Effects of direct contact of Pinusresinosa seeds and young seedlings with N-dimethylamino succinamic acid, (2-chloroethyl)trimethylammonium chloride, or maleic hydrazide

Abstract

Critical concentrations of two growth retardants, N-dimethylamino succinamic acid (Alar) and (2-chloroethyl)trimethylammonium chloride (CCC), and one growth inhibitor, maleic hydrazide, applied continuously to Pinusresinosa seedlings in the cotyledon stage greatly suppressed seedling growth and development and killed many seedlings. Both Alar and CCC arrested the elongation of stems, roots, cotyledons, and primary needles, inhibited the expansion of mesophyll cells, and decreased the amount of intercellular space in the cotyledons and cortex. Growth was inhibited by lower concentrations of CCC than of Alar. Maleic hydrazide reduced the growth of shoots, roots, cotyledons, and primary needles, with growth inhibited by much lower concentrations than those of Alar or CCC. Cell expansion was stimulated by maleic hydrazide at concentrations below 2500 ppm and inhibited by concentrations at or above 2500 ppm. Maleic hydrazide at 100 ppm caused chlorosis and induced wall thickening of ground tissue cells in the hypocotyl and cotyledons. The greater reduction of root growth than of shoot growth as well as the inhibition of the growth of primary needles by nonlethal concentrations of Alar, CCC, or maleic hydrazide will increase the mortality risk of Pinusresinosa seedlings in the cotyledon stage of development.