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Partially shelled popcorn seed saved for planting
In agriculture and gardening, seed saving (sometimes known as brown bagging) is the practice of saving seeds or other reproductive material (e.g. tubers) from vegetables, grain, herbs, and flowers for use from year to year for annuals and nuts, tree fruits, and berries for perennials and trees. This is the traditional way farms and gardens were maintained for the last 12,000 years.
In recent decades, beginning in the latter part of the 20th century, there has been a major shift to purchasing seed annually from commercial seed suppliers. Much of the grassroots seed-saving activity today is the work of home gardeners.
Seed storage method
To be successful at seed saving, new skills need to be developed to ensure that desired characteristics are retained in the landraces of the plant variety. Important considerations are the separation distance needed from plants of the same species to ensure that cross-pollination with another variety does not occur, and the minimum number of plants to be grown which will preserve inherent genetic diversity. It is also necessary to recognize the preferred characteristics of the cultivar being grown so that plants that are not breeding true are selected against, and to understand the breeding of improvements to the cultivar. Diseases that are seed-borne must be recognized so that they can be eliminated. Seed storage methods must be good enough to maintain viability of the seed. Germination requirements must be known so that periodic tests can be made.
Care must be taken, as training materials regarding seed production, cleaning, storage, and maintenance often focus on making landraces more uniform, distinct and stable (usually for commercial application) which can result in the loss of valuable adaptive traits unique to local varieties.
Additionally, there is a matter of localized nature to be considered. In the upper northern hemisphere, and lower southern, one sees a seasonal change in terms of a cooler winter. Many plants go-to-seed and then go dormant. These seeds must hibernate until their respective spring season.
Seed open pollination
Open pollination is an important aspect of seed saving. Plants that reproduce through natural means tend to adapt to local conditions over time, and evolve as reliable performers, particularly in their localities, known as landraces or "folk varieties."
While saving seed and even exchanging seed with other farmers for biodiversity purposes has been a traditional practice, these practices have become illegal for the plant varieties that are patented or otherwise owned by some entity (often a corporation). Under Article 28 of the World Trade Organization (WTO) Agreement on Trade-Related Aspects of Intellectual Property Rights (the TRIPS Agreement), "planting, harvesting, saving, re-planting, and exchanging seeds of patented plants, or of plants containing patented cells and genes, constitutes use" and can in some cases be prohibited by the intellectual property laws of WTO Members.
Significantly, farmers in developing countries are particularly affected by prohibitions on seed saving. There are some protections for re-use, called "farmer's privilege", in the 1991 International Union for the Protection of New Varieties of Plants (UPOV Convention), but seed exchange remains prohibited.
Seed wholesale: United States
Originally the farmer's privilege to save seeds to grow subsequent crops was considered protected by the Plant Variety Protection Act of 1970. American farmers, it was thought, could sell seed up to the amount saved for replanting their own acreage.
That view came to an end in the latter part of the 20th century and early part of the 21st century, with changes in technology and law. First, in 1981 Diamond v. Chakrabarty established that companies may obtain patents for life-forms—originally genetically engineered unicellular bacteria. In 2002 J.E.M. Ag Supply v. Pioneer established that valid utility patents could be issued on sexually reproduced plants, such as seed crops (e.g., corn). In 2013 Bowman v. Monsanto Co. established that it was patent infringement for farmers to save crop seeds (soybeans in that case) and grow subsequent crops from them, if the seeds or plants were patented. Seed corporations are able to earn massive profits from this control over commercial seed supplies, and consequently further loss of control has been taken from US farmers over their farm production process.
Seed Sovereignty edit]
Seed sovereignty can be defined as the right “to breed and exchange diverse open-sourced seeds.” It focuses largely on the rights of individuals to be able to save seed, and be independent from major seed companies. Seed sovereignty activists point to seed saving as an important practice in building food security, as well as restoring agricultural biodiversity. Activists also draw attention to the cultural importance of seed saving practices, especially their role in maintaining traditional plant varieties. It is closely connected to the food sovereignty movement and food justice movement.
Background and Aims Previous studies have suggested that the drying conditions routinely used by genebanks may not be optimal for subsequent seed longevity. The aim of this study was to compare the effect of hot-air drying and low-temperature drying on subsequent seed longevity for 20 diverse rice accessions and to consider how factors related to seed production history might influence the results.
Methods Seeds of rice, Oryza sativa, were produced according to normal regeneration procedures at IRRI. They were harvested at different times [harvest date and days after anthesis (DAA), once for each accession] and dried either in a drying room (DR; 15 % relative humidity, 15 °C) or in a flat-bed heated-air batch dryer (BD; 45 °C, 8 h d–1) for up to six daily cycles followed by drying in the DR. Relative longevity was assessed by storage at 10·9 % moisture content and 45 °C.
