Nationally, Florida ranks first in fresh-market tomato (Solanum lycopersicum) production value with an average crop value of US $448 million over the last three years [U.S. Department of Agriculture (USDA) 2016]. In the 2015 season, Florida had the largest fresh-market tomato acreage in the United States with 32,200 acres harvested and an average yield of 29,500lb/acre resulting in almost 1 billion pounds of tomato fruit (USDA 2016).
Wild tomato species are native to western South America from southern Ecuador to northern Chile and the Galapagos Islands (Peralta and Spooner 2007). Tomato domestication occurred in America (Bai and Lindhout 2007); however, the first domestication site is still not defined, with two hypotheses, a Peruvian domestication and a Mexican domestication, being considered (Peralta and Spooner 2007). Regardless of controversies related to the first domestication site and early history, tomatoes were first recorded outside the American continent in Italy in 1544 (Peralta and Spooner 2007). Tomatoes were first cultivated as ornamental plants due to people's beliefs that the fruit were poisonous. The acceptance of tomato as an edible vegetable occurred during the late 16th century in southern Europe (Peralta and Spooner 2007). Ever since, plant breeding has provided diversity of tomato types and varieties derived from the original lines, and the majority of the varieties currently grown are hybrids with a wide range of shapes, colors, and sizes (Bai and Lindhout 2007).
The most common types of tomatoes planted in Florida are round, cherry, grapes, and plums. The majority of the round and plum tomato cultivars grown in Florida are determinate plants with upright growth, which cease their growth when fruit set on the apical meristems (Ozores-Hampton et al. 2011). These tomatoes are commonly harvested at mature-green stage for the fresh market. Lodging of determinate upright tomatoes can reduce tomato fruit yield and quality (Adelana 1980), thus commercial hybrids that grow vertically to a certain height and then fall over require staking; if not staked, the vines would typically grow off the beds and into the aisles, where they could be run over by a tractor and where the fruit could be subject to rots from soil-borne pathogens. According to Davis and Estes (1993), labor costs related to practices such as transplanting, staking, pruning, tying, and harvesting may be as high as 55% of the total tomato production cost, which was estimated at $15,246.18/acre in 2014 for southwest Florida (VanSickle and McAvoy 2015). In addition to the labor costs, availability of farm labor and immigration issues are major concerns to the Florida tomato industry (McAvoy and Ozores-Hampton 2011; Scott, Hutton, and Strobel 2010). Mexican tomatoes may be produced at a reduced cost because of the lower labor and land costs when compared to the Florida tomato industry (McAvoy and Ozores-Hampton 2011). Therefore, alternatives to the traditional production system that reduce production cost would be economically beneficial to the Florida tomato industry.
Alternative tomato production systems that do not require staking, tying, and pruning have been used successfully by the California tomato industry for both processing and part of their fresh-market tomato production. The California processing tomato industry uses determinate varieties with a controlled growth habit (S. Schroeder, personal communication). These tomatoes are once-over mechanically harvested when 90% of the fruits are ripe (Hartz et al. 2008). California fresh-market tomato growers use two different growing methods: staked upright or bush varieties, with bush hybrids constituting the majority of the market (Le Strange et al. 2000). Bush hybrid tomatoes are harvested manually one or two times at the mature-green stage (Le Strange, Schrader, and Hartz 2000).
Compact growth habit (CGH) tomatoes are determinate varieties with a unique architecture that may provide the basis for a viable alternative production system for Florida. These tomatoes have low growth and spreading characteristics, forming compact plants that hold fruit above the ground due to its short branches (Kemble et al. 1994) (Figure 1). Therefore, CGH tomatoes do not require staking, tying, or pruning (Kemble et al. 1994). Thus, due to their unique plant growth, CGH varieties may be used by the Florida mature-green fresh-market tomato growers to reduce labor costs associated with staking, tying, and pruning.
Genetics and Morphology
Compact growth habit plants have determinate vines with a compact plant structure. Several genes have been reported to affect tomato plants' growth habit and/or branching (Ozminkowski et al. 1990a), such as decumbens (dec) (Stubbe 1959), procumbens-2 (prc-2) (Stubbe 1960), and brachytic (br) (Barton et al. 1955). Increased side branching has been related to the genes erecta-2 (er-2) (Clayburg et al. 1979), globiformis (glf), and globosa-2 (glo-2) (Clayburg et al. 1966) and also to reduced apical dominance (Campbell and Nonnecke 1974). The br gene (Barton et al. 1955) is the one responsible for the shortened internodes and strong side branching of CGH plants, which can be prostrate or upright in growth due to unidentified gene(s) (Ozminkowski et al. 1990b). This combination of traits results in a low-growing, spreading plant, approximately 24 inches in diameter with a reduction of 50% to 60% in internode length compared to staked upright varieties (Kemble et al. 1994) (Figure 2).
