Subtropical Maize Research Articles

Characterization of sub-tropical maize (Zea Mays L.) inbred lines for the variation in kernel row numbers (KRNs)

Characterization of sub-tropical maize (Zea Mays L.) inbred lines for the variation in kernel row numbers (KRNs)

Plant–water relations in subtropical maize fields under mulching and organic fertilization

The plant–water relationship of maize under conservation practices needs to be assessed to quantify the effectiveness of the practices in conserving soil water for crop production. This study evaluated in three trials how straw and plastic film mulching and organic manure application could potentially change water fluxes in the root zone and increase maize yield. A mathematical model HYDRUS-1D was calibrated against the observed soil water content and drainage data to predict the water fluxes in the root zone soil. The model simulated soil water dynamics in the root zone with satisfactory performance (RMSE of 0.6–2.3%, CD of 0.37–1.41, NSE of 0.18–0.88, and R2 of 0.62–0.91) during both the calibration and validation periods. The model predicted the observed drainage in a lysimeter with only a 5.5–11.7% bias and actual evapotranspiration (ETc) with a 2.6–6.7% bias for the control conditions in all three trials when the model was provided with measured plant growth, soil properties, and weather data. Both measurement and modeling confirmed that mulching augmented soil water storage by reducing ETc, i.e., 0.24–0.37 mm d-1 by straw mulching and 0.05–0.24 mm d-1 by plastic mulching during the trials. Manure application did not affect the ETc rate and resulted in the highest grain yield (6.8–8.3 Mg ha˗1) followed by plastic mulching (6.1–8.1 Mg ha˗1) and straw mulching (5.3–7.5 Mg ha˗1). Manure application increased the harvest index by optimally allocating biomass because of a steady supply of water and nutrients. The straw mulch, plastic mulch, and manure treatments increased grain yield by 13%, 24%, and 35%, respectively, compared to the control condition. Large-scale implementation of these practices would lessen blue water scarcity in agriculture.

Protocol optimization and assessment of genotypic response for inbred line development through doubled haploid production in maize

BackgroundDoubled haploid technology offers the fastest route of inbred line development by rapidly fixing the desirable combinations in a single year. However, the differential response of haploid induction to genetic background of maternal lines accompanied with low induction rate and high mortality rate due to artificial chromosomal doubling of haploid seedlings creates hindrance in doubled haploid production on a commercial scale under tropical conditions. To speed up the hybrid breeding programme in sub-tropical maize, efforts are reported here to optimize the protocol for efficient production of fixed lines using haploid inducers. The second-generation haploid inducers i.e. CIM2GTAILs obtained from CIMMYT, Mexico were used for haploid induction in 13 F1s of diverse backgrounds. For standardization of chromosomal doubling protocol, various concentrations of colchicine and two seedling growth stages were used to determine the extent of chromosomal doubling and survival rate of doubled haploid plants.ResultsA high mean haploid induction rate is obtained from CIM2GTAIL P2 (10%) as compared to CIM2GTAIL P1 (7.46%). Out of four treatments, CIMMYT reported protocol of chromosome doubling in tropical maize comprising combination of 0.07% colchicine and 0.1% DMSO at V2 stage is highly effective for acquiring doubled haploid plants in sub-tropical adapted maize with high survival rate of 52.7%. However, increasing the colchicine concentration from 0.07 to 0.1% led to high mortality rate.ConclusionAccording to the findings, the haploid induction rate, survival rate and overall success rate varied depending upon the genotype of the inducer and the source population along with the concentrations of chemical used. The optimized protocol developed using CIMMYT haploid inducer CIM2GTAIL P2 for efficient doubled haploid production will not only fasten the breeding programme but will also reduce the production cost of doubled haploid with great efficiency in sub-tropical maize.

Novel Combination of the Biophysical, Nutritional, and Nutraceutical Properties in Subtropical Pigmented Maize Hybrids.

