A suite of mechanisms or processes that together have been implicated in the acquisition and maintenance of desiccation tolerance in orthodox seeds is discussed in the context of the behaviour of desiccation-sensitive seeds, and where appropriate, parallels are drawn with the situation in vegetative plant tissues that tolerate dehydration. Factors included are: physical characteristics of cells and intracellular constituents; insoluble reserve accumulation; intracellular de-differentiation; metabolic ‘switching off’; presence, and efficient operation, of antioxidant systems; accumulation of putatively protective substances including LEAs, sucrose and other oligosaccharides, as well as amphipathic molecules; the presence and role of oleosins; and the presence and operation of repair systems during rehydration. The variable response to dehydration shown by desiccation-sensitive seeds is considered in terms of the absence or incomplete expression of this suite of mechanisms or processes. Three categories of damage are envisaged: (i) reduction in cell volume which can lead to mechanical damage; (ii) aqueous-based degradative processes, probably consequent upon deranged metabolism at intermediate water contents. This is termed ‘metabolism-induced damage’ and its extent will depend upon the metabolic rate and the rate of dehydration; and (iii) the removal of water intimately associated with macromolecular surfaces leading to denaturation: this is referred to as desiccation damage sensu stricto . The effects of drying rate and the maturity status of seeds are considered in relation to the responses to dehydration, leading to the conclusion that the concept of critical water contents on a species basis is inappropriate. Viewing seed postharvest physiology in terms of a continuum of behaviour is considered to be more realistic than attempting precise categorization. Rapid dehydration of excised embryonic axes (or other explants) from desiccation-sensitive seeds permits retention of viability (in the short term) to water contents approaching the level of non-freezable water. This opens up the possibility of long-term conservation, by cryopreservation techniques, of the genetic resources of species producing non-orthodox seeds.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0960258599000033

A review of recalcitrant seed physiology in relation to desiccation-tolerance mechanisms

Introduction. Ecologically Meaningful Germination Studies. Types of Seed Dormancy. Germination Ecology of Seeds with Nondeep Physiological Dormancy. Germination Ecology of Seeds with Morphophysiological Dormancy. Germination Ecology of Seeds with Physical Dormancy. Germination Ecology of Seeds in the Persistent Seed Bank. Causes of Within-Species Variations in Seed Dormancy and Germination Characteristics. A Geographical Perspective on Germination Ecology: Tropical and Subtropical Zones. A Geographical Perspective on Germination Ecology: Temperate and Arctic Zones. Germination Ecology of Plants with Specialized Life Cycles and/or Habitats. Biogeographical and Evolutionary Aspects of Seed Dormancy. Subject Index.

A Definitive Book on Seed Ecology@@@Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination

Woody Plants of Ghana and Their Uses@@@Woody Plants of Ghana, with Special Reference to Their Uses

Vegetation fires are an essential component of the Earth system but can also cause substantial economic losses, severe air pollution, human mortality and environmental damage. Contemporary fire regimes are increasingly impacted by human activities and climate change, but, owing to the complex fire–human–climate interactions and incomplete historical or long-term datasets, it is difficult to detect and project fire-regime trajectories. In this Review, we describe recent global and regional trends in fire activity and examine projections for fire regimes in the near future. Although there are large uncertainties, it is likely that the economic and environmental impacts of vegetation fires will worsen as a result of anthropogenic climate change. These effects will be particularly prominent in flammable forests in populated temperate zones, the sparsely inhabited flammable boreal zone and fire-sensitive tropical rainforests, and will contribute to greenhouse gas emissions. The impacts of increased fire activity can be mitigated through effective stewardship of fire regimes, which should be achieved through evidence-based fire management that incorporates indigenous and local knowledge, combined with planning and design of natural and urban landscapes. Increasing transdisciplinary research is needed to fully understand how Anthropocene fire regimes are changing and how humans must adapt.

/pdf/vegetation-fires-in-the-anthropocene-3d07mbud03.pdf

Vegetation fires in the Anthropocene

/pdf/the-use-and-exchange-of-microbial-genetic-resources-for-food-2o7bbe9gw3.pdf

THE USE AND EXCHANGE OF MICROBIAL GENETIC RESOURCES FOR FOOD AND AGRICULTURE Submission by the Food and Agriculture Organization of the United Nations (FAO)

Comparative Storage Biology of Tropical Tree Seeds

Combining community needs and preferences with dryland plant expertise in order to select suitable native species for
large-scale natural capital restoration is the approach that has been successful in the Sahel as part of Africa’s Great Green
Wall program. In order to increase plant diversity and restore degraded land, we investigated four cross-border regions of
Mali, Burkina Faso, and Niger, all located in dryland ecosystems of the Sahel. In 120 beneficiary village communities, with
a total population of over 50,000 farmers, including 51% women, participatory diagnostic meetings were conducted, leading
to the selection of 193 plant species, most of which were mainly used for food, medicine, fodder, and fuel. Of these, 170 were
native and considered suitable for enriching and restoring those village lands. The most environmentally well-adapted and
economically relevant species were prioritized, quality seeds were collected, and nursery seedlings produced under technical
supervision of villages. From 2013 to 2015, 55 woody and herbaceous species were planted to initiate restoration of 2,235 ha of
degraded land. On average, 60% of seedlings survived and grew well in the field after three rainy seasons. Due to its multiple
uses, including gum arabic production, Acacia senegal was preferred by local people in most cases, accounting for 30% of
seedlings planted. Such promising results, in an effort to restore degraded land for and with the help of thousands of farmers,
could not have been achieved without the combination of scientific plant expertise and efficient rural capacity development,
underpinned by high levels of community engagement.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/rec.12337

