Seeds of the threatened dry rainforest tree Cadellia pentastylis (Surianaceae) are non-dormant

Cadellia pentastylis (Surianaceae) is an Australian endemic threatened rainforest tree. Irregular flowering and fruiting events coupled with high rates of infertility and insect predation has meant that seed testing has not been possible for this species. Seeds were opportunistically collected from a wild population in early 2021, which allowed for the first germination tests to be conducted. In this study, the presence of physical dormancy was examined by performing an imbibition test using scarified and non-scarified seeds. We also investigated whether a 5-min heat shock treatment at temperatures ranging from 60 to 120°C improved germination success. The presence of physiological dormancy was also examined by recording germination success following a gibberellic acid or smoke-water pre-treatment. Both scarified and non-scarified seeds readily imbibed water over a 72-h period, and several seeds had germinated in both treatments after 48 h. Final germination proportion and t50 following a heat shock, gibberellic acid or smoke-water pre-treatment did not significantly differ from the controls. We conclude that C. pentastylis seeds are non-dormant. Although a palisade cell layer has been reported in the endocarp, our results suggest that this layer may not be sufficiently formed to restrict germination. We recommend that seeds are collected from populations following dispersal and propagated shortly after or stored as conservation collections in ex situ Seedbanks.

Overcoming dormancy in seeds of Dietes bicolor (Steud.) Sweet ex Klatt

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.

Ultrafine Bubbles Technology for Breaking Dormancy of Sandalwood Seeds (Santalum album L.

Sandalwood seed has two types of dormancy, namely physical dormancy and physiological dormancy which is a combination of the Two-part is called morphophysiological dormancy. There is for breaks dormancy in sandalwood for earlier embryo maturation and elongation also it has hard and impermeable skin. Its structure consists of layers of thick-walled palisade-like cells especially on the outermost surface and the inside has a waxy coating and curse material. The objective of this study was to break of seed dormancy with technology Ultrafine Bubbles (UFB) on the morphophysiological dormancy on sandalwood seeds. The experiments used a randomized complete block designed (RCBD) with 3 replications. The data were analyzed using ANOVA and will be continued using the DMRT test at the 5% level. The research was conducted from February - March 0f 2020. The results showed that immersion using UFB water with oxygen 20 ppm or either UFB free oxygen for 24 and 48 hours combined with physical scarification and chemical scarification could accelerate germination in 13 days after germination (appeared radicle), percentage of growth speed (GS) is 4.67%, maximum growth (MG) in 21 days after sowing is 66.67% with normal sprouts 2-4 leaves have grown.

Experimental Warming Hastens Physical Dormancy Break and Germination in Tropical Fabaceae

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.

Mechanical scarification technique breaks seed coat-mediated dormancy in wild oat (Avena fatua)

Wild oat is a herbicide resistance-prone global weed species that causes significant economic losses in dryland and horticultural agriculture. As a result, there has been a significant research effort in controlling this species. A major impediment to this research is the seed coat-mediated dormancy of wild oat, requiring a labor-intensive incision or puncturing of the seed coat to initiate seed germination. This study defines the most efficient settings of a mechanical thresher to overcome wild oat seed dormancy and then validates these settings using multiple populations collected from the Western Australian grain belt. We also compare the effects of rapid mechanical scarification and known germination stimulus tactics such as scarification with sulfuric acid (H2SO4), partial endosperm removal, sandpaper scarification of the seed coat, and immersion in sodium nitroprusside (NO donor SNP) solution on wild oat seedling growth rate. Threshing treatment of 1,500 rpm for 5 s provides equivalent germination compared with manually puncturing individual wild oat seeds, with no difference in seedling relative growth rate. The mechanical scarification of seeds using the thresher resulted in greater germination (66%) than H2SO4 scarification (0%), partial endosperm removal (10%), sandpaper seed coat scarification (25%), and exposure to NO donor SNP (34%). This study demonstrates that the physical dormancy of wild oat can be rapidly overcome using a commercially available mechanical thresher.

The effect of parental plant and washing materials on seed germination of F2 generation apple cactus (Cereus spp.)

Apple cactus (Cereus sp.) is a genus of cactus, and two species that are often crossed are long spines (Cereus jamacaru) and short spines (Cereus peruvianus). Those species have seeds with physical dormancy, that is, seed mucilage that can inhibit the germination process. This research aims to study the effect of parental plants and washing materials on the germination of F2 apple cactus seeds. This study used two-factor RCBD using 3 parental plants of the F2 generation of apple cactus (C. jamacaru open pollination, C. peruvianus × C. jamacaru, C. jamacaru × C. peruvianus) and 5 washing materials (without washing, pH 8, distilled water (pH 7), pH 5, and pH 9) which was carried out in 3 repetitions. The results showed that seeds of the cross C. jamacaru as female parent (C. jamacaru open pollination and C. jamacaru × C. peruvianus) produced better germination than seeds from the cross of C. peruvianus as female parent (C. peruvianus × C. jamacaru). Although the washing material didn’t significantly affect the germination of F2 apple cactus seeds, there was an influence of using pH 9 to minimize seed mucilage so that the extraction process was easier.