Maize (Zea mays L.) represents the main caloric source for much of the world's population. Pigmented maize varieties are an excellent source of nutraceutical compounds: blue and yellow maize are rich in anthocyanins as well as carotenoids and phenolic acids, respectively. However, blue maize is usually grown in small quantities as a specialty crop because it lacks the qualities and adaptations of commercial white and yellow varieties. Here, a new high-yield variety of blue maize called Vitamaiz was developed from inbred lines of subtropical blue, white, and yellow maize. The aim of this study was to characterize the nutraceutical and physical properties of 30 Vitamaiz hybrids in two subtropical locations. Kernel physical traits, nutrient composition, and nutraceutical components (free phenolic acids, FPA; cell wall-bound phenolic acids, BPA; total monomeric anthocyanin content, TAC; antioxidant capacity, AOX by oxygen radical absorbance capacity assay, and total carotenoid content, TCC) were evaluated. The biophysical traits of the hybrids were suitable for nixtamalized and flour maize industries. High levels of FPA (228 mg GAE/100 g), BPA (635 mg GAE/100 g), and AOX (2.0 and 8.1 mM Trolox equivalent/100 g for FPA and BPA, respectively) were also detected with elevated TAC levels (274 mg C3G/kg dw) and AOX activity (3.1 mM Trolox equivalent/100 g). This is the first study to characterize Blue × Yellow maize hybrids that adapt to subtropical environments.

Genetic diversity of subtropical double‐haploid maize lines selected for high oil content

AbstractThe inclusion of high‐oil maize germplasm into breeding programs may be an excellent alternative for increasing grain nutritional quality. Knowing the germplasm genetic diversity is crucial for assisting breeding programs. Here, the genetic diversity and population structure of four high‐oil‐content maize (Zea mays L.) populations (Bajio yellow population [BYP], northwestern yellow population [NYP], Bajio white population [BWP], and northwestern white population [NWP]) were analyzed by Diversity Arrays Technology sequencing. Three‐hundred ten double‐haploid (DH) lines were genotyped, and 19,078 single‐nucleotide polymorphism (SNP) markers were uniformly detected among populations after filtering by missing data >20% and minor allele frequency ≥0.05. Genetic diversity indexes showed polymorphic information content (PIC) values of 0.346, 0.352, 0.353, and 0.353; observed heterozygosity values of 0.221, 0.194, 0.284, and 0.177; and expected heterozygosity values of 0.188, 0.165, 0.219, and 0.152, for BYP, NYP, BWP, and NWP, respectively. Genetic structure results showed variations in pairwise genetic distance comparisons among the 310 DH lines, ranging from 0.119 to 0.385. Multidimensional scaling analysis and discriminant analysis of principal components grouped the DH lines into three different and five clusters, respectively, based on their origin region and grain color. On the other hand, STRUCTURE analysis revealed the presence of two different groups unrelated to grain color or origin region. The wide genetic variability among the analyzed DH lines highlights their potential to contribute new beneficial alleles into subtropical maize breeding programs and will facilitate the selection of parental lines and the identification of heterotic groups to generate high‐oil maize hybrids.

Genetic characterization of elite tropical, subtropical and temperate maize germplasm based on genome-wide SNP markers

Genetic characterization of elite tropical, subtropical and temperate maize germplasm based on genome-wide SNP markers

Association mapping and pathway analysis of ear rot disease caused byAspergillus flavusin a panel of tropical maize germplasm

AbstractThe fungusAspergillus flavuscan produce high, unsafe levels of aflatoxin in maize (Zea maysL.) and other high‐oil seed crops under environmental conditions favoring fungal growth and sporulation. At high levels, aflatoxin can kill, and chronic exposure to lower levels causes liver cancer, stunted growth during childhood, and depressed immune systems in humans and animals. Aspergillus ear rot (AER) is especially problematic in tropical environments, but most gene identification studies have been done in temperate or subtropical maize. Thus, the objectives of this research include identifying and mapping chromosomal regions and genes associated with AER resistance in tropical maize inbred lines via genome‐wide association study (GWAS) and tying these genes to metabolic pathways and potential resistance mechanisms. A panel of 320 tropical field corn and popcorn inbred lines was analyzed with phenotypic data for AER collected in two environments after harvest, and a set of 291,633 high‐quality polymorphic single‐nucleotide polymorphisms (SNPs) generated via genotyping by sequencing. Seven SNPs significantly associated with AER were identified. Pathway analysis identified 56 associated pathways, yielding possible resistance mechanisms related to flavonoid and phytoalexin plant compounds, plant signaling via hormones, starch biosynthesis, and general plant growth and metabolism. Many of the same genes were identified by both analyses, but GWAS and pathway analysis jointly identified more candidate genes than either alone.

