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Timothy W. Coolong and William M. Randle

To determine the extent to which sulfur (S) and nitrogen (N) fertility interact to influence the flavor biosynthetic pathway in onion (Allium cepa L.), `Granex 33' onions were grown in hydroponic solution culture with varying levels of S and N availability. Plants were grown at 5, 45, or 125 mg·L-1 sulfate (SO4 2-), and 10, 50, 90, or 130 mg·L-1 N, in a factorial combination. Total bulb S, total and individual flavor precursors and their peptide intermediates in intact onion tissue were measured. To measure the effect of S and N on alliinase activity, flavor precursors were also measured in onion macerates. Sulfur and N availability in the hydroponics solution interacted to influence all flavor compounds except S-methyl-L-cysteine sulfoxide. Levels of S-methyl-L-cysteine sulfoxide were influenced by N and S levels in the solutions; however, no interaction was present. At the lowest SO 4 2- or N levels, most precursors and peptides measured were present in very low concentrations. When SO 4 2- or N availability was adequate, differences among flavor compounds were small. Results indicated that S fertility had a greater influence on trans-S-1-propenyl-L-cysteine sulfoxide (1-PRENCSO) accumulation, while N availability had a greater influence on S-methyl-L-cysteine sulfoxide levels. Flavor precursors remaining in the onion macerates revealed that the percentage of intact precursors hydrolyzed by alliinase were not significantly influenced by either SO 4 2- or N levels in the solutions, except for 1-PRENCSO, which was affected by N levels. Nitrogen and S fertility interacted to influence the flavor biosynthetic pathway and may need to be considered together when manipulating onion flavor compounds.

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Timothy Coolong, William Randle and Ronald Walcott

Onion (Allium cepa L.) is an economically important vegetable in the United States. Though considered a minor crop in terms of total acreage, onions have high value when compared to other crops and, nationally, their value approaches $800 million. Because harvested onions are routinely stored for long periods, disease can be a major obstacle to the industry. The primary disease reported in stored onions is botrytis neck rot caused by the fungus Botrytis allii (syn. B. aclada). Losses from neck rot can approach 35% of the stored crop. In order to accurately quantify the level of B. allii inoculum in bulbs at harvest to be able to predict potential botrytis neck rot in storage, a quantitative real-time PCR test to quantify levels of B. allii DNA present in onion bulb tissue has been developed. We have employed the TaqMan real time PCR assay and report log-linear (R 2= 0.9915) relationship between B. allii DNA concentration and cycle threshold (Ct) value with a detection limit of 5 pico gram/microliter DNA. In addition, a log-linear standard curve plotting mycelial dry weight against Ct value has been developed to allow prediction of mycelial weight in onion tissue at harvest. Currently, the ability of this test to predict botrytis neck rot during storage is being tested.

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Luke Miller, George Vellidis, Osama Mohawesh and Timothy Coolong

A new smartphone vegetable irrigation scheduling application (VegApp) was compared with current irrigation scheduling recommendations and soil moisture sensor (SMS)–based irrigation for growing tomato (Solanum lycopersicum) in southern Georgia during Spring 2016 and 2017. Plants were grown using plastic mulch and drip irrigation following standard production. The VegApp-scheduled irrigation based on crop evapotranspiration (ETc) values calculated daily from meteorological data retrieved from nearby weather stations, whereas ETc rates for current water balance (WB)–based recommendations were calculated from historic averages for the region. Water usage, soil moisture tension, fruit yield and quality, and foliar macronutrient content were measured. In 2016, plants grown using SMS-based irrigation applied the least water followed by the VegApp- and WB-grown plants. In 2017, WB-treated plants received the least water, followed by VegApp- and SMS-grown plants. Total marketable yields were similar among treatments and years. Irrigation water use efficiency (IWUE) varied between year and irrigation regime, with SMS-grown plants having a significantly greater IWUE than the other treatments in 2016. Plants irrigated using the VegApp had a greater IWUE than SMS-irrigated plants in 2017. Differences in IWUE were largely the result of variable irrigation volumes and not changes in yield. Fruit total soluble solids (TSS) were unaffected by treatment in either study year. Fruit pH was affected by irrigation treatment in 2017. Foliar nitrogen concentrations were affected by irrigation regime in 2017, with VegApp-grown plants having significantly greater concentrations of foliar N than other irrigation treatments. The results of this study suggest that the VegApp could be a reliable tool that can be used by growers to produce yields comparable to currently accepted irrigation scheduling practices and reduce water use in some seasons.

