The field experiment was conducted at Bangladesh Agricultural Research Institute, On-Farm Research Division, Region-1, Agriculture Research Division, Shyampur, Rajshahi-6212. Bangladesh during the period from 9^th December 2021 to 16^th March 2022 to find out the effect of heat on the growth and yield of potato. On 9^th December 2021 minimum and maximum temperature were 13˚C and 25˚C respectively. Minimum temperature was 9˚C from 29^th to 30^th January 2022 and maximum temperature was 34˚C on 16^th March 2022 throughout the cultivation period of these potato lines. Average minimum-maximum temperature from 1^st December, 2021 to January, February 29^th March,2022 were 12.8˚C - 23.1˚C, 10.7˚C - 23.8˚C, 14.3˚C - 26.7˚C, 24.1˚C - 36.9˚C respectively. Maximum temperature was between 28˚C to 34˚C throughout 1^st March to 16^th March during cultivation. Details about maximum and minimum temperature as reported by Bangladesh Rice Research Institute R.S, Rajshahi. The experimental site located in the 11^th AEZ of Bangladesh named High Ganges River Floodplain [27] . The soils of this AEZ have been formed from the calcareous Ganges River alluvium [28] . The chosen location’s analytical results for the soil sample were P^H; 7.5, total nitrogen (%); 0.07, P; 32.0 ppm, K; 0.28 Cmole/kg; S; 24.2 ppm, Zn; 1.86 ppm, B; 1.00 ppm. Result obtained from the mechanical analysis of the initial soil sample was done in the (SRDI) Soil Resource Development Institute, Regional Research Station, Shyampur, Rajshahi.

A fertilizer does of N, P, K, Zn, S and B was supplied in the form of Urea (192 - 300 Kg/ha), Triple Super phosphate (105 - 150 Kg/ha), Muriate of potash (180 - 270 Kg/ha), Zinc sulphate (8 - 12 Kg/ha), Gypsum (60 - 82 Kg/ha) and Boric acid (3 - 5 Kg/ha) as recommended doses for AEZ 11 [29] . Row to row distance and plant to plant distance was 60 cm and 25 cm, respectively. Three replications were done with Randomized complete block design. Seed tubers were planting on 09^th December 2021. The twenty potato lines for heat tolerant are named TB15A-51, TB15A-118, TB15A-120, TB15A-141, TB15A-146, TB15B-05, TB15B-12, TB15B-19, TB16-09, TB16-10, TB16-11, TB19-01, TB19-06, TB19-07, TB19-09, TB19-17, TB19-23, TB19-25, TB19-39, TB19-19-40 were collected from Bangladesh Agricultural Research Institute. The heat tolerance lines were selected and used in this study on the previous screening by BARI and their recommendation. The sprouted seed tubers were treated with Dithane M-45 @ 2.5 g/L solution. Earthing up was done at 30, 40 and 60 DAP and the furrows turn into ridges up to 20 cm height. The second top dressing was completed 30 days after planting. First irrigation was done on 11^th December 2021 after sowing and second irrigation was done at 17^th January 2022. On 4^th February 2022 heavy rainfall and on 10^th February along with 24^th February 2022 light rainfall happened. To protect the crop from diseases especially late blight and insect pest (particularly aphids) Malathion @ 2 ml/liter and (Maladan 50 EC) with water were applied for control aphids at 40 DAP and Dithane M-45 @ 2 g/liter was done at 60 DAP. Weeding was done when required. Haulm cutting of the crop was completed 90 days after planting. From 7 days after haulm cutting, digging was done. Mature potatoes were harvested on 16^th March 2022.

Data on growth yield and yield contributing characters were recorded from the sample plants of each plot during experiment. The sampling was done randomly from each plot to record the data. Eight plants per plot were measured for sampling. Plant height and stem number were measured at 60 DAPS. Plant maturity was recorded at 70 DAP, 80 DAP and 90 DAP respectively due to heat /water shortage in 1 - 5 scale where 1 = Dead and 5 = very green. Plant maturities were recorded at 70 DAP, 80 DAP and 90 DAP due to heat /water shortage (1 - 5 scale, 1 = Dead and 5 = very green). To measure the yield tuber weight in a line was measured then yield per plant and Ton/Hectare were obtained.