Introgression of Maize Diversity for Drought Tolerance: Subtropical Maize Landraces as Source of New Positive Variants.

Current climate change models predict an increased frequency and intensity of drought for much of the developing world within the next 30 years. These events will negatively affect maize yields, potentially leading to economic and social instability in many smallholder farming communities. Knowledge about the genetic resources available for traits related to drought tolerance has great importance in developing breeding program strategies. The aim of this research was to study a maize landrace introgression panel to identify chromosomal regions associated with a drought tolerance index. For that, we performed Genome-Wide Association Study (GWAS) on 1326 landrace progenies developed by the CIMMYT Genetic Resources Program, originating from 20 landraces populations collected in arid regions. Phenotypic data were obtained from early testcross trials conducted in three sites and two contrasting irrigation environments, full irrigation (well-watered) and reduced irrigation (drought). The populations were genotyped using the DArTSeq® platform, and a final set of 5,695 SNPs markers was used. The genotypic values were estimated using spatial adjustment in a two-stage analysis. First, we performed the individual analysis for each site/irrigation treatment combination. The best linear unbiased estimates (BLUEs) were used to calculate the Harmonic Mean of Relative Performance (HMRP) as a drought tolerance index for each testcross. The second stage was a joint analysis, which was performed using the HMRP to obtain the best linear unbiased predictions (BLUPs) of the index for each genotype. Then, GWAS was performed to determine the marker-index associations and the marker-Grain Yield (GY) associations for the two irrigation treatments. We detected two significant markers associated with the drought-tolerance index, four associated with GY in drought condition, and other four associated with GY in irrigated conditions each. Although each of these markers explained less than 0.1% of the phenotypic variation for the index and GY, we found two genes likely related to the plant response to drought stress. For these markers, alleles from landraces provide a slightly higher yield under drought conditions. Our results indicate that the positive diversity delivered by landraces are still present on the backcrosses and this is a potential breeding strategy for improving maize for drought tolerance and for trait introgression bringing new superior allelic diversity from landraces to breeding populations.

Validation and Application of a Low-Cost Sorting Device for Fumonisin Reduction in Maize.

Fumonisin mycotoxins are a persistent challenge to human and livestock health in tropical and sub-tropical maize cropping systems, and more efficient methods are needed to reduce their presence in food systems. We constructed a novel, low-cost device for sorting grain, the “DropSort”, and tested its effectiveness on both plastic kernel models and fumonisin-contaminated maize. Sorting plastic kernels of known size and shape enabled us to optimize the sorting performance of the DropSort. The device sorted maize into three distinct fractions as measured by bulk density and 100-kernel weight. The level of fumonisin was lower in the heaviest fractions of maize compared to the unsorted samples. Based on correlations among fumonisin and bulk characteristics of each fraction, we found that light fraction 100-kernel weight could be an inexpensive proxy for unsorted fumonisin concentration. Single kernel analysis revealed significant relationships among kernel fumonisin content and physical characteristics that could prove useful for future sorting efforts. The availability of a low-cost device (materials~USD 300) that can be used to reduce fumonisin in maize could improve food safety in resource-limited contexts in which fumonisin contamination remains a pressing challenge.

Nitrogen leaching and grey water footprint affected by nitrogen fertilization rate in maize production: a case study of Southwest China.

