Soil salinization poses a global challenge to agricultural sustainability, crop productivity, and food security. In maize, salinity stress severely restricts root and shoot development, ultimately compromising yield and quality. Unlike the traditional descriptive structure, this review presents a method-validation-oriented workflow that summarizes the molecular and genetic basis of salinity tolerance and aims to integrate salt-responsive genic resources, mine candidate genes, and clarify their functional roles in maize. First, we synthesize independent studies on maize salinity tolerance and compile a curated set of reported salt-responsive genes. On this basis, we construct a regulatory network underlying plant responses to salinity stress, thereby outlining the evolving landscape of their genetic and molecular regulation. Second, we catalogue genic resources, including quantitative trait loci (QTLs), quantitative trait nucleotides (QTNs), and functionally validated genes, identify QTL/QTN hotspots, and validate a multi-omics integration strategy by mapping transcriptomic, proteomic, and metabolomic salt-responsive signals onto hotspot regions to prioritize candidate genes. Third, comparative collinearity analyses across maize, rice, wheat, and sorghum further reveal orthologous genes associated with salinity tolerance in maize. Through this workflow, we identify 19 previously uncharacterized genes involved in salinity stress responses, 14 of which are predicted to participate in three salt-responsive pathways: proline biosynthesis, ABA signaling, and the PEP bypass. Importantly, we further validate the practical utility of this review-derived prioritization by functionally testing two candidates using virus-induced gene silencing (VIGS). Collectively, this workflow provides a reusable, quality-controlled set of actionable targets for developing high-yielding, salt-tolerant maize and other crops through integrated genomics, systems biology, and advanced breeding technologies.

Genotype by environment (G×E) interactions are of great interest for breeders to identify test locations and adapted genotypes. In the present study, 20 sub-tropical maize hybrids along with 5 commercial checks were planted at different locations under different ecologies (drought, high temperature, water logging and optimum environments) and evaluated for grain yield through the Best Linear Unbiased Estimations (BLUEs) and the Best Linear Unbiased Predictors (BLUPs). Genotypic and phenotypic correlations were also obtained among the different locations within the diverse ecologies. The trials were conducted during winter 2023 under drought, Spring 2024 under high temperature stress and under water logging during rainy 2023, respectively. The Genotype main effect plus genotype x environment interaction (GGE) biplot indicated that first and second principal components (PC1 and PC2) explained 100% of variation in drought, heat stress, water logging conditions. Under optimal conditions, it explained 75.81% variation. As per BLUE and BLUP, DKC 9144 and BH 417177 under drought, RCRMH 20 was under heat stress and BH 417144 under waterlogging were the best. Dendrogram was generated using Ward’s method of cluster analysis. Genotype RCRMH 20 was identified as the best performing genotype under heat (at locations Begusarai, Godhra and Kolhapur) and at water logging (Ludhiana, Hyderabad and Varanasi) with mean yield of 60.07 q/ha and 50.52 q/ha respectively. Based on these results it is recommended that hybrids namely MFH 2265, BH 417144, RCRMH 20 and BH 417177 may be tested in larger plot size before recommendation for release for commercial cultivation based on their performance in respective zones.

In the Asian tropics, maize is predominantly grown as a rainfed crop during the summer-rainy season, which often suffers significant yield losses due to the erratic distribution pattern of monsoon rain that causes intermittent dry spells and/or excessive moisture within the season. The climate-induced abiotic stresses, particularly drought and waterlogging, pose significant threats to rainfed maize cultivation in the Asian tropics, where erratic patterns of monsoon rain and associated high genotype-by-environment interaction (GEI) effects undermine yield stability. To address these challenges, this study evaluated 61 advanced-stage maize hybrids developed under the Asia Waterlogging and Drought Tolerant (AWDT) product profile, designed to deliver hybrids with stable grain yields under variable moisture regimes without yield penalties under optimal conditions. Multi-environment trials (METs) were conducted across 19 locations in South and Southeast Asia (India, Bangladesh, Vietnam, and Thailand) under four moisture regimes: optimal, rainfed/random stress, reproductive-stage drought, and vegetative-stage waterlogging. A stratified ranking approach was employed to identify superior hybrids that matched or exceeded commercial checks under optimal conditions and outperformed them under at least one stress environment. Several elite hybrids demonstrated broad or specific adaptation to targeted stress-prone environments. These findings underscore the importance of targeted breeding and MET-based selection strategies in developing high-performing stress-resilient maize cultivars for climate-vulnerable agroecologies, with implications for food security, farmer livelihoods, and sustainable cropping systems in the face of escalating climate variability.

