George E. Boyhan

Five-Year Evaluation of Short-Day Onion Varieties

Short-day onion (Alliium cepa L.) production is important in many regions with mild winters. Onions are particularly important in southeastern Georgia, where Vidalia onions are produced. These onions represent the vegetable with the greatest farm gate value in the state and variety trials are an important part of University of Georgia research for this industry. Short-day onion variety trials were conducted in southeastern Georgia from 2004 to 2008. Data collected and evaluated included total yield, graded yield, harvest date, number of seed stems, number of doubles, number of onion centers, bulb shape, disease incidence, bulb pungency, and storability in controlled-atmosphere (CA) storage. Not all data were collected in all years. There were between 35 and 68 entries in the trials. Sixteen varieties appeared in all 5 years. Total yields were from ˜23,000 to ˜72,000 kg•ha−1. Marketable yields ranged from 23% to 99% of total yield depending on variety and year. Average marketable yield for the 5 years ranged from 61% to 82%, with the 2006–2007 season having the best average marketable yield. In general, later maturing varieties had lower marketable yields because of bacterial diseases such as sour skin, caused by Burkholderia cepacia Palleroni & Holmes 1981 ex Burhkolder 1950, that developed as temperature increased. Seed stems (flowering) and doubled bulbs differed over years. Both are believed to occur because of a combination of environmental and varietal effects. Average percentage marketable onions, after removal from CA storage, ranged from 48% to 82% depending on year. Botrytis neck rot, caused by Botrytis allii (Munn) Yohalem, was the primary disease affecting marketability post-CA. Onions held for 2 weeks after removal from CA storage under ambient conditions could see a reduction in average marketable onions from 17% to 33% depending on year.

Breeding for Organic and Sustainable Production

Plant breeding has been with humankind since the beginning of civilization. Modern plant breeding, however, is a relatively recent development—just over 100 years. Recently with the increase in popularity of organic farming and farm sustainability, there is a growing interest in breeding for organic or low-input farming systems. These endeavors are in their earliest stages bringing to bear both traditional and modern plant breeding techniques to address the specific needs of organic and low-input farming. This chapter gives an overview of these early efforts, some of the techniques involved, as well as some of the social and philosophical concerns with breeding and crop improvement for low-input farming.

Effect of Postharvest Chemical Treatments, Heat Curing, and Refrigerated Storage on Marketability of Short-day Onions

Vidalia onions (Allium cepa) are very susceptible to infection from pathogens and diseases compared with other types of onions. Botrytis neck rot (BNR) (Botrytis allii) is the most common and destructive storage disease, whereas sour skin (Pseudomonas cepacia) can cause significant bacterial losses, particularly, for late season cultivars. The objective of this study was to assess the effects of different fungicide and bactericide drenches on marketability of Vidalia onions using the cultivar Savannah Sweet grown, harvested, and graded for high-quality onions. Six different fungicide treatments were evaluated, including fludioxonil at two different rates, fluopyram and pyrimethanil in combination, and pyraclostrobin and boscalid in combination with a water-only and an untreated entry. In addition, four different bactericide treatments were evaluated, including copper hydroxide and copper sulfate pentahydrate with a water-only and untreated control. Treatments were applied by drenching the onion bags with 1 gal of solution at the desired concentration. Onions treated with fungicide were inoculated with the pathogen that causes BNR, whereas the bactericide treatments were inoculated with the pathogen that causes sour skin by placing a single inoculated bulb into each bag. Half of the bags were heat-cured for 48 hours and all of the onions were stored immediately under refrigerated conditions at 34 to 36 F for 2 or 4 months. Bactericide treatments were not heat-cured the second year of the study. Onions were evaluated after 1 and 14 days of shelf life. For both years, all the fungicide applications were effective with more marketable onions compared with the controls. Fludioxonil, fluopyram/pyrimethanil, and boscalid/pyraclostrobin had the highest percentage of marketable onions compared with the water or untreated controls. Fluopyram/pyrimethanil and boscalid/pyraclostrobin fungicides had significantly higher percentage of marketable onions than the controls but were similar to the low rate of fludioxonil. Bactericide applications were not effective in reducing losses when compared with the controls.

