Drought stress restricts plant growth and development by altering metabolic activity and biological functions. However, plants have evolved several cellular and molecular mechanisms to overcome drought stress. Drought tolerance is a multiplex trait involving the activation of signaling mechanisms and differentially expressed molecular responses. Broadly, drought tolerance comprises two steps: stress sensing/signaling and activation of various parallel stress responses (including physiological, molecular, and biochemical mechanisms) in plants. At the cellular level, drought induces oxidative stress by overproduction of reactive oxygen species (ROS), ultimately causing the cell membrane to rupture and stimulating various stress signaling pathways (ROS, mitogen-activated-protein-kinase, Ca²⁺, and hormone-mediated signaling). Drought-induced transcription factors activation and abscisic acid concentration co-ordinate the stress signaling and responses in cotton. The key responses against drought stress, are root development, stomatal closure, photosynthesis, hormone production, and ROS scavenging. The genetic basis, quantitative trait loci and genes of cotton drought tolerance are presented as examples of genetic resources in plants. Sustainable genetic improvements could be achieved through functional genomic approaches and genome modification techniques such as the CRISPR/Cas9 system aid the characterization of genes, sorted out from stress-related candidate single nucleotide polymorphisms, quantitative trait loci, and genes. Exploration of the genetic basis for superior candidate genes linked to stress physiology can be facilitated by integrated functional genomic approaches. We propose a third-generation sequencing approach coupled with genome-wide studies and functional genomic tools, including a comparative sequenced data (transcriptomics, proteomics, and epigenomic) analysis, which offer a platform to identify and characterize novel genes. This will provide information for better understanding the complex stress cellular biology of plants.

Global environmental changes with more extreme episodes of heat waves are major threats to agricultural productivity. Heat stress in spring affects the reproductive stage of maize, resulting in tassel blast, pollen abortion, poor pollination, reduced seed set, barren ears and ultimately yield loss. As an aneamophelous crop, maize has a propensity for pollen abortion under heat stress conditions. To overcome the existing challenges of heat stress and pollen abortion, this study utilized a broad genetic base of maize germplasm to identify superior alleles to be utilized in breeding programs. A panel of 375 inbred lines was morpho-physiologically screened under normal and heat stress conditions in two locations across two consecutive planting seasons, 2017 and 2018. The exposure of pollen to high temperature showed drastic decline in pollen germination percentage. The average pollen germination percentage (PGP) at 35 and 45°C was 40.3% and 9.7%, respectively, an average decline of 30.6%. A subset of 275 inbred lines were sequenced using tunable genotyping by sequencing, resulting in 170,098 single nucleotide polymorphisms (SNPs) after filtration. Genome wide association of PGP in a subset of 122 inbred lines resulted in ten SNPs associated with PGP35°C (p ≤ 10⁻⁵), nine with PGP45°C (p ≤ 10⁻⁶–10⁻⁸) and ten SNPs associated with PGP ratio (p ≤ 10⁻⁵). No SNPs were found to be in common across PGP traits. The number of favorable alleles possessed by each inbred line for PGP35°C, PGP45°C, and the PGP ratio ranged between 4 and 10, 3–13 and 5–13, respectively. In contrast, the number of negative alleles for these traits ranged between 2 and 8, 3–13 and 3–13, respectively. Genetic mapping of yield (adjusted weight per plant, AWP⁻¹) and flowering time (anthesis-silking interval, ASI) in 275 lines revealed five common SNPs: three shared for AWP⁻¹ between normal and heat stress conditions, one for ASI between conditions, and one SNP, CM007648.1-86615409, was associated with both ASI and AWP⁻¹. Variety selection can be performed based on these favorable alleles for various traits. These marker trait associations identified in the diversity panel can be utilized in breeding programs to improve heat stress tolerance in maize.

A research study was led to estimate the genomic composition of five diverse forms of maize genotypes by investigating their combining abilities. The outcomes showed that General Combining Ability (GCA) in maize inbred lines exhibited significant variations across all characteristics under both heat and control environments. Specific Combining Ability (SCA) had significant variation in most characteristics under study, except for anthesis silk interval and number of ears per plant under heat stress. The genotypes ILC 276 and FM ILC 10 were recognized as decent general combiners for traits such as days to 50% tasseling, plant height, grain yield, number of kernels per ear, canopy temperature, cell membrane thermo-stability, pollen viability, and chlorophyll content. The crosses FM-ILC 10 x ILC 22, FM-ILC 10 x ILC 276, and FM-ILC 144 x ILC 255 were the best specific combiners for traits such as plant height, grain yield, number of kernels per ear, canopy temperature, pollen viability, and chlorophyll content. These hybrids are the best for high yield. The crosses ILC-22 x ILC-50, ILC-22 x ILC-276, ILC-50 x ILC-255, and ILC-50 x ILC-276 had high mid parent and better parent values for heterosis, demonstrating that they are the top-execution crosses with important positive heterosis for grain yield. Bi-plot investigation amid crosses of maize ILC 276 x ILC 22, ILC 276 x FM-ILC 10, and ILC 255 x FM-ILC 144 exhibited extreme genetic variability, and traits such as canopy temperature, cell membrane thermo-stability, plant height, anthesis silking interval and number of kernels per ear were positively associated with each other. Cluster analysis grouped the maize crosses into four and three clusters under normal and heat stress conditions respectively. These recognized crosses can be employed in further breeding plans to grow heat-tolerant hybrids for commercial seed production of maize.