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Sacha J. Johnson and Carol A. Miles

Successful grafting of vegetables requires high relative humidity (RH) and optimal temperatures for ≈1 week following grafting to reduce transpiration of the scion until rootstock and scion vascular tissue are healed together and water transport is restored. This study evaluated the effect of three healing chamber designs on the survival of grafted eggplant (Solanum melongena), tomato (Solanum lycopersicum), and watermelon (Citrullus lanatus). The three healing chamber designs were 1) an industry design, which was hand-misted, 2) a research design, which contained a humidifier, and 3) a simplified design, which was shadecloth only and hand-misted. All plants were self-grafted using the splice grafting technique, placed in the healing chamber for 7 days after grafting and evaluated for signs of wilting and graft failure from day 6 to day 14 after grafting. During the 7-day healing period, the industry design had the greatest fluctuation in temperature, the research design had the greatest fluctuation in RH, and the shadecloth only design had the least fluctuation in both temperature and RH. When the healing chambers were closed on day 2 after grafting, the industry healing chamber had higher mean temperature and RH (24.9 °C, 98%) than both the research (23.4 °C, 81%) and shadecloth only (23.3 °C, 52%) healing chambers. These results suggest that a humidifier may not be necessary to maintain high RH. Mean graft survival rates in the industry (69%) and research (66%) healing chambers were similar, and both were higher than that in the shadecloth only healing chamber (52%). Tomato had the highest rate (98%), eggplant was intermediate (82%), and watermelon had the lowest mean survival rate (7%); there was no interaction between healing chamber and crop. The very low survival rate of watermelon was most likely due to the grafting technique used in this study, which is not optimal for watermelon. Tomato graft survival was high in all three healing chambers (96% to 98%), suggesting that high RH is not essential for tomato graft survival. Eggplant graft survival decreased from 90% to 60% when RH was decreased, suggesting that high RH is essential for eggplant graft survival.

Open access

Shuresh Ghimire, Edward Scheenstra, and Carol A. Miles

Plastic mulch is commonly used to produce many vegetable crops because of its potential to decrease days to harvest, control weeds, and improve soil moisture conservation. However, use of plastic mulch is relatively new for sweet corn (Zea mays L.) in North America. We compared five plastic soil-biodegradable mulches [BDMs; Bio360, Organix AG, Clear Organix AG, Naturecycle, and Experimental polylactic acid/polyhydroxyalkanoates (Metabolix, Inc., Cambridge, MA)] and a paper mulch (WeedGuardPlus) against standard black polyethylene (PE; nonbiodegradable) mulch and bare ground cultivation for growth, yield, and quality of sweet corn cultivar Xtra Tender 2171. This field experiment was carried out in Mount Vernon, WA, which has a Mediterranean-type climate with an average air temperature of 16.1 °C during the 2017 and 2018 growing seasons. The experiment was drip irrigated; and in both years, preemergence herbicides were applied to the entire experimental area 1 to 2 days after seeding, and post-emergence herbicides were applied to alleys. While most mulches remained intact until the end of the growing season, Clear Organix AG started to split shortly after laying, resulting in significant weed pressure by midseason in both 2017 and 2018. Plant height toward the end of the season was lowest for plants grown on bare ground, intermediate for Clear Organix AG and WeedGuardPlus, and highest for the black plastic BDM and PE mulch treatments both years, except for Bio360 in 2018 where plant height was intermediate. Days to 50% tasseling and 50% silking were delayed 9 and 13 days, respectively, for bare ground and WeedGuardPlus compared with all other treatments in both years. Marketable ear yield was highest with the black plastic BDMs and PE mulch and lowest with bare ground, WeedGuardPlus, and Clear Organix AG treatments in both years. Total soluble solid content of kernels, and length and diameter of ears grown on the plastic BDM and PE mulch treatments were equal to or greater than, but never lower than, bare ground and WeedGuardPlus. These results indicate that growth, yield, and quality of sweet corn grown with black plastic BDMs are comparable to PE mulch, making black plastic BDMs an effective alternative to black PE mulch for sweet corn production in a Mediterranean-type climate.

