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Richard L. Hassell and Dale W. Kretchman

Seed from six species of the Apiaceae and six parsley (Petroselinum crispum L.) cultivars with three seed lots of each parsley cultivar were tested for the presence of germination inhibiting substances. Aqueous leachate from seed of all six species inhibited germination of lettuce (Lactuca sativa L.) and radish (Raphanus sativus L.). Leachate from root parsley seeds (P. crispum tuberosum) were least inhibitory, while leachate from celery and celeriac (both Apium graveolens L.) seeds were most inhibitory. Inhibitory concentrations in leachate varied by seed lot within a cultivar. Aqueous leachate of seeds from the primary umbels caused less inhibition of germination than did leachate from tertiary umbels. Washing parsley seeds in aerated water for 3 hours or more removed some of the germination inhibitory substance as indicated by the germination bioassay. An aqueous extract prepared from seedcoat tissue, removed during mechanical scarification, inhibited radish seed germination; inhibition was proportional to the duration of scarification and the amount of seedcoat tissue extracted. Parsley seeds scarified ≤60 minutes germinated at rates comparable to washed seeds, but longer scarification time reduced germination. Washing seeds of Apiaceae prior to commercial drying and cleaning may be a practical solution for removal of inhibitors.

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Richard L. Hassell and D.W. Kretchman

Germination inhibitors found in parsley (Pertroselium hortense) seed have serious effects on field establishment. Studies have been conducted on chemical and physical attributes in relation to cultivar, age of seed and location of the seed on the seed stalk. Results indicate that the inhibitor is highly soluble in H2O and can be removed with as little as a half-hour aqueous wash. Soaking 30 g (∼500 seeds/g) of seed in an aerated graduated cylinder containing 100 ml distilled H2O for 24 hours then applied to radish, lettuce, and parsley seeds revealed complete germination inhibition of these seeds. Decreasing the soaking time did not reduce the inhibitory effects of the solution. Location of the inhibitor within the seed was found to be specific to the seed coat. The amount of inhibitor present varied with the cultivar and seed lot within that cultivar. Size and age of the seed had little effect on the amount and strength of the inhibitor. Location of the developing seed on the seed stalk effected the amount of inhibitor present. Primary umbels contained the least amount of inhibitor when compared to the secondary and tertiary umbels.

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Teri Hale*, Richard Hassell, and Tyron Phillips

Taste panel perception and preference of sweetness in three phenotypes (su, se and sh2) of sweet corn harvested at three maturities (early, mature and late) were compared to refractometer measurements and HPLC analysis of fructose, sucrose, and glucose. Panelist rating of sweetness and acceptability significantly correlated with HPLC analysis. These correlations were found for sucrose and total sugars present (for sweetness, r 2 = 0.70 and 0.61; acceptability, r 2 = 0.64 and 0.55). Sucrose significantly correlated with the total sugars present (r 2 = 0.95). The panelists' perception of flavor also correlated significantly with the amount of sucrose present and total sugars (r 2 = 0.66 and 0.59, respectively). Sucrose content was significantly different between se, sh2 and su, with sh2 having the highest level. Taste panels indicated this difference but showed not significant differnece between se and sh2 acceptablity. Su was only acceptable to panelists at early maturity. °Brix did not reflect the taste panels scores and HPLC measurements postively. Soluble solids and taste panel scores were negatively correlated in both the panel's perception of sweetness and acceptability (r 2 = -0.66 and -0.66, respectively) which indicates that as panel scores decreased °Brix increased. Comparison of soluble solids to HPLC analysis, indicate that °Brix was negatively correlated to sucrose and total sugar content, and that as soluble solids increased, the sucrose or total sugar concentration remained constant or decreased. Soluble solids measurements have been positively correlated with sucrose levels in other crops; but this was not the case with sweet corn.

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Richard L. Hassell and D.W. Kretchman

Two cultivars of tomato (Lycopersicon esculentum) and leaf lettuce (Lactuca sativa) were evaluated using two plug trays, polyethylene and polystyrene in two colors, black and white. Cells were 2 cm square inverted pyramid and 5 cm deep. Temperatures 0.3 cm below the surface of the media in the black trays average 2 to 4°C warmer than in the white trays. Night temperatures were not influenced by tray color. There was no apparent interaction between color and tray composition. Tomato plants grown in black trays had longer, smaller diameter stems than those in the white trays. Total leaf area, plant fresh and dry weights, however, were not affected by tray color. Leaf lettuce grown in black trays had greater total leaf area than those in white trays. Leaf numbers were not affected by tray color. Plants of tomato and lettuce grown in white trays were shorter, stockier, and easier to handle during transplanting than those produced in black trays. Both cultivars of tomato and lettuce responded similarly to tray color and composition.

