GENETIC ANALYSIS IN VARIOUS GENOTYPES OF BREAD WHEAT UNDER NORMAL AND HEAT-STRESS ENVIRONMENTS

Abiotic stresses have brought the crops to a destructive position towards yield production of crops, especially wheat. The present study was investigated to compare the relationship between normal and heat stress conditions under two different sowing dates viz. normal and late sowing dates (25 th Nov and 25 th Dec). The correlation coefficients varied with both sowing dates (normal and late planting). In normal planting number of grains showed a significant positive correlation with grain weight spike -1 (r = 0.618**), grain yield plant -1 (r = 0.591**), seed index (r =0 .456**), biological yield plant -1 (r = 0.540**) and harvest index (r =0 .667**). Grains spike -1 contributed significant positive correlation with grains spike -1 (r=0.094**), grain yield plant -1 (r=0.844**), biological yield plant -1 (r=0.936**), harvest index (r=0.556**), leaf area (r=0.791**), relative water content (r=0.763**), chlorophyll content (r=0.853**), cell membrane stability (r=0.828**) and stomatal conductance (r=0.292**). Grain yield plant -1 exhibited a significant positive correlation under normal planting with the number of tillers plant -1 , number of spikelets spike -1 , grains spike -1, and grain weight spike -1 (r=0.695**,0.207*,0.591**and 0.950**), respectively. Whereas, late planting declared grains spike -1 revelaed signficant positive correlation with grains spike -1 (r=0.094**), grain yield plant -1 (r=0.844**), biological yield plant-1 (r=0.936**), harvest index (r=0.556**), leaf area (r=0.791**),relative water content (r=0.763**), chlorophyll content (r=0.853**), cell membrane stability (r=0.828**) and stolatal conductance (r=0.292**). Under late planting, Yield showed a significant positive correlation with spike length, grains spike -1, and grain weight spike -1 (r=0.343**,0.844**, and 0.964**), respectively


Introduction
Wheat is a staple food crop of one-third of the population of world (Abhinandan et al., 2018).Pakistan is one of the major wheat-growing countries and its divergent consumption aptitude in human nutrition leads among the cereals (Farzi and Bigloo, 2010).Plants have altered dynamic responses to defend against abiotic stresses at the morphophysiological and biochemical levels (Pandiya et al., 2016).Avoidance mechanisms escaping heat stress, counting diffuse roots, reduced stomatal number, reduced leaf area, and leaf rolling, reduce evaporation stimulation (Goufo et al., 2017).Tolerance is characterized by cellular and biochemical modifications that display hydrostatic pressure, mainly through osmotic regulation (Blum, 2017).High temperature plays a crucial role in determining yield in crop growth and development (Gray and Brady, 2016).When temperatures approach high thresholds they may adversely affect plant growth and development of the wheat crop (Farooq et al., 2011).During the anthesis and grain filling period, the wheat crop is extremely affected by high-temperature stress, and seed development is disrupted (Ahmed et al., (2022) High temperatures during flowering and seed formation lead to substantial losses.Therefore, temperature is considered an important variable determinant of agricultural practices worldwide (Yang et al., 2016).Wheat gradually increases stress tolerance through the priming phase (Wang et al., 2011).Meanwhile, the flowering and booting stages of wheat crops were more affected by heat stress (Wang et al., 2011).High temperatures have the potential to disrupt pollen development before flowering, leading to reduced seed setting (Farooq et al., 2011;Mirosavljević et al., 2021).Exposure of wheat crops to high temperatures during reproductive stages may negatively affect grain number and grain filling (Farooq et al., 2011;Xu et al., 2022).Reproductive stages involving pollen, stigma viability, flowering, and stem tube growth are highly sensitive to high temperatures (Giorno et al., 2013;Hedhly, 2011).Grain size is greatly affected by high temperature during grain filling, as higher respiration affects quality characteristics (Ahmed et al., 2022).In wheat crops, high ambient temperature, and drought may reduce photosynthetic activity, cell size, and closure of stomata (Long et al., 2022).Further stated that high temperatures reduced photosynthesis by changing the structural organization of thylakoids (Khan et al., 2021).In brief, it was evident that high temperature significantly affected anatomical structures not only in the tissues, and cells but also in the sub-cellular.During reproduction, short-term heat stress can lead to significant reductions in spikelets and their abortions despite large differences in susceptibility within and between plant species and cultivars (Sato et al., 2006).Plants may not flower or flower without fruit or seeds, even during high temperatures during reproductive development (Maheswari et al., 2012).Planting crops at different sowing dates can search for heat-tolerant genotypes (Zhang et al., 2020;Long et al., 2022).Heat stress causes multifaceted and often adverse changes in plant growth, development, physiological processes, and yield (Hasanuzzaman et al., 2013).Such disaster was investigated during high temperature (30-35 0 C) effects.A similar study was carried out by who assessed three genotypes of wheat, one heat tolerant and the other two heat susceptible genotypes.Therefore, the present study was to investigate the relationship between normal and heat stress conditions in various genotypes including parents and hybrids as well as their inheritance pattern.

