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

The Myrtaceae is the ninth largest angiosperm family with c . 6000 species, and it diverged from its closest relative the Vochysiaceae c . 100 Ma in southern Gondwana before the final separation of South America and Australia from Antarctica. The family has trees and shrubs and a few viny epiphytes but no herbs and mainly occurs in the tropics and in temperate regions with a Mediterranean climate. Numerous fleshy-fruited species and dry-fruited species have evolved in moist and seasonally dry (fire-prone) regions, respectively. Five kinds of fully developed embryos are found in Myrtaceae seeds, and at maturity seeds are either nondormant (ND) or have physiological dormancy, regardless of embryo morphology, kind of fruit produced, life form, habitat/vegetation region or tribe. Dormant seeds of fleshy-fruited species in wet habitats become ND and germinate at high temperatures. Dormant seeds of dry-fruited species in seasonally dry habitats become ND during the hot, dry season and germinate with the onset of the wet season; seeds germinate only at high temperatures or over a range of low to high temperatures, depending on the species. Seeds of fleshy-fruited species are animal-dispersed, and some Myrteae and Syzygieae are desiccation-sensitive and/or exhibit totipotency. Relatively few species form a persistent soil seed bank, but many dry-fruited species in fire-prone habitats form an aerial seed bank (serotiny). Heat and smoke from fires have a negative, neutral or positive effect on germination, depending on the species. Challenges for maintaining the high species richness of Myrtaceae include habitat destruction/fragmentation, pathogenic fungi and climate change, especially patterns of precipitation.

Our aim was to quantify the life‐history strategies of the cold desert annual species Alyssum linifolium and Tetracme quadricornis (Brassicaceae), with particular emphasis on the seed stage. Freshly matured seeds were tested for germination over a range of alternating temperature regimes in light and in dark, and the effects of seed coat scarification, cold stratification, dry after‐ripening and GA3 on dormancy‐break and germination were determined. Seeds were buried in the field at 0 (surface), 2 and 5 cm and germination of exhumed seeds tested at monthly intervals for 2 years. Seedling emergence of both species was monitored in the cold desert, and survival to maturity of plants from autumn‐ and spring‐germinated cohorts was determined. Most fresh seeds were dormant, and dormancy was broken by all four treatments tested. In the early stages of dormancy‐break, seeds germinated to low percentages over the range of temperatures, and with additional dormancy‐break germination percentages increased. Thus, seeds have Type 6 non‐deep physiological dormancy. In the buried seed study, dormancy‐break occurred in summer (June–August), and germination peaked in late summer. By late autumn (November), all non‐germinated seeds had re‐entered dormancy. During snowmelt in late winter (February–March), some dormancy‐break occurred, and low percentages of seeds of both species germinated. In the field, seeds of both species germinate in autumn and in spring, with more seeds of A. linifolium germinating in autumn than in spring and more seeds of T. quadricornis germinating in spring than in autumn. A portion of plants from both seedling cohorts of both species survived to maturity (set seeds) with more spring‐ than autumn‐germinating plants doing so for both species. Thus, both species behave as facultative winter annuals. Synthesis. Seeds of A. linifolium and T. quadricornis have two dormancy cycles per year. In one cycle, dormancy is broken via warm temperatures in summer and in the other one via cold stratification in late winter. Semiannual dormancy cycling results in two germination cohorts in 1 year, and it may be a bet‐hedging strategy in the rainfall‐unpredictable cold desert environment.

Main conclusion Polyploidization (diploidy → polyploidy) was more likely to be positively associated with seed mass than with seed germination. Abstract Polyploidy is common in flowering plants, and polyploidization can be associated with the various stages of a plant’s life cycle. Our primary aim was to determine the association (positive, none or negative) of polyploidy with seed mass/germination via a literature review. We found that the number of cases of positive, none and negative correlates of polyploidization was 28, 36 and 21, respectively, for seed germination and 25, 5 and 3, respectively, for seed mass. In many plant species, ploidy level differs within and between populations, and it may be positively or negatively associated with germination (57.6% of 85 cases in our review). Ideally, then, to accurately assess intra- and interpopulation variation in seed germination, such studies should include ploidy level. This is the first in-depth review of the association of polyploidy with seed germination.

We have reviewed seed dormancy and germination in the Rubiaceae, the fourth-largest angiosperm family (in terms of species richness), in relation to ecology, life form, biogeography and phylogeny (subfamily/tribe). Life forms include trees, shrubs, vines and herbs, and tropical rainforest trees have the greatest number of tribes and species. The family has five kinds of embryos: investing, linear-full, linear-underdeveloped, spatulate and spatulate-underdeveloped, and seeds are non-dormant (ND) or have morphological (MD), morphophysiological (MPD) or physiological (PD) dormancy. Except for the occurrence of the investing embryo only in dry fruits of Dialypetalanthoideae, each kind of embryo is found in dry and fleshy fruits of Dialypetalanthodies and of Rubioideae. In tropical and temperate regions, there are species with ND seeds and others whose seeds have MD, MPD or PD. A complete seed dormancy profile (i.e. some species with ND seeds and others whose seeds have MD, MPD or PD) was found for tropical rainforest trees and shrubs and semi-evergreen rainforest shrubs. Dormancy-break occurs during cold or warm stratification or dry-afterripening, depending on the species. Some tropical species have long periods of dormancy-break/germination extending for 4–5 to 30–40 weeks. Soil seed banks are found in 5 and 15 tribes of Rubiaceae in tropical and temperate regions, respectively. With increased distance from the Equator, diversity of life forms and seed dormancy decreases, resulting in only herbs with PD at high latitudes. We conclude that the low species richness of Rubiaceae in temperate regions is not related to low diversity of seed dormancy/germination.

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.