Sigma calculates the period to lose one probit viability
(σ) under storage at a given
moisture content and temperature.
Sigma(vcindex, vcdirect, mc, temp, years = FALSE)
| vcindex | An integer value indicating the index of seed viability.
constants to be used from the |
|---|---|
| vcdirect | A numeric vector of length 4 with the four viability constants viz.: KE, CW, CH and CQ. |
| mc | Moisture content. |
| temp | Temperature in °C. |
| years | If |
The period to lose one probit in days or years (according to argument
years).
This function computes the period to lose one probit viability (σ) according to the improved seed viability equation of Ellis and Roberts (1980) as follows.
v = Ki − [ p ⁄ σ ]
or
v = Ki − (1 ⁄ σ)⋅p
Where, v is the probit percentage viability at storage time p (final viability), Ki is the probit percentage viability of the seedlot at the beginning of storage (seedlot constant) and 1⁄σ is the slope.
Germination percentages plotted against storage times yield a sigmoid seed survival curve which is converted to a linear relationship by the probit transformation with slope 1 ⁄ σ.
The slope is determined as follows.
σ = 10 KE − CW logm − CHt − CQt2
Where, v is the probit percentage viability at storage time p (final viability), Ki is the probit percentage viability of the seedlot at the beginning of storage (seedlot constant), m is the moisture content (fresh weight basis), t is the temperature and KE, CW, CH and CQ are the species-specific seed viability constants.
The value of the species-specific seed viability constants can be specified
either directly in the argument vcdirect or as the index value of the
required seed viability constants from the viabilityconstants
dataset through the argument vcindex.
The value of this prediction is appropriate for temperature between -20 to 90 °C and seed moisture content between 5 to 25%. For values beyond this range, a warning will be displayed.
Ellis RH, Roberts EH (1980). “Improved equations for the prediction of seed longevity.” Annals of Botany, 45(1), 13--30.
#---------------------------------------------------------------------------- # Days/Years to lose unit probit viability for rice seeds stored at # 5 degree celsius and 10% moisture content. #---------------------------------------------------------------------------- # Fetch the index from viabilityconstants dataset viabilityconstants[grepl("oryza", x = viabilityconstants$Species, ignore.case = TRUE),]#> # A tibble: 8 x 7 #> Index Species Ke Cw Ch Cq Reference #> <dbl> <chr> <dbl> <dbl> <dbl> <dbl> <chr> #> 1 85 Oryza glaberrima 9.41 5.04 0.0375 4.71e-4 Ellis et al., 2007 #> 2 86 Oryza glaberrima* 6.87 5.51 0.0329 4.78e-4 Bam, Hong, Ellis, Kumaga,~ #> 3 87 Oryza sativa 8.24 4.34 0.0307 5.01e-4 Ellis et al., 2007 #> 4 88 Oryza sativa* 8.67 5.03 0.0329 4.78e-4 Ellis et al., 1989 #> 5 89 Oryza sativa ssp.~ 8.81 4.90 0.0329 4.78e-4 Ellis, Hong, and Roberts,~ #> 6 90 Oryza sativa ssp.~ 8.42 4.90 0.0329 4.78e-4 Ellis et al., 1992 #> 7 91 Oryza sativa ssp.~ 6.63 5.51 0.0329 4.78e-4 Bam et al., 2008 #> 8 92 Oryza sativa ssp.~ 8.74 4.90 0.0329 4.78e-4 Ellis et al., 1992# Use index 87 Sigma(vcindex = 87, mc = 10, temp = 5)#> [1] 5382.388Sigma(vcindex = 87, mc = 10, temp = 5, years = TRUE)#> [1] 14.74627# Input the viability constants directly Sigma(vcdirect = c(8.242, 4.345, 0.0307, 0.000501), mc = 10, temp = 5)#> [1] 5382.388#> [1] 14.74627# Warning if moisture content is beyond limits (0-100 %) Sigma(vcindex = 87, mc = 110, temp = 5)#> Warning: "mc" is beyond limits (0 < "mc" < 100).#> [1] 0.1607399# Warning if temperature is beyond limits (-20 to 90 degree C) Sigma(vcindex = 87, mc = 10, temp = 95)#> Warning: "temp" is beyond limits (-20 < "temp" < 90).#> [1] 0.0002877233#---------------------------------------------------------------------------- # Days/Years to lose unit probit viability for soybean seeds stored at # -18 degree celsius and 8% moisture content. #---------------------------------------------------------------------------- # Fetch the index from viabilityconstants dataset viabilityconstants[grepl("glycine", x = viabilityconstants$Species, ignore.case = TRUE),]#> # A tibble: 2 x 7 #> Index Species Ke Cw Ch Cq Reference #> <dbl> <chr> <dbl> <dbl> <dbl> <dbl> <chr> #> 1 59 Glycine max 7.52 4.09 0.0329 4.78e-4 Ellis et al., 1982; Dickie et al~ #> 2 60 Glycine max 7.29 4.00 0.0295 4.91e-4 Ellis, 1988# Use index 59 Sigma(vcindex = 59, mc = 8, temp = -18)#> [1] 18719.85Sigma(vcindex = 59, mc = 8, temp = -18, years = TRUE)#> [1] 51.28725# Input the viability constants directly Sigma(vcdirect = c(7.292, 3.996, 0.0295, 0.000491), mc = 8, temp = -18)#> [1] 11354.51#> [1] 31.10825# Warning if moisture content is beyond limits (0-100 %) Sigma(vcindex = 59, mc = 110, temp = 5)#> Warning: "mc" is beyond limits (0 < "mc" < 100).#> [1] 0.1017231# Warning if temperature is beyond limits (-20 to 90 degree C) Sigma(vcindex = 59, mc = 10, temp = 95)#> Warning: "temp" is beyond limits (-20 < "temp" < 90).#> [1] 9.989644e-05