2017 ASHS Annual Conference

Chrysanthemum cinerariifolium Vis., or Dalmatian pyrethrum (Asteraceae), is an herbaceous perennial native to the eastern coast of the Adriatic Sea. Its flowers yield sustainable, natural or “organic” insecticide compounds, particularly pyrethrins (Py I, II), which are non-toxic to mammals. High expression of the precursor for a key pyrethrin biosynthetic enzyme (chrysanthemyl diphosphate synthese) is in the glandular trichomes on the seed coats. To breed for plants with increased Py I, II, chemical extraction of these compounds on a per flower or per plant basis is one method for parental selection. Chemical extractions are costly to perform with large, segregating populations of hybrid or inbred genotypes. Our research focused on the ability to screen flowers using portable scanning electron microscopy (SEM) to determine trichome number and density and their relation to Py I, II concentrations. This would streamline breeding studies for heritability and enhance the rate of selection. Fresh flower samples were bisected, mounted, and scanned with a TM3030 benchtop SEM; digital images of disc and ray florets were recorded and analyzed with Image J using a Huion H610 Pro Graphic Drawing Tablet. The highest concentration of trichomes occurred on the basal surface of each disc or ray floret’s 4-sided ovary epidermis. This surface area was measured as well as trichome lengths, number of trichomes/unit area, and the number of disc/ray florets (ovules) per flower. Based on these data, the total number of trichomes/flower was estimated. Cross-sections of flowers were examined under SEM for 1-2 sides of each ovary (the remainder could not be visualized). Trichome length range was 65-80 μm with a total production of 77-216 trichomes per unit area. The mean number of ovules was ~167/flower, producing an estimated total of 13,948 to 72,698 trichomes/flower. All traits varied significantly among genotypes demonstrating the opportunity to use these data to select parents for heritability studies and to increase Py I, II concentrations.