Longevity of seeds

Longevity parameters calculated from deterioration

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Unformatted text preview: cies (Tables 1–3). Values for f were directly related to the calculated P50 values, and ranged from 11.5 for Bromus sitchensis (Poaceae) to 904 for Trifolium campestre (Fabaceae), with a median of 74 (Table 1). Longevity parameters calculated from deterioration time courses in the Stanwood (unpublished) experiments (Table 2) follow similar patterns as the NPGS data, with the exponential factor ranging from 1 to 3.1 (median ¼ 1.2), f ranging from 10 to 730 10 C. Walters et al. Figure 1. Summary statistics of the initial germination (A), total storage time (B) and calculated P50 (C) of the 276 species in the USDA National Plant Germplasm System (NPGS) collection used in this study. Data are summarized from Table 1. (median ¼ 94), and P50 ranging from 8 to 497 years, with a median of 56 years (compared with a median of 54 years in the NPGS dataset). For several species common to both the NPGS collection and the Stanwood experiments, P50 estimates are nearly identical [e.g. Brassica oleracea (Brassicaceae), Helianthus annuus (Asteraceae), Lactuca sativa (Asteraceae), Glycine max (Fabaceae), Festuca spp. (Poaceae)] (Table 3). However, the slightly lower exponential factors and higher median f in the Stanwood data set led to higher calculated P50s for many species. Lower exponential factors are typical when storage times are too short (between 20 and 25 years in the Stanwood experiment) for seeds to enter into the cataclysmic decay phase. Hence, insufficiently long storage times led to an overestimate of P50 when Avrami parameters were calculated from a double-ln plot, suggesting that large discrepancies between P50s calculated for the NPGS collection and the Stanwood experiments [e.g. Apium graveolens (Apiaceae), Cucumis spp. (Cucurbitaceae), Spinacia oleracea (Chenopodiaceae), Vicia spp. (Fabaceae)] can be attributed to the insufficient duration of the Stanwood experiment. The low P50s observed in the Stanwood experiment for species such as Lespedeza cuneata (Fabaceae), Medicago sativa (Fabaceae) and Pennisetum glaucum (Poaceae) may not be representative, as the behaviour has been assessed from just one accession. The large number of species included in the NPGS collection allows comparison with P50 values determined in other survey studies reported in the literature (Table 3). For the 62 species common to both studies, P50 values reported by Priestley et al. (1985) were consistently less (median P50 ¼ 7 years) than values reported for the NPGS collection; but this is expected since seeds in the Priestley et al. (1985) study were stored under fluctuating temperature and moisture conditions. P50 values calculated using coefficients of the viability equations of Ellis et al. (1986, 1988, 1989, 1990a,b) were similar (median ¼ 48 years) to the P50 values determined from the NPGS and Stanwood storage experiments (see Table 3 for species in common, compare also with Tables 1 and 2 for all species). Estimated longevities for vegetable species in the Roos and Davidson (1992) study were also comparable, with a median P50...
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This note was uploaded on 03/03/2013 for the course SFSF 202 taught by Professor Sf during the Spring '13 term at Cambridge.

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