Florist gloxinia (Sinningia speciosa) is native to Brazil within the family Gesneriaceae. Gloxinia is a popular flowering potted plant grown for its fleshy, velvety leaves and large colorful flowers with various symmetries and forms. The wholesale value of potted gloxinia reached $500,000 in 2009 and 2014 (U.S. Department of Agriculture, 2021).
Depending on the cultivar, gloxinia have zygomorphic or actinomorphic flowers (Zaitlin, 2012). Actinomorphic floral symmetry is controlled by a recessive allele (cc), whereas a single dominant gene expressed in the homozygous (CC) or heterozygous (Cc) state results in zygomorphic floral symmetry (Hsu et al., 2017). The flower form is controlled by one single nuclear locus with two alleles, and that double flower is dominant over single flowers. The double-flowered heterozygote occasionally has markedly fewer petals than the double-flowered homozygote of gloxinia (Clayberg, 1975; Shalit, 2000). Double-flowered gloxinia cultivars with white leaf veins are commercially desirable but are currently rare.
Inheritance of foliar variegation has been studied in several genera of foliage plants such as aglaonema (Aglaonema sp.), caladium (Caladium sp.), and dieffenbachia (Dieffenbachia sp.), but not in the Gesneriaceae family. The presence of foliar variegation in aglaonema and dieffenbachia is dominant in nonvariegation (Henny and Chen, 2010). Inheritance of the white foliar midrib is controlled by a single dominant nuclear gene in three dieffenbachia cultivars (Henny, 1983). A single dominant allele determines the presence of silver–grey stripes overlaying the leaf veins in aglaonema cultivars (Henny, 1986). A single locus with three alleles determines the main vein color in caladium cultivars. The locus has been designated as V and the order of dominance is Vr (red vein) > Vw (white vein) > Vg (green vein) (Deng and Harbaugh, 2006). No information regarding the inheritance of the white vein in gloxinia is currently available.
Four mechanisms of foliar variegation have been identified by Hara (1957), namely, chlorophyll type, pigment type, air space type, and epidermis type. Most foliar variegation can be characterized into two basic categories. True variegation is demonstrated by leaves with areas of little or no chlorophyll (Aluru et al., 2001; Wang et al., 2018) or pigmentation (Hughes et al., 2014; Pao et al., 2020). Other types of variegation are caused in part, by anatomical features such as trichomes, scales, or air spaces between the upper epidermis and mesophyll cells (Sheue et al., 2012). Leaf coloration and variegation may alter photosynthetic efficiency. The variegation of Aglaonema nitidum ‘Curtisii’ is caused by the presence of air spaces, and such variegation is unavailable for photosynthesis (Fooshee and Henny, 1990). In contrast, the maximum quantum yield of photosystem II, as measured by Fv/Fm, does not differ significantly between the light and green areas in the air space type of variegated begonia such as B. formosana, B. diadema, and B. pustulata (Sheue et al., 2012). The mechanism of the white vein and comparative photosynthesis between the white and green leaf portions of gloxinia remain unclear.
The objectives of this study were to 1) understand the inheritance of vein color, flower form, and floral symmetry in our population, and to determine if the vein color character is linked with the flower form or floral symmetry; 2) develop new gloxinia progeny with white veins and double flowers; and 3) compare the anatomy and photosynthesis of the white and green leaf portions.
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