Key Results Initial drying in the BD resulted in significantly greater longevity compared with the DR for 14 accessions (seed lots): the period of time for viability to fall to 50 % for seeds dried in the BD as a percentage of that for seeds dried throughout in the DR varied between 1.3 and 372·2 % for these accessions. The seed lots that responded the most were those that were harvested earlier in the season and at higher moisture content. Drying in the BD did not reduce subsequent longevity compared with DR drying for any of the remaining accessions.
Conclusions Seeds harvested at a moisture content where, according to the moisture desorption isotherm, they could still be metabolically active (>16·2 %) may be in the first stage of the post-mass maturity, desiccation phase of seed development and thus able to increase longevity in response to hot-air drying. The genebank standards regarding seed drying for rice and, perhaps, for other tropical species should therefore be reconsidered.
Keywords: Seed longevity, genebank, rice, Oryza sativa, seed drying, seed development, desiccation phase, harvest moisture content.
Crop genetic resources comprising samples of landraces, modern and obsolete varieties, and their wild relatives are the biological basis of food security (FAO, 2013), and as such they are given high conservation priority (Maxted et al., 1997). Cultivated Asian rice (Oryza sativa) is the most important food crop of the developing world, being a staple for more than half the global population (FAO, 2003). Rice shows orthodox seed storage behaviour, meaning that the seeds can be dried and stored at low temperature and low moisture content in genebanks for long-term conservation (Ellis and Hong, 2007; Hay et al., 2013). At present there are >750 000 accessions of cultivated rice seeds (O. sativa and Oryza glaberrima) held in genebanks globally (FAO, 2010). The largest and most diverse collection (over 125 000 accessions) is stored in the International Rice Genebank (IRG) at the International Rice Research Institute (IRRI) in the Philippines. Although seeds remain viable for many decades under genebank storage conditions, over time their viability will decline and regeneration is required to maintain genetic integrity (Cromarty et al., 1982; Rao et al., 2006). It is therefore important that genebank staff regularly assess regeneration and management procedures to ensure that best practices are employed to conserve crop genetic resources for future generations.
The potential storage life of seeds is affected by pre- and post-harvest environments and practices (Hay et al., 2006; Probert et al., 2007). Seed quality traits (ability to germinate and survive air-dry storage) are acquired during the course of development and maturation (Hay and Smith, 2003; Probert et al., 2007). In many species, the ability of seeds to withstand desiccation to the low moisture levels required for storage occurs around mass maturity (end of seed-filling stage), but desiccation tolerance in rice is acquired earlier (Ellis and Hong, 1994). Although seeds can be stored as soon as they have become desiccation-tolerant, seed longevity in subsequent air-dry storage does not reach its maximum until some time later, during the desiccation phase of seed development (Ellis et al., 1993; Kameswara Rao and Jackson, 1996a, b; Hay and Smith, 2003; Ellis, 2011). During this desiccation phase, seeds become hygroscopic, i.e. their moisture status is now independent of the parent plant and instead is determined by ambient conditions (Ellis and Hong, 1994). Drying seeds at the end of this phase, once the seeds have equilibrated with ambient conditions (i.e. at harvest maturity), will reduce the rate of seed ageing thereafter and so maximize subsequent seed viability and longevity (Hay and Probert, 1995; Probert et al., 2007).
The 1994 Genebank Standards recommended that seeds should be stored hermetically at a moisture content (m.c.) of 3–7 % of fresh weight (depending on seed oil content) and −20 °C (FAO/IPGRI, 1994). In these conditions the rate of ageing is slow and viability can be maintained for long periods (Ellis et al., 1989, 1992; Ellis and Hong, 2006; Gómez-Campo, 2006; Pérez-García et al., 2009; Hay et al., 2013). To achieve this low moisture content, it was further recommended that seeds of orthodox species should be dried immediately after harvest in a drying chamber at 10–15 % relative humidity (RH) and 10–25 °C (FAO/IPGRI, 1994). More recently, this was modified to 10–25 % RH and 5–20 °C (FAO, 2013). A relatively low drying temperature was adopted to reduce the rate of ageing during the drying process, particularly when seeds still have high m.c. and/or for species with seeds easily damaged by high-temperature drying (Cromarty et al., 1982). However, it has been suggested that, in particular for tropical species, a low drying temperature may curtail late developmental processes in seeds and have a negative impact on subsequent longevity in storage (Hay, 1997). A preliminary study showed that initial intermittent high temperature drying (45–50 °C), before drying at 15 % RH, 15 °C, resulted in greater subsequent seed quality than drying throughout at 15 % RH, 15 °C in rice (Crisostomo et al., 2011). The aim of this study was to evaluate the effects of initial high-temperature drying of rice seeds from 20 diverse varieties for different periods before subsequent drying to equilibrium in the genebank dry room, compared with drying solely in the dry room, on subsequent longevity in storage. We further considered why the response varied between the different varieties (seed lots).