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Suzette P. Galinato and Carol A. Miles

Lettuce (Lactuca sativa) and tomato (Solanum lycopersicum) are popular fresh market vegetable crops. In western Washington, there is interest in growing them in high tunnel production systems because of the region’s mild, coastal climate. The objectives of this study were to contrast the economic potential of growing lettuce and tomato under high tunnel and open-field production systems, and identify the main factors affecting profitability within each production system. Economic data for this study were collected by interviewing experienced lettuce and tomato growers in western Washington during focus group sessions. Costs of production varied by crop and production system, and findings indicated that it was five times more costly to grow lettuce and eight times more costly to grow tomato in a high tunnel than in the open field in western Washington. For lettuce, the labor cost per square foot of growing area was found to be 6 times greater in a high tunnel than in the open field; and for tomato, labor costs were 10 times greater in a high tunnel than in the open field. Total labor cost comprised more than 50% of the total production costs of lettuce and tomato in both the high tunnel and open-field systems. The percentage of total labor cost was similar in both the high tunnel and open-field production for lettuce, but was higher in high tunnel tomato production than in the open field. Tunnel-grown lettuce and tomato had three and four times greater marketable yield compared with field-grown, respectively. Given the base crop yield and average price, it was 43% more profitable to grow lettuce in the open field than in the high tunnel, while in contrast, high tunnel-grown tomato was three times more profitable than open-field tomato production.

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Fairuz A. Buajaila, Pinki Devi, and Carol A. Miles

Many small-scale vegetable growers in the United States who graft their own vegetable transplants use healing chambers inside a greenhouse to heal their grafted plants. Under these conditions, light and relative humidity (RH) can fluctuate during the healing process, and growers need more research-based information regarding the impact of these factors on the survival of grafted transplants. To address this need, this study investigated the effect of different targeted levels of light (0%, 25%, and 50%) and RH (50% and 100%) (six combinations) in a small-scale healing chamber within a greenhouse, where the healing chamber was opened for increasing periods of time for 8 days, at which time plants were fully exposed to greenhouse conditions. The survival and growth of self-grafted eggplant (Solanum melongena), pepper (Capsicum annuum), and tomato (Solanum lycopersicum) were measured up to 25 days post grafting. Percent light in the closed healing chambers was similar for the 50% and 100% RH levels of each light treatment. When the healing chambers were closed, compared with the greenhouse, there was 0.1% light in the 0% light treatments, 25% light on average in the 25% light treatments, and 43% light on average in the 50% light treatments. On days 2 to 5 after grafting, when chambers were opened up to 1 hour, average RH in the healing chambers was 96% to 98% for the 100% RH treatments, and was 42% to 49% for the 50% RH treatments. On days 6 and 7, when chambers were opened for 3 to 8 hours, RH was 79% to 82% for the 100% RH treatments, and was 39% to 46% for the 50% RH treatments. Survival of grafted plants following healing was greatest when the healing chamber treatment was 100% RH and 50% or 25% light (95% and 90% survival, respectively), and plant survival with these two treatments did not significantly decline from 11 to 21 days after grafting, indicating plants were fully healed and acclimated when they were removed from the healing chambers on day 8. At 22 to 25 days following grafting, plants healed with 100% RH and 50% or 25% light had greater plant height, number of leaves per plant, and stem diameter than plants healed in the other light and RH combinations. SPAD reading and nitrate-nitrogen of fresh petiole sap were unaffected by any of the healing treatments tested in this experiment, or by crop type. Tomato and pepper had 14% greater survival rates on average than eggplant at all measurement dates, while tomato tended to have greater plant growth, followed by eggplant and pepper. Additional research is needed to improve survival of grafted eggplant.