Effective nitrogen (N) management measures are required to control environmental problems caused by N fertilizer use in intensive maize production systems. Soil N losses associated with high precipitation and over-fertilization in maize production can cause substantial environmental problems, whereas there is a lack of quantitative data and effective study countermeasures. A 2-year field study was conducted in the subtropical maize production system in Southwest China to quantify N leaching under varying N application rates of 0, 90, 180, 270 and 360 kg N ha-1 yr-1 . The results indicated that N leaching accounted for 16-38% of N fertilizer input. For farmer practice treatment (360 kg N ha-1 yr-1 ), N leaching loss was high at 110 kg N ha-1 yr-1 and accounted for 31% of the N applied. As an indicator of the ambient water quality pollution, the grey water footprint across all treatments ranged from 376 to 1092 m3 Mg-1 , with an average of 695 m3 Mg-1 . Reducing N rate to agronomically optimized treatment (180 kg N ha-1 yr-1 ) significantly decreased N leaching by 77%, and maintained high grain yield of 8.1Mg ha-1 . The grey water footprint was reduced by 52-63% with N rates from 270 or 360 kg N ha-1 yr-1 to 180 kg N ha-1 yr-1 . Nitrogen surplus (applied N rate minus N uptake by maize) resulted in higher soil residual nitrate concentration and consequently high N leaching. High precipitation and low soil pH were the main ecological factors leading to high N leaching. © 2021 Society of Chemical Industry.

Genome wide association mapping for heat tolerance in sub-tropical maize

BackgroundHeat 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.ResultsAn 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.ConclusionsThe 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.

Temperate testers’ efficiency in the screening of tropical and subtropical maize germplasm

Despite much effort, little exotic germplasm has been introduced in temperate maize breeding programs. Tropical and subtropical maize germplasm from CIMMYT is the most genetically diverse in the world and should be useful in widening the genetic base of temperate maize germplasm. Extracting the most suitable material from exotic germplasm is a tough challenge for plant breeding programs. This study aimed to determine the optimal number of testers to screen a maize line derived from tropical and subtropical CIMMYT germplasm. For this purpose, four temperate maize testers (MO17, B73, K47/3, and K18) and nine lines from CIMMYT were crossed. The 36 crosses along with two hybrid checks were assessed in a randomized complete block design with three replications at four maize growing regions in Iran. The GGE biplot procedure and methodology proposed by Fan et al. (2010) were used to analyze the results indicating a possibility of direct use of 2, 3, 4, and 9 CIMMYT lines to improve grain yield in temperate environments. Temperate maize testers B73 and K47/3, which belong to the Reid Yellow Dent heterotic group, were very efficient in selecting superior tropical and subtropical CIMMYT germplasm, whereas testers MO17 and K18 from the Lancaster Sure Crop heterotic group were fairly good and weak, respectively. Actually just one temperate tester could select most, if not all, of the top exotic tropical and subtropical lines, and a second tester would provide backup.

ANÁLISIS DE LA VARIABILIDAD MORFOLÓGICA DE MAÍCES NATIVOS Y EXÓTICOS EN VALLES ALTOS DE MÉXICO

El maíz (Zea mays L.) de origen tropical y subtropical de México es un reservorio de alelos útiles y diferentes a los existentes en razas de valles altos de México, que ayudaría a enfrentar distintos factores adversos y a contribuir a incrementar su adaptabilidad. El objetivo del presente estudio fue identificar la variabilidad morfológica existente entre poblaciones de maíz exóticas, adaptadas y sin adaptación previa a valles altos, y entre algunas de sus cruzas interraciales. El material genético evaluado estuvo integrado por nueve poblaciones originales de maíz exótico y sus ciclos avanzados de selección en valles altos, ocho cruzas simples, dos cruzas dobles, una cruza triple, las generaciones avanzadas de las cruzas y cuatro testigos locales. Las evaluaciones se realizaron en tres ambientes, mediante un diseño de bloques completos al azar con tres repeticiones; la unidad experimental consistió de dos surcos de 6 m de longitud, separados a 0.80 m y con una distancia entre plantas de 0.5 m. Se registraron 28 caracteres cualitativos y cuantitativos. Mediante análisis de componentes principales, agrupamiento jerárquico, análisis discriminante y comparación de medias con la prueba de Tukey se identificaron seis grupos contrastantes. Las variables de estructura morfológica, precocidad de planta y características de mazorca explicaron la variabilidad y agrupación de los genotipos. Las poblaciones exóticas originales fueron de mayor altura, más tardías y disminuyeron su rendimiento en mazorca. En contraste, las poblaciones seleccionadas para adaptación a valles altos mostraron mayor rendimiento en mazorca, menos días a floración, menor altura de planta, más ramas primarias de espiga y mazorcas cónicas. Estos atributos podrían incorporarse en programas de mejoramiento de maíz para valles altos de México o combinarse con el germoplasma local para mejorar su adaptabilidad y su heterosis.