MATERIALS AND METHODS
Seeds of 20 rice (Oryza sativa) accessions representing five variety groups (aus, aromatic, indica, and temperate and tropical japonica; McNally et al., 2009) (Table 1) were sampled from the IRG active collection and held at 50 °C for 5 d to break dormancy. They were sown on 23 November 2012 and transplanted on 18 December 2012 into plots on the IRRI experimental station. Normal rice production practices and routine plant protection measures were followed. Seed lots were harvested between March and April 2013. The target harvest time was 35 d after 50 % anthesis (DAA). However, due to biological/environmental (e.g. early shattering, late tillering) and/or workload constraints the actual harvest times were between 24 and 48 DAA (Table 1).
Information on the 20 rice seed lots used in the study showing date of harvest, the interval from 50 % anthesis to harvest date (DAA), initial seed moisture content (m.c.) and equilibrium relative humidity (eRH) at harvest
AccessionVariety nameVariety group1Harvest dateDAA¶Moisture content (s.e.), % fresh weighteRH, %IRGC 117264AzucenaTropical japonica19 March2422·4 (0·42)95·9IRGC 117265Dom-sufidAromatic11 March2422·7 (0·09)96·1IRGC 117266DularAus19 March3718·9 (0·11)92·9IRGC 117267FR 13 AAus4 April3616·8 (0·22)88·4IRGC 117268IR64-21Indica2 April4414·9 (0·04)74·4IRGC 117269Li-Jiang-Xin-Tuan-Hei-GuTemperate japonica11 March3826·8 (0·36)96·9IRGC 117270M 202Temperate japonica14 March3823·4 (0·23)97·4IRGC 117271Minghui 63Indica15 April3316·7 (0·06)91·6IRGC 117272MoroberekanTropical japonica10 April3517·7 (0·05)91·6IRGC 117273N 22Aus5 March2920·8 (0·12)91·9IRGC 117274NipponbareTemperate japonica5 March4028·9 (0·31)96·0IRGC 227275PokkaliIndica27 March3713·7 (0·02)69·8IRGC 117276Sadu-choIndica27 March2613·2 (0·09)67·8IRGC 117277Sanhuangzhan no. 2Indica10 April3816·2 (0·04)86·5IRGC 117278SwarnaIndica4 April3618·2 (0·28)91·7IRGC 117279Tainung 67Temperate japonica15 April4517·3 (0·08)86·7IRGC 117280Zhenshan 97BIndica14 March3823·3 (0·24)96·1IRGC 117281AswinaIndica25 March4819·3 (0·14)94·6IRGC 117282CypressTropical japonica25 March4118·8 (0·04)92·8IRGC 117283RayadaAus2 April3416·5 (0·16)83·8
1Variety group taken from McNally et al. (2009).
¶Estimated from time of mid-flowering to harvest date.
Immediately after harvest, the seeds were threshed and blown to remove debris. A sample taken at random from each accession was placed inside a 3·2-mL sample holder in the measuring chamber of an AW-D10 water activity station used in conjunction with a HygroLab 3 display unit (Rotronic South East Asia, Singapore). The temperature and equilibrium relative humidity (eRH) were measured once the reading had stabilized, after 20–40 min. Seed m.c. (fresh weight basis) was determined using three 5-g samples from each accession using the high-constant-temperature oven method (ISTA, 2013). The samples were ground in a Krups 75 coffee grinder and weighed before being placed at 130 °C for 2 h. The samples were removed from the oven and placed over silica gel for 1 h to cool before reweighing.
Seeds from each accession were divided into a maximum of seven 300-g samples (depending on the quantity available) and placed into 0·2 × 0·33 m (length × width) nylon mesh bags (1-mm diameter holes). They were stored inside sealed 0·6 × 0·3 × 0·132 m (length × width × height) electrical enclosure boxes (Ensto Finland Oy) at room temperature (∼22·5 °C) overnight. The following morning (0800 h), one sample was immediately placed in the genebank dry room (DR; 15 % RH, 15 °C) and the remaining samples (up to six) were placed into a locally fabricated flat-bed batch dryer (BD) at the IRRI experimental station. The change in weight and eRH of the DR samples was monitored daily. In the BD, air was heated (to ∼45 °C) with a burner fuelled by kerosene and blown into a chamber below the seeds before being driven up through the perforated base on which the seeds were placed. Seeds were exposed to 8 h of heated-air drying (0800–1600 h) per daily (24-h) cycle. At the end of this 8-h period, one sample was removed and a small subsample (∼15 g) was taken to determine seed eRH and m.c., as before. The remainder of the seeds of this sample was transferred within the nylon mesh bag to the DR, where all seed samples completed drying (i.e. equilibrating to 15 % RH, 15 °C; resulting in an m.c. of 6–7 %). The remaining 300-g samples were sealed inside 0·6 × 0·3 × 0·132 -m (length × width × height) electrical enclosure boxes at room temperature overnight (1600–0800 h) before they were returned to the BD for the next 8-h heated-air treatment period. Each accession consisted of different seed samples that had been dried using the BD for up to six daily cycles. This protocol resulted in all samples being dried to the same m.c. but individually differing in the number of daily heated-air drying cycles in the BD (0–6 d). Once equilibrated in the DR (up to 14 d), samples were sealed inside 0·17 × 0·12 -m (length × width) laminated aluminium foil packets and stored at 2–4 °C until experimental seed storage began in June 2013.
