Identification of Heat Tolerant Cotton Lines Showing Genetic Variation in Cell Membrane Thermostability, Stomata, and Trichome Size and Its Effect on Yield and Fiber Quality Traits

Heat stress in cotton reduces its productivity. The development of heat-tolerant cotton varieties having resilience against changing climate is feasible. The purpose of this study was to probe the genetic variability in upland cotton for heat tolerance, the association of cell membrane thermostability (CMT), stomata, and trichome size with cotton adaptation to high temperature and effective breeding strategy to advance the valued traits. Relative cell injury percentage (RCI%) in studied genotypes ranged from 39 to 86%. Seventeen genotypes were found heat tolerant on the basis of low RCI%, heat susceptibility index (HSI<1), higher number of boll/plant, and seed cotton yield (SCY). Scanning electron microscopy (SEM) of heat-tolerant genotypes revealed the presence of different size of stomata (21.57 to 105.04 μm2) and trichomes (177 to 782.6 μm) on leaves of selected genotypes. The regression analysis showed a strong and negative association of RCI% and stomata size with SCY. However, no association was observed between the trichome size, yield, and fiber traits. On the overall location basis, a significant genotype × environment interaction was observed. All selected genotypes produced a higher SCY as compared with check varieties. But the stability analysis showed that the high yielding genotypes NIA-M-30, NIA-80, NIA-83, and CRIS-342 were also wide adaptive with unit regression (bi∼1) and non-significant deviation from the regression line (S2d∼0). The ability for the combination of some heat-tolerant genotypes was estimated by using the line × tester method among nine hybrids along with their 3 testers (i.e., male) and 3 lines (i.e., females). Genotypes, CRIS-342 and NIA-Perkh, were observed as best general combiners for SCY with a negative general combining ability effects for RCI%. Five hybrids showed a positive specific combining ability and heterotic effects for studied traits and also found lowest for HSI. RCI% and SCY/plant displayed higher estimates of heritability and genetic advance, indicating the heritability due to additive gene effects and chances of effective selection. The identified heat-tolerant and wide adaptive germplasm can be further advanced and utilized in cotton breeding programs for developing heat-tolerant cultivars. Selection criteria involving CMT and stomata size concluded to be an effective strategy for the screening of heat-tolerant cotton.

Intra-Plant Variability for Heat Tolerance Related Attributes in Upland Cotton

Abiotic stress, particularly heat stress, affects various parts of the cotton plant and ultimately impacts the seed cotton yield. Different portions of a single cotton plant of a cultivar exhibit variable responses to stress during reproductive and vegetative phases. To test this hypothesis, physiological and morphological traits related to heat stress were observed for two flowering positions in 13 genotypes of upland cotton. These genotypes were sown in field conditions in triplicate following a randomized complete block design. Data were collected for pollen germination, pollen viability, cell membrane thermostability, chlorophyll content, boll weight, and boll retention for both the top and bottom branches of each genotype. The collected data were analyzed for the identification of variability within and between genotypes for these two flowering positions. Tukey’s test was applied to estimate the significance of differences between genotypes and positions within each genotype. Results showed that the two positions within the same plant statistically varied from each other. The bottom branches of the genotypes performed significantly better for all traits measured except boll weight. The genotype AA-933 performed best for pollen germination and boll retention, while CYTO-608 exhibited maximum pollen viability in both the bottom and top flower positions compared with other genotypes. Overall, MNH-1016 and CIM-602 showed better cell membrane thermostability and chlorophyll content, respectively. This intra-plant variability can be further exploited in breeding programs to enhance the stress tolerance capabilities of the resulting varieties.

