Journal of Applied Botany and Food Quality 90, 339 - 345 (2017), DOI:10.5073/JABFQ.2017.090.042 1Institute of Horticultural Sciences, University of Agriculture, Faisalabad, Pakistan 2Department of Horticultural Sciences, University College of Agriculture and Environmental Sciences, The Islamia University of Bahawalpur, Punjab, Pakistan 3Nuclear Institute of Agriculture and Biology, Faisalabad, Pakistan 4Department of Soil Sciences, Bahauddin Zakariya University, Multan, Pakistan 5Department of Agronomy, University College of Agriculture and Environmental Sciences, The Islamia University of Bahawalpur, Pakistan 6Departments of Environmental Sciences, Bahauddin Zakariya University, Multan, Pakistan Exploring the better genetic options from indigenous material to cultivate tomato under high temperature regime Araiz Nazir1, Muhammad Rashid Shaheen2, Choudhary Muhammad Ayyub1, Rashid Hussain2, Nadeem Sarwer3, Muhammad Imran4, Muhammad Aurangzaib5, Muhammad Nawaz6*, Muhammad Faizan Ali Khan6, Yussra Jawad6, Munawar Iqbal6 (Received May 5, 2017; Accepted September 19, 2017) * Corresponding author Summary Screening test was conducted on 54 genotypes of tomato to analyze the effect of heat stress and categorize them as heat tolerant or heat susceptible ones. Seedlings were grown at temperatures of 28/22 oC day/night. Four weeks after sowing, plants were exposed to high temperatures of 40/32 oC day/night for one week. Data for various morphological (root and shoot length, root and shoot fresh and dry weight, number of leaves) and physiological parameters (chlorophyll contents, sub-stomatal CO2, transpiration rate, stomatal conductance, photosynthetic rate, water use efficiency and leaf temperature) were recorded. Heat stress had a negative effect on all physiological and morphological processes of the genotypes. The results of this study revealed that “Parter Improved” and “Legend” were more heat tolerant genotypes whereas “Grus Chovka” and “Nepoli” were more heat sensitive among the genotypes under consideration. Keywords: Tomato, Genotypes, Screening, Heat stress Introduction Over 20th century, the global average surface temperature has risen about 0.6 ± 2 oC and is expected to further increase up to 1.4 - 5.8 oC during this century (HOUGHTON et al., 2001). The extreme climates including high temperature stress might result in loss of crop productivity which in turn would lead to famine (BITA and GERATS, 2013). A manifestation of the ever-increasing and unexpected climate changes in plants is through appearance of stress symptoms. Stress is defined as “the negative effect that an organism may suffer” and may be internal or external (MADLUNG and COMAI, 2004) and has been reported to have reduced agricultural productivity to as much as 50%. It has been estimated that each degree Celsius rise in temperature in average growing season results in 17% decrease in yield (LOBELL and ASNER, 2003). BRAY et al. (2000) estimates that 51 - 82% of the potential yield of annual crops is lost due to abiotic stresses. Among the abiotic stresses, heat stress has created the most alarming situation for Pakistan’s agriculture, causing several physical, physiological, biochemical and anatomical distortions in crop plants. Rise in temperature at vegetative stage of plants may have direct or indirect effects. Direct ones include protein aggregation and denaturation (WAHID et al., 2007; GOLAM et al., 2012) while indirect ones are the limited protein production, inactivation of enzymes in chloroplast and mitochondria (WAHID et al., 2007). Visually, high temperature manifests itself through burning of twigs, sunburn, hindered development of root (BATTS et al., 1998; PORTER and GAWITH, 1999) and shoot (GOLAM et al., 2012), scorching of leaves, leaf senescence and abscission, inhibition of growth and ultimately decreased productivity (GUILINI et al., 1997; ISMAIL and HALL, 1999; VOLLENWEIDER and GUNTHARDT-GOERG, 2005). Heat stress adversely affects radical growth in eggplant seedlings (SEKARA et al., 2012) and has been reported to have markedly reduced plant height, stem fresh and dry weight, leaf fresh and dry weight and leaf area of tomatoes (ABDELMAGEED et al., 2003). ABDELMAGEED (2009) found poor and stunted growth in tomatoes and negative impacts on leaf area, leaf fresh weight, leaf dry weight, stem fresh weight and stem dry weight, leaf area ratio and leaf weight ratio of the vegetable when exposed to high temperatures. PRASAD et al. (2006) stated after experimentation on Easter Lilies that se- vere heat stress resulted in decreased plant height and that day and night temperatures affect stem length in the flower (ERWIN et al., 1989). After an experiment on Rose with temperature ranges of 0, 6 and 10 °C for 2 and 14 days, it was concluded that increasing bandwidths reduced shoot lengths as well as their fresh weight at harvestable stage, irrespective of the days for which the temperature was applied (DIELEMAN et al., 2005). PORTER and GAWITH (1999) indicated that root growth is com- paratively more sensitive to heat stress than other organs, and decreases with heat stress. High temperature stress decreases root length as well as diameter. During reproductive phase, decreased carbon partitioning in roots causes the reduction in number of roots as well as their length (BATTS et al., 1998). Heat stress increases rate of evaporation and transpiration by influencing soil temperature and increasing water vapor deficit, respectively (PRASAD et al., 2008), and has been said to be associated with lack of water availability (SIMOES-ARAUJO et al., 2003). These alterations affect water relations, and tend to be severer during day time than night time (WAHID et al., 2007). Although drought has been known to be the major cause of water loss from plants, the severity of temperature tends to aggravate the situation (MACHADO and PAULSON, 2001). Especially during the day, water tends to decrease in plants due to transpiration which leads to decreased water potential and thus disturbance of many plant processes (TSUKAGUCHI et al., 2003). MORALES et al. (2003) reported heat stress to damage water relations and root hydraulic activity in tomato plants. In sugarcane, high temperature tends to change leaf water potential, even though the soil water content and relative humidity are optimal (WAHID and CLOSE, 2007). TODOROV et al. (2003) and SHARKEY and ZHANG (2010) indicated that heat stress not only adversely affects photosynthesis but also 340 A. Nazir, M.R. Shaheen, C.M. Ayyub, R. Hussain, N. Sarwer, M. Imran, M. Aurangzaib, M. Nawaz, M.F.A. Khan, Y. Jawad, M. Iqbal respiration. The rise in chlorophyllase activity and decreased photo- synthetic pigments leads to reduced photosynthetic and respirato- ry processes of plants. With increasing temperatures, respiration initially increases. However, at temperatures above 50 °C, damage to the respiratory mechanism causes decrease in the process (PRASAD et al., 1998). In a study conducted by SATO et al. (2000), effect of heat stress on respiration, photosynthesis, pollen production and release and dehiscence was examined and it was found that all plants kept under high temperature showed reduced photosynthesis and increased respiration. Photosynthesis is said to be the physiological process most sensitive to heat stress (WAHID et al., 2007). An increase in temperature (>40 °C) (PRASAD et al., 2008) damages the structural organization of thylakoid and disturbance in grana stacking, leading to reduced photosynthesis (WAHID et al., 2007). The rate of the energy con- suming photorespiration increases (LEA and LEEGOOD, 1999; NAKAMOTO and HIYAMA, 1999) and photosynthesis decreases (SCHUSTER and MONSON, 1990). WAHID et al. (2007) reported several changes in grapes when exposed to high temperature stress whereby chloroplast in the mesophyll cells of grape plants assumed a rounded shape, the stroma lamellae swelled, whilst the cristae were disturbed and mitochondria got to be vacant. Such changes bring about the structuring of antenna-depleted PSII and henceforth diminish photosynthetic and respiratory processes. Damage to photosystem II has also been reported in several studies (SANTARIUS, 1975; SANTARIUS and MÜLLER, 1979; BERRY and BJÖRKMAN, 1980; ENAMI et al., 1994). PRASAD et al. (1998) have indicated PSII to be most