Genetic analysis of maydis leaf blight resistance in subtropical maize (Zea mays L.) germplasm

Knowledge on the genetics of maydis leaf blight (MLB) is crucial to breed the resistant maize cultivars to combat disease epidemics as a sustainable and cost-effective approach. The present investigation was framed to understand the genetics of MLB resistance in subtropical maize. Two contrasting genotypes CM119 (susceptible) and SC-7-2-1-2-6-1 (resistant) were used to generate six genetic populations, namely P1, P2, F1, F2, BC1P1 and BC1P2, and evaluated in three target environments for MLB resistance under artificial epiphytotic condition. The CM119 and SC-7-2-1-2-6-1 showed susceptible and resistant reactions with mean disease reaction of 3.89-3.98 and 1.88-2.00, respectively. The derived generations, namely F1, F2, BC1P1 and BC1P2 showed mean disease reaction of 2.15-2.28, 2.44-2.51, 2.19-2.24 and 2.22-2.28, respectively in the test locations. The segregating generations (F2: 0.35-0.37; BC1P1: 0.24-0.29 and BC1P2: 0.17-0.20) showed variation for MLB disease resistance over the parental and first filial generations (P1: 0.11-0.17; P2: 0.08-0.13 and F1: 0.12-0.14). The genetic analysis of MLB resistance revealed the nonallelic interactions of duplicate epistasis type across the test locations. Among the gene interactions, dominance x dominance [l] effect was predominant over additive x additive [i] and additive x dominance [j] effects. The segregation analysis and the prediction of the number of major loci revealed at least two major genes associated with MLB tolerance in subtropical maize. Our investigation paved the foundation for the improvement of subtropical maize germplasm of MLB resistance.

Yield, Insect-Derived Ear Injury, and Aflatoxin Among Developmental and Commercial Maize Hybrids Adapted to the North American Subtropics.

The development of maize (Zea mays L.) hybrids that are adapted to subtropical areas of North America should consider yield potential under heat and moisture stress, and reduced susceptibility to insect herbivory and disease. To aid in this process, maize hybrids (43 developmental and seven non-Bt commercial hybrids) were evaluated for severity of ear injury to Helicoverpa zea (Boddie) and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), susceptibility to Aspergillus flavus (Link) (Deuteromycetes: Moniliales), and yield. In subtropical Corpus Christi and College Station, TX, field experiments conducted over three years revealed significant differences among maize hybrids with the rank of the selected measurements differing across the two locations. When the location by maize hybrid interaction was not significant, variation across the main factors of maize hybrid genetics (in all cases) and location (in some cases) was detected. In 2014, a significant location by maize hybrid interaction in yield but not aflatoxin and ear injury were likely associated with differences in weather between locations. In Corpus Christi in 2015, a location by maize hybrid interaction was detected for ear injury only. Overall, experimental maize hybrids, containing the inbred line Tx777, displayed partial resistance to insect derived ear injury in both locations, and some hybrid testcrosses exhibited low rates of aflatoxin accumulation while maintaining relatively high yields. Tx777 was selected from populations originating in Bolivia and adapted to subtropical climates. The most promising hybrid testcrosses had lower ear injury and aflatoxin accumulation, and good yield under varying heat and moisture stress at the two subtropical maize growing areas in this study.