Maize is the second most important staple food crop in the world after wheat. For maize hybrid seed production, a prominent step is detasseling in the female parent, which is laborious, time consuming, and increases the hybrid seed cost by 15 to 20 percent. Hence, to overcome this problem, exploitation of male sterility in maize crops gains special significance. In this direction, the research was conducted to transfer cytoplasmic male sterility (CMS-C) from a CMS donor (VL192114) into the female parents (CAL1514 and ZL153493) of heat- and drought-resilient maize hybrids (RCRMH-2 and RCRMH-3) by a marker-assisted backcross scheme. The present research used Diversity Array Technology (DArTag) and Kompetitive Allele Specific PCR (KASP)-based single-nucleotide polymorphic markers for background selection in backcross populations. Genome recovery percentage ranged from 64.25 to 72.70, 78.94 to 87.69 and 82.28 to 90.77 percent in the BC1F1, BC2F1 and BC3F1 population, respectively, in the CAL1514 population, while it was 63.47 to 73.55, 78.16 to 88.76 and 83.96 to 91.81 percent in the BC1F1, BC2F1 and BC3F1 population, respectively, in the ZL153493 population. When the near-isogenic CMS lines of both populations are compared for agro-morphological traits with their recurrent parents, the agronomic qualities of recurrent parents, as well as the attributes of distinctness, uniformity and stability, are shown. Therefore, male sterility-transferred, female lines of RCRMH-2 and RCRMH-3 maize hybrids can be used directly to produce maize hybrid seed without the need of the detasseling process.

High atmospheric temperatures can reduce maize production in different parts of Asia. Heat stress is the major driving force behind the need for varietal development that confers a heat tolerance trait (drought + heat tolerant) to maize hybrids. CIMMYT has developed heat-tolerant maize hybrids and deployed them in the market in collaboration with NARS partners. This study was conducted to estimate farmers’ willingness to pay for heat-tolerant maize hybrids in the Terai region of Nepal. A socioeconomic survey of 404 randomly selected maize-growing households was conducted to estimate farmers’ willingness to pay using the contingent valuation method. Given the economic importance of heat-tolerant maize hybrids in maize cultivation, the survey showed that the average WTP for heat-tolerant maize hybrids was 71% more than that for the current varieties in the market, including overall seed sources and subsidized seed. Without a subsidy, the farmers’ WTP price was at a 19% premium compared to the average price paid for conventional hybrids. Factors such as education, owning land, the interaction of hybrid adopters and owning land, soil depth, the number of goats/sheep, and the semi-pucca homes of households influenced the WTP for heat-tolerant maize hybrids. Heterogeneous demand was observed with respect to years of hybrid maize cultivation, farmers’ association with the network group, and the gender of the head of the household. In the context of climate change and global warming scenarios, Nepal’s agriculture policy should prioritize increasing domestic seed production and the distribution of heat-tolerant maize hybrids through a public–private partnership model.

Climate change-induced heat stress combines two challenges: high day-and nighttime temperatures,and physiological water deficit due to demand-side drought caused by increase in vapor-pressure deficit.It is one of the major factors in low productivity of maize in rainfed stress-prone environments in South Asia, affecting a large population of smallholder farmers who depend on maize for their sustenance and livelihoods. The International Maize and Wheat Improvement Center（CIMMYT） maize program in Asia, in partnership with public-sector maize research institutes and private-sector seed companies in South Asian countries, is implementing an intensive initiative for developing and deploying heat-tolerant maize that combines high yield potential with resilience to heat and drought stresses. With the integration of novel breeding tools and methods, including genomics-assisted breeding, doubled haploidy, fieldbased precision phenotyping, and trait-based selection, new maize germplasm with increased tolerance to heat stress is being developed for the South Asian tropics. Over a decade of concerted effort has resulted in the successful development and release of 20 high-yielding heat-tolerant maize hybrids in CIMMYT genetic backgrounds. Via public–private partnerships, eight hybrids are presently being deployed on over 50,000 ha in South Asian countries, including Bangladesh, Bhutan, India, Nepal, and Pakistan.

