GERMINATION RESPONSE to SEED PRETREATMENTS IN TWO GENOTYPES of MOUNTAIN LAUREL (Kalmia latifolia L.)

Mountain laurel, Kalmia latifolia, is an evergreen woody shrub in the family Ericaceae, and is found in the entire eastern portion of the United States from southwestern Maine to northern Florida.  Most mountain laurel germplasm used for breeding purposes in the U.S. is from the northern portions of its range.  Our research is directed towards breeding of mountain laurel germplasm better suited for the southern portion of its range.  The presented work investigates the differences in seed germination of two mountain laurel genotypes – one originating from a warmer location (USDA hardiness zone 8) and one originating from a colder location (USDA hardiness zone 6).  Six hundred seeds of each genotype were subjected to 4 treatments – soaking overnight in distilled water (control), soaking overnight in 100 ppm gibberellic acid (GA), soaking overnight in 200 ppm GA, and subjecting to scarification at -80º C for 24 hours with subsequent soaking overnight in distilled water. Seeds were placed on moistened germination paper in Petri dishes and the Petri dishes placed randomly in a growth chamber (324 µmoles·m^-2_·sec^-1 of light from 8 a.m. to 12 a.m. at a constant temperature of 21º C and relative humidity of 80%).  After 29 days the experiment was discontinued as no further germination was occurring.  All seeds subjected to scarification lost their vitality.  An interaction between seed origin and GA treatment was evident.  The 100 ppm GA treatment clearly inhibited germination in the southern genotype in terms of both germination dynamics and rate.  The same concentration applied to the northern genotype led to earlier germination and a higher germination rate compared to the control.  The 200 ppm GA treatment of the southern genotype seeds did not have an effect on either onset of germination, or on total germination compared to the untreated control.  The northern genotype responded to the same treatment with earlier and accelerated germination, however, as of day 19, germination reached a plateau with insignificant increase afterwards.  At the end of the experiment the germination rate of the northern genotype treated with 200 ppm GA was significantly lower than the control.