sensitive to heat stress which occurs at temperatures as high as 35 - 40 °C (TERZAGHI et al., 1989; THOMPSON et al., 1989; GOMBOS et al., 1994; ÇJÁNEK et al., 1998; YAMANE et al., 1998). However, moderate heat stress does not damage PSII but reduces photosynthetic activity (SHARKEY, 2005). Heat stress is also reported to be a cause of formation Reactive Oxygen Species (ROS) (ZINNET al., 2010). These ROS are formed due to alteration in protein aggregation (WAHID et al., 2007; GOLAM et al., 2012), limited protein production, and inactivation of enzymes in chloroplast and mitochondria (WAHID et al., 2007). In spite of being a summer vegetable, tomatoes are also affected by rise in temperature beyond their threshold level. KUO et al. (1993) has categorized tomato as a heat sensitive vegetable with more than 75% high temperature injury. Germination, seedling, flowering and fruit setting and ripening is adversely affected at temperatures above 35 oC (MILLER et al., 2001). The present study was aimed at screening of indigenous tomato genotypes to estimate its heat tolerance potential and categorizing them as heat tolerant and heat susceptible ones. Materials and methods The present study was conducted in growth room in controlled conditions of photoperiod, temperature and humidity. Fifty-four tomato genotypes were screened against heat stress. Each treatment consisted of four replications. Plants were grown in plastic pots of 8-inch diameter and sterilized sand was used as growth medium. Each pot was filled with 850 g sand and 160 ml water and 10 ml Hoagland’s solution was applied prior to sowing. Hoagland’s solution was later applied periodically as the nutrient medium. Optimum temperature of 28/22 oC (day/night) was provided for four weeks during germination and growth. Heat stress was applied four weeks after seedling growth by gradual- ly increasing 2 oC temperature per day, to avoid osmotic shock until desired high temperature of 40/32 oC day/night temperature was achieved. Plants were kept at this temperature for one week. After one week of stress, data was recorded. Morphological attributes such as number of leaves, shoot length (cm), root length (cm) were measured with meter rod, shoot fresh weight (g), root fresh weight (g), shoot dry weight (g) and root dry weight (g) was recorded with digital weighing balance. Physiological parameters such as transpiration rate (mmol/m2/s), Photosynthetic rate (μmol/m2/s), Sub-stomatal CO2 (vpm) and Sub-Stomatal Water and Leaf Surface Temperature (ºC) were all recorded using portable photosynthetic meter (model LCi-SD ADC Bioscientific, UK). Water Use efficiency was calculated using the formula: Rate of Photosynthesis (Pn) Water Use Efficiency (Pn/E) = Rate of Transpiration (E) Chlorophyll contents (SPAD value) were measured using a chlorophyll meter (CM 200plus, Bio-scientific USA). Completely Randomized Design (CRD) was applied to the experiment. Collected data was analyzed statistically by employing Fisher’s analysis of variance technique and significance of treatments were tested (Steel et al., 1997). Statistical analysis and correlations between variables were also estimated by using R. Principal Component Analysis (PCA) was employed to identify the patterns in data and to graphically express the data in such a way as to emphasize their similarities and differences. Results and discussion As stated by VOLLENWEIDER and GUNTHARDT-GOERG (2005), heat stress can cause marked reduction in shoot and root growth. Ex- periments conducted by RAHMANI et al. (2013) on impact of day and night temperatures on cauliflower showed that greater curd length, diameter, fresh weight and dry weight was observed at warmer night temperatures than day temperatures whereas greater leaf growth, leaf area, stem length, stem fresh and dry weight was observed at warmer day temperatures. Screening results (Tab. 1) demonstrated that “Parter Imported” exhibited greatest tolerance against heat stress, with 185 cm shoot length. “Grus Chovka” was most susceptible to heat stress with 4.9 cm shoot length. The genotype “Alaskan Fancy” had maximum root length under heat stress with 13.18 cm (Tab. 1). “Kaldera” was