Abiotic stresses (drought, heat) are one of the major impediments to enhancing the maize productivity of marginal farmers in the facet of climate change. The present study attempts to investigate the impact of heat-tolerant maize hybrid on yield and income in the Terai region of Nepal. This study uses cross-sectional farm household-level data collected in August 2021 from a randomly selected sample of 404 rural households. We used a doubly robust inverse probability weighted regression adjustment method to obtain reliable impact estimates. Adoption of heat-tolerant hybrid increases yields by 16% and income by 44% in the spring season (a stress condition). Overall, yield increases by 12%, net income by 31%, saving of 40% in seed costs, and per capita food expenditure increases by 8.50%. Hence a conducive environment must be created for scaling up heat-tolerant maize varieties to increase productivity, minimize risk, and transform of the maize sector.

Identification of high-yielding and stable cultivars across different environments through multi-location trials are very important inmaize breeding. A study was conducted to evaluate 30 maize hybrids in three diverse environments, viz., drought, rainfed and optimalconditions during the years, 2016 and 2017. Environments, genotypes and Genotype × Environment interactions (G × E) were foundto be highly significant in both the years. The biplot explained 69.49% of total variation which was partitioned into 53.61 and 15.88%relative to genotype and genotype by environment interaction. Genotype, ZH15449 performed considerably well in 2016 under optimum(113.41 q/ha) and drought (54.19 q/ha) while in 2017, under optimum (82.28 q/ha) and rainfed (65.37 q/ha) conditions. ZH 161285 gaveconsiderable grain yield at all three ecologies (108.70, 74.29, 60.60 q/ha) in year 2016, whereas genotype, ZH 161330 performed wellunder rainfed (67.76 q/ha) and drought (52.87q/ha) conditions in year 2017.

Unpredictable weather vagaries in the Asian tropics often increase the risk of a series of abiotic stresses in maize-growing areas, hindering the efforts to reach the projected demands. Breeding climate-resilient maize hybrids with a cross-tolerance to drought and waterlogging is necessary yet challenging because of the presence of genotype-by-environment interaction (GEI) and the lack of an efficient multi-trait-based selection technique. The present study aimed at estimating the variance components, genetic parameters, inter-trait relations, and expected selection gains (SGs) across the soil moisture regimes through genotype selection obtained based on the novel multi-trait genotype–ideotype distance index (MGIDI) for a set of 75 tropical pre-released maize hybrids. Twelve traits including grain yield and other secondary characteristics for experimental maize hybrids were studied at two locations. Positive and negative SGs were estimated across moisture regimes, including drought, waterlogging, and optimal moisture conditions. Hybrid, moisture condition, and hybrid-by-moisture condition interaction effects were significant (p ≤ 0.001) for most of the traits studied. Eleven genotypes were selected in each moisture condition through MGIDI by assuming 15% selection intensity where two hybrids, viz., ZH161289 and ZH161303, were found to be common across all the moisture regimes, indicating their moisture stress resilience, a unique potential for broader adaptation in rainfed stress-vulnerable ecologies. The selected hybrids showed desired genetic gains such as positive gains for grain yield (almost 11% in optimal and drought; 22% in waterlogging) and negative gains in flowering traits. The view on strengths and weaknesses as depicted by the MGIDI assists the breeders to develop maize hybrids with desired traits, such as grain yield and other yield contributors under specific stress conditions. The MGIDI would be a robust and easy-to-handle multi-trait selection process under various test environments with minimal multicollinearity issues. It was found to be a powerful tool in developing better selection strategies and optimizing the breeding scheme, thus contributing to the development of climate-resilient maize hybrids.