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Shawna L. Daley and Richard L. Hassell

Application of fatty alcohol compounds to rootstock meristems can control rootstock meristematic regrowth, thus decreasing the cost of producing grafted watermelon transplants by reducing the labor. Eight rates of Fair 85® and Off-Shoot T®, two commercially available fatty alcohol compounds, were applied to the meristem region of bottle gourd (Lagenaria sicereria cv. Emphasis) and interspecific hybrid squash (Cucurbita maxima × Cucurbita moschata cv. Carnivor) rootstocks to determine the optimal application rate to control regrowth without damaging the remaining plant parts. A water-only control treatment was also included. Rootstock seedlings were rated for damage and regrowth on Days 1, 7, 14, and 21 after treatment. Damage increased and regrowth decreased with increasing rates of fatty alcohol compound. In addition, a significant compound-by-rate interaction indicated that inert ingredients in the fatty alcohol formulation have an effect on both damage and regrowth. The optimal treatment rate, e.g., providing at least 95% control of regrowth with less than 10% damage, was found to be between a 5% (Off-Shoot T®) and 6.25% (Fair 85®) fatty alcohol application. At the optimal treatment rate, no adverse effects to grafting success were observed in the grafting procedure.

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Robert J. Dufault, Brian Ward, and Richard L. Hassell

The objective of this study was to determine the best combination of planting dates (PDs) and cultivars on yield and quality for long-term production of romaine lettuce. `Green Forest' (GF), `Apache' (AP), `Darkland' (DK), `Green Tower' (GT), `Ideal Cos' (IC), and `Tall Guzmaine' (TG) were successfully grown to harvest maturity on 19 PDs from September 1998 to April 2001. Lettuce planted in September and April PDs (pooled over cultivars and year), required as little as 47 and 49 days, respectively, to reach harvest (all cultivars harvested on the same day). Lettuce planted in October, November, February, and March PDs (pooled over cultivars and year), required on average 64, 66, 75, and 67 days to reach harvest, respectively, but in the coldest PDs of December and January, 90 and 98 days, respectively, were needed to reach maturity. Of the eight PDs evaluated, marketable numbers/plot (pooled over cultivars and years) were greatest in the September PD, followed by April (–8% decrease from September PD) > March (–13%) > October (–17%) > November (–21%) > December = January = February (about –30%) and heads weighed the most in September > January = February (–7% decrease from September PD) > March = April (–14%) > October (–21%) > December (–25%) > November (–31%). Cull heads/plot (pooled over cultivars and years) were greatest in April > December (–5% decrease from April PD) > January = February (–16%) > November (–27%) > October (–34%) > March (–44%) > September (–49%). Two out of three November PDs were lost to freezing damage and this PD should be avoided. Significant bolting occurred primarily in the September and October PDs (in 1 of 3 years) with negligible bolting in the November, December, and January PDs, but bolting recurred again in the February, March and April PDs. Marketable numbers/plot (pooled over all PDs and years) were greatest for GF > GT (–7% decrease from GF) > AP (–8%) > IC (–9%) > DK (–11%) > TG (–21%). The interaction effect of cultivar × PD indicated that GF yielded the most marketable heads in 6 out of 8 PDs. The best performing cultivars by PD (pooled over years) were September and February = GF and IC; October = TG; November = AP; December, January, March, and April = GF.

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Wenjing Guan, Xin Zhao, Richard Hassell, and Judy Thies

Grafting with resistant rootstocks is an effective strategy to manage a variety of soilborne diseases and root-knot nematodes in solanaceous and cucurbitaceous vegetables. In addition, improved resistance to some foliar diseases and viruses has also been reported in grafted plants. Hence, grafting technology is considered an important and innovative practice of integrated pest management and a promising alternative for soil fumigants in vegetable production. Inherent resistance within rootstocks and improved plant nutrient uptake are generally suggested as the main reasons for improved disease control in grafted vegetables. However, increasing evidence indicated that systemic defense mechanisms may also play an important role in plant defense as a result of grafting. This review analyzes current literature on the use of grafting techniques for disease management in vegetable crops, discusses potential mechanisms associated with grafting-conferred plant defense, and identifies needs for future research to promote more effective and efficient use of grafting technology to support sustainable vegetable production.