Screening of Maize Genotypes against Stalk Rot Disease in River Basin Area of Surkhet, Nepal

Stalk rot of maize (Zea mays L.) is becoming a serious threat in tropical and subtropical maize growing regions of Nepal. To identify the sources of disease resistance in maize genotypes, a field experiment was conducted under natural epiphytotic condition during the summer season of 2016 and 2017 with thirty genotypes in a randomized complete block design in two replications. Statistical analysis showed that percent disease incidence (PDI) and grain yield were highly significant among the tested genotypes. Most of the maize genotypes were resistant to moderately resistant, only few were susceptible in both years, indicating good sources of resistance in the available genotypes. During 2016, the highest PDI was found in Arun 4 (33.17%) followed by Rampur 27 (20.10%) and Arun 2 (20.06%) whereas TLBRS07F14 and TLBRS07F16 showed no disease incidence. Similarly, the highest and least grain yielders were identified as Rampur Hybrid 6 (6.77 t/ha) and Arun-4 (2.15 t/ha) respectively. In 2017, highest PDI was observed in Arun-2 (24%) followed by Arun-4 (22%) and no disease incidence was seen in TLBRS07F14. Highest grain yield was found in RAMS03F08 (7.38 t/ha) followed by Manakamana-3 (7.37 t/ha) and the lowest was recorded in Arun 4 (2.60 t/ha). These resistant genotypes can be utilized in national breeding program to develop stalk rot tolerant high yielding maize genotypes in future.

Screening of inbred lines of tropical maize for resistance to fall armyworm, and for yield and yield-related traits

The fall armyworm (FAW) (Spodoptera frugiperda J.E. Smith) is a major cause of crop loss and food insecurity in sub-Saharan Africa. There is a need to identify maize genetic resources with FAW resistance for breeding. The objectives of this study were to screen two sets of diverse maize germplasm and to select genotypes with FAW resistance and desirable yield-related traits. Set I and Set II, containing 60 and 253 maize genotypes, respectively, were selected based on their agronomic potential and adaptability for screening in FAW infested areas in Zambia. Highly significant differences (P < 0.001) were detected among the test genotypes for FAW-leaf damage (FLD) and FAW cob damage (FCD) and agronomic traits. The lowest FLD and FCD were 8.87% and 5.36%, recorded in genotypes CML304-B and CML442, respectively. Five principal components (PCs) accounted for ≥80% of the total variation showing that key traits included reduced anthesis-silking interval (ASI), plant height, FLD and FCD, desirable ear aspect and grain yield. Some genotypes, such as Pool 16 and ZM7114 from Set I, and CZL1310c, CML444-B, CZL15220 and TL1512847 from Set II had low mean FCD and FLD, showing that they were potential sources of FAW resistance. Grain yield was negatively correlated with mean FLD (r = −0.18, p < 0.05), and FCD (r = −0.15, p < 0.05). Promising maize genotypes including CZL1310c, CML444-B, CZL15220, TL1512847 and CML491 were selected for their low mean FLD, FCD, earliness to flowering and high grain yield potential. These genotypes will be useful in developing tropical and sub-tropical maize breeding populations with partial FAW resistance and yield gains.

Overview of Risk Factors and Strategies for Management of Insect-Derived Ear Injury and Aflatoxin Accumulation for Maize Grown in Subtropical Areas of North America

Abstract Pest and disease risk factors causing maize yield and kernel quality issues in subtropical areas of North America (between 35°N and 23.5°N latitude) are reviewed: preharvest Aspergillus flavus (Link) (Deuteromycetes: Moniliales) infection and propagation in maize ears and ear injury principally caused by Helicoverpa zea (Boddie) and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). Risk is affected by potentially interacting factors of maize genetics, ear feeding with insects, fungal inoculum and growth, and weather (rainfall, temperature, and humidity). This review gives special attention to integration of the most efficient pest and disease management strategy combinations and the potential interaction of insect ear feeding and A. flavus occurrence. Management strategies reviewed include maximizing partial genetic resistance to A. flavus and selection of appropriate hybrids for the area, biological control of A. flavus using non-aflatoxigenic strains, avoiding pests and diseases using cultural practices like early planting, and reducing H. zea and S. frugiperda ear injury using Bt transgenes. Understanding the combined influences and identifying combined management approaches may lead to reduced aflatoxin risk and maintaining yield. This review focuses on subtropical areas of North America because the amount of maize produced in warm environments within or similar to subtropical maize production areas is likely to increase due to projected increases in demand for maize and predicted increases in temperature may increase pest and disease risk.