Breeding for heat stress tolerance became a priority in sub-Saharan Africa (SSA), as projections are showing an increase in frequency, duration, and severity. In this study, 14 heat stress tolerant-donor lines (HSTDLs) sourced from CIMMYT-India (males) were crossed with 15 locally adapted elite lines (females) developed within the CIMMYT-Zimbabwe maize-breeding program using the North Carolina Design II mating scheme. The resultant 175 single crosses were evaluated alongside five commercial hybrids and adjacent to the trial of parental lines used in the crosses across two locations representing heat stress and optimal environments in Zimbabwe. The design II analysis showed significant (p < 0.01) general combining ability (GCA) effects for exotic heat donor lines and specific combining ability (SCA) effects on grain yield under heat stress, optimal conditions, and across locations; demonstrating additive and non-additive genetic inheritance of grain yield. High Baker’s ratios observed in this study indicate predominance of additive over non-additive gene effects. Three exotic HSTDLs, namely CAL14138, CAL152, and CAL1440, exhibited significant (p < 0.001) and positive GCA effects under heat stress conditions. The results imply that these exotic lines could serve as valuable genetic resources for introgression of heat tolerant alleles into local maize populations for accelerated yield genetic gains. Single crosses, DJ265-15 × VL1018816 and DJ267-9 × CAL1440, exhibited positive and significant (p < 0.01) and (p < 0.05) SCA effects for grain yield under heat stress conditions, respectively. These crosses can be used for further breeding and can contribute to grain yield performance under heat stress conditions. The exotic HSTDLs, CAL14138, CAL152, and VL109126 showed superior per se performance under heat, optimal conditions, and across environments. Overall data demonstrate the potential of exotic HSTDLs for improving the adaptation of maize to heat stress in sub-tropical breeding programs.

Understanding the impact of excess moisture (EM) on maize plants at various growth stages, and studying the phenological, physiological and molecular responses of tolerant maize genotypes towards adaptation to EM stress, could help define ways in which this trait could be improved through targeted breeding. Thus, this chapter discusses the (i) impact of EM stress on maize plants, (ii) phenological adaptations and physiological mechanisms leading to EM stress tolerance in maize, and (iii) molecular signature of EM stress tolerance. Genetic studies on EM stress tolerance in maize are presented, and the application of molecular mreeding for EM tolerance in maize is described.

Erratic rainfall often results in intermittent drought and/or waterlogging and limits maize (Zea mays L.) productivity in many parts of the Asian tropics. Developing climate-resilient maize germplasm possessing tolerance to these key abiotic stresses without a yield penalty under optimal growing conditions is a challenge for breeders working in stress-vulnerable agro-ecologies in the region. Breeding stress-resilient maize for rainfed stress-prone ecologies is identified as one of the priority areas for CIMMYT-Asia maize program. We applied rapid cycle genomic selection (RCGS) on two multiparent yellow synthetic populations (MYS-1 and MYS-2) to improve grain yield simultaneously under drought and waterlogging conditions using genomic-estimated breeding values (GEBVs). Also, the populations were simultaneously advanced using recurrent phenotypic selection (PS) by exposing them to managed drought and waterlogging and intermating tolerant plants from the two selection environments. Selection cycles per se (C1, C2, and C3) of the two populations developed using RCGS and PS approach and their test-cross progenies were evaluated separately in multilocation trials under managed drought, waterlogging, and optimal moisture conditions. Significant genetic gains were observed with both GS and PS, except with PS in MYS-2 under drought and with GS in MYS-1 under waterlogging. Realized genetic gains from GS were relatively higher under drought conditions (110 and 135 kg ha−1 year−1) compared to waterlogging (38 and 113 kg ha−1 year−1) in both MYS-1 and MYS-2, respectively. However, under waterlogging stress PS showed at par or better than GS as gain per year with PS was 80 and 90 kg ha−1, whereas with GS it was 90 and 43 kg ha−1 for MYS-1 and MYS-2, respectively. Our findings suggested that careful constitution of a multiparent population by involving trait donors for targeted stresses, along with elite high-yielding parents from diverse genetic background, and its improvement using RCGS is an effective breeding approach to build multiple stress tolerance without compromising yield when tested under optimal conditions