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Jeremy S. Cowan, Debra A. Inglis, and Carol A. Miles

Three potentially biodegradable plastic mulch products, Mater-bi®-based black film (BioAgri), experimental polyhydroxyalkanoate film (Crown 1), and experimental spunbonded polylactic acid fabric (SB-PLA-11), were evaluated over two broccoli (Brassica oleracea var. italica) growing seasons to determine deterioration before and after soil incorporation. Pretillage mulch deterioration was evaluated in both growing seasons by rating the percent visual deterioration (PVD). Crown 1 had the greatest PVD throughout the study (P ≤ 0.05) and BioAgri also had significant pretillage deterioration. SB-PLA-11 showed no appreciable deterioration based on PVD (<1.3%) in either growing season. Postincorporation mulch deterioration was measured for 13 months after rototilling at the end of the first growing season. The average fragment area of all mulch products decreased over time after soil incorporation. The number of postincorporation mulch fragments initially increased for all mulch products, with Crown 1 and BioAgri reaching maximum fragment counts 132 and 299 days after incorporation, respectively. As the number of fragments declined, the average area of fragments did not change, suggesting that a threshold fragment size may exist at which biodegradation accelerates. At the end of the study period, 397 days after soil incorporation, Crown 1 and BioAgri had deteriorated 100% and 65%, respectively; whereas SB-PLA-11 showed very little deterioration.

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Kristy A. Ott-Borrelli, Richard T. Koenig, and Carol A. Miles

Leafy green vegetables such as lettuce (Lactuca sativa), Asian greens (Brassica spp.) and spinach (Spinacia oleracea) have a tendency to accumulate high concentrations of potentially harmful nitrate–nitrogen (NO3-N). It would be advantageous for growers to have rapid and inexpensive methods to accurately measure plant tissue NO3-N to make fertility and harvest management decisions for these crops. This study compared fresh sap expressed from whole leaves and analyzed with a Cardy meter with the analysis of dry leaf tissue extracts analyzed with a benchtop ion selective electrode (ISE) and an automated colorimetric method for determining NO3-N concentration. Results from ISE and colorimetric analysis of the same dry leaf tissue extracts had a strong relationship (r 2 = 0.92). The ISE was relatively easy to operate and affordable, suggesting it is an adequate substitute for automated colorimetric analysis of dry plant tissue extracts. Results of fresh whole leaf sap analyzed with the Cardy meter showed a poor relationship with dry leaf tissue extracted and analyzed using the ISE (r 2 = 0.25) or with colorimetric analysis (r 2 = 0.21). When fresh whole leaf sap was diluted 1:1 with aluminum sulfate [Al2(SO4)3] to adjust for potential matrix effects, there was still a relatively poor relationship (r 2 = 0.41) between the diluted sap samples analyzed with a Cardy meter and the dry leaf tissue extracted and analyzed with the ISE. When the same dry leaf tissue extracts were analyzed with the Cardy meter and the ISE, the results related well (r 2 = 0.96). As a result of tissue processing and/or instrument differences, Cardy meter analysis of sap expressed from whole leaves was not comparable to ISE or colorimetric analyses of dry leaf tissue extracts for leafy green vegetables.

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Travis Robert Alexander, Jacqueline King, Andrew Zimmerman, and Carol A. Miles

In this study, four cider apple (Malus ×domestica) cultivars, Brown Snout, Dabinett, Kingston Black, and Yarlington Mill, were collected from four orchards, two in northwest Washington and two in central Washington, to compare juice quality characteristics. Northwest Washington has a cool, humid summer climate (16.0 °C on average during this study) and is the origin of the state’s cider apple industry, while central Washington has a hot, dry summer climate (22.1 °C on average during this study) and is the center of the state’s dessert apple industry. Each year from 2012 to 2015, fruit of the four cultivars were harvested and stored at each orchard until they were collected. Fruit were pressed and the juice analyzed for five quality characteristics important to cider making: soluble solids concentration [SSC (%)], specific gravity (SG), pH, titratable acidity [TA, malic acid equivalent (g·L−1)], and tannin [tannic acid equivalent (%)]. Harvest dates and climate data were recorded annually for each orchard location. There were no significant differences in any of the juice quality characteristics due to region and no significant interaction of region, cultivar, and/or year. Results did show, as expected, a significant difference in all five juice characteristics due to cultivar. ‘Brown Snout’, ‘Dabinett’, and ‘Kingston Black’ were higher in SSC and SG than ‘Yarlington Mill’; ‘Dabinett’ had the highest pH and lowest TA while ‘Kingston Black’ had the lowest pH and highest TA; and tannin was highest in ‘Yarlington Mill’ and lowest in ‘Kingston Black’. There was also a difference in SG and tannin due to year; SG was lowest in 2013 while tannin was highest in 2012. The difference in SG from year to year may be a result of variable year-to-year storage time at each orchard before collection of fruit. The difference in tannin from year to year was likely due to climatic variation over the four years of this study. On average, growing degree days (GDD) increased 10% and chilling hours (CH) decreased 10% from 2012 to 2015 in both regions. Classification of the four cultivars included in this study differed from historical records at the Long Ashton Research Station (LARS) in England; in the current study, the four cultivars exhibited tannin levels below 0.20% and would not be classified as bitter, unlike their historical classification at LARS. Results from this study indicate that variations in juice quality characteristics occur between cultivars as expected and occur within a cultivar from year-to-year, but for the four cultivars included in this study variations did not occur due to production region in Washington.

