Commercial nursery crop production in the United States involves the use of chemical plant growth regulators (PGRs) to control plant growth and height (Hayashi et al., 2001; Latimer and Scoggins, 2012). Compact plants are easier to transplant, maintain, and transport, and are more attractive to consumers than tall, stretched plants with elongated internodes (Latimer and Scoggins, 2012). In addition to improved plant growth habit and aesthetic value, management practices using PGRs may offer other advantages for nursery production practices. It has been shown that the application of PGRs can increase seedling survival and tolerance to transplanting shock (Cha-um et al., 2009; Dunlap et al., 1991), improve resistance to environmental stress (Al-Rumaih and Al-Rumaih, 2007; Duan et al., 2008; Lurie et al., 1995), enhance flowering (Banko and Landon, 2005; Cochran and Fulcher, 2013; Keever and McGuire, 1991), and increase fruit yield (Dunlap et al., 1991; Wang and Gregg, 1990).
The objective of this study was to evaluate the effect of uniconazole on potted vegetable transplants. Vegetable gardening is gaining popularity (National Gardening Association, 2009), and this is the only PGR that can legally be used on some vegetable crops. Uniconazole is a triazole growth retardant that has been approved for a few species in the Solanaceae family (e.g., tomato, pepper, eggplant); however, it can only be applied as a spray, no later than 14 d after the four-leaf stage, and the total amount of product used cannot exceed 10 mg·L−1 (Valent U.S.A. Corp., 2008).
Application of uniconazole has been shown to reduce stem elongation and control the height of certain vegetables (Dunlap et al., 1991; Hickman et al., 1989; Shin et al., 2009). However, there is little information on its effect on their flowering time and fruit yield. A limited number of studies have been conducted on the effect of uniconazole on tomato plants, and they have provided contrasting results. Hickman et al. (1989) found no differences in ‘Royal Flush’ tomato fruit yield when uniconazole was applied at concentrations from 0.25 to 5 mg·L−1; but increased or decreased fruit yields have also been reported in different cultivars and with different rates (Dunlap et al., 1991; Wang and Gregg, 1990). Other vegetables have also shown a wide range of responses to uniconazole. Lettuce (Latuca sativa) and broccoli (Brassica oleracea var. italica) decreased yield after treatment, but watermelon (Citrullus lanatus) and pepper increased or decreased yield, depending on the cultivar (Dunlap et al., 1991). To better understand the effects of uniconazole on the growth of vegetables, more studies testing the effect of this PGR on several species and cultivars are needed. We evaluated the effect of uniconazole on height and fruit yield of ‘Jalapeno’ pepper, ‘Millionaire’ eggplant, and two tomato cultivars with different growth habits, Early Girl (determinate) and Sun Sugar (indeterminate), all popular home grown vegetables in the United States (Gao et al., 2010; National Gardening Association, 2009).
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