most sensitive to heat stress with root length of 4.12 cm. Maximum shoot fresh weight was recorded for “Roma” (4.06 g) (Tab. 1) while “Grus Chovka” (0.7 g) had least shoot fresh weight. These results were similar to the results obtained by RAHMANI et al. (2013) who conducted experiments on impact of day and night temperatures on cauliflower. Temperatures of 24/12 °C, 12/24 °C, 20/16 °C, 16/20 °C and 20/20 °C in the first run and 24/20 °C, 20/ 12 °C and 20/16 °C in the second run revealed that greater stem fresh and dry weight was observed at warmer day temperatures. Genotype “Bush Beef Steak” had maximum root fresh weight of 2.02 g (Tab. 1). Minimum root fresh weight was recordrd for “Kaldera”, having 0.21 g. “Roma” showed greatest shoot dry weight of 0.31 g (Tab. 1). This genotype also had the highest shoot fresh weight. Similarly, “Grus Chovka” had least shoot dry weight of 0.07 g and also had least shoot fresh weight. Highest root dry weight was recorded to be 0.52 g (Tab. 1) which was for “Roma” and least was 0.06 g which was for “Pakit”. Highest number of leaves (33) were recorded for “Parter Improved” (Tab. 1). “UC-134” had 14 leaves which were recorded as the least number of leaves. Analysis of variance for individual traits i.e. morphological traits is given in (Tab. 3) which showed that root length, shoot length, root and shoot fresh and dry weight, and number of leaves were highly significant among the genotypes under study. Similarly analysis of variance for physiological traits is given in (Tab. 4) which showed that chlorophyll content, sub-stomatal CO2, stomatal conductance to water, photosynthetic rate, transpiration rate, water use efficiency and leaf temperature were highly significant in genotypes under observation. Screening of local germplasm for cultivation under heat stress conditions 341 V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11 V12 V13 V14 V15 V16 V17 V18 V19 V20 V21 V22 V23 V24 V25 V26 V27 V28 V29 V30 V31 V32 V33 V34 V35 V36 V37 V38 V39 V40 V41 V42 V43 V44 V45 V46 V47 V48 V49 V50 V51 V52 V53 V54 Tab. 1: Shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight and number of leaves of tomato genotypes under high temperature stress Genotype Genotype Shoot Length Root Length Shoot Fresh Root Fresh Shoot Dry Root Dry No. of Leaves Number (cm) (cm) Weight (g) Weight (g) Weight (g) Weight (g) CLN-2366 A LA-2662 LA-3120 Early Annie Sasha Altai KHT-15 Subartic Way Ahead Jagour Iles Yellow Latvian Zarnitza Pakit UC-134 Brdley Subarctic Lomg Keeper Parter Improved Roma Cchaus Legend Alaskan Fancy Raad Red Early Wonder Polar Beauty Zhezha Camp Bells Bonita Rio Grande New Yarker Beef Steak Leeper LA-2010 Grus Chovka Nepoli Dona Pres Cott Tai-1042 Bush Beef Steak Cold Set Naqeeb Kaldera Manatoba Caro Rich Tomato Forme De Coeur NTH-671 Spekled Sibrian Northern Delight Anahu Taxi Nagina Rio Grand Quantum Tima France Tomato 3383 F1 CM Selection 10.90±1.09 f-p 13.48±0.85 a-j 16.60±0.38 a-d 10.28±0.87 h-p 16.80±0.85 abc 8.88±1.71 i-q 12.60±0.85 b-l 7.23±0.70 m-q 11.50±1.02 d-n 10.90±1.39 f-p 8.68±1.06 j-q 7.10±0.81 m-q 10.65±0.53 g-p 14.48±0.80 a-h 12.53±0.92 b-l 12.73±0.98 b-l 18.50±0.54 a 14.75±0.75 a-h 11.50±0.74 d-n 16.38±1.13 a-e 15.60±0.58 a-g 11.45±0.55 e-n 12.10±0.50 c-m 17.33±1.22 ab 13.00±0.88 b-k 11.25±1.21 e-o 12.60±0.73 b-l 14.70±1.17 a-h 10.23±1.18 h-p 9.90±1.11 h-q 9.83±0.88 h-q 11.65±0.41 d-n 4.90±0.41 q 10.23±0.56 h-p 9.10±0.63 i-q 13.25±0.73 b-k 9.05±1.23 i-q 8.23±0.35 k-q 13.88±1.61 a-i 13.50±0.96 a-j 15.88±1.84 a-f 6.18±0.12 opq 10.50±0.61 g-p 5.00±0.74 q 10.83±1.01 f-p 13.50±1.02 a-j 11.10±0.46 f-p 10.63±0.77 g-p 6.75±0.25 n-q 8.73±0.63 j-q 11.00±0.35 f-p 6.08±0.88 pq 10.38±0.80 h-p 7.75±0.60 l-q 9.30±1.19 a-f 8.25±1.59 a-f 8.93±0.62 a-f 6.95±1.22 c-f 8.38±0.90 a-f 8.45±0.92 a-f 12.88±1.13 ab 6.18±0.62 c-f 9.75±0.41 a-e 9.38±1.83 a-f 7.83±1.34 b-f 5.90±0.46 def 7.38±0.31 c-f 7.68±0.84 b-f 8.30±0.45 a-f 9.35±1.43 a-f 8.90±1.33 a-f 9.08±0.79 a-f 6.95±0.55 c-f 7.98±0.71 a-f 13.18±1.37 a 8.23±1.17 a-f 11.43±1.17 abc 8.88±0.88 a-f 9.13±0.83 a-f 7.00±0.51 c-f 8.93±0.72 a-f 7.98±0.86 a-f 8.00±0.95 a-f 8.60±0.76 a-f 6.80±1.20 c-f 4.50±0.84 ef 5.88±1.09 def 7.00±0.71 