Stress Tolerance In Maize Research Articles

The impact of adopting stress-tolerant maize on maize yield, maize income, and food security in Tanzania.

Productivity growth emanating from scientific advances offered by biotechnology and other plant breeding initiatives offers great promise for meeting the growing food demand worldwide. This justifies investments in agricultural research and development that have led to the development of stress‐tolerant maize varieties (STMVs) in Africa. While most literature has documented the average impacts of STMVs on productivity, this paper is premised on the fact that benefits from technology adoption are not the same across household. The paper addresses this information gap by examining potential heterogeneity in yield, income, and food security benefits from of adopting STMVs using a sample of 720 maize‐producing households from Tanzania. The dose‐response continuous treatment effect method supported by an endogenous switching probit model was used to estimate the heterogenous impact of STMV adoption on the three outcomes of interest. Results show that, overall, the adoption of stress‐tolerant maize varieties increased maize grain yield by about 1 ton/ha, maize income by about $62/ha. The adoption of STMVs also reduced the propensity to report mild, moderate, and severe food insecurity by 34%, 17%, and 6%, respectively. There are substantial idiosyncratic variations in the productivity, income, and food security effects depending on the scale of adoption, with a higher impact at lower dose levels of adoption. The heterogenous and pro‐poor nature of STMV adoption is also revealed through nonparametric results showing higher productivity benefits among households that are less endowed with wealth and knowledge. These findings underscore the need for further scaling of stress‐tolerant maize varieties for greater impact on the livelihoods of poor small‐scale farmers in Tanzania.

Gene Action, Heterotic Patterns, and Inter-Trait Relationships of Early Maturing Pro-Vitamin A Maize Inbred Lines and Performance of Testcrosses under Contrasting Environments

Vitamin A deficiency is the leading cause of night blindness, total blindness, maternal and childhood mortality in developing countries. Drought, low soil nitrogen and Striga hermonthica parasitism are major constraints to maize production in sub-Saharan Africa (SSA). Thus, the development of multiple stress tolerant maize varieties with elevated levels of PVA is an economically feasible approach to simultaneously tackle malnutrition and food insecurity in SSA. The objectives of this study were to determine the gene action modulating the inheritance of grain yield and other traits, group the inbred lines, investigate inter-trait relationships among grain yield and other traits and assess the performance and stability of single-cross hybrids derived from a set of inbred lines under stress and non-stress environments. One hundred and ninety diallel crosses plus six hybrid checks were evaluated under managed drought at Ikenne during the 2016/17 and 2017/18 dry seasons, low soil N conditions at Mokwa and Ile-Ife, Striga infestation at Abuja and Mokwa, and optimal management conditions at Ikenne, Kadawa, Abuja, Bagauda and Mokwa during the 2016 and 2017 growing seasons. Both additive and non-additive gene actions were prominent in the inheritance of grain yield and other measured traits under stress and optimal management conditions. However, additive gene action was preponderant over the non-additive. The PVA inbreds were classified into three heterotic groups with TZEI 25 and TZEIOR 164 identified as inbred testers for heterotic groups 2 and 3, respectively. Plant and ear heights, ears per plant, plant and ear aspects were identified as reliable secondary traits for genetic enhancement of grain yield under both stress and non-stress conditions. Hybrids TZEIOR 4 × TZEIOR 158 and TZEIOR 119 × TZEIOR 158 were outstanding in performance and should be tested extensively for possible commercialization to combat malnutrition and food insecurity in SSA.

Transcriptome Analysis of Tolerant and Susceptible Maize Genotypes Reveals Novel Insights about the Molecular Mechanisms Underlying Drought Responses in Leaves.

