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  • Author or Editor: Leonard M. Pike x
  • Journal of the American Society for Horticultural Science x
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Fruit of TAMU breeding line 830397 are green in contrast to the cream or orange fruit of commercial cultivars at the mature-seed stage (MS-S). Inheritance of this trait for green MS-S fruit color in Cucumis sativus was investigated. A new locus, gn, is proposed as well as the elimination of the C locus. MS-S fruit color is controlled by two major genes, R and Gn. Fruit is orange when the genotype is R_ _ and green when the genotype is rrgngn. The cream MS-S fruit color trait is incompletely dominant over green, as the genotype rrGnGn is cream while rrGngn produces mature fruit from cream to intermediate in color between cream-colored and green fruit. Spine color is pleiotropic with or very tightly linked to the R locus, but heavy netting from PI 165509 appears not to be linked with the orange genotype and is polygenic.

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Onion growth responses to salinity levels were evaluated using five onion cultivars. In a plant growth study, eight salt levels were used with electrical conductivities (EC) ranging from 0.8 to 12.0 dS·m−1. Total area of the leaves and stem, dry weight, plant height, and leaf tip burn were measured after 45 days of growth. All five cultivars were sensitive to low salt levels, with significant reduction occurring at 1.4 dS·m−1. In a 2nd experiment germination percentage was evaluated for 8 days; a wider range of salt levels was tested (0.0–50.0 dS·m−1). Rate of germination was retarded 1–3 days with increasing salt concentrations, but germination percentage after 8 days was not significantly reduced in the 0.0–25.0 dS·m−1 salt levels. Germination was prevented at 45.0 dS·m−1 for all cultivars except ‘Texas Grano 1015Y’, which exhibited slight germination. These test results confirm that salt effects during germination are not related to later responses of the whole plant to salt. Screening onion for salt tolerance would best be done at the vegetative stage.

Open Access

The relatively low evolution rate of the chloroplast DNA has made it an ideal tool to study evolutionary processes in plants above the species levels. However, recent studies have demonstrated that intraspecific variation in the chloroplast DNA is also common. This variation has provided useful insights into population level evolutionary processes. The polymerase chain reaction and sequencing of a noncoding chloroplast region used to classify onion lines for cytoplasmic type facilitated the identification of one sterile and two normal plastome variants in onion (Allium cepa L.). Sequence comparison revealed that differences between plastome variants included the presence of single-nucleotide polymorphisms associated with cytoplasmic type and variable numbers of tandem repeats, possibly resulting from slipped-strand mispairing. Our observations support the use of chloroplast-specific markers to assist in the selection of specific cytoplasmic types, suggest the potential to facilitate genotype determination, and demonstrate the presence of additional variation within cytoplasm type which gives insight into plastome evolution and may facilitate more accurate genotyping and selection.

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The aglycone, or free quercetin, and total quercetin content of 75 cultivars and selections was analyzed by reverse-phase high-performance liquid chromatography. Quercetin glycosides were hydrolyzed into aglycones. Total quercetin content in yellow, pink, and red onions varied from 54 to 286 mg·kg-1 fresh weight in different onion entries grown during 1992. White onions contained trace amounts of total quercetin. Free quercetin content in all the onions was low (< 0.4 mg·kg-1) except in `20272-G' (12.5 mg·kg-1 fresh weight). Bulbs stored at 5, 24, and 30C and controlled atmosphere (CA) for 0,1,2,3,4, and 5 months showed a most marked change in total quercetin content at 24C compared to other treatments, with a rise in mid-storage followed by a drop. Storage at 5 and 30C also demonstrated a similar change. However, total quercetin content did not vary significantly in bulbs stored at CA for 5 months. We conclude that genetic and storage factors affect quercetin content on onions.

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Triploid or seedless watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] cultivars often have erratic germination and low seedling vigor. The morphology of the seedcoat on two triploid cultivars—Tri X 313 and Tri X Sunrise—was examined by scanning electron microscopy (SEM) to identify structural differences compared to diploid seeds. Triploid seeds incubated with oxygen-enhanced treatments that included nicking, 1% hydrogen peroxide (H2O2), and 40% oxygen were investigated at low and high medium moisture levels. Triploid seed has a thicker seedcoat with a dense endotesta layer and a larger and highly variable air space surrounding the embryonic axis as compared with diploid seed. All cultivars rapidly imbibed water (≈50% of the original weight) during the first hour of imbibition, with a faster increase for triploids than for diploids. High moisture affected germination to a lesser extent in diploid than triploid seeds. Triploid germination under low medium moisture ranged from 96% to 76%, but was severely reduced to <27% under high medium moisture. Triploid seed germination was significantly improved at high moisture by H2O2 and by 40% oxygen. Triploid watermelon seed is very sensitive to submerged conditions, possibly due to a combination of physiological and morphological defects. The rapid imbibition and excess water collected in the seedcoat and air space surrounding the embryo, could reduce oxygen diffusion and impair metabolic pathways leading to normal germination and seedling development.

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