c-f 7.15±1.41 c-f 5.88±0.59 def 6.88±1.68 c-f 5.38±0.38 def 4.13±0.13 f 7.75±0.92 b-f 4.13±0.63 f 7.05±0.57 c-f 10.65±0.83 a-d 7.48±0.93 c-f 6.00±0.29 def 5.25±1.03 ef 5.45±1.28 def 5.38±0.69 def 7.10±0.58 c-f 5.93±0.40 def 7.40±0.36 c-f 5.88±0.43 def 8.38±0.92 a-f 7.55±0.73 b-f 2.38±0.27 b-l 3.26±0.31 a-f 3.35±0.16 a-e 2.10±0.36 b-m 3.08±0.36 a-h 1.73±0.44 f-m 2.87±0.27 a-j 1.38±0.32 i-m 2.24±0.12 b-m 3.25±0.38 a-f 1.64±0.27 g-m 1.01±0.09 lm 1.36±0.18 i-m 2.68±0.42 a-k 2.09±0.14 b-m 2.23±0.40 b-m 3.69±0.33 ab 4.06±0.41 a 2.08±0.35 c-m 3.51±0.31 abc 3.11±0.27 a-g 2.34±0.42 b-l 3.43±0.36 a-d 2.43±0.33 b-l 2.57±0.33 a-l 2.02±0.34 c-m 2.93±0.37 a-i 2.28±0.43 b-m 1.51±0.31 g-m 2.07±0.28 c-m 1.10±0.20 klm 1.36±0.32 i-m 0.70±0.13 m 1.19±0.14 klm 1.51±0.17 g-m 1.89±0.20 d-m 1.47±0.30 i-m 1.73±0.08 f-m 1.78±0.38 e-m 1.66±0.31 f-m 1.40±0.25 i-m 1.49±0.04 h-m 2.12±0.18 b-m 1.31±0.18 j-m 1.99±0.18 c-m 1.95±0.30 c-m 1.98±0.25 c-m 2.01±0.14 c-m 1.12±0.07 klm 1.64±0.08 g-m 1.62±0.11 g-m 1.06±0.11 lm 2.12±0.23 b-m 1.68±0.34 f-m 0.94±0.26 b-j 0.76±0.15 c-j 1.20±0.31 a-h 0.97±0.27 b-j 0.52±0.10 e-j 0.40±0.09 g-j 1.20±0.24 a-h 0.63±0.15 d-j 0.75±0.04 c-j 0.88±0.17 c-j 0.44±0.05 g-j 0.45±0.07 g-j 0.52±0.04 e-j 0.58±0.12 d-j 0.75±0.15 c-j 0.49±0.16 f-j 1.08±0.26 b-i 1.37±0.28 a-e 0.45±0.08 g-j 0.66±0.13 c-j 1.01±0.18 b-j 0.70±0.17 c-j 0.89±0.20 b-j 0.48±0.08 g-j 0.48±0.11 g-j 0.45±0.07 g-j 0.78±0.18 c-j 0.45±0.09 g-j 0.46±0.09 g-j 0.56±0.05 d-j 0.31±0.06 ij 0.69±0.11 c-j 1.13±0.12 b-i 1.40±0.14 a-d 1.74±0.31 ab 1.34±0.27 a-f 1.51±0.22 abc 2.02±0.09 a 1.25±0.32 a-g 0.83±0.01 c-j 0.21±0.04 j 0.38±0.05 hij 0.35±0.08 hij 0.30±0.03 ij 0.35±0.06 hij 0.32±0.06 ij 0.50±0.12 f-j 0.32±0.02 ij 0.32±0.03 ij 0.35±0.05 hij 0.41±0.05 g-j 0.27±0.02 ij 0.37±0.04 hij 0.40±0.03 g-j 0.20±0.04 a-h 0.26±0.03 a-e 0.27±0.02 a-d 0.15±0.03 b-h 0.23±0.03 a-f 0.14±0.02 c-h 0.26±0.03 a-e 0.10±0.03 fgh 0.20±0.02 a-h 0.23±0.03 a-f 0.13±0.03 c-h 0.10±0.01 fgh 0.14±0.02 c-h 0.17±0.03 a-h 0.19±0.02 a-h 0.16±0.03 a-h 0.30±0.05 ab 0.31±0.03 a 0.17±0.04 a-h 0.28±0.03 abc 0.23±0.03 a-g 0.20±0.04 a-h 0.27±0.03 a-d 0.21±0.02 a-h 0.20±0.03 a-h 0.18±0.02 a-h 0.25±0.04 a-f 0.22±0.03 a-h 0.13±0.03 c-h 0.20±0.03 a-h 0.08±0.02 gh 0.15±0.01 b-h 0.07±0.02 h 0.11±0.01 e-h 0.13±0.02 d-h 0.16±0.02 b-h 0.15±0.03 b-h 0.18±0.03 a-h 0.16±0.04 b-h 0.19±0.04 a-h 0.14±0.02 c-h 0.12±0.01 d-h 0.20±0.02 a-h 0.13±0.03 c-h 0.20±0.00 a-h 0.18±0.03 a-h 0.17±0.03 a-h 0.19±0.02 a-h 0.10±0.00 fgh 0.15±0.02 c-h 0.16±0.01 b-h 0.13±0.00 d-h 0.21±0.02 a-h 0.16±0.02 b-h 0.13±0.03 k-s 0.29±0.01 c-l 0.29±0.04 c-m 0.31±0.04 b-k 0.12±0.03 l-s 0.08±0.02 qrs 0.32±0.05 b-j 0.21±0.03 f-s 0.22±0.02 e-s 0.37±0.06 a-g 0.08±0.02 rs 0.06±0.01 s 0.12±0.02 l-s 0.08±0.02 rs 0.20±0.03 g-s 0.11±0.02 m-s 0.43±0.03 abc 0.52±0.05 a 0.11±0.02 n-s 0.25±0.02 d-q 0.23±0.02 d-s 0.21±0.05 f-s 0.27±0.05 c-o 0.14±0.02 k-s 0.12±0.02 l-s 0.13±0.02 l-s 0.28±0.05 c-n 0.10±0.03 o-s 0.17±0.03 i-s 0.19±0.03 h-s 0.07±0.02 rs 0.27±0.02 c-o 0.38±0.05 a-f 0.36±0.03 a-h 0.39±0.04 a-e 0.39±0.04 a-e 0.34±0.03 b-i 0.47±0.05 ab 0.24±0.02 d-r 0.40±0.03 a-d 0.06±0.03 s 0.11±0.03 m-s 0.09±0.04 p-s 0.08±0.01 rs 0.07±0.03 rs 0.09±0.03 p-s 0.15±0.03 j-s 0.07±0.01 rs 0.26±0.02 c-p 0.09±0.02 p-s 0.08±0.02 qrs 0.08±0.01 rs 0.07±0.02 rs 0.09±0.02 p-s 27.25±2.29 a-h 30.50±1.04 abc 28.50±2.50 a-g 21.25±1.65 e-o 16.50±1.76 k-o 18.75±1.70 h-o 32.75±2.29 ab 22.00±2.35 c-o 22.75±0.95 c-n 26.00±2.04 a-j 21.50±1.55 d-o 16.00±0.91 mno 14.00±1.35 o 24.75±1.80 a-l 30.00±1.96 a-d 23.50±1.55 c-n 33.25±2.21 a 26.25±1.75 a-i 25.00±1.41 a-k 29.25±1.80 a-e 29.00±1.47 a-f 27.25±2.56 a-h 30.00±1.08 a-d 25.00±0.41 a-k 24.25±0.63 b-m 26.00±1.47 a-j 23.75±1.31 c-n 21.75±1.03 d-o 22.50±1.66 c-o 20.50±1.85 f-o 17.75±1.11 i-o 19.50±0.96 h-o 15.50±1.19 no 15.25±1.55 no 23.25±1.49 c-n 18.75±1.38 h-o 18.00±1.08 i-o 18.00±1.35 i-o 18.75±0.75 h-o 17.25±2.02 k-o 21.25±1.65 e-o 27.00±2.12 a-h 20.75±1.31 e-o 17.75±1.03 i-o 20.00±1.22 g-o 23.25±0.95 c-n 19.25±1.31 h-o 16.75±1.38 k-o 15.75±1.49 mno 15.25±0.48 no 15.50±0.50 no 15.75±1.44 mno 16.25±1.31 l-o 17.50±0.87 j-o Means sharing similar letter in a column are statistically non-significant (P>0.05) 342 