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

Abstract

summaryNumerous hydroponic studies have shown that root growth of tomato (Lycopersicon esculentum Mill.) is little affected 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 CaCl2, 4:1) was examined in the field, in large soil‐filled containers, and in hydroponics. The two cultivars, UC82B and CX8303, differed in susceptibility to a common root rot organism (Phytophthora parasitica Dast.), and were hypothesized to differ in root growth response to environmental stress. In agreement with the literature, root weight of young, hydroponically‐grown plants (as determined by multiple, destructive harvests) was unaffected by salinity in both cultivars. In contrast, root length density of cv. UC82B was reduced 40% by salinity in the field, whereas root length density of root rot‐tolerant cv. CX8303 was unaffected. Similar responses to salinity were observed in the containers, with root counts from horizontal minirhizotron tubes reduced in cv. UC82B, but not in cv. CX8303. Observations from windows in the sides of the containers showed that reduction in net root growth in cv. UC82B was primarily due to an increased rate of root death at high salinity. Root turnover remained low in cv. CX8303 under both low and high salinity. Differential effects of salinity on root growth of the two cultivars in containers were not evident until about 60 d after transplanting. This suggests that the discrepancy between 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, previously undocumented carbon cost to some genotypes exposed to salinity.