Project Abstract

<p>              <b>ABSTRACT</b><br></p><p> Despite the initial slow adoption of high tunnel production systems, Florida grower interest has increased in recent years. High tunnel production is generally used for achieving season extension, and high tunnel research has yet to be conducted in Florida, where climatic conditions may transform the primary function from passive solar heating to a variety of other applications. Tomato grafting has shown the potential to increase yields due to enhanced vigor, with the ability to reduce biotic and abiotic stress factors. Some of these factors may have an increased presence in the high tunnel production system, therefore increasing the potential benefits of grafting. Enhanced plant vigor from grafted plants may increase the potential benefits of high tunnel season extension. A side-by-side comparison of open field and high tunnel organic tomato production found grafting and high tunnel benefits were cumulative in many growth, yield, and fruit marketability metrics. Additionally, grafting reduced root-knot nematode soil population density, root galling severity, and the occurrence of blossom end rot, all of which demonstrated the potential to have increased levels in the high tunnel production system. <br></p>

Project Overview

<p><b>1.1 INTRODUCTION</b>&nbsp;</p><p> Sustainable, Organic, and Local Agriculture Sustainable agriculture involves production practices that are profitable over the longterm, improving soil, water, and air quality, and increasing the quality of life for the farmers and their communities (SARE, 2010). An important aspect of increasing the quality of life in both rural and urban communities is addressing the challenge of food security, including food availability, safety, and nutrition (Ceglie et al., 2016). Together, organic and local production systems have the potential to contribute to the fulfillment of sustainability and food security objectives. Economic profitability is the bottom line for evaluating the viability and potential sustainability of any cropping system. While many short-term trials indicate organic yields are inferior to conventional yields, long-term studies have demonstrated yield deficits may be overcome by increasing soil fertility. Results from Pimentel et al. (2005) validated a 5-year period during which organically managed yields were less than the conventional control, whereas subsequent yields were not significantly different. Drinkwater et al. (1998) also confirmed long-term yields and economic profitability may be comparable between conventionally and organically managed systems. However, average organic:conventional yield ratios vary by crop, and a meta-analysis study by Seufert et al. (2012) estimates tomato at 0.80. Innovative and integrated tools are therefore needed to increase productivity of organic tomato production systems. Increasing soil, water, and air quality, in addition to a focus on soil fertility and yield, are important aspects of land stewardship and system sustainability. Because organic agriculture relies on many practices that are based on ecological cycles, it minimizes the environmental&nbsp; impact, preserves long-term sustainability of soil, and minimizes the use of non-renewable resources (Gomiero et al., 2011). Consequently, long-term studies have reported higher soil organic matter content and reduced soil erosion with organic management (Pimentel et al., 2005; Reganold et al., 1987; Tilman, 1998). This results in increased soil fertility and quality and reduced water and air quality degradation by reduction of nitrate leaching and nitrous oxide emissions (Drinkwater et al., 1998; Petersen et al., 2006; Stalenga and Kawalec, 2008). While increasing the quality of life for farmers and their communities is difficult to quantify, it undoubtedly includes measurable attributes such as increasing the availability of safe and nutritious foods. Food safety of fresh produce consists of two main facets: risks of microbial pathogens and pesticide residues. Food pathogens are of highest concern, as a single contamination may result in an outbreak leading to multiple consumer illnesses and even deaths, whereas the consumer risk of pesticide residues is typically long-term, low-dose exposure. Some suggest organic produce may have higher microbial risks, due to the increased use of manures and lack of effective food sanitizers (Stephenson, 1997). While conceptually this may be true, multiple reviews indicate organic produce does not have greater microbial pathogen risks than conventional produce (Bourn and Prescott, 2002; Garcia and Teixeira, 2016; Lücke 2017). Pesticide residues, on the other hand, may be reduced in organic production systems. A review by Baker et al. (2002) reported organic produce consistently had about one-third the amount of pesticide residues of conventional produce. Smith-Spangler et al. (2012) characterized pesticide residues contamination risk as 30% lower for organic produce, correlating with findings from Baker et al. (2002), yet noted that risk