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- Author or Editor: Todd C. Wehner x
All available cucumber (Cucumis sativus L.) cultigens were tested for combining ability for fruit storage ability by crossing them with the gynoecious inbred Gy 14. Fruit weight and firmness were measured before and after storage, and fruits were rated for water loss after storage. The cultigens with the lowest percentage of fruit weight loss during storage were PI 172839, PI 344067, PI 264667, PI 171612, PI 339245, PI 220171, PI 279469, and PI 368550; those with the lowest percentage of loss in fruit firmness were PI 379284, PI 339241, PI 414159, PI 422177, `Regal', PI 109483, `Addis', PI 285603, PI 257486, and `Calypso'. The cultigens demonstrating the least fruit shriveling were `Dasher II', `Sprint 440', `Texas Long', PI 390255, PI 432870, `Pacer', PI 419078, PI 390247, PI 321011, and PI 414158. The 10 best cultigens from the initial screening study, along with the four worst cultigens and six checks, were retested directly (not as F1 progeny) for fruit keeping ability in two storage conditions and at two harvest dates. No significant differences were detected between the two harvest dates and storage conditions.
Combining the use of PCR and single-strand conformation polymorphisms (SSCP), nine sequences from the cucumber genome were successfully identified and cloned that encoded two well-conserved asparagine-proline-alanine (NPA) domain homologues to aquaporin genes. The sensitivity and detection efficiency of SSCP and restriction enzyme analysis for detecting DNA sequence variation were evaluated using similar-sized DNA fragments. The SSCP analysis was more sensitive and efficient for discriminating different clones than restriction enzyme analysis, although some sequence variation inside similar-sized DNA fragments could be identified by restriction analysis. Consideration of the results of SSCP analysis with DNA sequence information indicated that one or two base pair changes in the amplified regions could be detected. Moreover, the SSCP analysis results of genomic DNA PCR products that were amplified by degenerate primers can provide rough information about the number of member genes. If the SSCP bands of a cloned fragment (such as CRB7) did not have the corresponding bands from genomic DNA PCR products, that fragment might be a misamplified product. The PCR-based SSCP method with degenerate oligonucleotide primers should facilitate the cloning of member genes.
Two studies were conducted to test the effects of various tissue culture media on somatic embryogenesis from cotyledon tissue of cucumber (Cucumis sativus L.). The two best media for embryo initiation were Murashige and Skoog (MS) salts and vitamins containing either 1 or 2 mg 2,4-D/liter and 0.5 mg kinetin/liter. In the second study, embryos developed more normally. More plantlets developed when tissue was removed from the initiation medium after 3 weeks and transferred to MS containing 1 mg NAA/liter and 0.5 mg kinetin/liter for 3 weeks, rather than leaving the embryos on a medium containing 2,4-D. Histological evidence indicated that the embryos were multicellular in origin. Charcoal in the maturation medium inhibited embryo development. Chemical names used: (2,4-dichlorophenoxy) -acetic acid (2,4-D); N-(2-furanylmethyl)-lH-purine-6-amine (kinetin); 1-naphthaleneacetic acid (NAA).
Citrulline, arginine, and lycopene are naturally occurring compounds found in watermelon, Citrullus lanatus (Thumb) Matsum & Nakai, with beneficial effects on plant growth and human health. This study evaluated seven commercial cultivars and one breeding line for citrulline, arginine, and lycopene content in mature fruit grown at two locations in North Carolina. Correlations among these compounds and fruit quality traits (percent soluble solids and flesh pH) were evaluated. Watermelon cultigens evaluated were chosen for their fruit trait diversity. ‘Yellow Doll’ and NC-517 possessed the highest citrulline and combined concentration of citrulline and arginine of all cultigens evaluated. Lycopene content was highest in ‘Dixielee’, followed by ‘Sugar Baby’, and ‘Allsweet’, each of which have different shades of red flesh color. Location and its interaction with genotype had no significant effect on arginine or lycopene concentration. Broad-sense heritability was estimated for each trait. Arginine content (89%) and lycopene content (99%) had very high heritability. Citrulline content (41%), percent soluble solids (46%), and flesh pH (61%) had moderate heritability. Lycopene was positively correlated with flesh pH (r = 0.517) and negatively correlated with percent soluble solids (r = −0.344). Arginine content had a weak negative correlation with flesh pH (r = −0.343) and was not correlated with percent soluble solids.
