Argyreia is the most recently evolved genus in the Convolvulaceae, and available information suggests that most species in this family produce seeds with physical dormancy (PY). Our aim was to understand the evolution of seed dormancy in this family via an investigation of dormancy, storage behaviour, morphology and anatomy of seeds of five Argyreia species from Sri Lanka. Imbibition, germination and dye tracking of fresh intact and manually scarified seeds were studied. Scanning electron micrographs and hand sections of the hilar area and the seed coat away from the hilar area were compared. Scarified and intact seeds of A. kleiniana, A. hirsuta and A. zeylanica imbibed water and germinated to a high percentage, but only scarified seeds of A. nervosa and A. osyrensis did so. Thus, seeds of the three former species are non-dormant (ND), while those of the latter two have physical dormancy (PY); this result was confirmed by dye-tracking experiments. Since > 90 % of A. kleiniana, A. hirsuta and A. zeylanica seeds survived desiccation to 10 % moisture content (MC) and > 90 % of A. nervosa and A. osyrensis seeds with a dispersal MC of ~ 12 % were viable, seeds of the five species were desiccation-tolerant. A. nervosa and A. osyrensis have a wide geographical distribution and PY, while A. kleiniana, A. hirsuta and A. zeylanica have a restricted distribution and ND. Although seeds of A. kleiniana are ND, their seed coat anatomy is similar to that of A. osyrensis with PY. These observations suggest that the ND of A. kleiniana, A. hirsuta and A. zeylanica seeds is the result of an evolutionary reversal from PY and that ND may be an adaptation of these species to the environmental conditions of their wet aseasonal habitats.

Environmental factors, such as temperature and moisture, and plant factors, such as seed position on the mother plant, can affect seed viability and germination. However, little is known about the viability and germination of seeds in different positions on the mother plant after burial in soil under natural environmental conditions. Here, diaspores from three positions on a compound spike and seeds from two/three positions in a diaspore of the invasive diaspore‐heteromorphic annual grass Aegilops tauschii were buried at four depths for more than 2 years (1–26 months) under natural conditions and viability and germination monitored monthly. Viability of seeds in each diaspore/seed position decreased as burial depth and duration increased and was associated with changes in soil temperature and moisture. Germination was highest at 2 cm and lowest at 10 cm soil depths, with peaks and valleys in autumn/spring and winter/summer, respectively. Overall, seeds in distal diaspore and distal seed positions had higher germination percentages than those in basal diaspore and basal seed positions, but basal ones lived longer than distal ones. Chemical content of fresh diaspores/seeds was related to diaspore/seed position effects on seed germination and viability during burial. We conclude that seeds in distal diaspores/seed positions have a ‘high risk’ strategy and those in basal positions a ‘low risk’ strategy. The two risk strategies may act as a bet‐hedging strategy that spreads risks of germination failure in the soil seed bank over time, thereby facilitating the survival and invasiveness of A. tauschii .

Seed heteromorphism’ is a broadly- and loosely-defined term used to describe differences in size/mass, morphology, position on mother plants and ecological function (e.g. dispersal, dormancy/germination) of two or more seeds or other diaspores produced by an individual plant. The primary aim of this review paper was to characterize via an in-depth classification scheme the physical structural design (‘architecture’) of diaspore monomorphism and diaspore heteromorphism in angiosperms. The diaspore classification schemes of Mandák and Barker were expanded/modified, and in doing so some of the terminology that Zohary, Ellner and Shmida, and van der Pijl used for describing diaspore dispersal were incorporated into our system. Based on their (relative) size, morphology and position on the mother plant, diaspores of angiosperms were divided into two divisions and each of these into several successively lower hierarchical layers. Thus, our classification scheme, an earlier version of which was published in the second edition of ‘Seeds’ by Baskin and Baskin, includes not only heteromorphic but also monomorphic diaspores, the Division to which the diaspores of the vast majority of angiosperms belong. The scheme will be useful in describing the ecology, biogeography and evolution of seed heteromorphism in flowering plants.

Small isolated plant populations are one of the consequences of fragmentation of natural habitats by humans. We asked what effect does the creation of smaller populations from larger ones has on the plant fitness-related trait seed germination. Using information on 119 species (142 species entries) in 50 families, we found that seeds in only 35.2% of the species entries from larger populations germinated to higher percentages than those from smaller populations. In the other entries, seeds from large and small populations germinated equally well (57.7% of total entries) or seeds from small populations germinated better (7.0% of total entries) than those from large populations. These results indicate that population size is not a reliable predictor of seed germinability. Furthermore, there was little relationship between seed germination and either seed mass, genetic diversity or degree of population isolation, or between population size and genetic diversity.