$\text{Yield}\text{per}\text{plant}=\frac{\text{Total}\text{tuber}\text{weight}\text{in}\text{line}\text{in}\text{kg}}{\text{Total}\text{number}\text{of}\text{plants}\text{in}\text{line}}$;

$\text{Ton}/\text{Hectare}=\frac{\text{Yield}\text{per}\text{plant}\text{in}\text{kg}\times \text{Number}\text{of}\text{plants}\text{in}\text{one}\text{hactare}}{1000\text{kg}}$;

$\text{Number of plants in One Hectare}=\frac{10000{\text{m}}^2}{\text{Area}\text{needed}\text{in}{\text{m}}^2\text{for}\text{one}\text{plant}}$

To find out the significance of experimental results the data on different parameters were analyzed statistically by using STATISTIX 10 package program.

The growth parameter of plant influence by various physiological process [30] [31] . Plant height exhibited significant variation among the evaluated lines. Measurements taken 60 days after planting (DAP) revealed that the highest mean plant height (54.33 cm) was recorded in the line TB19-23, which was statistically identical to TB19-39, TB15A-146, TB19-07, and TB16-10. The lowest plant height (33.00 cm) was observed in the line TB15A-51, which was statistically similar to TB15A-120 ( Figure 1 ). [32] also reported significant differences in plant height among genotypes, with values ranging from 33.33 to 52.80 cm at 45 DAP. Although the present findings are comparable in magnitude, the observation period differs. In the same study, plant height at 60 DAP ranged from 38.60 to 64.67 cm, further supporting the genotypic variability in growth performance. Similarly, [33] reported that the cultivar “Asterix” exhibited the tallest plants (69.6 cm), while “Granola” showed the shortest (53.8 cm) at 60 DAPS, which differs from the present results in terms of absolute values. [34] observed that the highest plant height (56.68 cm) occurred in BARI Alu-40 with a December 20 sowing date, whereas the lowest (34.35 cm) was recorded for the same cultivar sown on November 20, consistent with the current study in terms of overall growth range. Moderate plant height and bushy growth habit are generally desirable traits for achieving higher yields (Rahman et al., 2014). Variations in plant height are primarily influenced by the plant’s genetic makeup and its corresponding growth characteristics [35] .

Stem number was found to differ significantly among the evaluated potato lines. Stem number per line was recorded 60 days after planting (DAP). The highest mean stem number (25.67) was observed in line TB19-25, which was statistically identical to TB16-10, TB15B-12, TB16-09, and TB16-11. The lowest mean (9.67) was recorded in TB15B-05, which was statistically similar to TB15A-141 ( Figure 2 ).

In a previous study, Asterix exhibited the highest number of stems per plant (6.66) at 60 DAP, while Lady Rosetta showed the lowest (3.67) [36] . However, that study was conducted using different potato varieties, whereas the present study focused on potato lines, with five plants established per line. Therefore, the observed range of stem numbers per plant in this study differs from the findings of [36] . Similarly, Hossain (2011) reported that Asterix had the highest number of stems per hill (7.10) and Granola the fewest (4.09) at 60 DAPS in the same agro-climatic zone. [37] also noted that the maximum number of stems per hill (5.70) occurred in BARI Alu-41, followed by BARI Alu-40 (5.60) and BARI Alu-37 (5.30), while BARI Alu-36 produced the fewest stems (3.80).

Plant maturity was assessed at 70, 80, and 90 days after planting (DAP) using a 1 - 5 scale, where lower values indicated early senescence and higher values represented greener, late-maturing plants. Significant variation in maturity was observed among the tested potato lines across all observation stages, reflecting differences in growth duration and physiological responses to environmental conditions. At 70 DAP, lines TB16-11, TB15A-141, TB16-10, and TB19-39 exhibited the highest maturity score (5.00), remaining vigorous and green, and were statistically identical to TB15B-12, TB19-07, and TB19-23. Conversely, the lowest score (2.67) was recorded in TB15A-51, which was statistically similar to TB15A-120, TB19-09, TB19-40, and TB15A-118, indicating early senescence. Most other lines displayed intermediate scores between 3.0 and 4.0, suggesting moderate maturity levels. These findings imply that genotypic variation significantly influenced foliage longevity and growth duration during early reproductive stages ( Figure 3 ).