Heat Tolerance in Sugarcane: Optimum Temperature and Phenological Stage to Determination of Thermotolerance as Selection Criteria

Heat stress is the major abiotic stressor in agriculture which reduces crop productivity and yield. Six sugarcane (Sacharum officinarum L.) genotypes were studied to investigate the impact of three temperature levels at four phenological stages on tissue electrolyte production and the feasibility of using the cell thermostability method (CTM) for the identification and selection of heat tolerant sugarcane genotypes. The cell membrane thermostability was quantified by measuring relative cell injury percentage with a modification in the temperature treatment on four phenological stages in a field experiment. Our results suggest that heat tolerance based on cell membrane thermostability can be improved using the existing genetic variability available within the commercial or experimental sugarcane germplasm. We conclude that the cell membrane thermostability test can be a useful screening procedure for selecting sugarcane genotypes that tolerate high temperature stress. The test can be used in conjunction with a temperature trait of 60 °C during the maturity stage. This procedure predicts the ability of sugarcane genotypes to maintain yield and juice quality under stressful field conditions.

Thermotolerance and Physiological Traits as Fast Tools to Heat Tolerance Selection in Experimental Sugarcane Genotypes

Heat stress limits the growth, development, and yield of crop plants when it occurs during short or long periods of time. An experiment was conducted with the objectives of (i) evaluating the cell membrane thermostability (CMT) as an indicator of heat tolerance in sugarcane and to determine its relationship with physiological parameters under heat-stressed conditions, and (ii) evaluating the utility of CMT for selecting heat-tolerant genotypes in a breeding program. A total of nine elite experimental, and four commercial sugarcane genotypes were evaluated for CMT, and the results are expressed as relative cell injury (RCI). Six genotypes were classified as highly tolerant and seven as highly sensitive. We concluded that the use of RCI, as an indicator of CMT in sugarcane genotypes, is a suitable useful parameter for selecting the genotypes tolerant to heat stress in a breeding program. This procedure, combined with other characters, helps to identify sugarcane plants with the ability to maintain a high yield photosynthetic rate under stressful field conditions. Furthermore, it offers an opportunity to improve selection efficiency over that of field testing, since high temperature stresses do not occur consistently under field conditions.

Evaluation of exotic wheat (Triticum aestivum L.) genotypes for heat tolerance on the basis of physiological phenotyping

Plant physiological parameters such as membrane thermostability, canopy temperature depression, leaf chlorophyll content and yield related traits like no. of spikelets per spike, no. of grains per spike, 200-grain weight and grain yield of 18 wheat genotypes were carried out to assess for heat tolerance. Performances of all the genotypes were found to have significant differences for all the traits except canopy temperature depression. But, canopy temperature depression with some other traits like leaf chlorophyll content, no. of grains per spike, 200-grain weight and grain yield per plant demonstrated significant differences when it grown in heat stress condition. In general, genotypes with higher leaf chlorophyll content and enhanced membrane thermostability demonstrated higher 200-grain weight or grain yield. Besides, in spite of having heat tolerant traits, several genotypes performed poor due to their poor genotypic potential. The present investigation has successfully isolated several genotypes viz. H024, H023, H022 and H018 with desirable traits related to heat tolerance based on overall performance while grown under heat stress. These genotypes can be used as gene source for future breeding program to improve heat tolerance of the local wheat cultivars. J. Bangladesh Agril. Univ. 16(3): 457–463, December 2018

Inducing salt tolerance in sweet corn by magnetic priming

<p>This study evaluates seed germination and growth of sweet corn under NaCl stress (0, 50, and 100 mM), after exposing the seeds to weak (15 mT) or strong (150 mT) magnetic fields (MF) for different durations (0, 6, 12, and 24 hours). Salinity reduced seed germination and plant growth. MF treatments enhanced rate and percentage of germination and improved plant growth, regardless of salinity. Higher germination rate was obtained by the stronger MF, however, the seedling were more vigorous after priming with 15 mT MF. Proline accumulation was observed in parallel with the loss of plant water content under 100 mM NaCl stress. MF prevented proline accumulation by improving water absorption. Positive correlation between H₂O₂ accumulation and membrane thermostability (MTI) was found after MF treatments, which revealed that MF primed the plant for salinity by H₂O₂ signaling. However, over-accumulation of H₂O₂ after prolonged MF exposure adversely affected MTI under severe salt stress. In conclusion, magnetic priming for 6 hours was suggested for enhancing germination and growth of sweet corn under salt stress.</p>