Editorial: Seed Science and Technology. Volume 49 Issue 3 (2021)

This issue of Seed Science and Technology is a good reflection of the wide scope of the field of study. Species of interest include major cultivated crops as well as wild and native species. Likewise, research topics span a wide array of subjects relevant to those interested in basic seed biology, production, testing, ecology, conservation and biodiversity. Understanding basic mechanisms of seed dormancy and germination remains a major topic of interest. Seed quality and its attributes are also of particular interest, as evidenced by research articles on seed vigour, health, genetic purity and physical characterisation.

Salt and Drought Effect on Germination and Initial Growth of Lavandula stoechas: A Potential Candidate for Rehabilitation of the Mediterranean Disturbed Coastal Lands

Information relating to germination and seedling emergence of a plant aids in determining the species spatiotemporal distribution and also facilitates in designing appropriate plant management strategies within an ecosystem. Lavandula stoechas L. (Lamiaceae), a naturally occurring shrub, is particularly used in pharmaceutical and cosmetic industries. This species, indeed, has the potential for rehabilitation of degraded costal lands. However, various aspects of its seed biology have not yet been recognised. Here, we aimed to assess the effects of different soluble salts (NaCl, CaCl2, MgCl2 and Na2SO4) and drought (as simulated by polyethylene glycol, [PEG]6000) on seed germination patterns and early seedling growth responses. Seeds treated with five iso-concentration (0–100 mM) salinities and five PEG6000 (0 to −1 MPa) levels were incubated in a controlled germinator set at 20°C. The preliminary results revealed that seeds of L. stoechas lacked primary/innate dormancy and they germinated abundantly (89.2% germination) and fast (7.4% day−1) in the absence of stress. Regardless of the kind of salt applied, the germination percentage (GP) and germination rate index (GRI) fell significantly with increasing salinity, and germination ceased completely at 100 mM Na2SO4. In fact, the salinity tolerance index (STI) showed that, among all salts tested, Na2SO4 appeared to have more inhibitory action on germination. In addition, L. stoechas was found to be tolerant to moderate salty stress (<50 mM) in early growth phase. The salt solution parameters (i.e. concentration, electrical conductivity [EC] and salt content) were best correlated with seed/seedling metrics. pH was not a good predictor for salt effects at the germination/seedling stages. Overall, this species seems to be sensitive to drought at the germination and initial growth phases. The germination recovery potential of L. stoechas in both stresses stipulates that this species can be regarded as a promising candidate in the rehabilitation of Mediterranean disturbed coastal habitats.

Lignocellulosic Biomass Production and Persistence of Perennial Grass Species Grown in Mediterranean Marginal Lands

Biomass production in marginal lands represents one of the most challenging and promising alternatives to sustainably produce biofuels. Native species seem to be the most adequate option to obtain a profitable output when low-input techniques are applied, and biomass is grown in depleted soils and harsh climatic conditions. In this study, a 5-year field trial in the island of Majorca served to investigate different autochthonous and naturalized Mediterranean perennial grasses as novel candidate lignocellulosic bioenergy crops for the semi-arid Mediterranean area and compare them with commercial ones (both Mediterranean and non-Mediterranean). Species and growing season had a significant effect on biomass production, perennialism and biomass quality. Arundo donax (winter crops) and Piptatherum miliaceum (autumn crops) performed better than the commercial species tested (Panicum virgatum for winter crops and Festuca arundinacea for autumn crops) in biomass production and perennialism. In terms of biomass quality, Panicum virgatum was the best species, having high structural content (mainly cellulose and hemicellulose), low non-structural content and the lowest ash. However, Ampelodesmos mauritanicus and Arundo donax rendered similar results, with no significant difference in terms of cellulose production for this latter but with higher lignin content. For the autumn species, Festuca arundinacea was the species with the best biomass quality but with the highest ash production for all the species considered. Hence, both for winter or autumn regimes, native or naturalized plants seem to be better suited than the commercial commonly used for biomass production with energy-producing purposes. Further research must be conducted in terms of seed biology and physiology, seedbed preparation methods, sowing time, seedling density and weed control before they can firmly be proposed as adequate alternatives for energy purposes.

Seed Science Research: Global Trends in Seed Biology and Technology

Seeds are the central components of the plant life cycle because the establishment of a new generation of plants depends on them [...]

Conditional Seed Dormancy Helps Silene hicesiae Brullo & Signor. Overcome Stressful Mediterranean Summer Conditions

Investigations on seed biology and ecology are of major importance for the conservation of threatened plants, both providing baseline information and suggesting practical approaches. In our study, we focused on the germination behavior of Silene hicesiae Brullo & Signor., a narrow endemic species to Panarea and Alicudi (Aeolian Archipelago, Italy), as well as one of the 50 most threatened Mediterranean island plants. Specifically, the effects of temperature, light, seed age, seed source, and collection year were evaluated; in addition, threshold temperatures and thermal–time parameters were estimated. The thermal range for fresh seed germination resulted between 5 and 15 °C, reaching up to 20 and 25 °C at increasing seed age, with 30 °C being clearly beyond the ceiling temperature. This behavior indicates that fresh seeds exhibit the Type 1 non-deep physiological dormancy, and that germination is regulated by conditional dormancy. This dormancy syndrome emerged as a highly efficient adaptation strategy for this species and, together with thermo-inhibition, would allow seeds to counteract or take advantage of Mediterranean environmental conditions. The comparison between the wild Panarea population and the corresponding ex situ cultivated progeny has enabled the identification of the latter as a suitable seed source for sustainable in situ reinforcement actions, at least in the short-term; indeed, plant cultivation for a single generation did not produce significant modifications in the germination behavior of the offspring.

