An overview of heat stress in tomato (Solanum lycopersicum L.)

Abstract

Heat stress has been defined as the rise of temperature for a period of time higher than a threshold level, thereby permanently affecting the plant growth and development. Day or night temperature is considered as the major limiting factor for plant growth. Earlier studies reported that night temperature is an important factor in the heat reaction of the plants. Tomato cultivars capable of setting viable fruits under night temperatures above 21 °C are considered as heat-tolerant cultivars. The development of breeding objectives is generally summarized in four points: (a) cultivars with higher yield, (b) disease resistant varieties in the 1970s, (c) long shelf-life in 1980s, and (d) nutritive and taste quality during 1990s. Some unique varieties like the dwarf "Micro-Tom", and the first transgenic tomato (FlavrSavr) were developed through breeding; they were distributed late in the 1980s. High temperature significantly affects seed, pollen viability and root expansion. Researchers have employed different parameters to evaluate the tolerance to heat stress, including membrane thermo stability, floral characteristics (Stigma exertion and antheridia cone splitting), flower number, and fruit yield per plant. Reports on pollen viability and fruit set/plant under heat stress by comparing the pollen growth and tube development in heat-treated and non-heat-stressed conditions are available in literature. The electrical conductivity (EC) have been used to evaluate the tolerance of some tomato cultivars in vitro under heat stress conditions as an indication of cell damage due to electrolyte leakage; they classified the cultivars into three groups: (a) heat tolerant, (b) moderately heat tolerant, and (c) heat sensitive. It is important to determine the range in genetic diversity for heat tolerance in tomatoes. Heat stress experiments under field conditions offer breeders information to identify the potentially heat tolerant germplasm.

Keywords: Heat shock proteins; Heat stress; High temperature; Stress response; Tolerance mechanism; Tomato.

Fig. 1

The effect of high-temperature on floral structure including the size and morphology of the floral constituents. A-B. LA3847 and LA4284, respectively, showing flowers under control (flower on the left) and heat conditions (flower on the right) without noticeable stigma exsertion under heat. C. LA4256 accession with stigma exsertion and deformation of the style as a sign of sensitivity to heat (flower on the right). D. LA0373 showing stigma exsertion above the anther cone similarly under control and heat conditions. E-G. LA1930 showing the mostly exserted stigmata among all accession. E. Flower with dissected anthredial cone showing the long style exserted above the level of anthers. F. Non-dissected flower showing the exserted stigma. G. Prolific production of self-incompatible flowers with exserted stigmata under control condition. H-I. LA0716 showing exserted stigmata under control and high temperature conditions, respectively (Alsamir et al., 2017d).