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  • Author or Editor: Donald N. Maynard x
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Short-day onions (Allium cepa L.) grown under humid, subtropical conditions at two locations were evaluated for bulb size and yield at five harvest dates (H1 to H5) ranging from 94 to 132 days after transplanting (DAT) for `Granex 33' and from 115 to 153 DAT for `Texas Grano 1015Y'. Maximum yields were attained by H4 for both cultivars and were attributed to increased bulb size rather than differences in plant (bulb) population. Nondried, large bulbs (>7.6 cm diameter) from each harvest were trimmed and stored at 1 or 10 °C and 80% relative humidity (RH) for 2 weeks plus 2 weeks at 20 °C and 80% RH to simulate commercial storage and handling. Initial respiration rates of bulbs of both cultivars decreased >60% between H1 and H4. Bulbs also retained higher fresh weight during storage as harvest was delayed. Storage for 2 weeks at 1 °C suppressed sprouting of immature (H1) `Texas Grano 1015Y' bulbs, but not of `Granex 33' bulbs from one location. Storage at 10 °C did not suppress sprouting of either cultivar. Decay became more prevalent with delayed harvest, but `Granex 33' was more resistant to decay than was `Texas Grano 1015Y', which developed up to 40% decay after 2 weeks at 20 °C. Harvest at 115 and 132 DAT resulted in acceptable yields for `Granex 33' and `Texas Grano 1015', respectively, and satisfactory postharvest quality of nondried bulbs following 2 weeks of storage at 1 °C and 80% RH plus 2 weeks at 20 °C.

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A joint breeding effort of the Universities of Puerto Rico and Florida involves the development of short-vined tropical pumpkin (Cucurbita moschata) genotypes that are able to reach maturity earlier than traditional long-vined types. Sixteen promising hybrids and inbreds were planted in Lajas, Puerto Rico, in June 1998. Pedigrees of this material included traditional tropical genotypes crossed with bush or compact temperate genotypes. Anthesis in both pistillate and staminate flowers occurred on average 49 days after planting. However, the variability of flowering dates among genotypes was far greater for pistillate (40 to 60 days) than staminate (46 to 54 days) flowers. Hybrids flowered earlier than inbred lines. Female flowers opened before male flowers in many genotypes. It seems likely that an inadequate source of pollen contributed to the low yields of some of the earliest genotypes. The five highest-yielding genotypes had pistillate flowers that opened after their male counterparts. All plots were once-over harvested 86 days after planting. Average yield per plant varied from 1.4 to 6.0 kg. Average fruit weight varied from 0.8 to 3.1 kg. High-yielding genotypes tended to have the highest fruit weight, a factor that should be considered when breeding for the next generation of short-vined genotypes. Yields were less than what could be expected from a long-vined tropical pumpkin. However, this yield could be obtained with a once-over harvest at about 90 days, compared to multiple harvests beginning at 120 days, saving costs of additional field practices, and allowing the land to be used for other purposes.

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Hybrids from crosses between bush/short-vined breeding lines and traditional, vining cultigens were evaluated in the fall 1993 season. Yields of individual hybrids were 0.51 to 1.73 times those of their vining parents and 0.83 to 4.41 times those of the bush/short-vined parents. The average yield response of 58 hybrids was 1.05 times that of vining parents and 2.15 that of bush/short-vined parents. Average fruit weight, flesh thickness, and flesh color of the hybrids tended to be intermediate between that of the bush/short-vined and vining parents. Plant habit of all hybrids was similar to that of the bush/short-vined parent early in the growth cycle, but some became viney later in the growth cycle. Fruit matured earlier on bush/short-vined parent and hybrid plants than on viney parent plants.

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Abstract

Tomato, tobacco, pepper, petunia, and eggplant were screened for their tolerance to continuous (NH4)2SO4 applications. Stem lesions, analogous to those which appear on tomato during ammonium toxicity, were formed on eggplant but not on the other species. Of the plants tested, tobacco was the most tolerant to applications of (NH4)2SO4. Potassium applications increased the ammonium concentration of tobacco tissues but lowered the ammonium concentration of tomato tissues. Diamine concentrations were increased by the application of (NH4)2SO4. The application of KCl decreased the putrescine concentration of tobacco and increased the concentration of cadaverine in tomato and tobacco. The application of putrescine-2HC1 in aqueous solution to cut stem ends of axillary shoots of tomato and tobacco induced the formation of stem lesions analogous to those formed by the (NH4)2SO4 fertilization of tomato. It is postulated that the tolerance of tobacco to stem lesion formation is related to putrescine utilization in nicotine synthesis.

