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Raised beds approximately 20 cm tall by 76 cm wide were formed on 1.8 m centers in the spring of 1988 and 1989. Beds were either left bare or seeded with rye (Secale cereale) or hairy vetch (Vicia villosa) at 84 or 45 kg ha-1 respectively. All plots were sprayed with glyphosate in August of each year. In 1988, a 30 cm strip was tilled in the center of each bed. In 1989, there was no tillage or mowing.
The design was a randomized complete block with four levels of nitrogen (45, 90, 134, and 179 kg ha-1) at each soil cover. Broccoli seedlings were transplanted in double rows on 30 cm spacings into the plots each year in late August.
Height of the raised beds was maintained with both rye and vetch. Broccoli yields were highest in the bare soil treatments In 1988, the lowest yield was with vetch, and in 1989 the lowest yield was with rye. There was a positive linear yield response to nitrogen. The number of heads harvested did not differ significantly between soil covers
To determine whether ethylene production was related to locular tissue breakdown in watermelon, plugs from ripe `Jubilee', `Black Diamond', `Tiger Baby', `Mirage', and `King of Hearts' were taken from the skin (epidermis and hypoderm), rind (hypoderm and mesocarp), and placenta (locular and heart) tissues. ACC oxidase activity was <0.05 nmol·g–1·h–1 in locule and heart locations for all cultivars. Skin tissue had the highest activity, ranging from 0. 1 8 for `Jubilee' to 0.5 to 0.62 nmol·g–1·h–1 for the other four cultivars. ACC (1-aminocyclopropane-1-carboxylic acid) and ACC oxidase activity were measured in unripe, ripe, and overripe `Jubilee' melons. ACC oxidase activity from skin tissue was lowest in unripe (0.05 nmol·g–1·h–1) and highest in overripe (0.13 nmol·g–1·h–1) melons, and was 0.05 nmol·g–1·h–1 or less in all other tissues. Free ACC was highest in the skin tissue (1.3 nmol·g–1·h–1), but there was no difference in ACC content with stage of ripeness for any tissue. Results indicate that ethylene may be transported from the outer skin and rind tissues to locular areas and that wounding of the skin tissue could lead to deleterious ethylene production.
A study was conducted to characterize the quality of seedless and seeded watermelon. The seeded cultivars 'Jubilee', 'Black Diamond' and 'Allsweet' were compared with seedless 'King of Hearts' for firmness, lycopene content, rind thickness, soluble solids concentration (SSC), ascorbic acid, sugar composition, sweetness index and sensory qualities. 'King of Hearts' melons had higher firmness and lycopene values but a lower sweetness index compared with the other cultivars. 'Black Diamond' and 'Jubilee' cultivars had greater rind thickness compared to the other cultivars. 'Allsweet' and 'Jubilee' fruit had the highest ascorbic acid concentration. 'Black Diamond' had greater fructose and glucose levels than 'Jubilee' or 'King of Hearts' but was lowest in SSC. Untrained taste panelists preferred 'Jubilee' and 'Allsweet' melons. In this study, SSC, sugar composition, sweetness index or firmness were not good indicators of watermelon preference.
Individually, green melon aphids (Aphis gossypi) and anthracnose (Colletotricum lagenarium) can cause serious economic damage to watermelons by reducing stands and marketable yields. Greenhouse-grown watermelon seedlings at the third true leaf stage were infected with anthracnose (106 spores/mL) and/or infested with 30 aphids per plant. At the 5th leaf stage (about 7 days after inoculation/infestation), leaf disks were harvested from plants and indicators of stress measured. Peroxidase activity increased from 0.03 to 0.28 absorbance units/mg protein-minute in leaves with anthracnose. When plants were infested with aphids after anthracnose inoculation, peroxidase activity was 0.40 absorbance units/mg protein-minute. Plants having both aphids and anthracnose had more anthracnose lesions when leaves were infested with aphids prior to anthracnose inoculation. The presence of aphids and/or anthracnose stimulated 1-aminocyclopropane-1-caroxylic acid (ACC) oxidase activity from 28 to 44 nL/g-h, indicating enhanced ethylene production. However, aphids had to be present on plants at least 5 days before ACC oxidase activity was stimulated above control levels. Aphids combined with anthracnose failed to elevate ACC oxidase levels higher than either aphids or anthracnose alone. Both peroxidase activity and ACC oxidase activity in watermelon plants increased with anthracnose infection. Thus, watermelon plants stressed by aphids and anthracnose responded differently from plants stressed individually by aphids or anthracnose.
High populations of melon aphid (aphis gossypii) reduce cantaloupe plant growth and yield; effects on subsequent fruit quality are unknown. The purpose of this study was to evaluate fruit quality from plants with high and low aphid populations. Up to 50% of melons from plants having high aphid populations were unmarketable due to surface sooty mold. Melons from plants with high or low aphid populations, but not cultivars, were similar in flesh quality. The internal color of `Perlita' and `Sweet Surprise' was a more yellow hue while that of `TAM Uvalde' was more orange. `Sweet Surprise' melons were lower in percent soluble solids concentration and titratable acidity, but were higher in mg fructose/ml juice compared to the other cultivars. A trained taste panel of 30 people evaluated melons from 2 cultivars showing little damage from melon aphid infestations and from 2 cultivars exhibiting high damage. All melons had similar taste qualities with acceptable sweetness, flavor, odor and texture. These results show that high aphid populations deleteriously affect cosmetic appearance, but not flesh quality, of melons.
The postharvest quality of one seedless and four seeded watermelon cultivars was studied. Melons were evaluated for ascorbic acid content, sugar composition, soluble solids concentration, lycopene concentration, color and sensory qualities. Ascorbic acid values were higher for `Allsweet' and `Jubilee' melons compared to the other cultivars. `Black Diamond' had higher fructose levels than `Calhoun Gray', `Jubilee' or `King of Hearts'. Soluble solids concentration was highest for `Allsweet' and lowest for `Black Diamond' melons. `King of Hearts' fruit had the highest lycopene content which was correlated with chroma color values. Untrained taste panelists preferred `Calhoun Gray', `Jubilee', and `Allsweet' for taste compared to `Black Diamond' melons.