Maize (Zea mays L.) is the most essential food crop in the world. However, maize is highly susceptible to drought stress, especially at the seedling stage, and the molecular mechanisms underlying drought tolerance remain elusive. In this study, we conducted comparative transcriptome and physiological analyses of drought-tolerant (CML69) and susceptible (LX9801) inbred lines subjected to drought treatment at the seedling stage for three and five days. The tolerant line had significantly higher relative water content in the leaves, as well as lower electrolyte leakage and malondialdehyde levels, than the susceptible line. Using an RNA-seq-based approach, we identified 10,084 differentially expressed genes (DEGs) with 6906 and 3178 DEGs been annotated and unannotated, respectively. Two critical sets of drought-responsive DEGs, including 4687 genotype-specific and 2219 common drought-responsive genes, were mined out of the annotated DEGs. The tolerant-line DEGs were predominantly associated with the cytoskeleton, cell wall modification, glycolysis/gluconeogenesis, transport, osmotic regulation, drought avoidance, ROS scavengers, defense, and transcriptional factors. For the susceptible line, the DEGs were highly enriched in the photosynthesis, histone, and carbon fixation pathways. The unannotated DEGs were implicated in lncRNAs, including 428 previously reported and 22% putative TE-lncRNAs. There was consensus on both the physiological response and RNA-seq outcomes. Collectively, our findings will provide a comprehensive basis of the molecular networks mediating drought stress tolerance of maize at the seedling stage.

Genome-wide association mapping in maize: status and prospects.

The online version contains supplementary material available at 10.1007/s13205-021-02799-4.

Plant biostimulating effects of the cyanobacterium Nostoc piscinale on maize (Zea mays L.) in field experiments

Biostimulants, when applied to plants in small amounts, increase crop yield and plant tolerance to abiotic and biotic stress. They play an important role in the development of new environmentally sustainable technologies. The aim of the current experiment was to investigate the potential of a cyanobacterium strain (Nostoc piscinale) to improve the growth, grain yield and stress tolerance of maize (Zea mays SY Zephir hybrid). Field trials were established at two sites. Freeze-dried biomass of N. piscinale resuspended in tap water (1g/L DW) was applied as a single foliar treatment (400 L/ha) at the V6-V7 phenological stage. Number of leaves, chlorophyll content, relative water content (RWC%) and free proline content were measured weekly. Grain yield, yield components and grain protein content were measured at harvest. N. piscinale treated maize had significantly earlier development in the vegetative growth stages with a higher number of leaves. Chlorophyll content (SPAD value) was significantly higher in the treated plants during the reproductive stages. There was little difference in the RWC and proline content compared to control plants. Faster vegetative growth and higher chlorophyll content in the cyanobacterium treated plants meant great photosynthetic light absorption over a longer period of time, resulting in significantly higher grain yield (6.5% and 11.5% at the two production sites) and increased grain protein content. Grain yield was significantly influenced by cob length and thousand grain weight. In conclusion, it was proved in field trials conducted in two different regions in Hungary that a single foliar application of a cyanobacterium-based biostimulant can contribute to crop production in a sustainable and environmentally friendly manner.

Associating primary and specialized metabolism with salt induced osmotic stress tolerance in maize.

This article is a Commentary on Liang et al. (2021), 230: 2355–2370.

Conservation agriculture improves adaptive capacity of cropping systems to climate stress in Malawi

ContextAdaptation to climate stress is an unprecedented challenge facing cropping systems. Most adaptation assessments focus on how adaptation options affect yields of a single crop under different weather or climate conditions. Yet, cropping systems often comprise more than one crop, and holistic assessments should consider all crops grown in a cropping system. One adaptation option is Conservation Agriculture that is commonly defined around a set of three principles: minimum mechanical soil disturbance, permanent soil organic cover, and crop species diversification. ObjectiveHere we estimated the statistical effect of Conservation Agriculture on cropping-system yields under historical climate conditions. MethodsThe cropping-system yields considered all crops grown including maize (Zea mays L.) and legumes in intercropping or rotation, or both. The climate conditions included conditions of heat stress for maize and precipitation balances during the maize growing season. Heat stress for maize was studied using growing degree days over 30 °C. Precipitation balance was the difference between precipitation and reference evapotranspiration. Data included 6296 yield observations from on-farm trials in farmer plots conducted over 14 seasons (2005–2006 to 2018–2019) in ten communities in Malawi. These yield data were coupled with daily weather data. We studied three treatments: (1) a Control Practice treatment where the soil was tilled, crop residues were removed, and there was no crop species diversification, (2) a No-Tillage treatment where the soil was not tilled, crop residues were retained, and there was no crop species diversification, and (3) a Conservation Agriculture treatment where the soil was not tilled, crop residues were retained, and there was crop species diversification through legume intercropping. The use of maize varieties and legume rotation changed over time; however, the treatments studied remained the same over the entire length of the on-farm trials period in all individual communities. Results and conclusionsResults of our study showed that heat stress for maize had a negative effect on cropping-system yields for non-stress-tolerant maize varieties and no legume rotation, although the Conservation Agriculture treatment reduced this negative effect compared with the Control Practice treatment. With the use of stress-tolerant maize varieties and legume rotation and Conservation Agriculture, our results suggest that heat stress for maize did not have a negative effect on cropping-system yields. SignificanceOur results demonstrate how Conservation Agriculture can improve the adaptive capacity of cropping systems and this provides urgently needed evidence on how farmers can adapt to climate stress.