A. Nazir, M.R. Shaheen, C.M. Ayyub, R. Hussain, N. Sarwer, M. Imran, M. Aurangzaib, M. Nawaz, M.F.A. Khan, Y. Jawad, M. Iqbal Tab. 2: Chlorophyll contents, sub-stomatal CO2, transpiration rate, stomatal conductance, photosynthetic rate, water use efficiency and leaf temperature of tomato genotypes under high temperature stress Genotypes Chlorophyll Sub-stomatal Transpiration Stomatal Cond. Photosynthetic Water Use Leaf Content CO2 Rate Water Rate Efficiency Temperature (SPAD value) (vpm) (mmol/m2/s) (ºC) (μmol/m2/s) (Pn/E) (ºC) CLN-2366 A LA-2662 LA-3120 Early Annie Sasha Altai KHT-15 Subartic Way Ahead Jagour Iles Yellow Latvian Zarnitza Pakit UC-134 Brdley Subarctic Lomg Keeper Parter Improved Roma Cchaus Legend Alaskan Fancy Raad Red Early Wonder Polar Beauty Zhezha Camp Bells Bonita Rio Grande New Yarker Beef Steak Leeper LA-2010 Grus Chovka Nepoli Dona Pres Cott Tai-1042 Bush Beef Steak Cold Set Naqeeb Kaldera Manatoba Caro Rich Tomato Forme De Coeur NTH-671 Spekled Sibrian Northern Delight Anahu Taxi Nagina Rio Grand Quantum Tima France Tomato 3383 F1 CM Selection 21.53±1.14 b-f 20.78±2.59 b-f 21.70±1.55 b-f 17.43±1.88 ef 25.28±2.68 b-f 20.53±1.86 b-f 28.25±3.32 b-f 18.85±2.09 c-f 31.38±1.97 b-e 23.50±1.84 b-f 19.95±2.90 b-f 49.03±3.26 a 22.45±3.34 b-f 20.78±4.02 b-f 22.10±1.03 b-f 27.55±2.30 b-f 21.45±4.80 b-f 18.68±0.79 def 30.30±3.19 b-f 17.28±2.51 ef 26.30±2.94 b-f 26.65±2.49 b-f 16.38±1.09 ef 22.95±2.57 b-f 34.28±3.18 a-d 16.15±2.80 ef 16.83±2.76 ef 23.50±2.79 b-f 23.43±2.70 b-f 21.50±1.44 b-f 25.60±4.82 b-f 20.33±1.45 b-f 31.13±2.95 b-e 18.65±1.44 def 34.53±2.43 abc 23.95±2.55 b-f 24.73±2.11 b-f 22.35±3.23 b-f 21.90±3.15 b-f 23.50±3.21 b-f 25.13±4.27 b-f 21.70±4.04 b-f 20.73±2.56 b-f 34.98±2.53 ab 25.68±3.26 b-f 14.85±3.48 f 17.05±2.42 ef 21.33±3.11 b-f 22.40±3.63 b-f 19.95±3.11 b-f 27.13±2.91 b-f 26.25±1.93 b-f 23.43±2.39 b-f 18.85±0.63 c-f 802.5±102.47 h-u 753.5±34.13 j-v 709.8±29.55 k-v 1113.8±24.37 c-h 1096.8±66.39 d-j 1394.0±37.52 a-d 766.3±55.43 i-v 1150.3±39.80 b-g 1103.0±57.68 d-i 1452.5±40.49 abc 1334.5±20.41 a-e 1487.5±15.95 ab 1555.0±67.57 a 989.0±91.27 f-m 883.3±127.85 f-s 549.0±6.86 r-v 467.8±8.68 uv 454.5±15.54 v 1153.8±126.24 b-f 1001.5±112.04 e-m 1036.0±142.82 e-l 944.8±85.87 f-o 1042.5±100.01 e-k 804.5±25.09 h-u 734.3±72.79 k-v 720.0±13.56 k-v 696.0±7.74 l-v 704.0±12.40 k-v 690.3±24.64 m-v 704.8±80.17 k-v 593.3±82.27 p-v 700.5±160.61 k-v 587.5±25.93 q-v 665.3±14.23 m-v 603.5±38.82 o-v 619.3±25.99 n-v 539.3±16.56 s-v 529.8±71.26 tuv 741.5±28.69 k-v 943.5±69.80 f-o 824.8±9.66 f-t 880.0±12.32 f-s 821.3±42.25 f-t 806.3±9.81 g-u 842.5±19.32 f-t 821.0±21.89 f-t 831.5±30.99 f-t 889.3±40.43 f-r 955.5±58.54 f-n 906.8±41.67 f-q 966.8±26.16 f-m 936.0±6.87 f-p 862.0±44.01 f-t 932.3±16.63 f-q 0.92±0.19 gh 1.63±0.17 a-h 2.30±0.27 a-h 2.10±0.11 a-h 2.82±0.63 a-d 1.99±0.28 a-h 2.49±0.13 a-g 2.21±0.19 a-h 2.61±0.24 a-f 3.18±0.35 ab 2.68±0.46 a-e 1.54±0.14 b-h 3.22±0.45 a 1.13±0.24 e-h 2.27±0.30 a-h 2.14±0.09 a-h 1.64±0.28 a-h 2.43±0.27 a-g 0.95±0.18 fgh 0.95±0.21 fgh 1.44±0.08 c-h 2.01±0.19 a-h 1.64±0.20 a-h 1.56±0.16 a-h 2.17±0.38 a-h 2.05±0.21 a-h 1.71±0.43 a-h 1.42±0.34 c-h 1.89±0.32 a-h 1.32±0.33 d-h 1.46±0.22 c-h 1.04±0.23 e-h 2.29±0.26 a-h 1.90±0.33 a-h 1.75±0.20 a-h 1.96±0.33 a-h 1.69±0.18 a-h 0.66±0.28 h 1.00±0.26 fgh 1.95±0.48 a-h 2.14±0.33 a-h 1.99±0.61 a-h 0.73±0.16 h 1.16±0.20 d-h 1.27±0.16 d-h 1.47±0.15 c-h 1.51±0.25 b-h 1.97±0.21 a-h 2.28±0.43 a-h 1.51±0.38 b-h 3.05±0.14 abc 2.32±0.23 a-h 1.38±0.41 c-h 2.46±0.27 a-g 0.055±0.017 a-g 0.085±0.010 a-f 0.115±0.016 ab 0.078±0.006 a-g 0.120±0.032 a 0.060±0.012 a-g 0.078±0.005 a-g 0.070±0.007 a-g 0.083±0.010 a-g 0.100±0.015 a-d 0.085±0.018 a-f 0.040±0.004 c-g 0.110±0.024 abc 0.048±0.013 a-g 0.093±0.016 a-e 0.080±0.004 a-g 0.055±0.012 a-g 0.085±0.012 a-f 0.073±0.017 a-g 0.060±0.020 a-g 0.068±0.005 a-g 0.078±0.012 a-g 0.050±0.008 a-g 0.043±0.005 b-g 0.068±0.015 a-g 0.060±0.008 a-g 0.050±0.017 a-g 0.038±0.011 c-g 0.055±0.013 a-g 0.035±0.012 d-g 0.043±0.008 b-g 0.025±0.006 efg 0.070±0.009 a-g 0.055±0.012 a-g 0.048±0.006 a-g 0.055±0.012 a-g 0.045±0.006 b-g 0.010±0.007 g 0.020±0.007 efg 0.053±0.017 a-g 0.055±0.012 a-g 0.055±0.022 a-g 0.015±0.005 fg 0.073±0.019 a-g 0.060±0.011 