RENDIMIENTO, COMPONENTES DE RENDIMIENTO Y HETEROSIS DE GERMOPLASMA DE MAÍZ ADAPTADO A VALLES ALTOS

Las variedades de maíz (Zea mays L.) introducidas de otras latitudes son una fuente de alelos favorables de utilidad en el mejoramiento genético, pero antes de ser empleados deben adaptarse a las condiciones climáticas de los ambientes de interés. El objetivo del presente estudio fue evaluar el rendimiento y sus componentes en poblaciones representativas de razas de maíz originarias del trópico y subtrópico adaptadas por selección masal recurrente a los Valles Altos de México, así como la heterosis de sus cruzas interraciales para identificar genotipos útiles al mejoramiento genético del maíz para esos ambientes. Se evaluaron nueve poblaciones de maíz adaptado, ocho cruzas de dos poblaciones, una cruza de tres poblaciones, generaciones avanzadas de las cruzas y cuatro testigos comerciales. Los genotipos se evaluaron en tres ambientes bajo un diseño experimental de bloques completos al azar con tres repeticiones. Se registró el rendimiento y sus componentes. Se realizó análisis de varianza, comparación de medias (Tukey, P ≤ 0.05), análisis de correlación y se estimó la heterosis con respecto al progenitor medio. Hubo diferencias significativas (P ≤ 0.01) entre genotipos para todos los caracteres; los materiales adaptados rindieron de 3.89 a 11.71 t ha-1 y los testigos de 8.06 a 11.56 t ha-1. El rendimiento correlacionó con el índice de prolificidad (r = 0.67), longitud (r = 0.64), diámetro de mazorca (r = 0.65) y número de granos por hilera (r = 0.64). La heterosis promedio para rendimiento y sus componentes fluctuó de -5.30 a 6.53 %, con 5.68 % para rendimiento, donde la cruza F1 P9 × P8 presentó la mayor heterosis (26.19 %). Las poblaciones adaptadas y sus cruzas presentaron rendimientos similares a los testigos comerciales; por esto, pueden aprovecharse per se o como participantes para mejoramiento genético del maíz local de Valles Altos.

Association of Insect-Derived Ear Injury With Yield and Aflatoxin of Maize Hybrids Varying in Bt Transgenes.

Environmental factors have been associated with the production of aflatoxin in maize, Zea mays L., and it is inconclusive whether transgenic, Bacillus thuringiensis (Bt), maize has an impact on aflatoxin accumulation. Maize hybrids differing in transgenes were planted in two locations from 2014 to 2017. Yield, aflatoxin, and ear injury caused by corn earworm, Helicoverpa zea (Boddie), and fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), were measured across three groups of hybrids differing in transgenes including near-isogenic hybrids, and water-stressed conditions. The hybrid groups consisted of non-Bt hybrids with no Bt transgenes, a second group with one or more Cry-Bt transgenes, and the third group with vegetative insecticidal Bt protein and Cry-Bt transgenes (Cry/Vip-Bt). Across the six data sets derived from 11 experiments, the Cry-Bt and Cry/Vip-Bt hybrids had less ear injury and aflatoxin on average than non-Bt hybrids. The effects of ear injury on yield and aflatoxin were more prominent and consistent in Corpus Christi, TX, where hybrids experienced more water-limited conditions than in College Station, TX. The trend of increased aflatoxin among hybrids with increased ear injury was further resolved when looking at Cry-Bt and Cry/Vip-Bt isogenic hybrids in Corpus Christi. The results supported that the maize hybrids with the inclusion of Cry-Bt and Cry/Vip-Bt transgenes warrant further investigation in an integrated approach to insect and aflatoxin management in sub-tropical rain-fed maize production regions. Research outcomes may be improved by focusing on areas prone to water-stress and by using hybrids with similar genetic backgrounds.