Differences in Branch Formation in Indeterminate and Determinate Tomato Types

Tomato plants differentiate a terminal flower bud on the apex of the main stem and formed flower truss, known as the determinate pattern with branching characteristics (Saito, 1982; Tabuchi, 2007). Then, the axillary bud adjacent to the terminal flower bud differentiates and grows as a uniaxial sympodial branch. The lateral shoot that extend a single main branch and continues to grow is referred to as indeterminate (Fig. 1). These types are cultivated mainly for the fresh product market. In contrast, plants with a self-pruning growth habit with only short sympodial branches that form 1 4 flower trusses (Yeager, 1927) are described as determinate. A new apex can differentiate from the highest node below the terminal flower bud in this branching type. These cultivars are mainly grown for processing tomatoes (Abe et al., 1965). In general, lateral shoots of indeterminate tomato cultivars need to be removed before becoming elongated to prevent nutrient competition between vegetative and reproductive organs. If lateral shoots are not removed, strong growth of shoots from some nodes occurs (Ohta, 2012). Because the sink strength of lateral shoots with flower trusses is stronger than that of the main stem (Shishido and Hori, 1991), strong growth of some lateral shoots may cause uneven distribution of photosynthetic products, resulting in undesirable effects on fruit production. During tomato cultivation during winter and summer in the Netherlands, lateral shoots generated from the first or second nodes below the terminal flower bud are used to increase stem numbers per area in indeterminate cultivars and increase tomato yield (Heuvelink, 2005). Aoki (1981) devised the continuous pinching cultivation method, which uses the lateral shoots to improve fruit quality and increase yield. The utilization of lateral shoots can both promote high-quality fruits (Fukuchi et al., 2004; Saito et al., 2006; Kusakawa et al., 2013) and also increase crop yield (Sasaki et al., 2013). In contrast, for determinate tomato cultivars, lateral shoots are generally not removed to save labor and ensure yield (Arima and Nakamura, 1969; Fukui et al., 1990; Ito, 1992; Yanokuchi, 1997). Differentiation of axillary buds occurs at every node during the growth of commercial cultivars. Although the axillary buds at lower nodes extend during the vegetative stage, the axillary buds at the upper nodes below the terminal bud do not extend much due to apical dominance (Saito, 1982; McSteen and Leyser, 2005). When the terminal flower bud at the shoot apex emerges and grows, the entire axillary bud in general begins to elongate. Branch formation in indeterminate cultivars differs from that in determinate ones. Also, the growth properties of lateral shoots generated from each node can be used as indices to increase yield and improve fruit quality. In addition, because the population of those who grow tomatoes in Japan is ageing, the ergonomics of this kind of work should be improved by developing a training method using lateral shoots originating from lower nodes. However, there has been little research to elucidate branching habits and the relationships between the emergence of the terminal flower bud and the elongation of lateral shoots in tomato. Because