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  • Journal of the American Society for Horticultural Science x
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Cannabis (Cannabis sativa) grown for flowers containing cannabinoids requires all female plants, which are susceptible to seed set from exposure to pollen. Created triploids demonstrated reduced seed production compared with diploids in field and greenhouse studies in which plants were challenged with pollen from males. In the field, seed production as a percent of floral biomass ranged from 6.7% to 18.0% for triploids and from 52.6% to 57.1% for diploids. The photoperiod-insensitive triploid genotype ‘Purple Star’ × ‘Wilhelmina’ had 98.5% fewer filled (containing a developed embryo) seeds than the photoperiod-insensitive diploid genotype ‘Tsunami’ × ‘Wilhelmina’. In the greenhouse, triploid ‘Wife’ had 99.5% fewer filled seeds than diploid ‘Wife’. Plant growth and flower production were similar with eight triploid and seven diploid genotypes evaluated over three greenhouse studies. There were a few superior triploid and diploid genotypes; however, their performance was more likely attributable to the parental cultivar combination than ploidy level. The optimal cross direction for producing triploid seed in large quantities is tetraploid × diploid because the diploid × tetraploid cross exhibits triploid block caused by endosperm paternal excess. Colchicine-induced tetraploid parent plants should be tested over a prolonged period to eliminate cryptic chimeral mixoploids or tetraploid plants should be derived from seed produced by crossing two colchicine-induced putative tetraploid plants to ensure that seeds from tetraploid × diploid crosses will be triploid. The latter approach is necessary for photoperiod-insensitive cultivars because a prolonged period of ploidy testing is not possible for these plants. These findings indicate that triploid plants have significantly reduced fertility and are a suitable alternative to diploids in situations in which pollen exposure is possible.

Open Access

The formation of onion (Allium cepa) bulbs is affected by photoperiod length and onion germplasm is commonly classified as short- (SD), intermediate-, or long-day (LD) types. The objectives of this study were to develop a segregating family from a cross between doubled haploids (DHs) of LD and SD onions and complete genetic analyses of bulb shape and volume, as well as daylength effects on bulbing. DH parents and F1 and F2 progenies were grown in a greenhouse under lengthening days. The diameters of the neck constriction and pseudostems were measured weekly and their ratio was used as the determinant of bulbing. Bulbs were harvested when the foliage collapsed and the diameters and heights of individual bulbs were measured and used to calculate a shape index (diameter divided by height) and bulb volume. Single nucleotide polymorphisms (SNPs) were genotyped and a genetic map of 112 SNPs constructed. Genetic analysis revealed two highly significant quantitative trait loci (QTL) affected bulbing under increasing daylengths, and both QTL showed significant additive effects with no dominance. One highly significant QTL was detected for bulb-shape index and explained 30% of phenotypic variation for bulb shape. Three additional QTL were slightly above the significance threshold, and together these four QTL explained over 50% of the phenotypic variation for bulb shape. No significant QTL were detected for bulb volume. These results reveal that bulb-shape and daylength effects on bulbing are relatively simply inherited, and this research should facilitate introgression of traits between onion populations of different daylength sensitivities and efforts to modify bulb shape.

Open Access

Rain cracking (hereinafter referred to as macrocracking) severely impacts the production of sweet cherry (Prunus avium). Calcium (Ca) sprays can reduce macrocracking, but the reported responses to Ca sprays are variable and inconsistent. The objective of this study was to establish the physiological mechanism through which Ca reduces macrocracking in sweet cherry fruit. Six spray applications of 50 mM CaCl2 had no effect on macrocracking (assessed using a standardized immersion assay) despite a 28% increase in the Ca-to-dry mass ratio. Similarly, during another experiment, there was no effect of up to nine Ca sprays on macrocracking, although the Ca-to-dry mass ratio increased as the number of applications increased. In contrast, CaCl2 spray applications during simulated rain (in a fog chamber) significantly reduced the proportion of macrocracked fruit. Additionally, immersion of fruit in CaCl2 decreased macrocracking in a concentration-dependent manner. Monitoring macrocrack extension using image analysis revealed that the rate of macrocrack extension decreased markedly as the CaCl2 concentration increased. This effect was significant at concentrations as low as 1 mM CaCl2. Decreased anthocyanin leakage, decreased epidermal cell wall swelling, and increased fruit skin stiffness and fracture force contributed to the decrease in macrocracking. There was no effect of CaCl2 on the cuticle deposition rate. Our results demonstrated that Ca decreased macrocracking when applied to a wet fruit surface either by spraying on wet fruit or by incubation in solutions containing CaCl2. Under these circumstances, Ca had direct access to the cell wall of an extending macrocrack. The mode of action of Ca in reducing macrocracking is primarily decreasing the rate of crack extension at the tip of a macrocrack.

