The effects of various temperature treatments during seed stratification on abscisic acid, germination and seedling growth in peach

Peach seeds (Prunus persica (L) Batsch), 'Halford', were used in studies of stratification temperatures in relation to germination, physiological dwarfing and abscisic acid (ABA) content.; Optimum chilling temperatures for germination after 12 weeks were 5{dollar}spcirc{dollar} to 7{dollar}spcirc{dollar}C, with significant responses at 0{dollar}spcirc{dollar}, 3{dollar}spcirc{dollar}, and 15{dollar}spcirc{dollar}, but no germination at {dollar}-5spcirc{dollar} and 25{dollar}spcirc{dollar}. The rate of dormancy release was relatively slow during the first 4 to 8 weeks of stratification.; Alternation of 5{dollar}spcirc{dollar}C with 10{dollar}spcirc{dollar} in daily cycles enhanced seed germination compared to continuous 5{dollar}spcirc{dollar}. However, diurnal temperatures of 5{dollar}spcirc{dollar}/15{dollar}spcirc{dollar} and 5{dollar}spcirc{dollar}/25{dollar}spcirc{dollar} resulted in partial and complete negation of the chilling effect, respectively. This indicates that the temperature threshold for promotion/inhibition in 'Halford' Peach seeds is between 10{dollar}spcirc{dollar} and 15{dollar}spcirc{dollar}.; Interruption of stratification at 5{dollar}spcirc{dollar}C with one week of 30{dollar}spcirc{dollar} after 3 weeks of the cold treatment resulted in induction of secondary dormancy. However, when this interruption was given after 6 weeks of 5{dollar}spcirc{dollar}, only partial induction of secondary dormancy occurred. This interruption shortened the new chilling needed for the seeds to germinate to a level similar to that obtained with continuous 5{dollar}spcirc{dollar}.; Physiological dwarfing responses (PDR) were lowest in plants produced after chilling at 5{dollar}spcirc{dollar}C, with higher incidences from lower or higher temperatures, from diurnal temperature cycles and from partially chilled seeds. The warm temperature interruption also resulted in higher PDR. PDR assayed were plant height, number of nodes and number of nodes with abnormal leaves.; Seed stratification at {dollar}-5spcirc{dollar}, 0{dollar}spcirc{dollar}, 3{dollar}spcirc{dollar}, 5{dollar}spcirc{dollar}, 7{dollar}spcirc{dollar}, 15{dollar}spcirc{dollar} and 25{dollar}spcirc{dollar}C for 12 weeks caused 63% to 86% decline in ABA levels, yet dormancy was not broken in all treatments. The decline in ABA content was faster and larger in seeds stratified at 5{dollar}spcirc{dollar}/10{dollar}spcirc{dollar}, 5{dollar}spcirc{dollar}/15{dollar}spcirc{dollar} and 5{dollar}spcirc{dollar}/25{dollar}spcirc{dollar} alternating daily temperatures. It ranged from 87% to 100%. In both the constant and alternating treatments, the major drop in ABA concentrations occurred during the first 4 weeks. Decline in ABA concentrations alone was not sufficient to terminate seed dormancy. Warm temperature interruption during stratification, that partially induced secondary dormancy, resulted in a significant drop in ABA concentration.