Plant Gene and Trait 2025, Vol.16, No.4, 142-151 http://genbreedpublisher.com/index.php/pgt 144 3.3 Classification by species and commercial availability In terms of types, dwarfing rootstocks can be divided into two categories. One type is “allogeneic rootstock”, which means using tomatoes themselves or their dwarfing mutants as rootstocks. Another category is “heterologous rootstocks”, such as eggplant (S. melongena) or wild tomato relatives (S. pennellii, S. torvum). The latter is usually more adaptable to harsh environments and more disease-resistant (Khapte et al., 2022; Latifah et al., 2023). At present, there are already many commercial dwarfing rootstock varieties on the market, such as ‘Powerguard’, ‘T1’, ‘L1’ and ‘B.Locking’. These rootstocks can maintain the balanced growth of tomatoes and have a good yield under greenhouse or long-term cultivation conditions (Lee et al., 2020). There are also some rootstocks, such as ‘DRO141TX’ and ‘Fortamino’, which perform better in drought or other adverse conditions. Not only do they have more fruits, but they also taste better (Davis et al., 2024). Figure 1 Schematic diagram of rootstock control scion vigour (Adopted from Hayat et al., 2021) 4 Physiological Mechanisms Behind Dwarfing Effects 4.1 Hormonal regulation: auxin, cytokinin, gibberellins Dwarfing rootstocks can affect the synthesis, transport and signal transduction of various plant hormones, thereby exerting a significant effect on the growth of tomatoes. Studies have found that when dwarfing rootstocks are used, the transport of auxin (IAA) is hindered, and the expression of some transport proteins (such as AUX1 and LAX2) decreases, which makes the aboveground parts of the plants grow more slowly (Zhou and Underhill, 2021; Verma et al., 2024). In addition, the contents of cytokinin (CK) and gibberellin (GA) in dwarfing rootstocks are usually low, or the signal transduction of these two hormones is inhibited, which leads to shorter internodes and shorter plants (Hayat et al., 2022b; Gu et al., 2023; Hayat et al., 2023a). There are also some transcription factors, such as WRKY, which can inhibit the synthesis genes of hormones like gibberellin and brassinolide (BR), thereby making the dwarfing effect more obvious (Hayat et al., 2023b). 4.2 Modulation of nutrient uptake and transport After using dwarfing rootstocks, the plant’s ability to absorb nutrients such as nitrogen and phosphorus will be weakened. Studies have found that the root system of this type of rootstock absorbs nutrients at a slower rate, and the growth of the upper part is also restricted (Hayat et al., 2021; Hayat et al., 2022a). When there is insufficient nitrogen or phosphorus in the soil, dwarfing rootstocks will cause the roots to grow more branches and expand the root area. Although this can better absorb the limited nutrients, the above-ground parts still do not grow very fast (Xie et al., 2023). In addition, dwarfing rootstocks often also affects water transportation. The water absorption and transportation capacity of the roots weakens, resulting in water deficiency in the upper part of the plant and thus affecting the yield (Biasuz and Kalcsits, 2022; Biasuz and Kalcsits, 2023).
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