Background Heat tolerance is becoming increasingly important where maize is grown under spring season in India which coincide with grain filling stage of crop resulting in tassel blast, reduced pollen viability, pollination failure and barren ears that causes devastating yield losses. So, there is need to identify the genomic regions associated with heat tolerance component traits which could be further employed in maize breeding program. Results An association mapping panel, consisting of 662 doubled haploid (DH) lines, was evaluated for yield contributing traits under normal and natural heat stress conditions. Genome wide association studies (GWAS) carried out using 187,000 SNPs and 130 SNPs significantly associated for grain yield (GY), days to 50% anthesis (AD), days to 50% silking (SD), anthesis-silking interval (ASI), plant height (PH), ear height (EH) and ear position (EPO) were identified under normal conditions. A total of 46 SNPs strongly associated with GY, ASI, EH and EPO were detected under heat stress conditions. Fifteen of the SNPs was found to have common association with more than one trait such as two SNPs viz. S10_1,905,273 and S10_1,905,274 showed colocalization with GY, PH and EH whereas S10_7,132,845 SNP associated with GY, AD and SD under normal conditions. No such colocalization of SNP markers with multiple traits was observed under heat stress conditions. Haplotypes trend regression analysis revealed 122 and 85 haplotype blocks, out of which, 20 and 6 haplotype blocks were associated with more than one trait under normal and heat stress conditions, respectively. Based on SNP association and haplotype mapping, nine and seven candidate genes were identified respectively, which belongs to different gene models having different biological functions in stress biology. Conclusions The present study identified significant SNPs and haplotype blocks associated with yield contributing traits that help in selection of donor lines with favorable alleles for multiple traits. These results provided insights of genetics of heat stress tolerance. The genomic regions detected in the present study need further validation before being applied in the breeding pipelines.

Spring maize area has emerged as a niche market in South Asia. Production of maize during this post-rainy season is often challenged due to heat stress. Therefore, incorporating heat stress resilience is an important trait for incorporation in maize hybrids selected for deployment in this season. However, due to the significant genotype × environment interaction (GEI) effects under heat stress, the major challenge lies in identifying maize genotypes with improved stable performance across locations and years. In the present study, we attempted to identify the key weather variables responsible for significant GEI effects, and identify maize hybrids with stable performance under heat stress across locations/years. The study details the evaluation of a set of prereleased advanced maize hybrids across heat stress vulnerable locations in South Asia during the spring seasons of 2015, 2016 and 2017. Using factorial regression, we identified that relative humidity (RH) and vapor pressure deficit (VPD) as the two most important environmental covariates contributing to the large GEI observed on grain yield under heat stress. The study also identified reproductive stage, starting from tassel emergence to early grain-filling stage, as the most critical crop stage highly susceptible to heat stress. Across-site/year evaluation resulted in identification of six high yielding heat stress resilient hybrids.

Northern Corn Leaf Blight (NCLB) caused by Setosphaeria turcica, is one of the most important diseases of maize world-wide, and one of the major reasons behind yield losses in maize crop in Asia. In the present investigation, a high-resolution genome wide association study (GWAS) was conducted for NCLB resistance in three association mapping panels, predominantly consisting of tropical lines adapted to different agro-ecologies. These panels were phenotyped for disease severity across three locations with high disease prevalence in India. High density SNPs from Genotyping-by-sequencing were used in GWAS, after controlling for population structure and kinship matrices, based on single locus mixed linear model (MLM). Twenty-two SNPs were identified, that revealed a significant association with NCLB in the three mapping panels. Haplotype regression analysis revealed association of 17 significant haplotypes at FDR ≤ 0.05, with two common haplotypes across three maize panels. Several of the significantly associated SNPs/haplotypes were found to be co-located in chromosomal bins previously reported for major genes like Ht2, Ht3 and Htn1 and QTL for NCLB resistance and multiple foliar disease resistance. Phenotypic variance explained by these significant SNPs/haplotypes ranged from low to moderate, suggesting a breeding strategy of combining multiple resistance alleles towards resistance for NCLB.