a-g 0.055±0.006 a-g 0.053±0.011 a-g 0.065±0.010 a-g 0.078±0.021 a-g 0.040±0.013 c-g 0.103±0.008 a-d 0.068±0.006 a-g 0.035±0.013 d-g 0.070±0.011 a-g 5.56±1.35 a-e 6.37±0.66 a-e 7.42±0.53 a-e 5.12±0.90 b-e 3.56±1.15 cde 5.52±0.75 a-e 6.36±2.39 a-e 5.14±0.53 b-e 4.26±1.56 cde 4.38±1.23 cde 3.73±0.92 cde 3.92±0.34 cde 4.62±1.09 b-e 4.77±0.50 b-e 7.37±1.50 a-e 2.40±0.18 de 4.91±0.84 b-e 3.15±1.05 cde 12.15±1.69 a 9.21±1.10 abc 9.03±2.00 a-d 11.12±2.35 ab 7.45±1.52 a-e 2.00±0.75 e 6.11±1.94 a-e 3.54±1.29 cde 2.34±0.79 de 1.58±0.66 e 3.60±0.45 cde 2.40±0.91 de 3.85±1.59 cde 1.62±0.82 e 2.94±1.13 cde 0.95±0.33 e 3.12±0.95 cde 5.18±2.88 b-e 1.02±0.33 e 1.12±0.42 e 1.04±0.17 e 2.62±1.25 cde 1.84±0.81 e 2.09±0.50 e 1.05±0.38 e 2.74±1.41 cde 1.60±0.83 e 2.44±0.94 de 1.29±0.63 e 2.76±1.06 cde 1.32±2.37 e 2.16±0.76 e 3.23±0.63 cde 2.69±1.10 cde 2.17±0.20 e 2.73±0.67 cde 6.97±1.79 bc 4.10±0.71 c-f 3.49±0.78 c-f 2.46±0.44 c-f 1.74±0.87 c-f 3.15±0.99 c-f 2.60±1.07 c-f 2.41±0.39 c-f 1.85±0.81 c-f 1.46±0.48 def 1.71±0.74 c-f 2.58±0.20 c-f 1.42±0.29 def 4.66±0.77 c-f 3.38±0.81 c-f 1.13±0.08 def 3.03±0.16 c-f 1.34±0.53 def 13.87±2.72 a 10.66±1.83 ab 6.38±1.54 bcd 5.99±1.61 b-e 4.82±1.37 c-f 1.25±0.44 def 3.38±1.36 c-f 1.80±0.66 c-f 1.31±0.16 def 0.99±0.24 def 2.18±0.55 c-f 2.32±1.06 c-f 2.70±0.89 c-f 2.93±2.22 c-f 1.19±0.40 def 0.53±0.16 f 1.71±0.41 c-f 2.78±1.82 c-f 0.59±0.17 ef 2.51±1.22 c-f 1.47±0.57 def 1.59±0.62 c-f 1.05±0.52 def 1.15±0.13 def 1.57±0.67 def 2.02±0.66 c-f 1.22±0.58 def 1.70±0.60 c-f 1.10±0.66 def 1.63±0.82 c-f 0.87±0.88 ef 1.78±0.69 c-f 1.08±0.22 def 1.11±0.36 def 2.10±0.70 c-f 1.15±0.29 def 27.30±0.45 s 30.83±0.19 q 32.38±0.19 mno 34.20±0.11 e-j 34.78±0.09 b-g 35.30±0.04 a-d 35.48±0.02 abc 35.63±0.02 ab 35.63±0.03 ab 35.15±0.03 a-d 34.65±0.06 c-g 34.60±0.00 c-g 34.40±0.07 d-i 29.23±0.29 r 30.83±0.18 q 31.68±0.11 opq 33.20±0.07 klm 33.45±0.03 jkl 26.68±0.49 s 29.25±0.37 r 31.93±0.30 op 33.63±0.31 i-l 35.23±0.19 a-d 34.60±0.04 c-g 34.68±0.08 c-g 34.75±0.03 b-g 34.70±0.00 b-g 34.68±0.08 c-g 34.78±0.09 b-g 34.98±0.08 a-g 34.05±0.09 g-k 34.08±0.03 g-k 34.10±0.04 f-k 34.18±0.05 e-j 34.18±0.02 e-j 34.48±0.25 d-i 34.48±0.06 d-i 34.58±0.06 c-h 35.05±0.06 a-e 35.80±0.04 a 35.45±0.06 abc 35.45±0.03 abc 34.75±0.12 b-g 26.93±0.38 s 29.40±0.25 r 31.05±0.13 pq 32.23±0.15 no 33.10±0.08 lmn 33.65±0.06 h-l 34.05±0.05 g-k 34.45±0.06 d-i 34.80±0.04 b-g 35.03±0.05 a-f 35.08±0.05 a-e Means sharing similar letter in a column are statistically non-significant (P>0.05) Screening of local germplasm for cultivation under heat stress conditions 343 In this investigation, PCA was used in order to investigate how the different genotypes perform different under high temperature stress condition. The biplot generated for different traits like shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, number of leaves, chlorophyll contents, sub-stomatal CO2, transpiration rate, stomatal conductance, photosynthetic rate, water use efficiency and leaf temperature is given in Fig. 1. The biplot generated for 54 genotypes is given in Fig. 2. According to Fig. 1, on the basis of leaf temperature (L Tmp) genotypes V41, V50, V54, V48, V53, V43, V45, V26, V28, V30 and V42 are the most tolerant for high temperature as they lay in the same region in the biplot generated for the genotypes in Fig. 2. On the other hand, genotypes V19, V22, V7, V21, V3 V18, V25 and V9 are most sensitive for leaf temperature as these genotypes lay in the opposite to the leaf temperature tolerant genotypes in the biplot in Fig. 2. In the same way on the behalf on Fig. 1, for photosynthesis (Photo), water use efficiency (WUE), root length (RL), stomatal conductance to water (St Conductance) genotypes V19, V22, V7, V21, V3 V18, V25 and V9 are most heat tolerant on the basis of the traits because these fall in the same region in biplot for genotypes given in Fig. 2. Genotypes V41, V50, V54, V48, V53, V43, V45, V26, V28, V30 and V42 are most sensitive for these traits as these genotypes lay in the opposite to the photosynthesis (Photo), water use efficiency (WUE), root length (RL), stomatal conductance to water (St Conductance) tolerant genotypes in the biplot in Fig. 