differences in exceeding the allowable limits were small. This is due to organic pest management relying on the promotion of beneficial biotic processes, with practices combining a multitude of community and ecosystem characteristics in order to minimize the amount of insecticide and fungicide inputs (Letourneau and Goldstein, 2001). With tomato listed as the second highest vegetable on the Environmental Working Group’s 2018 Dirty Dozen™ list, identifying tools to increase the profitability and sustainability of organic tomato production is crucial for providing consumers safe and nutritious foods (Lunder, 2018). The reduction of pesticides not only benefits consumers, but reduces potential hazards and therefore increases quality of life for farmers, their workers, and their communities. Whether or not organic produce has greater mineral nutrients or phytochemicals has received mixed reviews. Bourn and Prescott (2002) pointed out the extreme difficulty in comparative studies due to the wide range of factors that may influence crop composition, and the compounding factors that may occur with comparison methods. Published literature reviews have concluded that there is no consistent evidence that conventionally and organically grown foods differ in nutrient or phytochemical content (Bourn and Prescott, 2002; Smith-Spangler et al., 2012). On the other hand, Hunter et al. (2011) reviewed 33 studies and 908 micronutrient comparisons and identified that total micronutrient content and mean percent difference in micronutrient content were higher in organic produce, yet absolute levels of individual micronutrients were only significantly greater for phosphorous, while no differences in phytochemical levels were found. Human health studies comparing organic and conventional diets are also inconclusive (Smith-Spangler et al., 2012).&nbsp;</p><p> <b>Importance and Limitations of Florida Organic Tomatoes</b>&nbsp;</p><p>Tomato (Solanum lycopersicum) is considered a high value crop, with the potential to generate large revenues per unit area (O’Connell et al., 2012). Organic, open field tomato production ranks second for organic vegetables and ninth for all organic products, totaling $175 million in sales, with an additional $18 million grown under protected structures (USDA-NASS, 2014, 2017). Organic field tomato production grew approximately 102% between 2015 and 2016, the most of any of the top 10 organic commodities (USDA-NASS, 2017). Increased production indicates an increasing consumption trend, which may be due to an increase in consumers’ health conscious diets. Tomatoes are the major dietary source of lycopene, an antioxidant that has been linked to improved heart health and cancer prevention (Giovannucci, 1999; Karppi et al., 2012a, 2012b). Tomato is also considered a good source of dietary fiber, vitamin A, vitamin C, potassium, vitamin K, and folate (B9) (Bjarnadottir, 2015). However, tomato nutrient composition may be affected by ripeness stage at harvest, and, therefore, local tomatoes may be nutritionally different from those that are subject to long-distance shipping and intensive postharvest handling. Ascorbic acid, reducing sugars, pH, dry matter content, lycopene, β-carotene, and total carotenoids generally increase with increasing ripeness at harvest (Kader, 1977; Raffo et al., 2002). Research is limited, however, and exploration is needed to understand how direct marketing preharvest and postharvest practices affect tomato fruit quality. Tomato production in subtropical Florida has many challenges. High humidity, prolonged dew, and frequent rainfall often result in higher disease incidence and severity than in other climates. During mild winters, some agricultural pests remain active throughout the winter, and may result in earlier pest outbreaks during the subsequent growing season (Gomez and Mizell, 2015). High summer temperatures in subtropical Florida can lead to poor fruit color, fruit damage (sunscald), and discolored pericarp (Hochmuth, 2015). Eventually, high summer temperatures and humidity lead to poor pollination and reduced fruit set, limiting the production season. Alternatively, cool early spring and late fall temperatures commonly found in subtropical Florida may also negatively impact fruit quality, increasing cat-facing, yellow shoulder disorder, or in extreme cases cause fruit chilling injury (Hochmuth, 2015). Finally, spring temperature fluctuations are often rapid and drastic, inhibiting plant acclimatization and increasing plant stress. All these limitations require Florida conventional and organic tomato growers to employ innovative production practices to maximize plant health and productivity in order to achieve long-term sustainability. Grafting and low-cost high tunnel technologies may benefit Florida tomato growers in achieving this goal, and these technologies may be critical for organic growers due to the limited number of tools available in organic production.