2017 ASHS Annual Conference

Cucumber fruits are covered by a layer of cuticle (a thin lipophilic layer) and epicuticular waxes that function to restrict water loss and prevent infection by pathogens. The cuticle is formed from a complex matrix of mainly cutin and waxes, whose precursors are synthesized and secreted by epidermal cells aided by lipid bodies. This deposition of the cuticle and epicuticular waxes varies among species, cultivars, and developmental age. This study evaluates the natural variation of cuticle and epicuticular wax deposition in two cultivars of cucumber, Chinese Long ‘9930’, a Chinese fresh market cucumber, and ‘Gy14,’ a pickling type. Fruit of these lines differ in appearance; ‘9930’fruit is more elongated and darker green with striping and bumps, while ‘Gy14’ has wider fruit that are lighter green with a smoother surface. The fruits also differ for epidermal cell structure and cuticle and wax related traits. Thin-section samples (~0.1mm) were prepared from the mid-region of fruit harvested at 16 days post pollination (dpp), a time when most cuticle deposition has taken place and strong differences for cuticle thickness are observed. Sections were stained with Sudan IV to identify the cuticle and epicuticular waxes and imaging software was used to evaluate samples for: cuticle thickness, depth of wax intercalation between epidermal cells, epidermal cell size and shape, and number and size of lipid bodies. ‘9930’ is characterized by flatter epidermal cells (approximately 35µm in length and 29 µm in width), while ‘Gy14’ has columnar shaped epidermal cells (approximately 54 µm in length and 17µm in width). The cuticular layer for ‘9930’ was 2-3 fold thinner than for ‘Gy14’ (average thickness of 1.6 µm vs. 4.3 µm, respectively) with reduced intercalations between cells (average depth of 5.2 µm vs. 30 µm). The epidermal cells of ‘Gy14’ had a larger number and larger sized lipid bodies (average of 33 lipid bodies per 450 µm epidermal cell layer with an average diameter of 6.2µm for ‘Gy14’ vs. 16 lipid bodies and 4.3µm average diameter for ‘9930’). A recombinant inbred line (RIL) population, consisting of 112 lines developed from these two cultivars, is being utilized to examine inheritance of these traits and their relationship to each other. Plants were grown in the greenhouse and three hand-pollinated fruits per line were harvested at 16 dpp. Microscopic samples are currently being evaluated for cuticle thickness, depth of intercalation, epidermal size and orientation, and presence and size of lipid bodies.