Seedling Rate of Development Index: Indicator of Vigor and Seedling Growth Response

Abstract

Seedling growth analysis has been shown to be a useful tool to supplement the results of the standard viability test when evaluating seed lots for vigor. A number of indices have been proposed to describe the vigor of a particular seed lot. Few of these indices have been rigorously tested for their response to varying hypothetical emergence distributions during initial seedling development. Seedling rate of development index (SRDI), which incorporates the concepts of completeness, rate, uniformity of germination, and morphological development during initial seedling growth, was compared with five previously published indices of seed vigor. The indices were evaluated for their response to emergence distributions, which varied by number of mode levels, degree and direction of skewness, kurtosis, and seedling mortality after initial emergence. None of the five previously published vigor indices gave satisfactory results for all of the simulated conditions. The SRDI produced acceptable results for all test conditions and was particularly good for detecting latent seedling mortality after initial emergence. Data from actual seed lots grown under controlled conditions did not dispel the conclusions based on simulations. The SRDI may be a useful supplementary tool to use in combination with standard germination percentage when evaluating seedling vigor of different seed lots or genetic stocks or when measuring seedling response to varying environmental conditions.