Abstract
Heat stress is a major limiting factor for crop productivity. Tomato is highly sensitive to heat stress, which can result in a total yield loss. To adapt to current and future heat stress, there is a dire need to develop heat tolerant cultivars. Here, we review recent attempts to improve screening for heat tolerance and to exploit genetic and genomic resources in tomatoes. We provide key factors related to phenotyping environments and traits (morphological, physiological, and metabolic) to be considered to identify and breed thermo-tolerant genotypes. There is significant variability in tomato germplasm that can be harnessed to breed for thermo-tolerance. Based on our review, we propose that the use of advanced backcross populations and chromosome segments substitution lines is the best means to exploit variability for heat tolerance in non-cultivated tomato species. We applied a meta quantitative trait loci (MQTL) analysis on data from four mapping experiments to co-localize QTL associated with heat tolerance traits (e.g., pollen viability, number of pollen, number of flowers, style protrusion, style length). The analysis revealed 13 MQTL of which 11 were composed of a cluster of QTL. Overall, there was a reduction of about 1.5-fold in the confidence interval (CI) of the MQTL (31.82 cM) compared to the average CI of individual QTL (47.4 cM). This confidence interval is still large and additional mapping resolution approaches such as association mapping and multi-parent linkage mapping are needed. Further investigations are required to decipher the genetic architecture of heat tolerance surrogate traits in tomatoes. Genomic selection and new breeding techniques including genome editing and speed breeding hold promise to fast-track development of improved heat tolerance and other farmer- and consumer-preferred traits in tomatoes.
Highlights
Heat stress is a major abiotic factor limiting crop productivity worldwide [1,2]
In a study to assess the impact of heat stress on both vegetative and reproductive development, Xu et al [23] showed that under long-term moderate heat, there was a decrease in female fertility and subsequently in seeded fruits
Saeed et al [68] found a positive association between membrane thermostability and yield while this parameter was negatively associated with pollen thermosensitive sub-traits, such as antheridial cone splitting, stigma tube elongation, and number of flowers shed
Summary
Heat stress is a major abiotic factor limiting crop productivity worldwide [1,2]. Based on several scenarios, by the end of the 21st century (2081–2100), global temperatures are projected to increase on average in the range of about 1 ◦ C to 3.7 ◦ C relative to their levels in 1986–2005 [3]. Heat stress reduces the tomato growing window (the number of days per year with optimal temperatures for tomato production), especially in open field and non-controlled growing conditions, which are the prevailing tomato cropping systems in tropical regions. In these regions, Silva et al [9] predicted that over 2050–2100, heat and drought stress would negatively affect tomatoes’ growth and yield in open fields and reduce the optimal area for production. We discuss the recent advances in understanding genetic architecture of heat tolerant traits in tomato and the new breeding techniques that can be leveraged to accelerate breeding for heat tolerance in tomato
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