Thermal Stresses in Maize: Effects and Management Strategies

Climate change can decrease the global maize productivity and grain quality. Maize crop requires an optimal temperature for better harvest productivity. A suboptimal temperature at any critical stage for a prolonged duration can negatively affect the growth and yield formation processes. This review discusses the negative impact of temperature extremes (high and low temperatures) on the morpho-physiological, biochemical, and nutritional traits of the maize crop. High temperature stress limits pollen viability and silks receptivity, leading to a significant reduction in seed setting and grain yield. Likewise, severe alterations in growth rate, photosynthesis, dry matter accumulation, cellular membranes, and antioxidant enzyme activities under low temperature collectively limit maize productivity. We also discussed various strategies with practical examples to cope with temperature stresses, including cultural practices, exogenous protectants, breeding climate-smart crops, and molecular genomics approaches. We reviewed that identified quantitative trait loci (QTLs) and genes controlling high- and low temperature stress tolerance in maize could be introgressed into otherwise elite cultivars to develop stress-tolerant cultivars. Genome editing has become a key tool for developing climate-resilient crops. Moreover, challenges to maize crop improvement such as lack of adequate resources for breeding in poor countries, poor communication among the scientists of developing and developed countries, problems in germplasm exchange, and high cost of advanced high-throughput phenotyping systems are discussed. In the end, future perspectives for maize improvement are discussed, which briefly include new breeding technologies such as transgene-free clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated (Cas)-mediated genome editing for thermo-stress tolerance in maize.

Achromobacter sp. PHED2 enhances the phenanthrene degradation and stress tolerance in maize involving the participation of salicylic acid

Phenanthrene (PHE) is harmful to human health and is difficult to be eliminated from environment. In this study, two aerobic bacteria capable of utilizing PHE as a sole source of carbon and energy were isolated and classified as Burkholderia sp. PHED1 and Achromobacter sp. PHED2 according to 16S rDNA analysis. The combined use of maize plants and strain PHED1 or PHED2 enhanced the removal efficiency of PHE (200 mg/kg) from the soil. Moreover, PHED2 inoculation showed more enhancement of root dry weight in comparison with PHED1. PHED2 inoculation also showed more increases of chlorophyll content, net photosynthesis rate and transpiration rate in maize plants in comparison with PHED1. In the PHE degradation pathway by strain PHED2, it was proposed that the salicylic acid (SA) was formed from the 1-hydroxy-2-naphthoic acid, through the intermediate of 1, 2-dihydroxynaphthalene. The SA as the PHE degradation product by PHED2 could enhance the growth of maize plant, increase the reduced form of glutathione content and glutathione reductase activity, which participated in the promotion of PHE degradation and stress tolerance in maize plants. • Strains PHED1 and PHED2 could degrade phenanthrene as a sole carbon source. • Salicylic acid was identified as phenanthrene degradation product by PHED2. • PHED2 enhanced salicylic acid content and stress tolerance in maize. • PHED2 improved the phenanthrene degradation in maize plants.

A maize calcineurin B-like interacting protein kinase ZmCIPK42 confers salt stress tolerance.

