Understanding the mechanism for heat tolerance is important for the hot pepper breeding program to develop heat-tolerant cultivars in changing climate. This study was conducted to investigate physiological and biochemical parameters related to heat tolerance and to determine leaf heat damage levels critical for selecting heat-tolerant genotypes. Seedlings of two commercial cultivars, heat-tolerant ‘NW Bigarim’ (NB) and susceptible ‘Chyung Yang’ (CY), were grown in 42 °C for ten days. Photosynthesis, electrolyte conductivity, proline content were measured among seedlings during heat treatment. Photosynthetic rate was significantly reduced in ‘CY’ but not in ‘NB’ seedlings in 42 °C. Stomatal conductivity and transpiration rate was significantly higher in ‘NB’ than ‘CY’. Proline content was also significantly higher in ‘NB’. After heat treatment, leaf heat damages were determined as 0, 25, 50 and 75% and plants with different leaf heat damages were moved to a glasshouse (30–32/22–24 °C in day/night). The growth and developmental parameters were investigated until 70 days. ‘NB’ was significantly affected by leaf heat damages only in fruit yield while ‘CY’ was in fruit set, number and yield. ‘NB’ showed fast recovery after heat stress compared to ‘CY’. These results suggest that constant photosynthetic rate via increased transpiration rate as well as high proline content in heat stress condition confer faster recovery from heat damage of heat-tolerant cultivars in seedlings stages.

High temperature (HT) significantly affects crop physiological traits and reduces productivity in plants. To increase yields as well as survival of crops under HT, developing heat-tolerant plants is one of the main targets in crop breeding programs. The present study attempted to investigate the linkage of the heat tolerance between the seedling and reproductive growth stages of tomato cultivars ’Dafnis‘ and ’Minichal.’ This research was undertaken to evaluate heat tolerance under two experimental designs such as screening at seedling stage and screening from reproductive traits in greenhouses. Survival rate and physiological responses in seedlings of tomatoes with 4-5 true leaves were estimated under HT (40 °C, RH 70%, day/night, respectively) and under two control and HT greenhouse conditions (day time 28 °C and 40 °C, respectively). Heat stress significantly affected physiological–chemical (photosynthesis, electrolyte conductivity, proline) and vegetative parameters (plant height, shoot fresh weight, root fresh weight) in all tomato seedlings. The findings revealed that regardless of tomato cultivars the photosynthesis, chlorophyll, total proline and electrical conductivity parameters were varied in seedlings during the heat stress period. The heat tolerance rate of tomatoes in the seedling stage might not always be associated with reproductive parameters. HT reduced fruit parameters such as fruit weight (31.9%), fruit length (14.1%), fruit diameter (19.1%), and fruit hardness (9.1%) compared to NT under HT in heat-susceptible tomato cultivar ‘Dafnis’, while in heat-tolerant cultivar ‘Minichal’ fruit length (7.1%) and fruit diameter (12.1%) was decreased by the effects of HT, but on the contrary fruit weight (3.6%) and fruit hardness (8.3%) were increased. In conclusion, screening and selection for tomatoes should be evaluated at the vegetative and reproductive stages with consideration of reproductive parameters.

Tomato is often exposed to diverse abiotic stresses and cold stress is one of harsh environmental stresses. Abnormal low temperature affects tomato growth and development, leading to, e.g., physiological disorders, flower drops, and abnormal fruit morphology, and causing a decrease in tomato yield and fruit quality. It is important to identify low temperature-(LT) tolerant tomato (Solanum lycopersicum L.) cultivars relying on different fruit types. In this study, our focus was to analyze the physiological traits of 35 tomato accessions with three different fruit types (cherry, medium, and large sizes) under night temperature set-points of 15 °C for control temperature (CT) and 10 °C for LT, respectively. Plant heights (PH) of most tomato accessions in LT were remarkably decreased compared to those in CT. The leaf length (LL) and leaf width (LW) were reduced depending on the genotypes under LT. In addition, the number of fruits (NFR), fruit set (FS), fruit yield (FY), and marketable yield (MY) were negatively affected in LT. The variation was further investigated by the correlation, the principal component (PCA), and the cluster analysis. Interestingly, positive correlations between different vegetative and reproductive traits were uncovered. Multivariate analysis including the PCA and hierarchical clustering classified the LT-treated 35 tomato accessions into four major groups. The identified accessions were associated with vegetative and reproductive parameters on positive directions. The results might be utilized for establishing breeding programs on selecting LT-tolerant tomato cultivars with different selection indices relying on fruit types during vegetative and/or reproductive stages.

Climate change is an important emerging issue worldwide; the surface temperature of the earth is anticipated to increase by 0.3 °C in every decade. This elevated temperature causes an adverse impact of heat stress (HS) on vegetable crops; this has been considered as a crucial limiting factor for global food security as well as crop production. In tomato plants, HS also causes changes in physiological, morphological, biochemical, and molecular responses during all vegetative and reproductive growth stages, resulting in poor fruit quality and low yield. Thus, to select genotypes and develop tomato cultivars with heat tolerance, feasible and reliable screening strategies are required that can be adopted in breeding programs in both open-field and greenhouse conditions. In this review, we discuss previous and recent studies describing attempts to screen heat-tolerant tomato genotypes under HS that have adopted different HS regimes and threshold temperatures, and the association of heat tolerance with physiological and biochemical traits during vegetative and reproductive growth stages. In addition, we examined the wide variety of parameters to evaluate the tomato’s tolerance to HS, including vegetative growth, such as leaf growth parameters, plant height and stem, as well as reproductive growth in terms of flower number, fruit set and yield, and pollen and ovule development, thereby proposing strategies for the development of heat-tolerant tomato cultivars in response to high temperature.

Pepper plants are subject to complex environmental factors including abiotic and biotic stresses in fields, as well as the significant effects of climate changes, including low and high temperatures. Low temperature stress in the growth and development of pepper plants is one of the most critical issues, and directly impacts the crop yield and productivity of pepper plants. Therefore, it is essential to select and breed low temperature-(LT) tolerant pepper (Capsicum annuum L.) cultivars. This research was conducted to assess the agronomical traits of 39 pepper accessions belonging to the chili and bell fruit varieties which were cultivated under two different night temperature set-points: at 15 °C for a suboptimal temperature (CT) and at 10 °C for a low temperature (LT). The plant heights (PH) of most pepper accessions in a LT were significantly decreased compared to those in a CT. The stem diameter (SD) and the length of main axis (LMA) varied depending on the genotypes under LT. Moreover, the number of flowers (NFL), total number of fruits (NFR), fruit yield (FY), fruit fresh weight (FFW), fruit length (FL), fruit diameter (FD), and number of seeds in a fruit (NSF) remarkably declined in a LT compared to in a CT. The evaluated agronomical traits between LT and CT were further applied for the correlation analysis, principal component analysis (PCA), and hierarchical cluster analysis. Notably, the FY trait was correlated with other reproductive traits including NFR, FFW, FD, and FL on the positive directions and thirty-nine LT-treated pepper accessions were clustered into seven groups by the hierarchical clustering analysis. The selected accessions were primarily involved in the positive trends with the reproductive index including NFR, FL, FD, and FFW traits and could be used for pepper breeding programs to develop LT-tolerant cultivars.