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Zheng Wang, Mark Williams, Krista Jacobsen and Timothy Coolong

Trials were conducted in 2011 and 2012 with ‘Aristotle’ bell pepper (Capsicum annuum L.) grown under different tillage methods and irrigation regimes in organically and conventionally managed production systems. Treatments consisted of strip tillage or plastic mulch in well-watered or water-restricted irrigation regimes. Within organic and conventional production systems, the study was arranged as a split-plot randomized block design with strip tillage or plastic mulch as the main plot and irrigation regime as subplot. Leaf water potential (ΨL), soil penetration resistance (compaction), volumetric water content (VWC), soil temperature, and pepper yield were measured. Soil VWC was greater in strip-tillage plots compared with plastic mulch plots under both well-watered and water-restricted conditions for plots in the organic system in 2011 and conventional system in 2012. In addition, soil VWC was numerically lower, if not always statistically different, in water-restricted plots compared with well-watered plots. The trend of soil temperatures within each production system were similar in 2011 and 2012, with plastic mulch plots having slightly higher soil temperatures than strip tillage, despite using white-on-black plastic mulch. Midday ΨL was affected by water regime, with well-watered plants having a significantly lower ΨL than water-restricted plants; however, there were no effects of irrigation on predawn ΨL. Tillage method and sampling location (between row and within row) significantly interacted to affect soil penetration resistance in 2011 and 2012. There was a significant interaction of tillage by irrigation regime on yield within conventional systems in both years, but not in organically managed plots. In 2011, yield data also indicated that the date at which 50% of marketable fruit were harvested (yield_mid) were later for strip–tillage-grown plants than plastic mulch–treated plants within conventional and organic production systems, respectively.

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Timothy W. Coolong, Ronald R. Walcott and William M. Randle

A real-time polymerase chain reaction (PCR) assay has been developed for the detection and quantification of Botrytis aclada (Fresenius), a causal agent of neck rot in onion (Allium cepa L.) bulbs. The assay uses TaqMan probe-based chemistry to detect an amplicon from the L45-550 region of B. aclada while using a DNA sequence from the onion serine acetyl transferase gene (SAT1) as a control. The assay detection limits for B. aclada and onion were 10 pg·μL−1 of genomic DNA. The detection limit for lyophilized B. aclada mycelium was 1 μg. The presence of onion tissue in the samples did not affect the performance of the real-time PCR assay. The assay distinguished among different amounts of B. aclada mycelium growing on onion disks that were inoculated with 0, 102, or 104 B. aclada conidia. Visual observations during the incubation period corresponded with changes in real-time PCR results. This assay could be used to determine the amount of B. aclada mycelium in bulbs during growth, harvest, and storage, thus giving researchers an objective and efficient tool by which to quantify the growth rate and virulence of B. aclada strains in vivo.

Open access

Timothy Coolong, Andre Luiz Biscaia Ribeiro da Silva and Justin Shealey

High-value vegetable crops such as bell pepper (Capsicum annuum) are heavily fertilized by growers who seek to maximize yields. Field experiments were conducted in Spring 2016 and 2017 evaluating two liquid fertilizers with and without calcium (Ca), applied at three nitrogen (N) and potassium (K) levels in two varieties of bell pepper to determine whether current fertilizer recommendations were adequate and whether fertilizer source impacted fruit yield and quality. Plants were grown using plastic mulch and drip irrigation following standard production practices for the region. Two liquid fertilizer programs [7N–0P–5.8 (7–0–7) and 4N–0P–6.6K/9N–0P–0K–11Ca (4–0–8/CN9)] were applied twice weekly at three N rates (175, 200, and 225 lb/acre N). Yield, cull rate, and foliar nutrient concentrations were measured. In 2016, total marketable yields were greatest [910 boxes/acre (28 lb/box)] and blossom end rot (BER) incidence (14.4%) lowest in plants grown with the supplemental Ca (4–0–8/C9 fertilizer) at 175 lb/acre N. Cull rates increased in plants grown without supplemental Ca during the season (7–0–7 fertilizer), with BER incidence ranging from 22.9% to 27.2%. Yields ranged from 590 to 740 boxes/acre in plants grown without supplemental Ca in 2016. In 2017, yields ranged from 530 to 790 boxes/acre in plants grown with supplemental Ca at 200 and 175 lb/acre N, respectively. Culls due to BER were lower in 2017 than in 2016. In 2016, BER incidence was greater in ‘PSO9979325’ compared with ‘Antebellum’, despite no differences in total yield. Foliar nutrient levels were largely unaffected by fertilizer program; however, foliar N and K concentrations increased with the rate of N and K fertilization. The results of this study suggest that using liquid fertilizer program containing some Ca may benefit bell pepper growers in some, but not all, growing seasons.

