Collecting Time Affected Immature Seed Germination of Kalmia latifolia L. Hybrids

Kalmia latifolia L. (mountain laurel), a member of Ericaceae, is a beautiful ornamental shrub native to North America. The plant is not common in southeastern US landscapes because of its limited heat tolerance. Rapid breeding of heat-tolerant mountain laurel cultivars requires better germination of seeds from the cross-hybridization. To prevent seed abortion from incompatibility and shorten germination time, the collecting time for immature seed germination was investigated. Fresh fruits of two mountain laurel hybrids were harvested weekly from the 14^th of July to the 22^nd of September 2015 and disinfected. Cleaned immature seeds were then extracted and cultured in Murashige and Skoog (MS) medium with 3% sucrose and pH at 5.0. As collecting time went later, germination percentages and number of true leaves produced by immature seeds increased significantly. The germination percentages of ‘Minuet’ x ‘Snowdrift’ and ‘Pinkcharm’ x ‘Freckles’ ranged from 20.0% to 80.0% and from 12.5% to 82.5%, respectively. The lowest germination percentage occurred in July collection. Seeds collected in September germinated in 2-3 weeks and could yield 80.0% of germination. Seeds produced significantly more true leaves in September collection (5 leaves) than that of late August collection (2) after 8 weeks. Majority of seeds collected in July and early August failed to produce true leaf after germination. Early to mid-September should be recommended to collect mountain laurel hybrid fruits for immature seed germination when most of seeds became capable to yield good germination and vigorous growth.