Factors influencing physical dormancy and its elimination in two legumes

Introduction: Prosopis laevigata (Humb. & Bonpl. ex Willd.) M. C. Johnst, P. glandulosa Torr., Vachellia schaffneri (S. Watson) Seigler & Eibinger, V. pennatula (S. Watson) Seigler & Eibinger and V. farnesiana (L.) Wight & Arn. are characteristic species of semi-arid areas. Their seeds show physical dormancy and are naturally scarified by chewing, trampling, digestive tract of fauna, fire, or washing away during rains. Objective: To describe the morphology of the seed coat of three species of Vachellia and two of Prosopis, and to assess the chemical, mechanical and thermal scarification of seeds. Materials and methods: Chemical (HCl for 30, 120, 150 and 180 min), thermal (80, 100, 120 and 140 °C for 3 min) and mechanical (sanding) scarification were applied. Resistance to breaking by compression was measured. The experimental design was randomized complete blocks per species. Results and discussion: Seeds showed a layer of lignified and impermeable macrosclereids, but the aleurone layer could not be detected. Sanding allowed germination from 81.2 to 100 %. Chemical and thermal treatments showed no differences, only in the case of P. laevigata, chemical scarification for 180 min caused higher germination (72.5 %) compared to the control. Vachellia schaffneri seeds were more resistant to compression (669 N) and had more intense dormancy (0.83), while P. glandulosa had the lowest dormancy (0.42). Conclusions: Mechanical scarification was the best method to eliminate dormancy in Vachellia and Prosopis seeds.

Seed germination biology of sweet acacia (Vachellia farnesiana) and response of its seedlings to herbicides

Sweet acacia [Vachellia farnesiana (L.) Willd.]is a problematic thorny weed species in several parts of Australia. Knowledge of its seed biology could help to formulate weed management decisions for this and other similar species. Experiments were conducted to determine the effect of hot water (scarification), alternating temperatures, light, salt stress, and water stress on seed germination of two populations of V. farnesiana and to evaluate the response of its young seedlings (the most sensitive development stage) to commonly available POST herbicides in Australia. Both populations behaved similarly to all the environmental factors and herbicides; therefore, data were pooled over the populations. Seeds immersed in hot water at 90 C for 10 min provided the highest germination (88%), demonstrating physical dormancy in this species. Seeds germinated at a wide range of alternating day/night temperatures from 20/10 C (35%) to 35/25 C (90%) but no seeds germinated at 15/5 C. Germination was not affected by light, suggesting that seeds are nonphotoblastic and can germinate under a plant canopy or when buried in soil. Germination was not affected by sodium chloride concentrations up to 20 mM and about 50% of seeds could germinate at 160 mM sodium chloride, suggesting its high salt tolerance ability. Germination was only 13% at −0.2 MPa osmotic potential and no seeds germinated at −0.4 MPa, suggesting that V. farnesiana seeds may remain ungerminated until moisture conditions have become conducive for germination. A number of POST herbicides, including 2,4-D + picloram, glufosinate, paraquat and saflufenacil, provided >85% control of biomass of young seedlings compared with the nontreated control treatment. Knowledge gained from this study will help to predict the potential spread of V. farnesiana in other areas and help to integrate herbicide use with other management strategies.

Morphological Characterization and Physical Dormancy of Bauhinia winitii Seed: Living Collection of Purwodadi Botanic Garden

Bauhinia winitii Craib (Fabaceae, Caesalpinioideae) is a woody climber which is currently included in endangered species list. B. winitii seeds are orthodox seeds in which it has hard coat morphologically. Therefore, B. winitii seeds often undergo physical dormancy which can be broken through immersion in certain liquid media. This study aimed to characterize the morphology of B. winitii seeds and determine the pre-sowing treatment method to accelerate the seeds germination of B. winitii. External morphological characterization was carried out by observing the seeds quantitative and qualitative parameters. Characterization of seeds internal morphology was conducted using a digital microscope. Physical dormancy breaking was carried out by immersion in warm and cold water for 24 hours. Morphological characterization data were analyzed descriptively, while seed germination data were analyzed quantitatively by using one-way ANOVA followed by LSD test (with confidence level of 95%). B. winitii has pod-shaped fruits with 2-6 seeds per pod, the seeds are 1.36 cm x 1 cm in size, 0.47 cm thick and weighed 0.5 g, oblong to conical in shape, smooth and shine surface, with light to dark brown in color. Seeds immersion treatment in warm water could break the physical dormancy of B. winitii seeds thus 63% of the seeds were able to germinate and it was significantly different compared to control and cold water immersion treatment. Technical to germinate B. winitii seed can be known from pre-sowing treatment. This study can be used as a reference for seed identification and germination technical of B. winitii seed.

Chemical Methods to Improve Seed Germination and Seedling Growth of Honey Locust (Gleditsia triacanthos L.)

The present study aimed to improve the seed germination and plantlet development of honey locust (Gleditsia triacanthos) using two types of edaphic substrate (peat and peat+sand) and different chemical substances. Breaking physical dormancy for some forest seeds is a challenge for researchers and forest managers in order to obtain a homogeneous germination on larger areas. Germination percentage of honey locust seeds were investigated by using different chemical treatments as follows: calcium hydroxide; concentrated solution of sodium 4-nitrophenolate; solution with a content of auxines; copper sulphate; potassium permanganate and concentrated sulfuric acid. The highest percentage of seed germination was obtained when the seeds were immersed in an aqueous solution of sulfuric acid (14%), followed by 12.5% (concentrated solution of sodium 4-nitrophenolate) and 12.3% (solution with a content of auxins). The lowest values (5%) were recorded when copper sulphate was used. Regarding the different types of studied substrates, the highest percentage of germination was obtained on peat + sand. As regards to seedling development, the highest values were obtained on the peat + sand substrate, with seeds treated with sulfuric acid (15.0 cm). The concentrated solution of sodium 4-nitrophenolate and solution with auxins recorded also high values, 15.2 cm, respectively 14.9 cm. The lowest values for seedling height (11 cm) was noted when seeds were treated with potassium permanganate.