2. According to Fig. 1, on the basis of shoot fresh weight (SFD), shoot dry weight (SDW), shoot length (SL), root fresh weight (RFW), root dry weight (RDW) genotypes V17, V23, V24, V27, V5 and V14 are most heat tolerant on the basis of the traits because these fall in the same region in biplot for genotypes given in the Fig. 2. While genotypes V33, V35, V12, V38, V37, V44, V34, V8, V48, V52, and V13 are most sensitive for these traits as these genotypes lay in the opposite to these traits in the biplot for genotypes in Fig. 2. In the similar way in Fig. 1, for sub-stomatal conductance to CO2, transpiration rate and chlorophyll content genotypes V33, V35, V12, V38, V37, V44, V34, V8, V48, V52, and V13 are most heat tolerant on the basis of the traits because these fall in the same region in biplot for genotypes given in the Fig. 2. While genotypes V17, V23, V24, V27, V5 and V14 most sensitive for these traits as these genotypes lay in the opposite of these traits in the biplot for genotypes in Fig. 2. Sub-stomatal CO2 was highest (Tab. 2) at 1555.6 vpm for “UC- 134” and lowest for “Roma”at 454.5 vpm. As revealed by studies conducted on CO2 concentration and its relation with plant growth rate, the results have varied. Some studies revealed CO2 to have a positive effect on photosynthetic rates and plant tolerances to heat stress (FARIA et al., 1996; FERRIS et al., 1998; HUXMAN et al., 1998; TAUB et al., 2000) whereas others reported the effect to be Tab. 3: Analysis of variance for individual trait (Morphological traits) Serial No Trait Significant level 01 Shoot Length ** 02 Root Length ** 03 Shoot Fresh Weight ** 04 Root Fresh Weight ** 05 Shoot Dry Weight ** 06 Root Dry Weight ** 07 No. of Leaves ** NS = Non-significant (P>0.05); * = Significant (P<0.05); ** = Highly significant (P<0.01) Tab. 4: Analysis of variance for individual trait (Physiological traits) Serial No Trait Significant level 01 Chlorophyll Content ** 02 Sub-stomatal CO2 ** 03 Stomatal Conductance to Water ** 04 Photosynthetic Rate ** 05 Transpiration Rate ** 06 Water Use Efficiency ** 07 Leaf Temperature ** NS = Non-significant (P>0.05); * = Significant (P<0.05); ** = Highly significant (P<0.01) Fig. 2: Biplot graph of 54 genotypes under high temperature stress on the basis of various traits. Fig. 1: Biplot graph of 54 genotypes under high temperature stress for various traits. 344 A. Nazir, M.R. Shaheen, C.M. Ayyub, R. Hussain, N. Sarwer, M. Imran, M. Aurangzaib, M. Nawaz, M.F.A. Khan, Y. Jawad, M. Iqbal negative (RODEN and BALL, 1996; HUXMAN et al., 1998; TAUB et al., 2000). Some studies suggested there to be no effect of CO2 on photosynthetic rates. “UC-134” showing highest sub-stomatal CO2 also had highest transpiration rate of 3.22 mmol/m2/s (Tab. 2). “Bush Beef Steak” with 0.66 mmol/m2/s had the lowest transpiration rates. Greatest amount of sub-stomatal water was recorded for “Sasha Altai” with 0.120 whereas “Bush Beef Steak” which had the lowest transpiration rate also had the lowest sub-stomatal water of 0.010. The highest photosynthetic activity was of “Cohaus” with 12.15 μmol/ m2/s, whereas “Nepoli” had the least photosynthetic rate of 0.95 μmol/m2/s (Tab. 2). Data collected for water use efficiency showed that “Cohaus” had highest water use efficiency (13.87). Least water use efficiency was recorded for “Nepoli” (0.53).“Naqeeb” showed highest leaf surface temperature of 35.08 °C, while the least leaf surface temperature was recorded for “Cohaus” at 26.68 °C. After experimentation it was revealed that tolerant genotypes of tomato and sugarcane exhibited the tendency of increasing their chlorophyll a:b and decreasing chlorophyll carotenoid content (CAMEJO et al., 2005). Screening results showed that highest chlorophyll contents were recorded for “Pakit” with a SPAD value of 49.03. “Spekled Sibrian” had the least chlorophyll contents of 14.85 followed by “Campbells” with 16.15 SPAD value. Conclusion It may be concluded from the present study that genotypes varied significantly for their heat tolerance potential and this variation can successfully be implied in breeding programs. 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