A hydrothermal time model explains the cardinal temperatures for seed germination

Abstract

Temperature ( T ) and water potential ( y ) are two primary environmental regulators of seed germination. Seeds exhibit a base or minimum T for germination ( T b ), an optimum T at which germination is most rapid ( T o ), and a maximum or ceiling T at which germination is prevented ( T c ). Germination at suboptimal T can be characterized on the basis of thermal time, or the T in excess of T b multiplied by the time to a given germination percentage ( t g ). Similarly, germination at reduced y can be characterized on a hydrotime basis, or t g multiplied by the y in excess of a base or threshold y that just prevents germination ( y b ). Within a seed population, the variation in thermal times to germination among different seed fractions ( g ) is based on a normal distribution of y b values among seeds ( y b ( g )). Germination responses across a range of suboptimal T and y can be described by a general hydrothermal time model that combines the T and y components, but this model does not account for the decrease in germination rates and percentages when T exceeds T o . We report here that supra-optimal temperatures shift the ψ ψ ψ ψ b ( g ) distribution of a potato ( Solanum tuberosum L.) seed population to more positive values, explaining why both germination rates and percentages are reduced as T increases above T o . A modified hydrothermal time model incorporating changes in ψ ψ ψ ψ b ( g ) at T > T o describes germination timing and percentage across all T and ψ ψ ψ ψ at which germination can occur and provides physiologically relevant indices of seed behaviour.

CARDINAL TEMPERATURES FOR GERMINATION OF THE MEDICINAL ANDDESERT PLANT, Calotropis procera

“…Establishment of the species in new sites depends on seed dispersal, germination and the establishment of seedlings. Seed germination is affected by light, temperature, and a host of other environmental factors (Bewley & Black, 1994). Temperature during seed imbibitions has been found to influence the germination rate and the ultimate percentage of germination (Flores & Briones, 2001).…”

“…Temperature during seed imbibitions has been found to influence the germination rate and the ultimate percentage of germination (Flores & Briones, 2001). Since as early as 1860, it has been recognized that three cardinal temperatures (minimum or base temperature T b , optimum temperature, T opt and maximum temperature, T Max ) describe the temperature range over which the seeds of a particular species can germinate (Bewley & Black, 1994). Seeds of each species possess the capacity to germinate within a defined temperature range, which is referred to as the cardinal temperature (Alvarado & Bradford, 2002).…”

“…Since as early as 1860, it has been recognized that three cardinal temperatures (minimum or base temperature T b , optimum temperature, T opt and maximum temperature, T Max ) describe the temperature range over which the seeds of a particular species can germinate (Bewley & Black, 1994). Seeds of each species possess the capacity to germinate within a defined temperature range, which is referred to as the cardinal temperature (Alvarado & Bradford, 2002). Cardinal temperatures for germination of most crop plants tend to be similar to those of normal vegetative growth (Gardner et al, 1985).…”

“…The optimum cardinal temperature is the temperature at which crop growth and performance are at their maximum. The maximum cardinal temperature is the highest temperature at which plant growth can occur (Alvarado & Bradford, 2002). Some methods have previously been developed to describe species growth data (e.g.…”

Temperatura cardeal e potencial hídrico na germinação de sementes de corda-de-viola (Ipomoea triloba)

“…Cada espécie necessita de quantidade diferente de água para que os processos metabólicos germinativos comecem (Alvarado & Bradford, 2002).…”