Open Access

Variegated temple bamboo (Sinobambusa tootsik f. luteoloalbostriata) is one of the native variegated bamboo species has some whole green (WG) and whole white (WW) leaves in addition to striped green and white ones. The life span of WW leaves is short, but the life span of striped leaves (SLs) is unaffected by the area of white mesophyll, and the SL phenotype is well maintained. To explore the mechanism of phenotypic stability of SL, we took five leaf phenotypes as study materials: WG, WW, SL, the green part of SL (SG), and the white part of SL (SW). Through the measurement of photosynthetic pigments, leaf nutrient elements, chloroplast synthesis–related hormones and their precursors in the leaves, and antioxidant system parameters, we examined the antioxidant adaptation mechanism of the white mesophyll cells of S. tootsik f. luteoloalbostriata. The results indicated that abscisic acid (ABA) levels were substantially higher in WW leaves than in SW leaves, and salicylic acid (SA) levels were significantly higher in SW leaves compared with WW leaves. Levels of 12-oxo-phytodienoic acid (OPDA), and SA were substantially higher in WW and SW than in the leaves of the other three phenotypes. Glutathione (GSH) levels were substantially higher in SW than in SG and reactive oxygen species (ROS) levels were significantly lower. Overall, the white mesophyll cells of S. tootsik f. luteoloalbostriata had strong antioxidant properties. SA and OPDA jointly act on the antioxidant pathway to reduce the content of ROS in leaves, thus ensuring the stability of SL.

Open Access

Snap beans are cultivars of common bean (Phaseolus vulgaris) that are cultivated for their fleshy immature pods that exhibit a wide diversity of pod shapes and sizes. The genetic basis of the snap bean pod shape is complex and involves the interaction of multiple genes. This study used a snap bean diversity panel composed of heirloom and improved cultivars used in North America and genome-wide association studies (GWAS) to investigate the genetic basis of pod morphological characteristics, including length, width, height, width/height ratio, and coefficients of variation (CVs). The GWAS detected multiple genomic regions associated with each pod trait, with a total of 20 quantitative trait loci (QTLs) for pod length, 9 for pod width, 14 for pod height, and 10 for pod width/height ratio. Regarding the CV of each pod trait, genome-wide association analyses detected six QTL for length CVs, five for width CVs, 15 for height CVs, and six for width/height ratio CVs. Thirteen regions in seven chromosomes were associated with two or more pod traits. Eighteen QTLs for pod traits in this study colocated with previously reported QTLs for pod and seed traits. The QTL intervals encompass gene models with homologues in other species that are involved in the control of developmental processes. These results capture the complex nature of the genetic control of snap bean pod traits and confirm the significance of genomic regions harboring overlapping QTLs identified in this and other studies. The phenotypic expression of pod traits in snap bean appears to be under the control of a few genomic regions with a strong effect with additional contributions of multiple small-effect regions. Validation of the function of the candidate genes identified in associated regions will contribute to our understanding of legume pod development.