Similar to normal growth habit tomatoes, each short branch, including the terminal bud, terminates in a flower cluster in CGH plants; however, CGH plants develop a more concentrated fruit set that is early in maturity. The average height of CGH plants ranges from 19 to 21 inches and average plant volume is approximately 8.9 ft3 (Coelho Frasca et al. 2014). When in the field, plants of CGH tomatoes cover the polyethylene-mulched bed but will not grow into the row middles, holding most of the fruit above the bed surface (Scott, Hutton, and Strobel 2010) (Figure 3).
Compact growth habit tomato varieties with jointless pedicels that would be commercially acceptable have not been completely developed for the Florida market. Since the fruit set is concentrated and all fruit may be harvested at one time, it is particularly important to ensure that the varieties are not prone to fruit defects such as cat facing or gray wall. In addition, fertilization programs are critical for CGH varieties because it is important to get crown fruit set to maintain a proper reproductive/vegetative balance. High nitrogen levels may cause excessive vegetative growth and consequently low yields and can also contribute to the defects mentioned above. Perception of lower yield potential may be attributed to the growth characteristic of these tomato plants that lie on the polyethylene-mulched bed, which, combined with high temperatures and relative humidity, may favor the proliferation of plant pathogens under typical Florida weather conditions. However, there is no evidence that yields are reduced by plant pathogens when CGH plants are grown in Florida environmental conditions. Coelho Frasca et al. (2014) conducted a study with CGH breeding lines and neither yield or fruit quality were affected by weather-related events. CGH tomato breeding lines grown in Florida, harvested twice, manually had average marketable yields lower than expected yields of staked-upright tomato hybrids that may be harvested three times, but higher than Florida average yields (Coelho Frasca et al. 2014). The same study also revealed that CGH breeding lines evaluated presented suitable characteristics for mature-green harvest regarding postharvest fruit quality (Coelho Frasca et al. 2014).
In order to minimize the effect of possible weather-related issues and possibly improve marketable yields, alternative production systems can be developed for CGH varieties, including factors that influence plant growth and development such as fertilization, spacing, and row arrangements (Davis and Estes 1993).
In Florida, the majority of fresh-market tomatoes are hand-harvested at the mature-green stage with specific criteria for size, shape, color, and defects (USDA 1997). Compact growth habit tomatoes can be harvested by hand or potentially mechanically harvested when the plants have the jointless-pedicel characteristic, eliminating the need for expensive hand-harvesting labor (Scott, Hutton, and Strobel 2010). In jointless varieties, when the fruits are harvested the calyx and stem remain attached to the plant, whereas in jointed varieties, part of the stem and the calyx often remain attached to the fruit (Zahara and Scheuerman 1988). Due to unknown environmental conditions, stems and calyxes are sometimes difficult to pry off fruit, especially for some cultivars. Stems that remain attached to fruit of jointed tomatoes at harvest may puncture or bruise other fruit during transportation and packing, affecting quality. In addition, hand harvest of jointed cultivars requires additional time for workers to remove stems and calyxes in order to avoid fruit damage, which increases labor costs (Zahara and Scheuerman 1988).
Compact growth habit tomatoes generally reach maturity one to two weeks earlier than typical staked varieties. In addition, manual harvest can be done once or twice in CGH tomatoes because they have a concentrated fruit set, reducing the harvesting cost when compared to the currently staked-upright tomato varieties that are generally harvested three times. Thus, CGH tomatoes can reduce the time from transplant to final harvest by approximately one month as compared to the currently staked-upright varieties. Therefore, total production costs would be lower than current commercial upright tomatoes. Ultimately, CGH tomato cultivars could be once-over harvested by machine, which would further reduce harvest costs, although there would be considerable costs in purchasing harvest machine(s).
Compact growth habit tomato varieties are not currently available for the Florida market, but the University of Florida Tomato Breeding Program is working on the development of breeding lines suitable for the mature-green fresh market. The unique plant architecture of CGH tomatoes may be used by Florida fresh-market tomato growers as an alternative production system to reduce labor costs associated with staking, tying, and pruning. Furthermore, CGH tomatoes with the jointless-pedicel characteristic may be mechanically harvested, reducing costs associated with manual harvest.
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