Alleviation of High Temperature Stress by Preplant Permeation of Phthalimide and Other Growth Regulators into Lettuce Seeds via Acetone

Abstract

A preplant acetone permeation of ‘Grand Rapids’ and ‘Mesa 659’ lettuce (Lactuca sativa L.) seeds with either cyclohexanecarboxamide 1-(3-chlorophthalimide) (phthalimide) or gibberellin A 4+7 (GA) in combination with kinetin (KIN) and/or (2-chloroethyl) phosphonic acid (ethephon) markedly relieved the adverse effect of high temperature (20°, 12 hr night/30°C day regime) on seedling emergence from soil. Permeation of GA in ‘Grand Rapids’ seeds increased seedling hypocotyl length by 121% compared to only 25% for phthalimide permeated seeds. In ‘Mesa 659’ seeds, the corresponding increases with GA and phthalimide permeation were 52% and 26%, respectively. Permeation of GA + ethephon + KIN and phthalimide + ethephon + KIN increased seedling hypocotyl elongation over the control by 126% and 60% in ‘Grand Rapids’ and 91% and 21% in ‘Mesa 659’, respectively. Seed permeation with phthalimide tended to increase the leaf chlorophyll content of emerging seedlings. Permeation of GA decreased leaf chlorophyll up to 28% in ‘Mesa 659’ and up to 13% in ‘Grand Rapids’. These findings indicate that phthalimide could be substituted for GA in seed treatments needed to alleviate the adverse effects of high temperatures on germination and seedling establishment and to improve growth characteristics of emerged seedlings.

Emergence at High Temperature and Seedling Growth Following Pretreatment of Lettuce Seeds with Fusicoccin and Other Growth Regulators

“…The stimulating effect of GA or K on lettuce seed performance has been demonstrated (1,2,19). However, GA has caused excessive hypocotyl elongation and etiolated seedlings (1,10).…”