Aquaporins and their implications on seeds: A brief review

Aquaporins (AQPs) are water channel proteins. They play a key role in maintaining water balance and homeostasis in cells under stress conditions in living organisms. AQPs are pore forming transmembrane proteins that facilitate water movement and various small neutral solutes across cellular membranes. Aquaporin expression and transport functions are modulated by various phytohormones mediated signalling in plants. Transcriptome analysis revealed the role of aquaporins in regulating hydraulic conductance in plant roots and leaves. Different AQPs found in the seed system have individual functions that are more time and tissue specific, ultimately helping in the seed imbibition process to complete seed germination. Seed specific TIP3s aquaporin helps to maintain seed longevity under expressional control of ABI3 during seed maturation and heat shock proteins and late embryogenic abundant proteins. Under stress circumstances, the major significance of aquaporin expression in seeds is to maintain water influx and efflux rates, as well as protein modification, post translational alterations, nutritional acquisition and allocation, subcellular trafficking and CO2 transport. The present review mainly focused on aquaporin structure, classification, role and functional activity during solute transport, reproductive organs development, plant growth development, abiotic stress response and also various roles in seeds such as seed biology, seed development and maturation, seed dormancy, seed germination and longevity.

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.

Differential germination response of Navua sedge (Cyperus aromaticus) populations to environmental factors

Navua sedge (Cyperus aromaticus) is a hard to control C4 perennial weed species in tropical regions of Australia. Knowledge of its seed biology could help to develop integrated weed management programs for this species. This study was conducted in laboratory and screenhouse conditions to evaluate the effect of alternating day/night temperatures, light, pretreatment high temperatures, burial depth, and flooding depth on the germination and emergence of two populations (Ingham and Tablelands) of C. aromaticus. Both populations germinated at temperatures ranging from 20/10 to 35/25 C; however, the Ingham population germination (76%) was greater than the Tablelands population (42%) at the highest temperature regime (35/25 C). None of the populations germinated at 15/5 C. Darkness completely inhibited germination in both populations, suggesting that the seeds are positively photoblastic. Seeds (dry and wet) of both populations germinated after exposure to pretreatment temperatures of up to 100 C for 5 min. After pretreatment at 150 C, only the Ingham population germinated, and the germination of dry seeds (62%) was greater than wet seeds (1%). None of the populations germinated after the exposure to 200 C. For both populations, maximum germination was observed for seeds at 0 cm, and a burial depth of 0.5 cm completely inhibited emergence of the Tablelands population and 2.0 cm inhibited germination of the Ingham population. A flooding depth of 10 cm greatly reduced emergence in both populations compared with 0 cm (62 and 78%) but 12 to 14% of seedlings still emerged, suggesting the need to integrate flooding with other management tools. The results also suggest that the Ingham population may have a greater potential to spread into new areas or become more invasive than the Tablelands population. Knowledge gained from this study can be used to manage C. aromaticus by fire/burning, tillage, and flooding.

Seed germination behaviour of the narrow endemic Daphne arbuscula (Thymelaeaceae) compared to the more widespread Daphne cneorum

Diminished reproduction success in species with narrow distribution ranges might be one of the factors responsible for their limited dispersal and colonization abilities. We investigated here various aspects of the seed biology of the West Carpathian endemic Daphne arbuscula (Thymelaeaceae) and compared it with its more widespread relative D. cneorum. In both species, we investigated (i) differences in seed viability and germination ability; (ii) differences between the two observed fruit morphotype groups, and (iii) the effect of cold stratification in breaking seed dormancy and enhance germination in stored seeds. To determine seed viability, a tetrazolium test and an imbibed cut test were performed. Several seed germination tests with gibberellic acid and with a sequence of cold and warm stratification, using different temperatures and durations, were carried out. We uncovered that (i) D. arbuscula seeds show significantly lower viability than D. cneorum seeds, but this difference is due to the smaller-fruit morphotype; (ii) seed quality and viability of the big-fruit morphotype are significantly greater than the smaller-fruit morphotype in both species, although the seed viability of the latter is not null and the dormancy level seems to differ between them; (iii) a warm stratification at 15°C for 13 weeks, followed by cold stratification at either 0 or 5°C for 28 weeks, followed by 4 weeks at 15°C, break physiological dormancy and allow the majority of seeds of D. arbuscula (63%) to germinate. We recommend including both fruit morphotypes when collecting seed of Daphne for ex situ conservation and reintroduction initiatives, to maintain the original genetic diversity of the species.