The herbaceous legume Mimosa pudica is an invasive weed in many tropical and subtropical regions, as a serious problem for farmers since it is difficult to clear by hand. Moreover, it has water impermeable seeds, i.e. physical dormancy (PY), which could persist longer in the soil seed bank than non-dormant seeds, making big challenge in weed control. The aim of this study were to test the effect of various methods known to break PY in seeds of M. pudica, to identify the site(s) of water entry into seeds of M. pudica and also compare results of dormancy-breaking methods for seeds of M. pudica with those of 36 other species of Mimosa reported in the literature. Mechanical scarification, wet heat and cycles of wet heat and ice water effectively broke PY. Following wet heat at 80 ˚C for 10 min, water uptake was via the hilar region but not the pleurogram. Since PY has been reported in 36 species of Mimosa tested that includes invasive, rare and endemic species, it seems obvious that this kind of dormancy is not the cause of weediness in M. pudica. Further, the 36 species represent four of the five taxonomic sections of Mimosa, and thus it is likely that seeds of most of all of the about 500 species in the genus have PY.

While there is long‐standing interest in the role of inter‐ and transgenerational plasticity via the maternal line, it rarely has been studied via the paternal line. Thus, consequences of the paternal environment for parental fitness and for performance of offspring in the environments experienced by either fathers or mothers are not known. We studied the intergenerational plasticity (IGP) of the plant species Paeonia ostii (Paeoniaceae) and tested the hypothesis that exposure of fathers to environmental stress (i) reduces parental fitness and performance of offspring grown under non‐stressful conditions, but (ii) mitigates the negative effects of environmental stress on fitness of parents and performance of offspring. Crosses were made in a greenhouse within six families of P. ostii between parents grown under drought and in a mesic environment, and the offspring of each cross were grown under both dry and mesic conditions. Production and germination of seeds and morphological and physiological traits of offspring were measured as indicators of parental fitness and offspring performance, respectively. Paternal drought decreased seed number per fruit, except when maternal plants also were grown in drought conditions. Offspring drought decreased seedling performance. However, when fathers experienced drought this negative effect on the offspring was partly mitigated, in particular when mothers also had experienced drought. In contrast, offspring grown in mesic conditions had improved seedling performance, especially when either parent (or both) also were grown in mesic conditions. Such statistical differences remained when seed mass was included as a covariate. Overall, paternal pollen of P. ostii mediated IGP to drought almost as well as it did for maternal ovules. IGP was adaptive if environments remained constantly dry across generations but maladaptive if environments changed. Hence, under future climate changes, paternal IGP might be both a blessing and a curse, with the blessing occurring when the focal habitat becomes drier and pollen comes from already‐dry places, while the curse may dominate in predictably moist habitats surrounded by drier habitats. Read the free Plain Language Summary for this article on the Journal blog.

We investigated seed dormancy and germination characteristics of two endangered medicinal species, Rhodiola crenulata and R. fastigiata , from the high altitude (alpine) Hengduan Mountains in China. Germination of fresh seeds was tested in light and dark at six constant (1, 5, 10, 15, 20 and 25°C) and three alternating (5/1, 15/5 and 25/15°C) temperatures and again, after six months of dry after-ripening (DAR) and cold-wet stratification (CS). Fresh seeds of R. crenulata germinated to ≥ 80% at 10, 15, 25/15 and 15/5°C in light, but germination was significantly lower at 1, 5, 20 and 25°C. Germination of fresh seeds in dark was 0 to 25% across the range of temperatures. DAR and CS for six months increased germination and/or decreased mean germination time in both light and dark. Fresh seeds of R. fastigiata germinated to > 95% in both light and dark, except at 1°C in light and 1, 5, and 5/1°C in dark, where germination was < 50%. DAR and CS for six months increased germination and/or decreased mean germination time. Seeds of the two Rhodiola species have (conditional) non-deep physiological dormancy. Germination responses to temperature and light prevent seeds from germinating in the autumn of dispersal, but allow them to germinate quickly after snow melt the next spring. This study provides a method for obtaining plants from seeds of the two Rhodiola species for medicinal uses, which could reduce the harvesting pressure placed on natural populations.