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  • Author or Editor: T. A. Campbell x
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The early competitive relationships of sweet corn (Zea mays L.), barnyardgrass (Echinochloa crusgalli (L.) Beauv.), large crabgrass (Digitaria sanguinalis (L.) Scop.), common lambsquarter (Chenopodium album L.), and redroot pigweed (Amaranthus retroflexus L.) during the first 4 weeks of growth were studied in the greenhouse using a modified diallel analysis. Heights of individual plants at 2, 3, and 4 weeks after seeding were measured as well as dry weights at 4 weeks. Analyses indicate that sweet corn was the most competitive species. Barnyardgrass offered the most competition to sweet corn relative to the other weed species which offered much less competition to sweet corn and comparable competition to each other. Competitive relationships remained fairly constant over time with perhaps a slight increase in the competitive ability of crabgrass. A slight increase in compatibility between sweet corn and barnyardgrass, and between crabgrass and pigweed occurred during the 4th week of growth.

Open Access
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Abstract

Stokes aster [Stokesia laevis Hill (Greene)] is a perennial ornamental; achenes are a prospective source of vernolic acid for the chemical industry. Responses of achenes of 6 Stokes aster accessions to temperatures of 0° to 20°C were studied. There was no germination below 11°; germination was near 0 at 11° and reached a maximum at 20°. Achenes equilibrated at 15% moisture generally germinated more rapidly than those at 5% moisture. In hydration-chilling experiments, more than one day of exposure to chilling prior to germination decreased germination and increased the frequency of abnormal seedlings in some entries. Equilibration at 15% moisture prior to chilling reduced damage slightly compared to 5% moisture. There seemed to be a direct relationship between early imbibition rate and susceptibility to chilling damage. Gradual chilling and warming of germinated achenes resulted in a significant reduction in damage compared to abrupt chilling and warming.

Open Access

Abstract

The horticultural potential of 20 vegetable amaranth (Amaranthus spp.) entries was evaluated in the field at Beltsville, Md., during the summers of 1979 and 1980. Mean fresh yields (leaves and stems) for 5 experiments ranged from 4.0 to 16.5 MT/ha. Yields were highest for A. dubius, intermediate for A. cruentus, and least for A. tricolor. Yield was negatively correlated with leaf:stem ratio (r=−0.56**). Entries with the highest leaf: stem ratios were found within A. tricolor.

Open Access

Abstract

Appearance, flavor, texture, and overall eating quality of 20 steamed amaranths (Amaranthus spp.) were rated on hedonic scales by consumer sensory panels. Several entries of A. tricolor had nonsignificantly lower scores than spinach (Spinacia oleracea L.). Of the A. tricolor entries, ‘Chin’ was the best overall and ‘Tampala’ (most readily available entry in the U.S.) was intermediate. A. dubius was intermediate and A. cruentus entries were least acceptable.

Open Access

Mechanical stress received by pickling cucumbers (Cucumis sativus L.) during harvest can cause physiological degeneration of the placental tissues, rendering the cucumbers unsuitable for use in some pickled products. Cucumbers were subjected to controlled stresses by dropping and rolling under weights to induce such degeneration. Following storage at various temperatures for O, 24, and 48 hours, refreshed delayed light emission from chlorophyll (RDLE) was measured and transmission electron micrographs of chloroplasts were made. Mechanical stress rapidly suppressed RDLE and induced accumulation of starch granules within the chloroplasts. Rolling usually had a greater effect on RDLE than did dropping. After 48 hours, RDLE suppression persisted; starch granules were no longer evident in chloroplasts from mechanically stressed fruit, but very electron-dense inclusions had developed in the chloroplasts. Storage temperatures affected RDLE levels but had minimal interaction with stress responses. Cucumber lots subjected to excessive mechanical stress likely could be detected using RDLE measurement.

Free access

Results from a preliminary study (growth parameters and foliar analyses) comparing a new specialty Osmocote formulation (12N-5.5P-12.4K) designed specifically for poinsettias with a standard Osmocote formulation (19N-2.6P-9.9K) revealed that the new formulation provided inadequate levels of nutrients at 1.0× and 1.5× the recommended rate. Average plant height (cm) for plants produced with 1.0× 12N-5.5P-12.4K, 1.5× 12N-5.5P-12.4K, 1.0× 19N-2.6P-9.9K was 33, 34, 37. Average plant diameter (cm) and foliar N content (%) was 42, 46, 53, and 2.8, 3.5, 4.1, respectively. Follow up studies (growth parameters and foliar analyses) comparing replacement shipments of three specialty Osmocote formulations (12N-5.5P-12.4K for poinsettias, 12N-4.4P-14.1K for potted chrysanthemums, and 13N-5.5P-9.1K for zonal geraniums) with Osmocote 19N-2.6P-9.9K and Peter's 20N-4.4P-16.6K injected at 200 mg N per liter of water at every irrigation showed all specialty formulations to be adequate sources of plant nutrients-comparable to the standard Osmocote. Average chrysanthemum height (cm) for plants produced with 1.0× 12N-5.5P-12.4K, 1.5× 12N-5.5P-12.4K, 1.0× 19N-2.6P-9.9K, Peter's 20N-4.4P-16.6K was 30, 30, 30, 29. Average chrysanthemum diameter (cm) and foliar N content (%) was 51, 50, 49, 50, and 4.5, 4.8, 4.4, 5.2, respectively.

