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Milton E. McGiffen Jr. and John A. Manthey

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Jinhe Bai, Kristi Barckley, and John Manthey

Pear texture is similar to that of apple—firm and crispy—and is one of the potential alternatives to apple. However, at a crispy stage the taste is flat. Improving the taste of pears is considered the key to the success of pear salad. This study evaluated the effect of harvest maturity on the quality of pear salad. Fruit were harvested at commercial maturity or 1 month delayed. After 2 and 5 months (1 and 4 months for delayed harvested fruit) of storage at –1 °C, fruit were sliced (eight to 10 wedges per fruit), treated with an anti-browning dip, packaged in zip-lock bags (10 pieces per bag), and stored at 1 °C for up to 21 days. Delayed harvested fruit were larger in size (≈12.5% increase in weight), had lower flesh firmness (≈5 N decrease), lower titratable acidity content (≈20% decrease), and a lower phenolic content (≈45% decrease in pulp). There was no significant difference in soluble solids content. After 2 months of storage, ethylene production and respiration rate were initially lower in delayed harvested fruit in either the intact fruit or cut slices, but tended to similar after 7 days in storage. Sensory evaluation results show that about 80% of the panel preferred delayed-harvested fruit over commercial harvest, especially in terms of visual quality (71% to 92%), sweetness (75% to 93%), taste (69% to 92%), texture of skin (61% to 92%), texture of flesh (53% to 92%), and overall quality (73% to 92%) during 21 days of storage at 1 °C. After 5 months of storage, cutting surface was dry-looking in delayed harvested fruit. However, sensory evaluation showed panels still preferred the delayed-harvested fruit. The results indicate that salad quality of pears can be improved by delaying harvest.

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David E. Crowley, Woody Smith, Ben Faber, and John A. Manthey

Methods for Zn fertilization of `Hass' avocado (Persea americana Mill.) trees were evaluated in a 2-year field experiment on a commercial orchard located on a calcareous soil (pH 7.8) in Ventura County, Calif. The fertilization methods included soil- or irrigation-applied ZnSO4; irrigation-applied Zn chelate (Zn-EDTA); trunk injection of Zn(NO3)2, and foliar applications of ZnSO4, ZnO, or Zn metalosate. Other experiments evaluated the influence of various surfactants on the Zn contents of leaves treated with foliar-applied materials and on the retention and translocation of radiolabeled 65ZnSO4 and 65Zn metalosate after application to the leaf surface. In the field experiment, tree responses to fertilization with soil-applied materials were affected significantly by their initial status, such that only trees having <50 μg·g–1 had significant increases in foliar Zn contents after fertilization. Among the three soil and irrigation treatments, ZnSO4 applied at 3.2 kg ZnSO4 per tree either as a quarterly irrigation or annually as a soil application was the most effective and increased leaf tissue Zn concentrations to 75 and 90 μg·g–1, respectively. Foliar-applied ZnSO4, ZnO, and Zn metalosate with Zn at 5.4, 0.8, and 0.9 g·liter–1, respectively, also resulted in increased leaf Zn concentrations. However, experiments with 65Zn applied to leaves of greenhouse seedlings showed that <1% of Zn applied as ZnSO4 or Zn metalosate was actually taken up by the leaf tissue and that there was little translocation of Zn into leaf parenchyma tissue adjacent to the application spots or into the leaves above or below the treated leaves. Given these problems with foliar Zn, fertilization using soil- or irrigation-applied ZnSO4 may provide the most reliable method for correction of Zn deficiency in avocado on calcareous soils.