Chlorophyll content (RG):
This physiological trait exhibited significant positive associations with days to 75% heaidng, days to 75% maturity, plant height, number of tillers plant-1, grains spike-1, grain weight spike -1 , grain yield plant -1, seed index, biological yield plant and harvest index.However, under late sowing this character showed a positive significant association with days to 75% heading, days to 75% maturity, plant height, spike length, grains spike, grain weight spike and grain yield plant -1, biological yield plant -1 and leaf area.Cell membrane stability (%): Cell membrane stability in wheat genotypes marked significant positive correlation with number of tillers plant -1 , grain weight spike -1 , grain yield plant -1, seed index, biological yield plant -1 , harvest index, leaf area, relative water content, chlorophyll content, cell membrane stability and stomatal conductance (r = 0.823**, 0.618**, 0.787**, 0.925**,0.437**,0.926**,0.865**, 0.935**,0.523**and 0.921**), respectively under normal planting.Accordingly, late planting showed a significant relationship with almost all the characters except for number of tillers plant -1 and seed index.From the present research work, it is regarded that the cell membrane stability showed a close but very strong positive significant association with stomatal conductance (Table 1).Islam et al. ( 2017) recorded that cell membranes showed a very strong positive correlation with various characteristics.Stomatal conductance: This physiological trait also showed a significant positive association with a number of tillers plant -1 , grains spike -1 , grain weight spike -1 , grain yield plant -1 , seed index, biological yield plant -1, harvest index, leaf area, chlorophyll content, and cell membrane stability.However, under late planting significant positive associations were depicted with tiller plant -1 , spike length, number of spikelets, grains spikelets, seed index, biological yield plant -1, and harvest index, respectively.

Heritability Estimates
The heritability estimates of bread wheat genotypes for morphological traits grown under normal and heat stress conditions: The higher heritability estimates for various quantitative traits of bread wheat genotypes determined during present study with regard days to 75% heading, days to 75% maturity, plant height, number of productive tillers plant -1 , spike length spike -1 , number of spikelets spike - 1 , number of grains spike -1 , grains weight spike -1 , grains yield plant -1 , seed index, biological yield plant - 1 and harvest index perceived with broad sense were: h 2 = 95.84, 99.86, 98.85, 83.55, 89.84, 90.21, 98.47, 99.96, 99.99, 93.99, 99.90 and 99.62% respectively in non-heat stress condition.Wherease the heritability estimates in heat stress conditions for yield morphological traits observed were; h 2 = 94.35,94.72,98.45,82.56,84.78,90.06,97.36,99.54,98.38,92.85,.These findings are in agreement of Ahmed et al.,(202)It is concluded that the lines, testers, and crosses exhibited significant relationship with most of the characters under both normal and heat stress conditions.However, correlation analysis showed significant and positive association with most of the characters including yield.Late and early planting observed to have difference in correlation with yield characters.Though high heritability was influenced by both early and late sowing dates.

AUTHORS' CONTRIBUTION:
Raza Ali Rind analyzed and interpreted the data, Wajid Ali Jatoi designed the experimental design, Shabana Memon helped with the manuscript writeup and Aijaz Ahmed Soomro supported the data interpretation.

ONFLICT OF INTEREST:
Authors have no conflict of interest.
reproductive and grain-filling phases.Critical Reviews in Plant Sciences,