A pound of organic heirloom tomatoes costs $5 at the Larimer County Farmers’ Market in Fort Collins, CO. Nonorganic heirlooms range from $2–6.50/lb, whereas other tomatoes at the local market, both organic and noncertified, range from $3–5/lb (Colorado Department of Agriculture, 2018). Trends in the national fresh tomato (Solanum lycopersicum) market indicate the increase in demand for both organically grown and heirloom types. In addition, organic tomatoes are often sold at a 15% to 20% price premium over conventionally grown crops (O’Connell et al., 2012). The market for organic produce in general has shown strong growth during the past two decades and currently makes up 5.3% of total food sales of the United States (Organic Trade Association, 2018). The objective of this study was to evaluate differences in yield and quality of tomatoes using two fruit cluster pruning treatments and three cultivars of indeterminate tomatoes grown in an intensively managed, certified organic high tunnel.
Many tactics are used to grow high-quality fresh produce for direct markets such as farmers’ markets, community-supported agriculture (CSA), and local restaurants. The use of a high tunnel is one of the most successful tactics for growing high-quality, high-yielding, and valuable crops. A high tunnel, or hoop house, is a temporary, movable, or semipermanent structure that may be single- or multispan (i.e., many connected structures). High tunnels may be covered in polyethylene film, insect netting, or shadecloth, or left bare, and are typically unheated and passively ventilated. Crops are usually planted directly in the soil within high tunnels, although containers and soilless media are used occasionally. A high tunnel provides multiple benefits for the grower over open-field cultivation, including season extension, insect exclusion, reduced disease pressures, protection from environmental damage (such as hail avoidance), and greater marketable yields. Furthermore, high tunnels provide valuable services in organic agricultural systems because they can improve the quality and yield of vegetables over open-field growing systems (Rogers and Wszelaki, 2012).
Tomatoes are the most popular and often the most profitable plant for high-tunnel growers. They are an excellent crop choice as a result of their high value in the fresh market and the crop’s ability to produce high yields (Mefferd, 2017). Indeterminate tomatoes produce fruit throughout the growing season and benefit from both the high tunnel environment and trellising. Indeterminate cultivars of tomato allow growers to meet consumer demand consistently. High tunnels provide a protected microclimate and longer harvests, and allow for continuous production of fresh fruit (Rogers and Wszelaki, 2012).
Fruit cluster pruning of tomatoes has been shown to influence total yield, marketability, individual fruit fresh weight, and various indicators of quality, such as dry matter and SSC. Fruit cluster pruning is used to limit the number of fruit per cluster and reduce competition to increase individual fruit weight (Hanna, 2009). Studies across the world (Turkey, South Africa, the Netherlands, Italy, and the United States) have produced conflicting results on the efficacy of cluster pruning of tomatoes in various controlled environments (Table 1). Specifically, there is a lack of research on cluster pruning in intensively managed organic systems, in high tunnels, and on the Front Range of Colorado.
A literature summary of tomato fruit cluster pruning controlled environments.
Cultivar selection is a critical component for growers who are concerned about the maximization of yield, the fresh market appeal of their products, and the general performance (e.g., pest and disease resistance, physiological traits, and quality) of their crops (Healy et al., 2017). Growers evaluate cultivars for their desired fruit qualities, shelf life and storage characteristics, and potential yield (Hanna, 2009). Although most hybrid cultivars of tomatoes are bred for increased yield, visual appeal, and shipping durability, open-pollinated heirloom cultivars of tomatoes are valued for their unique colors, shapes, flavors, and legacies. However, heirloom tomatoes generally lack uniformity, have thinner skins, lack disease resistance, and have lower yields than most modern hybrid cultivars (O’Connell et al., 2012).
SSC, represented in °Brix, is a common measurement used by tomato growers, processors, and fresh market growers. In the fresh market, soluble solids levels provide an approximation of how sweet the tomato may taste; however, many components define the overall flavor of each tomato, including sugars, acids, volatiles, and other compounds. An SSC measurement in °Brix, using a refractometer, is a quick, reliable, and inexpensive field test for quality. Although measurements can be an early indication of sweetness and flavor, SSC can fluctuate as a result of many factors, including crop, cultivar, maturity, growing environment, and storage conditions (Kleinhenz and Bumgarner, 2015). Healy et al. (2017) found that tomatoes had a greater SSC when grown in a high tunnel compared with open-field production.
Tomato vegetative growth is pruned regularly when the crop is grown in a controlled environment. Tomato plants develop side shoots in their leaf axils; these axillary shoots will continue to grow and produce leaves and fruit clusters if not removed. Axillary shoots should be removed regularly (often repeatedly) to maintain a single leader, or main stem. This is an effective way to maximize production space, and can improve the yield and quality of tomatoes (Maboko et al., 2011). It is also common practice in intensive greenhouse operations to remove any leaves below the lowest ripening cluster. The lower canopy receives little sunlight and is unnecessary for continued plant growth and fruit production. In addition, the removal of superfluous leaves allows the plant to allocate more energy to vertical growth and fruit development while also reducing disease pressure by maximizing air flow.
The overall objective of this study was to evaluate the differences between two tomato fruit cluster pruning treatments and a control on three cultivars of indeterminate tomatoes: Cherokee Purple, Jet Star, and Lola. We hypothesized that 1) cluster pruning would decrease total yield, 2) cluster pruning would increase the quality of the organic tomatoes, and 3) cultivars would respond differently to the cluster pruning treatments for the parameters analyzed in the study. To test these hypotheses, differences between cluster pruning treatments and cultivar performance were assessed in terms of total yield, individual fresh fruit weight, SSC, marketable yield, and nonmarketable yield.
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