Free access

Fruit firmness is a key quality component of tomatoes (Lycopersicon esculentum Mill.) for fresh-market and processed product applications. We characterized inheritance of firmness in processing tomato germplasm developed from interspecific L. esculentum Mill. × L. cheesmanii f. minor (Hook. f.) C.H. Mull. and intraspecific L. esculentum crosses. Although firmness is a key quality attribute of tomato, there is no standard method for measuring it. We measured the elastic portion of firmness by compression (compression Fmax) and puncture (puncture Fmax), and the viscoelastic portion by force-relaxation. The experimental design incorporated six genotypes in a complete 6 × 6 diallel. Compression Fmax and force measurements recorded at 0.5, 1.0, 5.0, and 10.0 seconds of relaxation were strongly related to each other, while relaxation parameters (A, B, C) describing relaxation curve shape were generally independent. Compression Fmax, relaxation curve parameter A, and puncture Fmax were significantly different among hybrids. Significant differences between Maryland and Ohio environments were evident for compression Fmax and relaxation curve parameter A. The patterns of firmness means differed among firmness measurement methods, namely for compression Fmax and puncture Fmax, indicating that they measure different aspects of tomato fruit firmness. Soft-fruited parents generally exerted a negative effect on compression Fmax, whereas firm-fruited parents most often exerted a positive effect on compression Fmax. The force required for fruit compression best approximated subjective assessment of fruit firmness. Force required for fruit puncture was subject to a significant environmental × hybrid influence in the genotypes evaluated. Shape of the force relaxation curve (i.e., parameter A) was not predictive of relative fruit firmness. General combining ability (GCA) and specific combining ability were both significant with GCA being the principal source of genetic variation. In agreement with combining ability estimates, narrow-sense heritability estimates for compression Fmax and puncture Fmax were relatively high.

Free access

Abstract

‘Tahiti’ (Citrus latifolia Tan.) lime fruit varying in turgor, estimated by fruit water potential and rind oil release pressure, were collected and assayed for susceptibility to stylar-end breakdown. Susceptibility was determined by heating fruit for 3 hours at 42°C in a constant temperature water bath. Incidence of stylar-end breakdown was about 40% in the most turgid fruit, water potential ≥–4 bars and rind oil release pressure ≤2.0 kg. Decreasing turgor resulted in a linear decrease in susceptibility. Minimum susceptibility of from 0% to 2% was found in limes with water potential ≤–11 bars and rind oil release pressure ≥4.5 kg. Stylar-end breakdown can be controlled by maintaining strict picking schedules so that fruit are not allowed to get too large, controlling postharvest field heat, and harvesting fruit with reduced turgor pressure.

Open Access

Mango (Mangifera indica L.) germplasm can be classified by origin with the primary groups being cultivars selected from the centers of diversity for the species, India and Southeast Asia, and those selected in Florida and other tropical and subtropical locations. Accessions have also been classified by horticultural type: cultivars that produce monoembryonic seed vs. cultivars that produce polyembryonic seed. In this study we used 25 microsatellite loci to estimate genetic diversity among 203 unique mangos (M. indica), two M. griffithii Hook. f., and three M. odorata Griff. accessions maintained at the National Germplasm Repository and by Fairchild Tropical Botanic Garden in Miami, Fla. The 25 microsatellite loci had an average of 6.96 alleles per locus and an average polymorphism information content (PIC) value of 0.552 for the M. indica population. The total propagation error in the collection (i.e., plants that had been incorrectly labeled or grafted) was estimated to be 6.13%. When compared by origin, the Florida cultivars were more closely related to Indian than to Southeast Asian cultivars. Unbiased gene diversity (Hnb) of 0.600 and 0.582 was found for Indian and Southeast Asian cultivars, respectively, and both were higher than Hnb among Florida cultivars (0.538). When compared by horticultural type, Hnb was higher among the polyembryonic types (0.596) than in the monoembryonic types (0.571). Parentage analysis of the Florida cultivars was accomplished using a multistage process based on introduction dates of cultivars into Florida and selection dates of Florida cultivars. In total, 64 Florida cultivars were evaluated over four generations. Microsatellite marker evidence suggests that as few as four Indian cultivars, and the land race known as `Turpentine', were involved in the early cultivar selections. Florida may not represent a secondary center of diversity; however, the Florida group is a unique set of cultivars selected under similar conditions offering production stability in a wide range of environments.

Free access