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Timothy Coolong, Derek M. Law, John C. Snyder, Brent Rowell and Mark A. Williams

Thirty-eight leafy greens, eight kale (Brassica oleracea acephala group), nine mustard (Brassica juncea), six arugula (Eruca sativa), five swiss chard (Beta vulgaris var. cicla), five collards (B. oleracea acephala group), and five turnip (Brassica rapa ssp. rapa) varieties were evaluated during Spring and Fall 2007–08 to determine suitability for organic production with respect to yield and stability. Trials were conducted on certified organic land using organic production practices. For mustard, kale, collards, and arugula, there were significant variety by season by year interactions. Despite these interactions, some varieties consistently performed well throughout the trial. ‘Florida Broadleaf’ was the highest yielding mustard in three of the four seasons evaluated. ‘Siberian’, ‘White Russian’, and ‘Red Russian’ were in the highest yielding group of kale varieties for overall yield. For collards, ‘Georgia/Southern’ and ‘Flash’ were part of the highest yielding group as determined by Duncan’s multiple range test in three of the four seasons examined. Turnip and swiss chard had significant year by variety interactions. Overall yields of ‘Alamo’ and ‘Alltop’, both F1 hybrids, were better than other turnip varieties assessed. Despite the interaction, ‘Fordhook Giant’ had superior yields in both years of the study. Arugula performance was significantly and negatively affected in Spring 2008. Overall, ‘Astro’, ‘Apollo’, and ‘Arugula’ had the greatest yields. This trial was designed to provide recommendations specifically for organic growers marketing directly to consumers.

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Timothy W. Coolong, William M. Randle, Heather D. Toler and Carl E. Sams

Rapid cycling Brassica rapa L. were grown for 7 days in the presence of 11 levels of zinc (Zn) in hydroponic solution culture and evaluated for changes in Zn and glucosinolate (GS) content. Zinc levels were 0.05, 1, 5, 10, 25, 50, 75, 100, 125, 150, and 200 mg·L-1 Zn. Plants grown in solutions with ≥50 mg·L-1 Zn displayed severe Zn toxicity symptoms, grew little, or died and were not subsequently evaluated for GS content. Shoot Zn concentrations increased linearly with increasing Zn treatment levels. Gluconapin, which accounted for nearly 90% of the aliphatic GSs present, was the only aliphatic GS influenced by Zn, and decreased linearly with increasing Zn levels. Accumulation of glucobrassicin and 4-methoxyglucosbrassicin, both indole GSs, responded with a linear increase and quadratically, respectively, to Zn fertility. An aromatic GS, gluconasturtiin, was also influenced by Zn levels in solution, and had a quadratic response to increasing Zn. This suggested that Zn fertility can influence changes in GS that may affect flavor (bitterness, etc.) or medicinal attributes associated with the GS and their breakdown products, as well as elevate the nutritional status of Zn in the leaves of Brassica.

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Elsa S. Sánchez, Ermita Hernández, Mark L. Gleason, Jean C. Batzer, Mark A. Williams, Timothy Coolong and Ricardo Bessin

The goal of this study was to develop a systems-based strategy for organic muskmelon (Cucumis melo var. reticulatus) in Pennsylvania (PA), Iowa (IA), and Kentucky (KY) to manage bacterial wilt (Erwinia tracheiphila) and nutrients while safeguarding yield and enhancing early harvest. Spunbond polypropylene rowcovers deployed for different timings during the growing season were evaluated for suppressing bacterial wilt and locally available compost was applied based on two different estimated rates of mineralization of organic nitrogen (N) to manage nutrients. In KY only, the use of rowcovers suppressed bacterial wilt incidence compared with not using rowcovers. However, the timing of rowcover removal did not impact wilt incidence. Under lower cucumber beetle [striped cucumber beetle (Acalymma vittatum) and spotted cucumber beetle (Diabrotica undecimpunctata howardi)] pressure in PA and IA, rowcovers did not consistently suppress season-long incidence of bacterial wilt. In four of five site-years in PA and IA, more marketable fruit were produced when rowcovers were removed 10 days after an action threshold (the date the first flower opened in PA; the date when ≥50% of plants in a subplot had developed perfect flowers in IA and KY) than when no 10-day delay was made or when no rowcovers were used. In addition, the no-rowcover treatment consistently had lower weight per marketable fruit. In KY, the same action threshold without the 10-day delay, followed by insecticide applications, resulted in the largest number of marketable fruit, but did not affect marketable fruit weight. In PA, marketable yield was higher using compost compared with the organic fertilizer in 1 year. No yield differences were observed by nutrient treatments in 2 years. In IA, marketable yield was lower with the low amount of compost compared with the organic fertilizer and yields with the high amount of compost were not different from the low amount or the organic fertilizer in the year it was evaluated. In KY, marketable yield was unaffected by the nutrient treatments in the year it was evaluated. Given these results, muskmelon growers in PA, IA, and KY who use compost may choose the lower compost rate to minimize production costs. Overall, these findings suggest that rowcover-based strategies for organic management of bacterial wilt need to be optimized on a regional basis, and that fertilization with compost is compatible with these strategies.