Peach Seedling Emergence and Growth in Response to Isothermal and Cycled Stratification Treatments Reveal Two Dormancy Components

Abstract

Dormant seeds of `Johnson Elberta' peach [Prunus persica (L.) Batsch] were stratified at constant 2, 6, or 14 °C or cycled between 2 and 14 °C in 12/12, 14/10, 16/8, 20/4, 22/2, or 23/1 h cycles. Emergence (measured every 3 d after planting) and normal seedling growth (measured after 49 d) increased with longer stratifiction durations. Seeds stratified at 2 °C had the most rapid emergence (only 28 d of stratification was required) but seedling growth was abnormal until 70 d of stratification. Isothermal stratification at 6 °C resulted in normal seedlings after 56 d of stratification but quality and quantity of growth improved with stratification up to 70 d. Seeds stratified at 14 °C showed limited improvement in seedling emergence with time; seedling growth was poor and cotyledonary reserves were not used. Seedling growth after cycled stratification treatments gained normalcy faster than in the constant 2 °C treatment. The 22/2 and 20/4 (2/14 °C) cycles produced normal growth after 56 d of stratification that was comparable to the growth produced by the constant 6 °C treatment. Other cycles required 70 d or more for equivalent seedling growth. Improved seedling growth under cycled treatments could be due to developmental or growth promoting temperature effects of 14 °C during stratification or a combined effect of thermal accumulation and chilling occurring together after a minimal chilling requirement has been completed.