Community participation and ecological criteria for selecting species and restoring natural capital with native species in the Sahel

Neem (Azadirachta indica) seed is reputed to have limited tolerance to desiccation, to be sensitive to chilling and imbibitional stress, and to display intermediate storage behaviour. To understand this behaviour the properties of water in seed tissues were studied. Water sorption isotherms showed that at similar relative humidity (RH), the water content was consistently higher in axes than in cotyledons, mainly due to the elevated lipid content (51€in the cotyledons. Using differential scanning calorimetry, melting transitions of water were observed at water contents higher than 0.14 g H2O g-1 DW in the cotyledons and 0.23 g H2O g-1 DW in the axes. Beside melting transitions of lipid, as verified by infrared spectroscopy, changes in heat capacity were observed which shifted with water content, indicative of glass-to-liquid transitions. State diagrams are given on the basis of the water content of seed tissues, and also on the basis of the RH at 20 °C. Longevity was considerably improved, and the sensitivity to chilling/subzero temperatures was reduced when axis and cotyledons were dehydrated to moisture contents of approximately 0.05 g H2O g-1 DW. However, longevity during storage at very low water contents was limited. A possible mechanism for the loss of sensitivity to chilling/subzero temperatures at low water contents is discussed. The results suggest that dry neem seeds in the glassy state have great potential for extended storability, also at subzero temperatures

/pdf/a-study-of-water-relations-in-neem-azadirachta-indica-seed-4k45s4tjl7.pdf

A study of water relations in neem (Azadirachta indica) seed that is characterized by complex storage behaviour

Storage of neem (Azadirachta indica) seeds is difficult because of their sensitivity to chilling stress at moisture contents (MC) > or =10% or imbibitional stress below 10% MC. The hypothesis was tested that an elevated gel-to-liquid crystalline phase transition temperature (Tm) of membranes is responsible for this storage behaviour. To this end a spin probe technique, Fourier transform infrared microspectroscopy, and electron microscopy were used. The in situ Tm of hydrated membranes was between 10 degrees C and 15 degrees C, coinciding with the critical minimum temperature for germination. During storage, viability of fresh embryos was lost within two weeks at 5 degrees C, but remained high at 25 degrees C. The loss of viability coincided with an increased leakage of K+ from the embryos upon imbibition and with an increased proportion of cells with injured plasma membranes. Freeze-fracture replicas of plasma membranes from chilled, hydrated axes showed lateral phase separation and signs of the inverted hexagonal phase. Dehydrated embryos were sensitive to soaking in water, particularly at low temperatures, but fresh embryos were not. After soaking dry embryos at 5 degrees C (4 h) plus 1 d of further incubation at 25 degrees C, the axis cells were structurally disorganized and did not become turgid. In contrast, cells had a healthy appearance and were turgid after soaking at 35 degrees C. Imbibitional stress was associated with the loss of plasma membrane integrity in a limited number of cells, which expanded during further incubation of the embryos at 25 degrees C. It is suggested that the injuries brought about by storage or imbibition at sub-optimal temperatures in tropical seeds whose membranes have a high intrinsic Tm (10-15 degrees C), are caused by gel phase formation.

/pdf/viability-loss-of-neem-azadirachta-indica-seeds-associated-2dqb0npwkf.pdf

Viability loss of neem (Azadirachta indica) seeds associated with membrane phase behaviour

Garcinia kola is highly used as chew-stick for dental care in West Africa, but it is nearly commercially extinct in nature. To help find methods to increase rate and percentage of germination, we investigated its seed germination responses by using several collections and pre-treatments. Seeds processed from 6-week old green fruits did not germinate, whilst those of 10-week old partly-mature, at the intermediate stage through full development, germinated 46%. Seeds from orange mature fruits reached maximum 54–62% germination. Radicles emerged 6 weeks after sowing and normal germination with emergence of the primary single shoot growth occurred after 12 weeks. There was no significant difference (P ≥ 0.05) between germination responses of seeds from Ghana and Cote d’Ivoire. Seeds did not germinate when dried to below ca. 30% MC. De-coating seeds or soaking intact seeds in a 70% ethanol solution increased germination to 82–92%, and also increased germination rate; however germination was not uniform. Because difficulties in germinating these seeds stem from the physical presence of the seed coats and the slow growth of the embryos contained therein, we recommend that fresh seeds from mature fruits be de-coated and immediately sown in preferably, an aerated medium (e.g., sawdust) for cultivation.

https://link.springer.com/content/pdf/10.1007%2Fs11056-007-9054-7.pdf

M. Sacandé

Papers

Comparative Storage Biology of Tropical Tree Seeds

Community participation and ecological criteria for selecting species and restoring natural capital with native species in the Sahel

A study of water relations in neem (Azadirachta indica) seed that is characterized by complex storage behaviour

Viability loss of neem (Azadirachta indica) seeds associated with membrane phase behaviour

Improving the collection and germination of West African Garcinia kola Heckel seeds