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Richard L. Hassell, Tyron L. Phillips, and Teri Hale

The small, B size potatoes (<2 inches but ≥1.25 inches in diameter) represent a keen interest in new, specialty food items. Exotic shapes and color shades of the specialty varieties are also known for intense flavors and variations in textures in firmness and fiber that consumers are looking for today in an ever increasing health consciousness among consumers. In 2006, the varieties `French Fingerling' (West Edmonton, Alberta, Canada), Villetta Rose (Univ. of Wisconsin) and B1145-2 (USDA, Beltsville, Md.) were planted in a double row 8 inches between tubers and 18 inches between rows in a replicated trial using colored mulches. The mulch color included red, white, black, blue, green, and silver foil. These plastic mulches were laid on 6-ft centers. The mulches were shown to affect the microclimate of soil temperature, as expected, and therefore affecting yield. These temperature differences were measured with a Campbell CR 10X weather station (Logan, Utah) probes at a 2 inches above the soil surface and 4 and 6 inches below the soil surface. Plant stands were excellent with all mulches, however, blue mulch caused early emergence while white and silver delayed emergence. Just the opposite effect happened when it came to yields. The highest individual tubers per plant came from the white mulch with the green having the lowest tuber yields. Cultivar differences were also seen in there ability to produce marketable tubers. `Villetta Rose' had the highest plant vigor and also the most marketable tubers per plant. B1145-2 produced most of its tubers >2 inches in diameter with the tubers nonuniform in shape. French Fingerling produced a very uniform oblong tuber with few defects. Yields and quality were above normal for all cultivars when grown on either the silver reflective mulch or the white mulch.

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Teri A. Hale, Richard L. Hassell, and Tyron Phillips

The refractometer has been proposed as a rapid, inexpensive technique for determining sugar levels in fresh sweet corn (Zea mays). High performance liquid chromatography (HPLC) analysis of sugars in three phenotypes (su, se, and sh2) of sweet corn harvested at three maturities indicated that sucrose content was highly correlated with the total sugars (R = 0.95). Sucrose and total sugar concentration were significantly different among all phenotypes. Soluble solids concentration (SSC) was high in su and se compared to the lower SSC of sh2. Early, mature, and late harvested samples differed in sucrose and total sugar content. Sugar concentration varied within phenotypes at each maturity level. Sh2 indicated no difference in sucrose and total sugars at early and mature harvests, but increased at late harvest. In contrast, sucrose and total sugar content decreased between early and mature harvests, then increased to highest levels at late harvest in se and su phenotypes. Overall, phenotype SSC increased significantly from early to late harvests, probably due to increased water-soluble polysaccharides in the su and se cultivars. Unlike other crops, a negative relationship was found in sweet corn between SSC and sucrose or total sugars, with an overall correlation of –0.51. This relationship was most affected by maturity, especially mature and late harvested sweet corn. Among phenotypes, sucrose, total sugar, and SSC were poorly correlated. Our results indicate that a refractometer should not be used to estimate total sugars or sucrose of sweet corn.

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Shawna L. Daley, Jeffrey Adelberg, and Richard L. Hassell

Application of fatty alcohol to rootstocks used for vegetable grafting has been shown to increase the efficiency of producing grafted transplants by controlling cucurbit (Cucurbitaceae) rootstock meristematic regrowth and by allowing the rootstocks to accumulate carbohydrates, especially starch, over time in the hypocotyl and cotyledon. A grafting experiment was conducted to determine the effect of increased carbohydrates on survival of watermelon (Citrullus lanatus) grafts using standard grafting procedures. ‘Carnivor’ interspecific hybrid squash (Cucurbita maxima × C. moschata) and ‘Macis’ bottle gourd (Lagenaria sicereria) rootstocks at 1, 7, 14, and 21 days after fatty alcohol treatment were grafted with ‘Tri-X 313’ seedless watermelon using the one-cotyledon method. Graft survival on ‘Macis’ rootstock was acceptable or significantly increased up to day 14, with a slight decrease at day 21. Graft survival on ‘Carnivor rootstock was also acceptable up to day 21, with a significant increase between days 1 and 7. The second experiment was conducted to determine whether the increased carbohydrates provide sufficient energy to successfully graft without the rootstock cotyledon, a method that has previously shown inconsistent results. Graft survival was improved by 90% using treated ‘Carnivor’ rootstock 7 days after fatty alcohol treatment and ‘Macis’ rootstock 14 days after fatty alcohol treatment. Adoption of the hypocotyl-only graft method in commercial production may increase efficiency by better using greenhouse space and could decrease disease probability by removing the cotyledons before grafting.