GermIndex {germinationmetrics}

Germination Index

Description

Compute the Germination index according to Melville et al. (1980) and its modification by de Santana and Ranal (2004) (Ranal and de Santana 2006).

Usage

GermIndex(
  germ.counts,
  intervals,
  partial = TRUE,
  total.seeds,
  modification = c("none", "santanaranal")
)

Arguments

germ.counts

Germination counts at each time interval. Can be partial or cumulative as specified in the argument partial.

intervals

The time intervals.

partial

logical. If TRUE, germ.counts is considered as partial and if FALSE, it is considered as cumulative. Default is TRUE.

total.seeds

Total number of seeds.

modification

The modification to be applied. Either "none" or "santanaranal". Default is "none" (see Details).

Details

Germination index (\(GI\)) is computed as follows (Melville et al. 1980).

\[GI = \sum_{i=1}^{k}\frac{\left | \left ( T_{k} - T_{i} \right ) N_{i}\right |}{N_{t}}\]

Where, \(T_{i}\) is the time from the start of the experiment to the \(i\)th interval (day for the example), \(N_{i}\) is the number of seeds germinated in the \(i\)th time interval (not the accumulated number, but the number corresponding to the \(i\)th interval), \(N_{t}\) is the total number of seeds used in the test, and \(k\) is the total number of time intervals.

A modified germination index (\(GI_{mod}\)) was proposed by (de Santana and Ranal 2004) where total number of seeds tested (\(N_{t}\)) is replaced by the total number of germinated seeds (\(N_{g}\)) in the expression of Melville et al. (1980) to remove the effect of sample size (Ranal and de Santana 2006). It is computed as follows (Specified by the argument modification = "santanaranal").

\[GI_{mod} = \sum_{i=1}^{k}\frac{\left | \left ( T_{k} - T_{i} \right ) N_{i}\right |}{N_{g}}\]

The term Germination index (\(GI\)) has also been used to describe the mathematical expression for Speed of germination (GermSpeed) by AOSA (1983).

Value

The value of the Germination index in the same unit of time as specified in the argument intervals.

References

AOSA (1983). Seed Vigor Testing Handbook. Association of Official Seed Analysts, Ithaca, NY, USA.

Melville AH, Galletta GJ, Draper AD, Ng TJ (1980). “Seed germination and early seedling vigor in progenies of inbred strawberry selections.” HortScience, 15(6, I), 749–750.

Ranal MA, de Santana DG (2006). “How and why to measure the germination process?” Brazilian Journal of Botany, 29(1), 1–11.

de Santana DG, Ranal MA (2004). Analise Da Germinacao: Um Enfoque Estatistico. Universidade de Brasilia, Brasilia.

See Also

GermSpeed

Examples

x <- c(0, 0, 0, 0, 4, 17, 10, 7, 1, 0, 1, 0, 0, 0)
y <- c(0, 0, 0, 0, 4, 21, 31, 38, 39, 39, 40, 40, 40, 40)
int <- 1:length(x)

# From partial germination counts
#----------------------------------------------------------------------------
GermIndex(germ.counts = x, intervals = int, total.seeds = 50)
GermIndex(germ.counts = x, intervals = int, total.seeds = 50,
          modification = "none")
GermIndex(germ.counts = x, intervals = int, total.seeds = 50,
          modification = "santanaranal")

# From cumulative germination counts
#----------------------------------------------------------------------------
GermIndex(germ.counts = y, intervals = int, partial = FALSE,
          total.seeds = 50)
GermIndex(germ.counts = y, intervals = int, partial = FALSE,
          total.seeds = 50,
          modification = "none")
GermIndex(germ.counts = y, intervals = int, partial = FALSE,
          total.seeds = 50,
          modification = "santanaranal")