Globally, downy mildews are among the important foliar diseases of maize that cause significant yield losses. We conducted a genome-wide association study for sorghum downy mildew (SDM; Peronosclerospora sorghi ) resistance in a panel of 368 inbred lines adapted to the Asian tropics. High density SNPs from Genotyping-by-sequencing were used in GWAS after controlling for population structure and kinship in the panel using a single locus mixed model. The study identified a set of 26 SNPs that were significantly associated with SDM resistance, with Bonferroni corrected P values ≤ 0.05. Among all the identified SNPs, the minor alleles were found to be favorable to SDM resistance in the mapping panel. Trend regression analysis with 16 independent genetic variants including 12 SNPs and four haplotype blocks identified SNP S2_6154311 on chromosome 2 with P value 2.61E-24 and contributing 26.7% of the phenotypic variation. Six of the SNPs/haplotypes were within the same chromosomal bins as the QTLs for SDM resistance mapped in previous studies. Apart from this, eight novel genomic regions for SDM resistance were identified in this study; they need further validation before being applied in the breeding pipeline. Ten SNPs identified in this study were co-located in reported mildew resistance genes.

The negative effects of heat stress on maize growth and reproduction is often expressed in terms of significant yield penalty. Germplasm selection based on yield potential along with heat stress adaptive secondary traits, and establishing their interaction under stress helps in identifying suitable heat tolerant genotypes. To dissect intricate nature of heat stress tolerance, two field trials were conducted during spring 2014 and 2015 under natural heat stress conditions. Planting was adjusted to expose reproductive and grain filling period to high temperature regimes during May month in Hyderabad, India. Correlation analysis between grain yield under stress and secondary traits observed in two year experiments indicated that the traits such as - leaf firing (LF) (r = -0.34** and 0.06), tassel blast (TB) (r = -0.18 and -0.25), tassel sterility (TS) (r = -0.08 and -0.38*), anthesis-silking interval (ASI) (r = -0.24* and -0.02) and senescence (SEN) (r = -0.27** and -0.34*) were negatively correlated, while pollen shedding duration (PSD) (r = 0.33** and 0.4*), seed set percentage (SSP_OP) (r = 0.76** and 0.58**) and chlorophyll content (CHL) (r = 0.55** and 0.41*) were positively associated with grain yield under stress in 2014 and 2015, respectively. An ASI of 2-4 days and PSD of 2-4 days were found advantageous to grain yield under heat stress. Stigma receptivity was less affected under heat stress when compared to pollen viability, yet stigma initiation was delayed under heat stress, which resulted in prolonged AR Overall effect of heat stress was expressed in terms of SSP_OP, which explained yield variation by 78.5 and 57.8% for experiment 1 and 2, respectively. Thus, traits that are indicative of reproductive success under heat stress (ASI, TB, TS, pollen viability, stigma receptivity and SSP_OP) and other morpho-physiological traits (LF, SEN and CHL) may be used along with grain yield in index selection of suitable germplasm for heat stress tolerance. (C) 2017 Elsevier B.V. All rights reserved.

Maize (Zea mays L.) is an important cropknown for its carotenoid diversity among cereals which accumulates significant levels of proA (provitamin A) and non-proA carotenoids its kernels.The proA components of maize endosperm promises to solve themajor global problem VAD (Vitamin A deficiency).Among several genes involved in -carotene biosynthetic pathway, crtRB1is very important gene associated with three polymorphisms viz., 5 'TE, In Del4 and 3'TE (Transposable Element) responsible for variation in carotenoid levels in maize endosperm.Due to insertion of TE at 3' UTR (Un Translated Region), crtRB1again exhibits polymorphism with 3 alleles, however, only allele 1(favourable allele; 543bp amplicon) of this crtRB1-3'TE gene will double the -carotene concentration in maize endosperm and allele 2 and 3 termed as unfavourable.This study was undertaken to find out the allelic difference for crtRB1gene loci.Totally 228 tropical maize inbred lines were screened for allele1 of crtRB1gene using crtRB1-3'TE gene specific markers.Among 228 in breds, 226 inbreds showed the presence of allele 2 and the two inbredsVL1016247 and VL1016213 possessed both alleles 1 and 2 which are found to be heterozygous for crtRB1loci.This study indicated the possible use of (VL1016247 and VL1016213) these two inbreds for developing provitaminA (proA) rich maize hybrids using marker assisted selection (MAS).