Open Access

Grape (Vitis) production and fruit quality traits such as cluster size, berry shape, and timing of fruit development are key aspects when selecting cultivars for commercial production. Molecular markers for some, but not all, of these traits have been identified using biparental or association mapping populations. Previously identified markers were tested for transferability using a small (24 individual) test panel of commercially available grape cultivars. Markers had little to no ability to differentiate grape phenotypes based on the expected characteristics, except the marker for seedlessness. Using a biparental interspecific cross, 43 quantitative trait loci (QTLs) (previously identified and new genomic regions) associated with berry shape, number, size, cluster weight, cluster length, time to flower, veraison, and full color were detected. Kompetitive allele-specific polymerase chain reaction markers designed on newly identified QTLs were tested for transferability using the same panel. Transferability was low when use types were combined, but they were varied when use types were evaluated separately. A comparison of a 4-Mb region at the end of chromosome 18 revealed structural differences among grape species and use types. Table grape cultivars had the highest similarity in structure for this region (>75%) compared with other grape species and commodity types.

Open Access

The color of vegetables is an important factor in consumer food choices and in cultivar choice by growers and processors for production. In absorbing a broad spectrum of light, leaves support plant development by influencing factors such as biomass accumulation, chlorophyll content, and reproductive growth. The edible organ of the snap bean (Phaseolus vulgaris L.) is the pod, and its color is not only one of the most important traits for commercial consideration, but also influences phytonutrient content. Although chlorophyll provides the base color, other compounds such as carotenoids and flavonoids may affect leaf and pod color. Darker yellow- or blue-green pods are preferred for processing, but there is more leeway for fresh market, with lighter-colored pods being acceptable. This research characterized leaf and pod color variation in the 378-member Snap Bean Association Panel. Leaf and pod colors were measured with a colorimeter using the L*a*b* scale, which was then transformed to L* (lightness), C* (chroma), and H° (hue angle) for analysis. Both green and wax bean accessions had predominantly green leaves, even though both exterior and interior colors of pods varied by accession. The leaves at the upper level in the canopy were lighter than lower and middle-level leaves. C* of leaves was similar across environments but leaves from the field were greener than leaves of greenhouse-grown plants when converted to Royal Horticultural Society (RHS) values, even though they had similar H°. L* did not differ for corresponding leaf positions of both field and greenhouse leaves. Purple pods were darker (lowest L*) and yellow pods were lighter (highest L*). Although wax beans had similar exterior and interior colors, accessions with purple exterior of pods had green interiors. Green pods were generally two times higher for L* and lower in C* compared with leaves. Pod interior L* was darker than exterior in both years. Pod exterior L* was not significantly different among accessions, whereas pod interior L* differed significantly between years. Broad sense heritabilities ranged from 0.69 to 0.88 for L*, 0.12 to 0. 87 for C*, and 0.81 to 0.89 for H°. Although greater variation was observed in pods than leaves, lower heritability was determined. Moderate correlations between leaf L* and the interior and exterior pod L* implies that it would be possible to select for pod color on the basis of leaf color, with verification using standard cultivars.

Open Access

Pea (Pisum sativum) dominant for the fundamental color gene A showed a high level of resistance to Globisporangium ultimum (formerly Pythium ultimum) seed rot. Reciprocal crosses demonstrated that, with our materials, such resistance was associated with the testa (seedcoat) phenotype but not the embryo phenotype. Dominance of A over a was complete for this trait. Neither wrinkled seed form (r) nor green cotyledons (i) diminished resistance when A was dominant, although both recessive alleles diminished resistance when seeds were borne on white-flowering (a) plants. The product of the A gene functions in the pathway leading to flavonoids, including proanthocyanidins (PAs) and anthocyanidins. We found that resistance to G. ultimum seed rot was closely associated with not only dominant A but also testa PAs and testa sclerenchyma. Even A testas that lacked anthocyanins but contained PAs and sclerenchyma showed a high level of seed rot resistance. Moreover, a mutation removing PAs and sclerenchyma in a narrow zone from the hilum to the radicle markedly increased susceptibility. The PAs in pea testas were predominantly prodelphinidins in seeds from purple-flowered plants (A B) and procyanidins from pink-flowered plants (A b). Compared with procyanidins, prodelphinidins have higher antioxidant activity but are more likely to sequester iron, a particular concern with dry pea. Although A B testas were more resistant than A b to seed rot, the difference seemed too slight to militate against growing pink-flowered pea. We stressed the need for more histological comparisons of A B and A b testas, and we indicated that genes and their phenotypic effects examined during the current study could be useful for modeling biosynthesis of PAs and related cell walls.

Open Access