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Travis Robert Alexander, Jaqueline King, Edward Scheenstra, and Carol A. Miles

In this 2-year study, ‘Brown Snout’ specialty cider apples (Malus ×domestica) that had been hand harvested or machine harvested with an over-the-row shake-and-catch small fruit harvester were ambient stored (56 °F mean temperature) for 0, 2, and 4 weeks to evaluate yield, fruit damage, yield loss, and juice quality characteristics. The average yield (pounds per acre) of fruit picked and retained by the mechanical harvester was 74% that of the hand-harvest yield and 81% that of the hand-harvest yield when fruit that fell out of the harvester was included in the machine-harvest yield. Percent fruit bruised and cut were greater for machine harvest (97.5% and 25.5%, respectively) than for hand harvest (47% and 0.5%, respectively), on average for 2014 and 2015. Yield loss to rot was greater for machine harvest than for hand harvest, and increased for both methods over time; percent rot doubled from 2 to 4 weeks storage for machine harvest (22% to 41%), and while negligible, tripled from 2 to 4 weeks storage for hand harvest (0.7% to 2.1%). Juice quality characteristics did not differ due to harvest method, but did differ due to year and storage time. Soluble solids concentration [SSC (%)] and specific gravity (SG) did not change due to storage in 2014, but in 2015, SSC and SG were greater on average for 2 and 4 weeks storage duration (15% and 1.062, respectively) than at harvest (13.31% and 1.056, respectively). Titratable acidity (grams per liter malic acid) decreased in 2014 from 2.98 g·L−1 at harvest to 2.70 g·L−1 on average for 2 and 4 weeks storage duration, but did not differ due to storage in 2015. Tannin [tannic acid equivalent (%)] was unchanged in 2014 from harvest to 4 weeks storage, but increased in 2015 from 0.16% at harvest to 0.19% by 4 weeks storage. These results indicate that harvest efficiency could be improved with some engineering modifications of the over-the-row mechanical harvester and training modifications for the trees. A comparison of the aromatic and phenolic contents of mechanically harvested and hand-harvested ‘Brown Snout’ would be a valuable next step in evaluating shake-and-catch mechanical harvest technology for cider apple production.