Calcineurin B-like (CBL) and CBL-interacting protein kinase (CIPK) play a crucial role in biotic and abiotic stress responses. However, the roles of different CIPKs in biotic and abiotic stress responses are less well characterized. In this study, we identified a mutation leading to an early protein termination of the maize CIPK gene ZmCIPK42 that undergoes a G to A mutation at the coding region via searching for genes involved in salt stress tolerance and ion homeostasis from maize with querying the EMS mutant library of maize B73. The mutant zmcipk42 plants have less branched tassel and impaired salt stress tolerance at the seedling stage. Quantitative real-time PCR analysis revealed that ZmCIPK42was expressed in diverse tissues and was induced by NaCl stress. A yeast two-hybrid screen identified a proteinase inhibitor (ZmMPI) as well as calcineurin B-like protein 1 and protein 4 (ZmCBL1, ZmCBL4) as interaction partners of ZmCIPK42. These interactions were further confirmed by bimolecular fluorescence complementation in plant cells. Moreover, over-expressing ZmCIPK42 resulted in enhanced tolerance to high salinity in both maize and Arabidopsis. These findings suggest that ZmCIPK42 is a positive regulator of salt stress tolerance and is a promising candidate gene to improve salt stress tolerance in maize through genetic manipulation.

The transcription factor ZmNAC49 reduces stomatal density and improves drought tolerance in maize.

Drought stress severely limits the growth, development, and productivity of crops, and therefore understanding the mechanisms by which plants respond to drought is crucial. In this study, we cloned a maize NAC transcription factor, ZmNAC49, and identified its function in response to drought stress. We found that ZmNAC49 is localized in the nucleus and has transcriptional activation activity. ZmNAC49 expression is rapidly and strongly induced by drought stress, and overexpression enhances stress tolerance in maize. Overexpression also significant decreases the transpiration rate, stomatal conductance, and stomatal density in maize. Detailed study showed that ZmNAC49 overexpression affects the expression of genes related to stomatal development, namely ZmTMM, ZmSDD1, ZmMUTE, and ZmFAMA. In addition, we found that ZmNAC49 can directly bind to the promoter of ZmMUTE and suppress its expression. Taken together, our results show that the transcription factor ZmNAC49 represses ZmMUTE expression, reduces stomatal density, and thereby enhances drought tolerance in maize.

Computational identification of maize miRNA and their gene targets involved in biotic and abiotic stresses

Plant interactions with biotic and abiotic stresses are complex and entail changes at the transcriptional, cellular and physiological level. MicroRNAs (miRNAs) are small (∼20-24 nt), non-coding RNAs that play a vital role in wide range of biological processes involved in regulation of gene expression through translation inhibition or degradation of their target mRNAs during stress conditions. Therefore, identification of miRNAs and their targets are of immense value in understanding the regulatory networks triggered during stress. Advancement in computational approaches has opened up ways for the prediction of miRNAs and their possible targets with functional pathways. Our objective was to identify miRNA and their potential targets involved in both biotic and abiotic stresses in maize. A total of 2,019,524 downloaded ESTs from dbEST were processed and trimmed by Seq Clean. The program trashed 264,000 and trimmed 284,979 sequences and the resulting 1,755,534 sequences were submitted for clustering and assembled to RepeatMasker and TGICL. A total of 30 miRNAs were found to hybridize with the potential targets of gene families such as CoA ligase, lipoxygenase 1, Terpenoideyclases, Zn finger, transducing, etc. Ten of the identified miRNAs targeted cytochrome c1 family. Zm_miR23 class targeted 11 different genes. The identified targets are involved in the plant growth and development during biotic and abiotic stresses in maize. These miRNAs may be further used for functional analysis. Furthermore, four and two of the miRNA targets were validated in response to waterlogging tolerance and southern leaf blight resistance, respectively, to understand the miRNA-assisted regulation of target miRNAs. The functional annotation of the predicted targets indicated that these stress-responsive miRNAs regulate cellular function; molecular function and biological process in maize at the post-transcriptional level. The present results have paved way towards better understanding the role of miRNAs in the mechanism of stress tolerance in maize.

