Effects of salinity on root growth and death dynamics of tomato, Lycopersicon esculentum Mill.

SUMMARY Numerous hydroponic studies have shown that root growth of tomato {Ly coper sicon esculentum Mill.) is littleaffected by salinity. In contrast, data from soil-grown plants show salinity may induce reductions of up to 50 "„in root length density. In this study, root growth of two tomato cultivars exposed to salinity (NaCl and CaClj, 4:1)was examined in the field, in large soil-filled containers, and in hydroponics. The two cultivars, UC82B andCX83O3, differed in susceptibility to a common root rot organism {Phytophthora parasitica Dast.), and werehypothesized to differ in root growth response to environmental stress. In agreement with the literature, rootweight of young, hydroponically-grown plants (as determined by multiple, destructive harvests) was unaffectedby salinity in both cultivars. In contrast, root length density of cv. UC82B was reduced 40 % by salinity in thefield, whereas root length density of root rot-tolerant cv. CX83O3 was unaffected. Similar responses to salinitywere observed in the containers, with root counts from horizontal minirhizotron tubes reduced in cv. UC82B, butnot in cv. CX83O3. Observations from windows in the sides of the containers showed that reduction in net rootgrowth in cv. UC82B was primarily due to an increased rate of root death at high salinity. Root turnover remainedlow in cv. CX83O3 under both low and high salinity. Differential effects of salinity on root growth of the twocultivars in containers were not evident until about 60 d after transplanting. This suggests that the discrepancybetween salinity responses of hydroponic and soil-grown plants was primarily due to differences in phenology.Enhanced rates of root death during the reproductive growth stage may represent an important, previouslyundocumented carbon cost to some genotypes exposed to salinity.Key words: Tomato {Lycopersicon esculentum), salinity, root growth, root turnover, root-observation methodology.

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