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Kanjana Mahattanatawee, Elizabeth Baldwin, Kevin Goodner, John Manthey, and Gary Luzio

Fourteen tropical fruits from southern Florida [red guava, white guava, carambola, red pitaya (red dragon), white pitaya (white dragon), mamey, sapodilla, lychee, longan, green mango, ripe mango, green papaya and ripe papaya] were evaluated for antioxidant activity, ascorbic acid (vitamin C), total fiber and pectin. ORAC (oxygen radical absorbance capacity) and DPPH (1,1-diphenyl-2-picrylhydrazyl, radical scavenging activity) assays were used to determine antioxidant activity. The total soluble phenolics (TSP), ORAC, and DPPH ranged from 205.4 to 2316.7 μg gallic acid equivalent/g puree, 0.03 to 16.7 μmole Trolox equivalent/g puree and 2.1 to 620.2 μg gallic acid equivalent/g puree, respectively. Total ascorbic acid (TAA), total dietary fiber (TDF) and pectin ranged from 13.6 to 159.6 mg/100 g, 0.88 to 7.25 g/100 g and 0.2 to 1.04 g/100 g, respectively. The antioxidant activities, TSP, TAA, TDF and pectin appeared to be influenced by cultivar (papaya, guava and dragon fruit) and ripening stage (papaya and/or mango). Data demonstrate the potential benefits of several of these fruits for human health.

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William S. Castle, James Nunnallee, and John A. Manthey

A broad range of plant selections across the orange subfamily Aurantioideae were screened in solution and soil culture for their tolerance to low iron (Fe) stress. Young seedlings grown in soil were transferred to tubs of +Fe nutrient solution, which was later replaced after a brief period with a –Fe solution. Over several trials, ≈20 white root tips were harvested periodically from the plants in each tub and assayed for their ability to reduce Fe3+. The procedure was miniaturized to determine if a fewer number of root tips could be assayed to screen individual plants and to estimate the required sample size. For solution screening, seven root tips were estimated to be adequate for representing a single plant. Seedlings of a few selections were also grown in small containers of soil amended with 0% to 5.9% CaCO3. The results in solution and soil culture were consistent with each other and with previous assessments of the various selections. Based on a summary of the solution and soil responses, the citrus selections were grouped in descending order of Fe3+ reduction rates as Volkamer lemon/Rangpur/sour orange selections/Citrus macrophylla > mandarins and mandarin hybrids > citranges > citrumelos > trifoliate orange. Of the citrus relatives tested in solution culture only, those in the genera Glycosmis, Citropsis, Clausena, and Murraya had high Fe reduction rates with good seedling growth and new leaves developed a light yellow color or showed no loss of greenness. Other citrus relatives in the genera Severinia, Atalantia, and Fortunella and most somatic hybrids had low seedling vigor and produced too few root tips to be properly assessed. The results are useful because of the breadth of selections screened, the identification of various citrus relatives as potential sources of low-Fe stress tolerance in breeding new rootstocks, and the apparent positive relationship between the Fe3+ reduction responses, soil screening responses, and field experiences with carbonate-induced Fe chlorosis responses.

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Milton E. McGiffen Jr., John Manthey, Aziz Baameur, Robert L. Greene, Benjamin A. Faber, A. James Downer, and Jose Aguiar

A 1992 article by Nonomura and Benson (Proc. Natl. Acad. Sci. 89:9794-979X) reported increased yield and drought tolerance in a wide range of C3 species following foliar applications of methanol. The article was widely reported in the trade and popular press, which created a huge grower demand for information on the use and efficacy of methanol. To test the validity of the reports, we applied methanol with and without nutrients to a wide range of crops across California following Nonomura and Benson's (1992) protocol. Crops included watermelon, creeping bentgrass, lemons, savoy cabbage, carrots, romaine lettuce, radish, wheat, corn and peas. Environments included the greenhouse and field tests in coastal, inland valley, and desert locations. To test whether methanol improved drought tolerance, the savoy cabbage and watermelon experiments included both reduced and full irrigation. In no case was yield increased or drought tolerance attributable to methanol treatment. In some cases, methanol caused significant injury and decreased yield.