Seeds of each treatment combination [accession (20) × drying treatment (7)] were removed from cold storage (2–4 °C) and equilibrated to room temperature (22·5 °C) before opening. Each sample was split into 5-g subsamples (maximum of 29) and placed into 30-mm-diameter open Petri dishes and held over a non-saturated LiCl solution (60 % RH) in a sealed 0·6 × 0·3 × 0·132-m (length × width × height) electrical enclosure box for 7 d at 22·5 °C. The RH provided by the solution was checked at weekly intervals, using the water activity-measuring instrument described above, and the bulk solution was adjusted if necessary by adding distilled water, stirring and allowing equilibration before re-checking RH (Hay et al., 2008).
Seed m.c. reached equilibrium with this environment after 7 d. Four 5-g subsamples from each treatment combination were taken and seed eRH was measured. Three of these subsamples were used to determine m.c. and the fourth to estimate initial ability to germinate (prior to experimental storage). The remaining 5-g subsamples were each sealed inside 0·12 × 0·09-m (length × width) laminated aluminium foil packets and then placed in an incubator at 45 °C. One packet per treatment combination was removed at 1- to 3-d intervals up to 45 d for germination testing (see below). For some seed lots, in which viability was lost before 45 d, sampling was discontinued earlier; for a few seed lots, later samples were at longer intervals due to an unexpectedly slow rate of viability loss. At 21 d (mid-storage) and at the end of the storage experiment, m.c. was determined using three additional 5-g packets of seeds each time.
Ability to germinate was estimated with four replicates of 30 seeds, sown on two layers of Whatman No. 1 paper wetted with 7·5 mL distilled water in 90-mm-diameter Petri dishes. They were incubated at constant 30 °C (12 h light and 12 h dark cycle). Germination was scored after 2, 3, 4, 5, 7 and 14 d. Non-germinated seeds were dehulled and tested for an additional 7 d before final scoring. Seeds were scored as germinated when the radicle had emerged by at least 2 mm.
Seed survival (ability to germinate after different periods of air-dry storage in the experimental regime) curves were fitted by probit analysis using GenStat for Windows, Version 15 (VSN International Ltd., Oxford, UK), thereby fitting the following equation to estimate the period (days) for viability to fall to 50 % (p50), Ki and σ:
v = Ki– (p/σ)
where v is the viability (ability to germinate) in normal equivalent deviates (NED) of a seed lot stored for a period of p (days), Ki is the initial viability (NED) and σ (days) is the standard deviation of the normal distribution of seed deaths in time (Ellis and Roberts, 1980). The estimate of p50 was used as the measure of longevity. For those accessions also showing loss in dormancy during (early) storage, i.e. after-ripening, a probit model combining loss in dormancy with loss in viability was applied:
g = (Kd + β1p) × [Ki– (p/σ)]
where g is ability to germinate (NED), p, Ki and σ are as in eqn (1), Kd is the initial proportion of non-dormant seeds (NED) and β1 is the probit rate of loss of dormancy (Kebreab and Murdoch, 1999). Eqn (2) was fitted using the FITNONLINEAR directive in GenStat. Probit analysis was carried out for all seed lots within an accession simultaneously, fitting the full model (different estimates for all parameters) and reduced models in which one or more parameters were constrained to a common value for all seed lots. An approximate F-test was used to determine the best model.
The difference in longevity (p50) between the highest value from the BD treatments (BD p50) and the DR treatment (DR p50) was calculated as a proportion of the DR p50 according to the equation: 100 × ((BD p50 – DR p50)/DR p50). Split-line regression analysis was used to explore the relationships between different variables and relative difference in longevity. A modified version of the D’Arcy-Watt equation (D’Arcy and Watt, 1970) was used to describe the relationship between seed m.c. [converted to water content (WC) as a proportion of dry weight] and eRH, as follows (also fitted using the FITNONLINEAR directive in