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Free access

Patrick Chesney, Linda Wessel-Beaver, and Donald N. Maynard

Most cultivars of tropical pumpkin (Cucurbita moschata Duchesne) are large, trailing plants. New semi-bush (SB) genotypes need to be tested against traditional long vine (LV) types. Both types of pumpkin have large amounts of interplant space during the early stages of growth that might allow for the planting of an intercrop. To test this hypothesis, as well as the performance of tropical pumpkins of varying growth habit, double rows of beans (Phaseolus vulgaris L.) or cowpeas [Vigna unguiculata (L.) Walp.] were intercropped between rows of SB or traditional LV tropical pumpkin in Spring and Fall 1993 in Lajas and Isabela, Puerto Rico. In general, interactions between intercrop treatment and pumpkin genotype were not significant. At its maximum percentage cover (MC) the LV genotype covered, or nearly covered, the entire plot while the SB genotype covered 50% of the plot or less. The SB pumpkin was harvested 5 to 27 days earlier than the LV type. Yield was two to 12 times greater, and average fruit size three to six times greater in the latter. Planting of an intercrop did not reduce pumpkin yield. Green-shelled yields of intercropped legumes averaged ≈700 kg·ha-1. Genotype of the pumpkin maincrop did not affect legume green-shelled yields in Lajas. In Isabela, legume green-shelled yields were 50% higher in SB than in LV pumpkin plots. Legume dry grain yields were greatly reduced in LV compared to SB plots. Intercropping of tropical pumpkin with a short season legume that can be harvested green-shelled is an efficient intercropping system that offers additional yield from the legume without sacrificing yield from the pumpkin maincrop. Both SB and LV pumpkins can be used in an intercrop system, but pumpkin yields were much greater with the LV genotype.

Open access

Allen V. Barker, Donald N. Maynard, and Harry A. Mills

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

Peter J. Stoffella and Donald N. Maynard

Abstract

The effects of replanting stand-deficient plots on marketable tomato (Lycopersicon esculentum Mill.) fruit size and yields were investigated at Bradenton, Fla. during the 1986 spring and fall seasons. Treatments consisted of a control (10-plant plot) and plots with 9, 8, and 7 (10%, 20%, and 30%) missing plants. Other plots with the same stand deficiency were replanted to attain a complete stand 2 or 3 weeks and 1, 2, or 3 weeks after initial transplanting in the spring and fall experiments, respectively. Plots with 30% stand reduction produced a lower weight and number of marketable fruit per hectare than control plots in both seasons. In spring, replanting stand-deficient plots did not increase marketable fruit yields relative to plots not replanted, regardless of the time of replanting or percentage of stand reduction. In fall, under an unfavorable environment due to a late infestation of bacterial spot, replanting plots with 30% stand reduction increased marketable fruit yields over similar plots that were not replanted, when the replanting occurred 1 or 2 weeks after initial transplanting, but not when replanting was delayed 3 weeks. Small, medium, or extra-large marketable fruit weight per hectare were similar in both seasons for plots with 30% stand reduction, whether replanted or not. Mean fruit size (g/fruit) did not differ significantly among treatments in either experiment. These results suggest that replanting improved marketable tomato yields only when the level of stand deficiency reached 30% and only in a stressed environment.

Open access

Jean E. English and Donald N. Maynard

Abstract

Seedlings of 44 tomato strains were screened in low (16.5 mg/plant) Ca nutrient solutions. Tolerance to low Ca was rated according to plant appearance and efficiency ratios, i.e., tissue produced (g) per unit of Ca (mg) in the tissue. Correlations among various symptom ratings and Ca-efficiency ratios for roots, stems and petioles, and laminar tissue showed that only 1 deficiency symptom and dry weight or 1 symptom and 1 efficiency ratio were necessary to rank plants. These methods showed that Plant Introductions (PI) 340909, 341984, and 341988 (all L. esculentum) were Ca-inefficient, whereas PI 205040 (L. esculentum cv. Yellow Peach) and PI 129021 (L. esculentum × L. pimpinellifolium) were Ca-effi-cient. Differences in efficiency were maintained when these selections were grown with higher Ca concentrations.

Open access

Donald N. Maynard and Allen V. Barker

Abstract

Brussels sprouts (Brassica oleracea var. gemmifera, Zenker) were grown in sand culture at variable Ca levels in the greenhouse. More Ca accumulated in leaves than in sprouts. With plant growth restricted by late seeding and low greenhouse temp, typical Ca deficiency symptoms occurred on the growing points of plants cultured at low Ca levels, but internal browning did not occur. When growth was enhanced by cultural modifications, sprout internal browning occurred at low Ca levels and decreased as Ca levels were increased. The incidence of internal browning was related to low Ca concn in sprouts.

Open access

Harry A. Mills, Allen V. Barker, and Donald N. Maynard

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

Frederick C. Olday, Allen V. Barker, and Donald N. Maynard

Abstract

Cucumber (Cucumis sativus L.) plants accumulate more NO3¯ 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 NO3¯ in their roots. Only 2% of the NO3¯ reductase activity of cucumber was found in its roots, whereas nearly 92% of the activity was found in the blades. In pea, NO3¯ 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

Frederick C. Olday, Allen V. Barker, and Donald N. Maynard

Abstract

‘America’ spinach (Spinacia oleracea L.) is a savoy-leafed cultivar and tends to accumulate NO3¯ 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 NO3¯ than ‘America’ especially when NO3-N nutrition is high. A greater NO3¯ reductase activity in Hybrid 424, especially in its leaf blades, may account for its lower NO3¯ content compared to that of ‘America’.

Free access

Donald N. Maynard, Gary W. Elmstrom, Stephen T. Talcott, and R. Bruce Carle

Free access

Jonathan R. Schultheis*, Richard L. Hassell*, Wilfred “Bill” R. Jester, Donald N. Maynard, and Gilbert A. Miller

Demand for triploid watermelons has outpaced the demand for diploid watermelons in the United States in recent years. The size of most triploid watermelons sold in U.S. markets is from 6 to 9 kg. Recently, a new produce item, seedless watermelons weighing about 1.8 to 3.6 kg, have been introduced and created excitement in the produce industry. Several vegetable seed companies have developed proprietary miniwatermelon hybrids. Syngenta Seeds and Seminis Vegetable Seeds have received the most publicity, with the PureHeart and Bambino brands being featured in the 15 June 2003 New York Times. The 2003 season was the first year that cultigens (cultivars and advanced lines) were generally available. At least four trials were conducted in the southeastern United States to evaluate yields and quality of mini-watermelons; Bradenton, Fla., Ediston, S.C., Charleston, S.C., and Kinston, N.C. Cultural practices and the number of cultigens varied among locations (9 to 17). Fruit less than 3.6 kg that yielded best in all locations were `Petite Perfection' (Syngenta) and RWT 8149 (Syngenta). Other cultigens that yielded well in at least one location were; `Precious Petite' (Syngenta), `Vanessa' (Sunseeds), ZG 8905 (Zeraim Gedera), SR 8103 WM (Sunseeds), SW 8002 (Southwestern), and HA 5130 (Hazera). Rind thickness varied from 6 to 25 mm and soluble solids ranged from 10 to 13%, depending on location and cultigen. New cultivars will be made available in 2004. Key characteristics that seem important to overall success in the market of the triploid miniwatermelon is consistent quality. This includes high yields of uniform sized fruit from about 1.6 to 3.8 kg; high soluble sugars (11% to 13%); and fruit with bright red, crisp flesh with a thin rind that endures shipping.