Chilling-induced water stress: Variation in shoot turgor maintenance among wild tomato species from diverse habitats
Department of Plant Sciences, University of California-Davis, One Shields Avenue, Davis, California 95616, USA.American Journal of Botany (Impact Factor: 2.6). 09/2013; 100(10). DOI: 10.3732/ajb.1200508
• Premise of the study: Cultivated tomato, Solanum lycopersicum, suffers chilling induced wilting because water movement through its roots decreases with declining soil temperatures. Certain wild tomato species exhibit resistance to chilling-induced wilting, but the extent of this chilling tolerance in wild tomatoes is not known.• Methods: We measured shoot wilting during root chilling in wild Solanum accessions from habitats differing in elevation, temperature, and precipitation. We also measured shoot wilting during root chilling in introgression lines (ILs) with chromosome 9 segments collinear to the shoot turgor maintenance QTL stm9 region from chilling-tolerant S. habrochaites, chilling and drought-tolerant S. lycopersicoides, or drought-tolerant S. pennellii.• Key results: Wild tomato species, which experience chilling temperatures (<10°C) in their native habitat, maintain shoot turgor under root chilling. Among accessions of S. lycopersicum var. cerasiforme, a typically chilling sensitive species, shoot turgor maintenance during root chilling was correlated with the precipitation of the native habitat. By contrast, S. pennellii, a species that is typically drought adapted, did not maintain turgor under root chilling. Grafted plants with roots containing S. habrochaites and S. lycopersicoides introgressions improved shoot turgor maintenance under root chilling.• Conclusions: Resistance to chilling-induced water stress is an important adaptation to chilling temperatures in wild tomatoes. There is some overlap in adaptation to drought and chilling stress in some tomato species. Root-based resistance to chilling-induced water stress in wild tomatoes may involve orthologous gene(s).
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ABSTRACT: A quantitative trait locus (QTL) stm9 (shoot-turgor maintenance; located on chromosome 9) from chilling-tolerant Solanum habrochaites S. Knapp & D.M. Spooner maintains plant water status via stomatal closure in response to root chilling, which induces a rapid onset form of root water stress. Here we examined the effect of an introgressed S. habrochaites chromosome 9 region, which contains QTL stm9, on water relations, photosynthesis, and yield in the field. Three near-isogenic lines (NILs) of cultivated tomato (Solanum lycopersicum L.) with and without S. habrochaites chromosome 9 introgressions, and their parent cultivar T5, were evaluated in 2 yr of field experiments in Davis, CA. The NILs with a S. habrochaites introgression exhibited predawn and midday leaf conductances that were 23 and 10% smaller, respectively, than those of the NIL without the S. habrochaites introgression and the parent cultivar. This resulted in the NILs with the S. habrochaites region having 23% higher predawn leaf water potential, 13% higher midday leaf water potential, and 13% lower net photosynthesis than the NIL without the S. habrochaites introgression and the parent cultivar. Yield in the NILs containing small (NIL175) and large (NIL1322) introgressions of S. habrochaites decreased an average of 42 and 71%, respectively, compared with the NIL without the introgression and the parent cultivar. The effect of the introgression from S. habrochaites under nonchilling conditions may prove useful for understanding tradeoffs between productivity and transpiration.
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ABSTRACT: Key message QTL stm9 controlling rapid-onset water stress tolerance in S. habrochaites was high-resolution mapped to a chromosome 9 region that contains genes associated with abiotic stress tolerances. Abstract Wild tomato (Solanum habrochaites) exhibits tolerance to abiotic stresses, including drought and chilling. Root chilling (6 °C) induces rapid-onset water stress by impeding water movement from roots to shoots. S. habrochaites responds to such changes by closing stomata and maintaining shoot turgor, while cultivated tomato (S. lycopersicum) fails to close stomata and wilts. This response (shoot turgor maintenance under root chilling) is controlled by a major QTL (designated stm9) on chromosome 9, which was previously fine-mapped to a 2.7-cM region. Recombinant sub-near-isogenic lines for chromosome 9 were marker-selected, phenotyped for shoot turgor maintenance under root chilling in two sets of replicated experiments (Fall and Spring), and the data were used to high-resolution map QTL stm9 to a 0.32-cM region. QTL mapping revealed a single QTL that was coincident for both the Spring and Fall datasets, suggesting that the gene or genes contributing to shoot turgor maintenance under root chilling reside within the marker interval H9–T1673. In the S. lycopersicum reference genome sequence, this chromosome 9 region is gene-rich and contains representatives of gene families that have been associated with abiotic stress tolerance.
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