Cultigens frequently are tested for eventual monoculture production conditions in trials with different cultigens in adjacent rows. We determined the effect of using different cultigens of pickling and fresh-market cucumber (Cucumis sativus L.) in bordered (three-row) and unordered (l-row) plots. Cultigens contrasted in characteristics important in competitive effects: plant architecture (tall vs. dwarf), anthracnose resistance (susceptible vs. resistant), and sex expression (monoecious vs. gynoecious). In all four test years, there was no significant interaction of border with center row in unordered vs. bordered plots, with three exceptions: there was a significant reduction in yield of M 21 in 1982 when bordered by `Calypso' (a large-vined genotype), and a reduction in yield of `Southern Belle' in 1984 when bordered by `Calypso' or SMR 58. In most cases, there was an increase in yield if the border genotype had short vines. We concluded that. in most cases, trials can be run using unordered plots without significant effect or yield.
Field and detached-fruit screening tests were developed for evaluating cucumber (Cucumis sativus L.) plant introduction accessions, breeding lines, and cultivars (hereafter collectively referred to as cultigens) for resistance to fruit rot caused by Rhizoctonia solani Kuhn. The factors that were examined for developing a detached-fruit test were five inoculum levels of R. solani AG-4 and two cover treatments. The major influence on disease reaction was inoculum level. The best method used 50-mm-diameter fruit placed on sterile soil inoculated with 6400 oat grains/m2 colonized with R. solani and watered initially, then misted every 3 days for 1 minute, left uncovered, and rated after 10 days for the percentage of the fruit surface covered with lesions. Field and detached-fruit tests were conducted using two different inoculum levels of R. solani (3200 and 4800 oat grains/m2). The four most resistant cultigens, based on the results of field and detached-fruit tests, were PI 163216, PI 197088, PI 357852, and PI 280096. One field and detached-fruit test pair was not significantly correlated (detached-fruit screening test one vs. field screening test one), but the other (detached-fruit test two vs. field screening test two) was correlated (r = 0.50). The detached-fruit test could be used for general classification of resistance or susceptibility. Resistant cultigens could be identified with either method, but the field test had slightly lower coefficients of variation.
Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] flesh color is controlled by several genes to produce red, canary yellow, salmon yellow, and orange. Our objective was to study the interaction of three gene loci with two or three alleles at each C (canary yellow vs. red), y (salmon yellow vs. red), yo (orange), and i (inhibitory to C permitting Y to produce red flesh color). Five crosses were used to study gene action: `Yellow Baby' × `Sweet Princess', `Yellow Baby' × `Tendersweet Orange Flesh', `Yellow Baby' × `Golden Honey', `Yellow Doll' × `Tendersweet Orange Flesh', and `Yellow Doll' × `Golden Honey'. Based on the performance of six generations (PA, PB, F1, F2, BC1A, and BC1B), the parents had the following genotypes: `Yellow Baby' = CCYYII, `Yellow Doll' = CCYYII, `Sweet Princess' = ccYY ii, `Tendersweet Orange Flesh' = ccyoyoII, and `Golden Honey' = ccyyII. Segregation of flesh colors in the progeny of the five families demonstrated that there was a multiple allelic series at the y locus, where YY (red) was dominant to yo yo (orange) and yy (yellow). Also, yoyo was dominant to yy. In conclusion, epistasis is involved in genes for the major flesh colors in watermelon, with ii inhibitory to CC (Canary), resulting in red flesh, and CC in the absence of ii epistatic to YY, producing canary flesh.
