Climate warming may threaten the germination strategies of many plants that are uniquely adapted to today’s climate. For instance, species that employ physical dormancy (PY) – the production of seeds that are impermeable to water until high temperatures break them, consequently synchronizing germination with favorable growing conditions – may find that their seeds germinate during unfavorable or potentially fatal periods if threshold temperatures are reached earlier in the year. To explore this, we subjected the seeds of five species with physical dormancy (from the genera Abrus, Bauhinia, Cassia, Albizia, and Acacia) to “mild” (+2°C) and “extreme” (+4°C) future warming scenarios and documented their germination over 2 years relative to a control treatment. Under current climatic conditions, a proportion of seeds from all five species remained dormant in the soil for 2 years. A mild warming of 2°C had little to no effect on the germination of four of the five study species. Contrastingly, an extreme warming of 4°C dramatically increased germination in all five species within the first year, indicating a reduction in their ability to persist in the soil long-term. Cassia fistula was particularly susceptible to warming, exhibiting a similar increase in germination under both mild and extreme warming relative to control. Our findings suggest that climate warming in the tropics may cause the seeds of species that rely on physical dormancy to stagger the risk of unsuccessful germination across years to leave soil seed banks prematurely – the long-term implications of which remain unknown.

Abstract The aim of this work was to verify the effect of size classification on the physical and physiological quality of Eucalyptus spp. seeds to optimize the selection for covering. The seeds were separated in sieves with six size classes: 850, 710, 600, 500, 425 µm, and a non-perforated bottom (< 425 µm). Were evaluated the sieve retention, purity, weight of a thousand seeds, germination, and first count of germination. Sieve classification is effective for the separation of materials according to the best physical and physiological qualities. E. grandis seeds from the 710 µm sieve, E. robusta from the 850 µm sieve, and E. urophylla from the 710 and 850 µm sieves can be selected for covering, as they present maximum physical and physiological quality. For the three species, the smallest materials, retained in the 500, 425, and bottom <425µm sieves, must be discarded due to low purity and germination potential.

Objective: The objective was to evaluate different scarification treatments to improve germination in chepil seeds (Crotalaria longirostrata Hook. & Arn.). Design/Methodology/Approach: The study was established in the School of Veterinary Medicine and Zootechnics N. 2 of the Universidad Autónoma de Guerrero. The chepil seeds were weighed and counted; 2 experiments were established through a CRD with 4 treatments of 4 repetitions each. Imbibition and germination were evaluated. The data were analyzed with the statistical software package SAS® 9.0.Results: The use of water at different temperatures and times presented positive results in imbibition and increased the germination percentages. The treatment with water at 100 °C until cooling reached a germination of 80%, and the control of 12.3%.Study Limitations/Implications: Chepil is a wild species that has seeds with physical dormancy, which is something that requires more research in order to accelerate and increase the germination percentages. Findings/Conclusions: The imbibition and germination was affected by the treatments applied. Chepil seeds presented physical or superficial dormancy that may be eliminated with the use of heat treatments; however, evaluations still need to be performed to accelerate and find a higher percentage of germination

Understanding the germination cues of rare plants is critical to their conservation, restoration, and management. We used a greenhouse study to investigate the germination of Eriodictyon capitatum Eastw. (Lompoc yerba santa) seeds to understand the species' life history and to inform restoration efforts. Eriodictyon capitatum is a woody shrub that is listed as rare by the state of California and endangered by the U.S. Fish and Wildlife Service. Limited to just seven extant occurrences, E. capitatum does not currently readily produce seeds at most sites, but it does spread clonally, sometimes leading to low genetic diversity in aboveground vegetation. We collected seeds from one wild occurrence and measured germination rates in response to each of five physical treatments: control, dry heat, hot soak, liquid smoke, and scarification. Each physical treatment was replicated under both light and dark conditions. The highest percent germination was recorded with the liquid smoke treatment and the fastest germination occurred when seeds were sown in the dark and treated with liquid smoke. The significant impact of liquid smoke on seed germination suggests that E. capitatum is adapted to fire and that periodic fires could potentially promote aboveground genetic diversity by eliciting a flush of germination from the soil seed bank. These results can facilitate future propagation efforts, inform management, and also highlight the important role of fire in the life history of this endangered plant.

ABSTRACT The study on the native species of fast growth and nodulation capacity, Ormosia discolor, intends to conserve genetic resources and make available seed lots of high vigor for seed orchards. This work evaluates the physical and physiological characteristics of seeds from 20 O. discolor trees as a subsidy for selecting superior mother trees. Twenty matrices selected from a population in the state of Amazonas were inventoried. Physical tests were performed on the seeds collected, including water content, biometrics, the weight of one thousand seeds, and coat permeability test. For vigor estimates and classification regarding seed storage, the seeds were frozen for five months. The germination test was carried out at a constant temperature of 30 °C. It was used a completely randomized design consisting of 20 mother trees, 4 replicates, and 25 seeds per plot. The germination characteristics evaluated were germination percentage, speed index, mean germination time, and synchronization index. Cut seeds are more efficient for determining water content. All biometric variables are representative for the selection of vigorous lots, with emphasis on geometric diameter, surface area, and sphericity of seeds. Species seeds were classified as orthodox and as having physical dormancy. The protrusion of the primary root is the best morphological characteristic for evaluating germination in the laboratory. The mother trees 7, 16, and 10 showed superior characteristics for dendrometric and technological data, being indicated for marking, phenological monitoring, and planting.

Seminiferous propagation of Dietes bicolor is hindered by the probable physical and/or morphophysiological dormancy. The objective was to analyze the efficacy of different methods of overcoming dormancy in D. bicolor seeds to determine a possible pre-germination treatment for the species. Two experiments were conducted: (I) Evaluation of the breaking of physical dormancy, in which the treatments of mechanical scarification were carried using sandpaper #100; chemical scarification with sulfuric acid (H2SO4) for 5 and 10 minutes and immersion in hot water (70 ºC), also, for 5 and 10 minutes, were evaluated. The intact seed was considered a control. (II) Evaluation of morphophysiological dormancy, in which the seeds were submitted to combined treatments of stratification of hot temperature (20-35 °C) and/or cold temperature (9 ºC), distributed in periods of 0, 1, and 2 weeks, totalizing 9 treatments. In both experiments, germination percentage (G), germination speed index (GSI), and first count (FC) were determined, using a randomized block design, and evaluated by the Scott-Knott test at 1% and Dunnett’s test at 5%. The use of H2SO4 10 minutes induced 42% germination, 0.52 GSI, and 18% FC, but only FC was significantly different from the control. In the second trial, the treatment that spent only two weeks in hot temperatures (20-35 ºC) showed the highest germination (30%), compared to the control (G = 22%). These results provide relevant information for understanding the physiology of D. bicolor germination, in addition to contributing to the optimization of pre-germination practices for this important ornamental species.