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Milton E. McGiffen Jr., Robert L. Green, John A. Manthey, Ben A. Faber, A. James Downer, Nicholas J. Sakovich, and Jose Aguiar

To test the usefulness of methanol treatments in enhancing yield and drought tolerance, we applied methanol with and without nutrients to a wide range of crops across California: lemon (Citrus limon L.), creeping bentgrass (Agrotis palustris Huds.), romaine lettuce (Lactuca sativa L.), carrot (Daucus carota L.), corn (Zea mays L.), wheat (Triticum aestivum L.), pea (Pisum sativum L.), and radish (Raphanus sativus L.). Environments included greenhouse and field tests in coastal, inland-valley, and desert locations. Methanol did not increase the yield or growth of any crop. In some cases, methanol caused significant injury and decreased yield.

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Anne Plotto, Elizabeth Baldwin, Jinhe Bai, John Manthey, Smita Raithore, Sophie Deterre, Wei Zhao, Cecilia do Nascimento Nunes, Philip A. Stansly, and James A. Tansey

A 3-year study was undertaken to establish the effect of field nutritional sprays, combined with insecticide treatments or not against Asian Citrus psyllid, on the fruit quality of ‘Valencia’ orange trees affected by the greening disease Huanglongbing (HLB). Four replicated plots were harvested, juiced, and pasteurized. Nine to twelve trained panelists evaluated the juice using seven flavor, five taste, four mouthfeel and three aftertaste descriptors. There was little difference between treatments in 2013; only orange peel flavor and bitterness were significantly lower for the insecticide treatment. In 2014, positive attributes, such as orange and fruity flavor, sweetness and mouthfeel body, were significantly higher in the insecticide treatment. Sourness was highest in untreated control, and there were no differences between treatments for bitterness. In 2015, negative attributes, such as grapefruit, orange peel and typical HLB flavor, sourness, bitterness, and astringency, were significantly higher in untreated control fruit, suggesting perhaps that the beneficial effect of nutritional and insecticide treatments was cumulative, only manifesting on the 3rd year of the study, and or because of the progression of the disease affecting untreated controls. Data are discussed in relation to juice chemical composition, including volatiles, sugars, acids, limonoids, and flavonoids, adding to the fundamental knowledge concerning chemical drivers of orange flavor.

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Elizabeth Baldwin, Jinhe Bai, Anne Plotto, John Manthey, Smita Raithore, Sophie Deterre, Wei Zhao, Cecilia do Nascimento Nunes, Philip A. Stansly, and James A. Tansey

‘Valencia’ orange trees from groves with 90% infection by Candidatus liberibacter asiaticus (CLas), the presumed pathogen for citrus greening or huanglongbing (HLB) disease, were treated with insecticide (I), a nutritional spray (N), and insecticide plus nutritional spray (I + N). Controls (C) were not treated. Fruit were harvested in March to April, 2013, 2014, and 2015, juiced, and the juice was frozen for later chemical analyses. Titratable acidity (TA), soluble solids content (SSC), SSC/TA ratio, many volatiles, flavonoids, and limonoids showed differences because of season, whereas SSC, several volatiles (ethanol, cis-3 hexenol, α-terpinene, ethyl acetate, and acetone), flavonoids (narirutin, vicenin-2, diosmin, nobiletin, heptamethoxy flavone), and limonoids (nomilin and nomilinic acid glucoside) showed differences because of treatment. However, consistent patterns for chemical differences among seasons were not detected. TA tended to be higher in N and C the first two seasons and SSC/TA higher in I and I + N for all seasons (not significant for 2014). Bitter limonoids tended to be higher in I, N or I + N over the seasons. Principal Component Analysis showed that there was a good separation by season overall and for treatment in 2013. In 2014 and 2015, the insecticide treatments (either I or I + N) had the highest sugar and SSC/TA levels and lowest TA levels, although not always significant, as well as higher juice CLas cycle threshold (Ct) levels, indicating lower levels of the pathogen.