Silicon Defensive Role in Maize (Zea mays L.) against Drought Stress and Metals-Contaminated Irrigation Water

Irrigation water rarity and its contamination with toxic metals are increasing gradually and have become imperious issues for the environment at personal and governmental levels. Silicon (Si) can increase plant tolerance to abiotic stressors and beneficially affect plant growth and productivity. The main purpose of the current study was to investigate the effect of Si as a foliar application on growth, photosynthetic efficiency, plant-water status, metals accumulation, water-use efficiency (WUE) and yield of maize grown under drought and metals-contaminated irrigation water stresses. We conducted two-season field experiments in 2017 and 2018 summer seasons on maize grown under two irrigation regimes (Full irrigation (FI = 100%) and deficit irrigation (DI20% = 80%) of crop evapotranspiration) combined with 0 (Si0), 2 (Si2), and 4 (Si4) mM of Si in form of Na2SiO3 applied at 40 and 60 days after planting as a foliar application. In both seasons, maize plants were irrigated with metals-contaminated redundant water (Ni2+; 5.5 ppm, Cd2+; 0.27 ppm, and Cr3+; 5 ppm). Exogenous application of Si increased drought stress tolerance in maize by enhancing photosynthetic efficiency, stomatal conductance (gs) and cell membrane integrity as evaluated by membrane stability index. These results were positively reflected in improving plant growth, WUE, and productivity along with decreasing accumulation of Ni+2, Cd+2, and Cr+3 in leaves and grains under drought stress by metals-contaminated irrigation water. Deficit irrigation and metal-contaminated irrigation water conditions reduced growth and productivity of maize plants. However, foliar application of Si was effective in enhancing the physiological performance, water use efficiency, and productivity of maize under drought and/or contaminated irrigation water conditions. Therefore, Si may, in future, find value as a potential plant growth stimulant under different abiotic stresses.

Exogenous Glycinebetaine Application Contributes to Abiotic Stress Tolerance in Maize

Plant growth and development are adversely affected by various environmental stresses. In this study, we investigated the possible function of glycinebetaine (GB) in improving abiotic stress tolerance in maize plants by exogenous application. Results indicated that GB application could effectively improve maize germination percentages, biomass weights and grain yield per plant under abiotic stresses. Moreover, GB-treated plants showed higher reactive oxygen species (ROS)-scavenging capacities, therefore less oxidative destruction than control plants under stresses. In addition, abscisic acid (ABA) levels were increased in GB-treated plants compared to control plants. The comparison of transcriptome profile was performed to analyze the possible mechanism underlying the enhanced tolerance mediated by GB. Many differentially expressed genes (DEGs) between GB-treated and control plants were found to be involved in responses to oxidative stress, abiotic stress and ABA. Taken together, these results indicated that GB might enhance abiotic stress tolerance in maize by regulating ROS-scavenging capacities and ABA-mediated stress-responsive pathways.

Rapid method of screening for drought stress tolerance in maize (Zea mays L.)

Drought stress is the major production constraint in rainfed maize. Screening for drought tolerance is severely affected by the lack of a simple and reliable phenotyping technique. The objective of this study was to standardize a simple hydroponic based drought screening technique in maize. In this context, one week old uniform seedlings of 55 inbreds and 5 hybrids were transferred to hydroponic solution in the glass house. The seedlings were allowed to acclimatize for next one week in hydroponic solution. The drought stress was imposed by removing seedlings from nutrient solution and exposed to air for 6 and 4 hours daily for a period of 5 and 4 consecutive days in hybrids and inbreds, respectively. Data were recorded on all shoot and root parameters, and based on stress symptoms, a drought tolerance score was given to each genotype. The percent deductions in shoot and root fresh weight from non-stress to stress ranged from 11.7 to 84.4 and 2.1 to 77.5, respectively. Six inbred lines, namely, DQL790-4, CML334, CM140, CML422, CM125 and HKI488 and three hybrids namely DMRH1306, DMRH1410 and PMH4 were found drought tolerant. The effectiveness of this screening technique was compared and confirmed using pots screening as well as by expression profiling of key antioxidant genes (Sod2, Sod4, Sod9 and Apx1) playing role in drought stress tolerance. This phenotyping technique is very short, low cost and simple which can be utilized in preliminary drought screening for large set of maize germplasm and mapping populations.