High Tunnel and Field System Comparison for Spring Organic Lettuce Production in Georgia

High tunnels may help mitigate unfavorable climate and weather on lettuce (Lactuca sativa L.) production leading to greater yields and quality, yet information for using these systems in the Southeast region is lacking. This study evaluated the effect of high tunnels and three planting dates (PDs) (earlyMarch, late-March, andmid-April) on spring organic lettuce production. A 25% to 36% increase in marketable fresh weight for butterhead and romaine lettuce, respectively, was observed under high tunnels compared with the field in 2016, but there was no difference among the two growing systems in 2015. High tunnel lettuce was harvested ’2 to 7 days earlier than in the field in 2015 and 2016, respectively. Pest and disease pressure (e.g., Sclerotinia sclerotiorum) as well as the incidence of physiological disorders (i.e., bolting, tip burn, and undersized heads) were similar between the two systems indicating that our high tunnel system did not provide a benefit for these issues. High tunnel air temperatures were ’3 to 5 8C greater on the coldest mornings and only 1 8C greater on the warmest days compared with the field. Average relative humidity (RH), leaf wetness, and light levels were all lower under the high tunnels. Our results indicate that high tunnels can help increase the production of spring organic lettuce in Georgia, but that the advantage may depend on yearly weather conditions. Lettuce (Lactuca sativa L.) is a popular, cool-season vegetable with a total U.S. production value of nearly

Effects of Nitrogen, Phosphorus, and Potassium Rates and Fertilizer Sources on Yield and Leaf Nutrient Status of Short-day Onions

1.5 billion in 2013 (AgMRC, 2015). From 2005 to 2011, the amount of U.S. farmland allocated to the organic lettuce production increased from 4% to 12%, was worth

Vidalia Onions-Sweet Onion Production in Southeastern Georgia

264 million in sales, and was the number one organic crop commodity (ERS, 2013; USDA, 2015). Currently, most of the organic lettuce is produced in California and Arizona (Toland and Lucier, 2011). Georgia can grow lettuce; however, as is typical of the Southeast region, unpredictable weather patterns, heat, and humidity canmake crop production challenging. Alternative production techniques such as high tunnels may help growers mitigate unfavorable climate and weather conditions leading to increased lettuce production in the region. This would help meet growing demands for local produce, organic produce, or both (USDA, 2015). The optimum temperatures for growing lettuce range from 7 C/16 to 21 C (nighttime/daytime) (AgMRC, 2015; Sanders, 2001). In addition, lettuce requires a minimum of 15 mol·m·d of light (Korczynski et al., 2002; Runkle, 2011; Waycott, 1995). Given these criteria, Georgia is conducive to growing lettuce about 9 months out of the year (e.g., fall through spring). Lettuce production during late spring and early summer can be difficult as average daily temperatures may quickly or unpredictably rise above the preferred range. Warm temperatures may result in the induction of physiological disorders, such as bolting, bitterness, and tipburn (Prohens-Tom as and Nuez, 2008). In addition, it is predicted that the region will experience a growing number of days with temperatures greater than 35 C and a steady increase in extreme precipitation events (EPA, 2016; Kunkel et al., 2013). Precipitation and related periods of high RH may increase the incidence of fungal diseases, soilborne diseases or both, whereas strong winds can tear and abrade lettuce leaves. Precipitation events before or during the crop season can also delay field preparation activities. Management techniques such as high tunnels that increased crop protection and the ability to manipulate the crop microenvironment have the potential to increase yield and quality of lettuce production in Georgia. High tunnels (i.e., hoop houses) are unheated, passively ventilated greenhouse-like structures which can provide some protection to crops from adverse weather events (i.e., cold, precipitation, wind, soil splash back, etc.), selected pests and diseases, or season extension (Alves et al., 2014; Borrelli et al., 2013; Carey et al., 2009; O’Connell et al., 2012; Rogers and Wszelaki, 2012). Early or late season extension may help growers receive premium prices (Alves et al., 2014; Sydorovych et al., 2013) and attract new customers. Furthermore, farmers that use high tunnels may be able to obtain a greater yield or higher quality product by manipulating the microenvironment compared with the field. High tunnel benefits and management practices are often regionally specific because of local climate characteristics and market preferences. The following research efforts have been executed by others and provided a basis for our project goals which focus on challenges for high tunnel lettuce production in warm, humid regions. An organic high tunnel lettuce study conducted in Tennessee (TN), Texas, and Washington (WA) evaluated season extension; they observed greater bolting incidence in the field compared with under high tunnels in the regions where temperature fluctuations were more frequent (Wallace et al., 2012). A summer lettuce study conducted in Kansas found lower bolting rates when shadecloth was used in conjunction with high tunnels compared with the field but recommended further investigations (Zhao and Carey, 2009). A lettuce study conducted in South Carolina (SC) evaluated the best PDs for yield and quality in the field (Dufault et al., 2006). These researchers observed increased bolting when lettuce was planted in September, October, February, and March, but bolting rates were not different with PDs from November through January. Cultivar choice also influenced days to harvest and yield in this SC study (Dufault et al., 2006). A study conducted in WA determined that winter high tunnel production of Asian greens, spinach, and lettuce was possible, but could be optimized with more informed cultivar selection, seeding dates, and planting densities (Borrelli et al., 2013). A study conducted in North Carolina to evaluate the performance of organic tomatoes in high tunnels suggested that with proper management, one can achieve better yields, increased fruit Received for publication 12 July 2017. Accepted for publication 5 Oct. 2017. We are grateful for funding provided by a private foundation that wishes to remain anonymous and by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award #GS15-147 through the Southern Sustainable Agriculture Research and Education program. We also like to acknowledge the assistance of Hannah Bundy and the peer reviewers. Corresponding author. E-mail: soco@uga.edu. This is an open access article distributed under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/). 1518 HORTSCIENCE VOL. 52(11) NOVEMBER 2017 quality, and provide season extension opportunities (i.e., early spring fruit) for high-value horticultural crops (O’Connell et al., 2012). Another high tunnel tomato study in TN found that high tunnel tomatoes had increased marketability and size and benefitted from earlier PDs compared with the field (Rogers and Wszelaki, 2012). The Southeastern region’s mild winters present opportunities to grow crops from fall through spring seasons under high tunnels as they may help protect crops from abiotic stressors including cold temperatures, precipitation, wind, etc. However, managing excessive heat during late spring through early fall presents a challenge for growing cool-season crops such as lettuce under high tunnels. Therefore, the goals of this study were to evaluate the effect of high tunnels and PD on early to late spring organic lettuce production in Georgia. Objectives included a comparison of 1) butterhead and romaine lettuce yields grown under high tunnels and the field, 2) butterhead and romaine lettuce yields among three spring PDs, and 3) microenvironmental data for both types of production systems. Materials and Methods Site characteristics and history. The experiment was conducted during the spring of 2015 and 2016 at the Durham Horticulture Farm, located in Watkinsville, GA (lat. 33 53#12.804