At 80 DAP, overall maturity scores declined compared with 70 DAPS, indicating progressive senescence. However, significant differences among lines persisted ( Figure 3 ). TB16-10 recorded the highest mean score (4.67), statistically identical to TB19-23, TB16-11, and TB15A-141, demonstrating superior foliage retention and delayed leaf yellowing. In contrast, TB15A-51 exhibited the lowest maturity score (2.00), similar to TB15A-120 and TB19-09, reflecting early senescence and reduced vegetative activity. The moderate-performing lines TB15B-12, TB15B-19, and TB19-07 maintained intermediate scores between 3.5 and 4.0. Notably, TB16-10 remained the greenest at this stage, suggesting high photosynthetic persistence and stress tolerance under late-season conditions. By 90 DAP, senescence progressed substantially across all genotypes. The highest mean score (3.00) was recorded in TB19-23, statistically identical to TB16-10 and TB15A-141 ( Figure 3 ), indicating relatively delayed maturity. The lowest score (1.00) was observed in TB15A-51 and TB16-09, denoting complete senescence and maturity completion. Several lines, including TB15A-120, TB19-01, TB19-06, TB19-09, and TB19-17, scored between 1.0 and 1.5, representing nearly mature plants. Only TB19-23 maintained a comparatively higher maturity score, suggesting a slower aging process and prolonged canopy activity.

Overall, the findings demonstrate clear genotypic differences in maturity behavior. Lines such as TB15A-51 showed consistent early maturity across all stages, which may be advantageous for short-duration cultivation or early harvesting. In contrast, TB16-10, TB15A-141, TB16-11, and TB19-23 retained green foliage for a longer period, reflecting delayed senescence and potentially higher assimilate production during late growth stages. These genotypes could therefore be promising candidates for environments favoring extended growth duration and high yield potential. The variation in maturity patterns may be attributed to genetic factors influencing leaf longevity, chlorophyll degradation, and stress tolerance mechanisms, aligning with earlier studies highlighting genotypic variability in physiological aging among potato cultivars.

Significant differences in yield were observed among the tested potato lines. For yield per line, the highest mean (4.00 kg) was recorded in TB19-23, which was statistically identical with TB16-10, TB16-11, and TB19-25. The lowest mean (1.25 kg) was observed in TB15A-120, statistically similar to TB19-09, TB15A-51, and TB15-01. Yield comparison across different harvesting times showed that tuber yield was maximized at 90 DAP, confirming this stage as the most appropriate for harvesting [36] . In contrast, harvesting at 100 DAP reduced yield due to increased soil and air temperatures, which adversely affect tuber bulking [38] . For yield per plant, TB19-23 again showed the maximum performance (0.81 kg), statistically identical with TB16-10, TB16-11, and TB19-25, while TB15A-120 produced the lowest yield per plant (0.26 kg), statistically similar to TB19-01. In terms of yield per hectare, TB19-23 achieved the highest mean yield of 53.36 t/ha, which was statistically identical with TB16-10 and TB19-25. In contrast, TB15A-120 recorded the lowest mean yield (16.59 t/ha), statistically identical with TB19-01 and TB15A-51 ( Figure 4 ).

These results considerably surpass the yields reported for established varieties such as Asterix (31.46 t/ha) and Granola (24.82 t/ha) [39] . Previous studies have reported yield ranges of 25 - 35 t/ha for Asterix, 25 - 40 t/ha for Cardinal and Diamant, and 20 - 30 t/ha for Granola [40] . The observed variation in tuber yield among lines may be attributed to genotypic differences, plant growth vigor, crop duration, and adaptability to prevailing environmental conditions, as supported by earlier findings [41] - [45] . Overall, TB19-23 consistently demonstrated superior yield performance across all parameters, with 53.36 t/ha yield exceeding that of widely cultivated commercial varieties, highlighting its strong potential for variety development under heat stress conditions. However, multi-environment trials are necessary to confirm the stability and adaptability of the promising TB19-23 line