&nbsp;</p><p><b>Tomato Grafting&nbsp;</b></p><p>Tomato grafting has the potential to increase crop vigor, as measured by an increase in stem diameter, leaf area, aboveground biomass, and root biomass, which may be measurable as early as 1 month after grafting (Öztekin and Tüzel, 2017; Rahmatian et al., 2014). Tomato marketable and total yields, as well as average fruit weight, may increase compared to non- grafted fruit, although the increase in yield is typically attributed to an increase in fruit number (Barrett et al., 2012a; Djidonou et al., 2013a; Rahmatian et al., 2014; Rivard et al., 2012; Savvas et al., 2010). With appropriate rootstock selection, grafting has the potential to increase waterand nitrogen-use efficiency, and to improve tomato salinity tolerance (Djidonou et al., 2013a, Di Gioia et al., 2013). Grafting may also help reduce blossom end rot, the most common preharvest tomato physiological disorder (Fan et al., 2011; Krumbein and Schwarz, 2013). Tomato grafting often targets the suppression of diseases caused by soil-borne pathogens, including root-knot nematodes (Meloidogyne spp.), bacterial wilt (Ralstonia solanacearum), Fusarium wilt (Fusarium oxysporum f. sp. lycopersici), Fusarium crown and root rot (F. oxysporum f. sp. radicis-lycopersici), Verticillium wilt (Verticillium spp.), southern blight (Sclerotium rolfsii), damping off (Rhizoctonia solani), and corky root rot (Pyrenochaeta lycopersici), while variable amounts of foliar pathogen suppression have also been found (Guan et al., 2012; King et al., 2008; Rivard et al., 2012; Rivard and Louws, 2008; Yamakawa, 1983). The grafting benefits may be especially advantageous for organic production, in which nutrient limitations, the potential rise of salinity (due to high application rates of organic amendments), and high disease incidence and severity are more likely than in conventional production systems (Rivard and Louws, 2008). In addition to suppressing biotic stresses and improving plant growth, grafting has also demonstrated benefits for alleviating water and temperature stresses. Flooding reduces oxygen levels at the soil-root interface, reducing growth and yields of flood sensitive crops (Schwarz et al., 2010). Drought stress, on the other hand, decreases plant growth due to decreased cellular water potential and stomatal conductance (Kumar et al., 2017). Grafting tomato onto eggplant rootstock has been identified as a tool to mitigate detrimental flooding effects, while some tomato rootstock cultivars have also demonstrated similar effectiveness (Bahadur et al., 2015; Wang and Chen, 2017). Furthermore, a review by Kumar et al. (2017) highlighted drought stress tolerance may be achieved with selected rootstock cultivars. Low temperatures limit water and nutrient uptake, reducing plant growth and development and potentially causing wilt and necrosis (Rivero et al., 2003a). Grafting mitigation of these effects is highly rootstock dependent, with high-altitude S. habrochaites and interspecific hybrids (S. lycopersicum × S. habrochaites) having demonstrated consistent success (Schwarz et al., 2010; Venema et al., 2008). High temperatures increase phenolic production in tomato vegetative tissue as a stress mitigation response, and drastic biomass reductions have been identified at air temperatures between 25 and 35 °C (Rivero et al., 2003b). Grafting reduces the increase in phenolic production and correspondingly lessens the reduction in plant biomass (Rivero et al., 2003b). While water and temperature stress mitigation by grafting has been demonstrated, grafted and stressed plants either under-performed compared with non-stressed plants or were not compared. Despite the benefits of grafting as a cultural management tool to address many different site-specific challenges faced by Florida organic tomato growers, other growing constraints may not be adequately overcome without an integrated approach. Other tools are needed to mitigate the detrimental effects of temperature extremes, drastic temperature fluctuations, and heavy rainfall experienced in subtropical Florida. Production limitations for implementing grafting technology are primarily based on cost. For example, grafted and non-grafted tomato plants range from $0.59 to $0.78 and $0.13 to $0.17, respectively, in subtropical regions from Florida to eastern North Carolina, although heating costs can increase costs in cooler climates (Barrett et al., 2012b; Djidonou et al., 2013b; Rivard et al., 2010a). Additionally, opportunity costs are increased by grafting, as about 7 to 10 19 days are added to the transplant production cycle (Lee, 1994; Rivard and Louws, 2006). Economic analyses using a partial budget method typically omit field production costs due to the large variation in tomato grower production systems (Barrett et al., 2012b). However, it should be noted that increased vegetative growth and fruit load may require additional supporting structures and therefore increase production system costs. Alternatively, when grafting is combined with other production technologies, other growing methods may be necessary to maximize the benefits of grafted plants. &nbsp; &nbsp;&nbsp;</p>