Open Access

Abstract

Eighteen spinach cultivars were found to vary considerably in NO3 concentrations in their leaves. Smooth-leafed cultivars were lower in NO3 concentration than heavily savoyed cultivars. Some medium or semisavoyed cultivars were low NO3 accumulators, and others were high accumulators. A low degree of savoyedness appears to be a useful factor in the selection of spinach cultivars with tendencies for low NO3 accumulation.

Open Access

Abstract

A tissue infusion method was used to demonstrate nitrate reductase activity in the leaves of Vaccinium corymbosum L. grown with 3 N sources and in 2 pH regimes. Activity was not detectable by the extraction and assay of homogenized leaves of Kalmia latifolia L., Leucothoe catesbaei Gray, Malus sylvestris Mill., Pieris japonica D. Don., and Rhododendron catawbiense Michx. or in the roots of Leucothoe and Zea mays L., but it was detectable in both leaves and roots by the tissue infusion method.

Open Access

Abstract

The total number and length of new shoots of Leucothoe catesbaei Gray were significantly greater, and the plants were of better quality with NO3 nutrition than with NH4 or urea nutrition. Especially with the NH4-N sources, growth was as good as or significantly greater at pH 6 to 7 than at 4 to 5. The total number and length of new shoots of Rhododendron catawbiense Michx. cv. Roseum Elegans were not significantly affected by the N source or pH, although plant appearance was significantly better with NO3 nutrition than with NH4 or urea nutrition. The nitrification inhibitor, a substituted pyridine, had no significant effect on the growth and development of either leucothoe or rhododendron.

Open Access

Abstract

Consumption of spinach (Spinacia oleracea L.) with high NO3-N contents may be a health hazard to infants. Spinach leaves accumulate NO3-N when the plants are grown in a soil with high NO3-N availability. Experiments designed to evaluate the influence of nitrapyrin, a nitrification suppressor (2-chloro-6-(trichloromethyl)pyridine), on NO3-N concentrations in ‘America’ spinach and to develop a means of fertilization for maximum growth and minimum NO3-N levels in spinach were conducted. Nitrate accumulation in whole leaves and leaf fresh weights were lower with (NH4)2SO4 fertilization than with KNO3 fertilization. Nitrapyrin caused a further depression of NO3-N concentrations and plant growth with (NH4)2SO4 but had no effect on NO3-N accumulation and little effect on yield of plants fertilized with KNO3. The lesser growth with (NH4)2SO4 was apparently due to NH4-N toxicity. When half of the N was supplied as NH4-N and half as NO3-N, growth was equivalent to that of plants receiving only NO3-N, and NO3-N accumulation in the leaves was reduced by 35% without nitrapyrin and by over 50% with nitrapyrin. With this fertilizer combination, no toxicity to plant growth resulted from nitrapyrin applied at its recommended rate.

Open Access

Abstract

‘America’ spinach (Spinacia oleracea L.) is a savoy-leafed cultivar and tends to accumulate NO 3 ¯ in its leaf blades, petioles, and roots when the level of NO3-N nutrition is relatively high. ‘Hybrid 424’ spinach is smooth-leafed, larger in size, and accumulates much less NO 3 ¯ than ‘America’ especially when NO3-N nutrition is high. A greater NO 3 ¯ reductase activity in Hybrid 424, especially in its leaf blades, may account for its lower NO 3 ¯ content compared to that of ‘America’.

Open Access

Abstract

Cucumber (Cucumis sativus L.) plants accumulate more NO 3 ¯ than pea (Pisum sativum L.) plants. The differences in accumulation appear to be due to differences in the abilities of the two species to reduce NO 3 ¯ in their roots. Only 2% of the NO 3 ¯ reductase activity of cucumber was found in its roots, whereas nearly 92% of the activity was found in the blades. In pea, NO 3 ¯ reductase activity was more evenly distributed throughout the plant;67% of the activity was in the blades, 18% in the roots, and the remainder in the stems and petioles. Nitrate-N comprised 80% of the N present in bleeding sap of roots of cucumber plants from which the shoots had been excised. In contrast, NO3-N constituted only 30% of the N in the sap from pea roots, the remaining 70% of the N consisting of amino acids and amides. Asparagine or aspartic acid was the major carrier of reduced N in pea, and glutamine was the major carrier in cucumber. The differences in N transport and assimilation appear to bear considerably on plant composition and efficiency of N usage.

Open Access