Information on the mode of inheritance of powdery mildew resistance in watermelon is important for designing a breeding strategy for the development of new cultivars. Resistance in the watermelon accession PI 270545 was investigated by generation means analysis by crossing it with susceptible PI 267677. The analyses showed involvement of two genes, a recessive resistance gene, pmr-1, and a dominant gene for moderate resistance, Pmr-2. Resistance to powdery mildew in the leaf had a large dominance effect and a heritability of 71%. The additive-dominance model was inadequate in explaining variation in leaf resistance as revealed by the joint scaling test. However, nonallelic interactions could not be detected by the nonweighted six-parameter scaling test. For stem resistance, the additive-dominance model was adequate, and inheritance was controlled mainly by additive effects. A high narrow-sense heritability of 79% suggested that selection for stem resistance in early generations would be effective.
All available luffa (Luffa aegyptiaca Mill.) cultivars, breeding lines, and plant introduction accessions (collectively referred to as cultigens hereafter) were evaluated at Clinton, N.C., over 3 years. Plants were grown in plots 1.5-m-long on a 1.8-m-high trellis. Border rows and tiers on the sides and ends of the trial were used to reduce the edge effect. Plots were planted in May and evaluated for vine height and sex expression. Fruit were harvested in October to determine fruit number and length after frost killed the vines. Sponges were processed from the fruit and evaluated for seed cell number, wall thickness, sponge strength, fiber denseness, and other quality traits. The tallest vined cultigens were PI 286425 and Fletcher, and the shortest vined were PI 381869 and PI 540921. The highest yielding (sponge number per hectare) cultigens were PI 540921 and PI 391603, and the lowest yielding cultigens were Luffa 30310 and Luffa 97321. Of the cultigens tested, PI 391603 had the longest fruit overall, whereas PI 540921 had the shortest.
Watermelon fruit [Citrullus lanatus (Thumb) Matsum & Nakai] is a natural source of phytonutrients, including lycopene, citrulline, and arginine. Two segregating, highly outcrossed North Carolina watermelon populations, NC High Yield (NCHYW) and NC Small Fruit (NCSFW), were evaluated for these traits and for indicators of ripeness (pH and soluble solids content). Parents tested in 2015 (NSF = 300, NHY = 300) were sampled for the above and offspring were tested in 2016 if the sampled fruit of the parents were of qualifying ripeness [soluble solids concentration (SSC) ≥8, pH 5.5–6.5], resulting in 251 families (NSF = 72, NHY = 175). Narrow-sense heritability was estimated in each of the populations using the methods of 1) parent-offspring regression and 2) variance of half-sibling family means. Heritability for citrulline in NCHYW was moderate in both parent-offspring and half-sibling estimations (38% and 43%), as was arginine (40% and 44%) and lycopene (46% and 47%, respectively). Estimates for these traits in NCSFW were considerably different, with parent-offspring and half-sibling estimations for citrulline (65% and 22%), arginine (9% and 20%), and lycopene (44% and 68%). In NCHYW, moderate phenotypic correlations were found between SSC and citrulline (0.40), arginine (0.40), their combination (0.45), and lycopene (0.30) all of which were significant, except lycopene. Lycopene was significantly and weakly correlated to citrulline (0.22), but was not correlated to arginine (0.06). Similar correlations were found in NCSFW; SSC was significantly correlated to citrulline (0.24), arginine (0.18), and their combination (0.23), whereas lycopene was slightly correlated to citrulline (0.15) and not significantly correlated to arginine. Based on these heritabilities and phenotypic correlations, tandem selection for high lycopene and citrulline content may be accomplished efficiently using progeny rows with minimal replication using the NCSFW population, whereas replication with multiple years, rows, and locations may be necessary for creating stable lines using the NCHYW population.