ADAPTION OF A SPECTROPHOTOMETRIC ASSAY FOR PUNGENCY IN ONION TO A MICROPLATE READER

N, long. –083 25#9.876

Genotype × Environment Interaction and Stability Analysis for Watermelon Fruit Yield in the United States

W and elevation 236 m). The plant hardiness zone for the site is 8a (USDA, 2012). The soil type at the site was a well-drained Cecil sandy clay loam subsoil (CYB2) that has been eroded overtime so the plow layer now extends into the red sandy loam subsoil (USDA, 1968). Soil analysis in high tunnel and field areas indicated a pH of 6.6 and a composition of 67% sand, 15% silt, and 18% clay before the experiment (Agricultural & Environmental Services Laboratories, Athens, GA). The project site has been certified organic since 2012, and all agricultural production methods were performed under USDA regulations 7 U.S.C. §6507. High tunnel design. Two commercial-size gothic-shaped high tunnels (Atlas Greenhouse Inc., Alapaha, GA) (29.3 · 9.1 · 3.7 m) and a comparative field area (45.7 · 9.1 m) in close proximity to the high tunnels ( 5 m to the north) were used for the study. High tunnels were oriented east–west, to be perpendicular to the prevailing winter winds at the site. The field was also oriented east– west. High tunnels had inflated double polyethylene film roofs that comprised 152.4-um plastic with 90% light transmission, 25% light diffusion, and 95% blocking of ultraviolet wavelengths <350 nm (SunView 4; POLY-AG. Corp., San Diego, CA). The end walls comprised 8-mm thick polycarbonate. Automated 1.83 m tall z-lock drop-down side curtains constructed from 304.8-um weave fabric were used. In both years, before our experiment, the field area was planted with an oat cover crop (Avena sativa) at a rate of 112 kg·ha (Welter Seed and Honey Co., Onslow, IA) and high tunnel areas planted with a variety of Brassicaceae cash crops across the 2014–16 Fall/Winter seasons before lettuce. Transplant management. Butterhead and romaine lettuce plants were grown in an organic greenhouse with air temperature set points at 13 C/21 C (nighttime/daytime). Seeds were sown into six-pack trays (4 · 4