Open access

Abigail Attavar, Lydia Tymon, Penelope Perkins-Veazie, and Carol A. Miles

Grafting is used in watermelon [Citrullus lanatus (Thunb.) Matsum and Nakai] production as a means to combat soilborne diseases. To support the development of new rootstock cultivars in the United States, we screened cucurbit germplasm accessions for resistance to verticillium wilt (caused by Verticillium dahliae Kleb.) and for compatibility as watermelon rootstocks. Screening was done using a field naturally infested with V. dahliae [5 and 7.5 colony-forming units (cfu)·g−1 soil in 2017 and 2018, respectively], and plants were inoculated at transplanting (1.5 and 104 cfu of V. dahliae per plant in 2017 and 2018, respectively). In 2017, 56 germplasm accessions from three genera commonly used as rootstocks, Cucurbita, Lagenaria, and Benincasa, were sourced from the U.S. Department of Agriculture (USDA) National Plant Germplasm System and area under the verticillium wilt (disease) progress curve (AUDPC) values ranged from 16 to 397. The 14 accessions with the lowest AUDPC values and good germination (>40%) were used as rootstocks along with the commercial rootstock cv. Tetsukabuto (control), and all were grafted with watermelon cv. Secretariat as the scion in 2018. Grafted plant survival rate was greatest for ‘Tetsukabuto’ (90%) and the accession PI 381840 (L. siceraria) (89%), and ranged from 22% to 85% for all other accessions. All grafted treatments that produced mature fruit in 2018 tended to flower at the same time as nongrafted ‘Secretariat’, with first male and female flowers occurring in 45 to 50 days and 44 to 51 days after transplanting, respectively. There were no significant differences in AUDPC values due to grafting or when accessions were compared with ‘Tetsukabuto’. Only six accessions produced mature fruit when grafted with ‘Secretariat’, indicating they were compatible for watermelon grafting. Fruit weight and number as well as total soluble solids, pH, lycopene content, rind firmness and thickness, and dry matter content were similar for all accessions and ‘Tetsukabuto’ grafted on ‘Secretariat’. Only fruit flesh firmness differed and was highest for ‘Secretariat’ grafted on ‘PI 491316’ and lowest for ‘Secretariat’ grafted on ‘PI 49174’. The six verticillium wilt-tolerant accessions that were compatible with watermelon could potentially be used as rootstocks or as sources of genetic resistance in rootstock breeding programs.

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Carol A. Miles, Jacqueline King, Travis Robert Alexander, and Edward Scheenstra

Little information exists on the bloom and fruit characteristics of cider apple (Malus ×domestica) cultivars grown in the United States for the juice and alcoholic beverage markets. In this study, a total of 17 cider apple cultivars, including 4 American, 9 English, and 4 French, plus 1 Danish standard dessert apple cultivar (Red Gravenstein, Worthen strain) commonly used for cider, all grown in northwest Washington, were evaluated from 2000 to 2015 for commercially relevant traits. Trees were rated each year and the cultivars were categorized accordingly by relative bloom time, bloom habit, and productivity. The mean full bloom (FB) date of the 18 apple cultivars evaluated ranged from 25 Apr. to 25 May, with 6 cultivars categorized as early season bloomers, 9 as midseason, and 3 as late season. The mean bloom density (BD) rating (measured on a scale of 1–5) for all cultivars was (mean ± sd) 3.8 ± 0.6 (moderate bloom), with the bloom habit of 1 cultivar categorized as biennial, 11 as consistent, and 6 as strongly consistent. The mean productivity rating (measured on a scale of 1–5) for all cultivars was 2.9 ± 0.6 (light fruiting), with the productivity of 4 cultivars categorized as biennial, 10 as consistent, and 4 as strongly consistent. The mean fruit diameter of the 18 apple cultivars was 2.7 ± 0.4 inches (medium sized), with the fruit size of 2 cultivars categorized as small-fruited, 15 as medium-fruited, and 1 as large-fruited. For the 18 cultivars, the mean tannin and titratable acidity (TA) were 0.20% ± 0.14% and 0.54% ± 0.28%, respectively, and using the English cider apple classification system of juice type, 4 of the cultivars were classified as bittersweet, 1 as bittersharp, 3 as sweet, and 10 as sharp. Three of the cultivars had tannin content lower than what was historically recorded at the Long Ashton Research Station (LARS) in Bristol, England, for those same cultivars. The mean specific gravity (SG) of the 18 cultivars was 1.052 ± 0.007, the average predicted alcohol by volume (ABV) was 6.9% ± 0.9%, and the mean pH was 3.68 ± 0.39. Classification of three cultivars in northwest Washington, based on juice characteristics, differed from their historical classification in England, likely because of differences in climate and management. Only cultivars Golden Russet (sharp), Grimes Golden (sharp), and Yarlington Mill (sweet, but borderline bittersweet) were strongly consistent in productivity, but none produced high levels of tannin, whereas only cultivars Bramtot (bittersweet), Chisel Jersey (bittersweet), and Breakwell Seedling (bittersharp) were consistent in productivity and produced high levels of tannin.