Low-N stress tolerant maize hybrids have higher fertilizer N recovery efficiency and reduced N-dilution in the grain compared to susceptible hybrids under low N conditions

ABSTRACT Developing high yielding maize (Zea mays L.) varieties that have relatively high grain protein content under low nitrogen stress is critical to ensure food and nutrition security in sub-Saharan Africa. This study evaluated the efficiency for fertilizer N recovery, grain yield and grain protein content of 10 maize hybrids selected for their contrasting yield performance under low-N stress conditions in the field. The hybrids were grown under 6 N rates (0-10-20-40-80 and 160 kg Ammonium Nitrate ha−1) at 2 sites that differ for residual soil nitrogen (N-NO3). Fertilizer N recovery, estimated using the difference method, decreased with increasing N rates or residual soil N and was significantly higher for the low-N tolerant (LNT) hybrids than low-N sensitive (LNS) hybrids, especially at low N rates. Although there was yield increase with increased N rate, the yield of tolerant hybrids responded more strongly than that of sensitive ones. Under low residual soil N, higher grain yield was associated with lower grain protein content in both low-N tolerant and susceptible hybrids but tolerant ones exhibited a significantly lower decrease in grain protein content compared to susceptible hybrids. In addition, LNT hybrids were able to maintain relatively higher grain protein content at high yield level under depleted soil N conditions as well as under high N level. We concluded that LNT hybrids could contribute to optimizing the use of small N fertilizer rates by resource-poor smallholder farmers to increase the nutritional value and profitability of producing maize.

A novel PGPR strain Kocuria rhizophila Y1 enhances salt stress tolerance in maize by regulating phytohormone levels, nutrient acquisition, redox potential, ion homeostasis, photosynthetic capacity and stress-responsive genes expression

High salinity is harmful for crop physiology and yield. Accumulating evidences indicate that plant growth promoting rhizobacteria (PGPR) can enhance crop growth and reduce the negative impacts of salt stress through regulation of some molecular, biochemical and physiological features. In the present study, a novel halo-tolerant strain Y1 was isolated from maize rhizosphere soil. Sequence analysis of 16S rRNA gene confirmed its identity as Kocuria rhizophila. This strain tolerated up to 10 % NaCl and showed two growth promoting traits like phosphate solubilization and IAA production. The impacts of K. rhizophila Y1 on maize (Zea mays L.) growth and development with salt treatment (0, 100 and 200 mM NaCl) were further examined. The results showed that inoculation with K. rhizophila Y1 strain could protect maize from salt stress by regulating plant hormones (IAA and ABA) levels and improving nutrient acquisition. In detail, inoculation with K. rhizophila Y1 significantly improved growth performance, biomass production, seed germination rate, photosynthetic capacity, antioxidant levels, relative water content and chlorophyll accumulation in maize under saline conditions in comparison with non-inoculation treatment. Moreover, strain Y1 inoculated maize showed lower levels of Na+ and electrolyte leakage under salt treatment compared to non-inoculated ones. Inoculated maize also showed higher transcript levels of genes encoding antioxidants (ZmGR1 and ZmAPX1) and genes involved in salt tolerance (ZmNHX1, ZmNHX2, ZmNHX3, ZmWRKY58 and ZmDREB2A) than in non-inoculated plants. In summary, this study indicated the important contribution of K. rhizophila Y1 in mitigating the deleterious effects of salinity on maize growth and development by regulating plant hormones and nutrient acquisition, and thereby maintaining ion homeostasis, improving photosynthetic capacity, enhancing redox potential and stress-responsive genes expression.

Molecular characterization of the promoter of the stress-inducible ZmMYB30 gene in maize

The ZmMYB30 is a member of the myeloblastosis (MYB) transcription factor superfamily, which has been shown to be a transcription regulator in abiotic stress tolerance in maize (Zea mays). To further identify the biological function of ZmMYB30 and reveal how its expression is induced in response to stress, we isolated the ZmMYB30 promoter and conducted a functional analysis. A 1461-bp promoter fragment was cloned and sequenced. Motif prediction using PlantCARE revealed several stress-responsive elements in the promoter sequence. Deletions in the promoter sequence affected the activity of the promoter and demonstrated that putative stress-responsive motifs, including TC-rich repeats (ATTCTCTAAC), abscisic acid responsive element (ABRE, ACGTG), and MYB binding site (MBS, CAACTG), played important roles in regulating the expression of ZmMYB30. Promoter β-glucuronidase (GUS) analysis also showed that GUS expression under the control of the ZmMYB30 promoter responded to drought and salinity. Many natural variations in the ZmMYB30 promoter sequence were found among 31 inbred maize lines, including 22 single nucleotide polymorphisms (SNPs), 17 insertion and deletion (InDels), and approximately 400-bp long deletions. The ZmMYB30 expression varied greatly among the different inbred lines. The long fragment deletion in the promoter region did not impair the ZmMYB30 expression, whereas SNP (-374) in the MBS motif in the 62R and LH82 lines greatly decreased the ZmMYB30 expression. A site-specific mutation in the MBS motif also decreased the expression of the reporter GUS gene driven by the ZmMYB30 promoter sequence. The expressions of three stress-responsive genes ZmSOS1, ZmSOS2, and ZmABF3 were found to be consistent with the ZmMYB30 expression. Our results provide new evidence to support the role of ZmMYB30 as an important regulator in maize stress tolerance.

On-farm performance and farmers’ participatory assessment of new stress-tolerant maize hybrids in Eastern Africa

The development and deployment of high-yielding stress tolerant maize hybrids are important components of the efforts to increase maize productivity in eastern Africa. This study was conducted to: i) evaluate selected, stress-tolerant maize hybrids under farmers’ conditions; ii) identify farmers’ selection criteria in selecting maize hybrids; and iii) have farmers evaluate the new varieties according to those criteria. Two sets of trials, one with 12 early-to-intermediate maturing and the other with 13 intermediate-to-late maturing hybrids, improved for tolerance to multiple stresses common in farmers’ fields in eastern Africa (drought, northern corn leaf blight, gray leaf spot, common rust, maize streak virus), were evaluated on-farm under smallholder farmers’ conditions in a total of 42 and 40 environments (site-year-management combinations), respectively, across Kenya, Uganda, Tanzania and Rwanda in 2016 and 2017. Farmer-participatory variety evaluation was conducted at 27 sites in Kenya and Rwanda, with a total of 2025 participating farmers. Differential performance of the hybrids was observed under low-yielding (<3 t ha−1) and high-yielding (>3 t ha−1) environments. The new stress-tolerant maize hybrids had a much better grain-yield performance than the best commercial checks under smallholder farmer growing environments but had a comparable grain-yield performance under optimal conditions. These hybrids also showed better grain-yield stability across the testing environments, providing an evidence for the success of the maize-breeding approach. In addition, the new stress- tolerant varieties outperformed the internal genetic checks, indicating genetic gain under farmers’ conditions. Farmers gave high importance to grain yield in both farmer-stated preferences (through scores) and farmer-revealed preferences of criteria (revealed by regressing the overall scores on the scores for the individual criteria). The top-yielding hybrids in both maturity groups also received the farmers’ highest overall scores. Farmers ranked yield, early maturity, cob size and number of cobs as the most important traits for variety preference. The criteria for the different hybrids did not differ between men and women farmers. Farmers gave priority to many different traits in addition to grain yield, but this may not be applicable across all maize-growing regions. Farmer-stated importance of the different criteria, however, were quite different from farmer- revealed importance. Further, there were significant differences between men and women in the revealed-importance of the criteria. We conclude that incorporating farmers’ selection criteria in the stage-gate advancement process of new hybrids by the breeders is useful under the changing maize-growing environments in sub-Saharan Africa, and recommended to increase the turnover of new maize hybrids.

Genome-wide identification, phylogenetic and expression analysis of the maize HECT E3 ubiquitin ligase genes

HECT (homologous to the E6AP carboxyl terminus) ubiquitin ligase genes (E3s) are enzymes with diverse functions influencing plant growth, development, and responses to abiotic stresses. However, there is relatively little information available regarding the maize HECT E3 gene family. In the present study, 12 maize HECT E3 genes (ZmUPL1 to ZmUPL12) were identified at the whole-genome level. The phylogenetic relationships, structures, and expression levels of the maize HECT E3 genes were then analyzed. On the basis of the constructed maximum likelihood phylogenetic tree, the HECT E3 genes were divided into six groups. The quantitative real-time polymerase chain reaction assay results revealed that all of the maize ZmUPL genes were expressed in most of the examined tissues and were responsive to three abiotic stresses. Considered together, the study results may provide a useful foundation for future investigations of maize stress-tolerance genes as well as functional analyses of the E3 enzymes in diverse agriculturally important crop species.