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Although resistance to diseases is genetically controlled, the environment has a strong influence on the reaction of plants to pathogens. Thus, the selection of superior genotypes in plant breeding programs can be more efficient the more intrinsically the environmental factors that influence the trait of interest are considered. This study aimed to investigate the adaptive genetic capacity of popcorn maize plants in relation to the occurrence of southern corn leaf blight (SCLB) in contrasting environments regarding nitrogen availability. Gene effects were estimated based on the implementation of a full diallel without reciprocals from which 28 hybrids were obtained. These hybrids, together with their parents, were evaluated in four environments in relation to SCLB reaction. The studied characteristics were area under the disease progress curve, estimated for severity and incidence. The experimental design was a 6 × 6 square lattice with three replications. Significant effects were found on the interactions between genotype, general combining ability, and specific combining ability × environment, demonstrating severe implications of soil nitrogen concentration on the performance of parent lines and hybrids. Dominant gene effects prevailed in the expression of resistance to SCLB. Considering the need for an environmentally and economically sustainable awareness in the control of this disease, it is of interest to take advantage of the heterotic effect contained in the combination L77 × P7, which stood out in relation to the other hybrids for the evaluated environments.

The development of superior hybrid cultivars depends on the identification of lines with greater combining ability. This study compared the discrimination and combining ability of four testers when crossed with 43 partially endogamous S3 popcorn (Zea mays L. var. everta) progenies by the Residual or Restricted Maximum Likelihood and Best Linear Unbiased Prediction (REML/BLUP) approach. Yield and morphological components of genotypes were evaluated. The experiment was arranged in a complete block design with three replicates at two locations (in the North and Northwestern regions of the State of Rio de Janeiro, Brazil). The REML/BLUP approach was able to efficiently discriminate and estimate the combining abilities for all traits assessed. Testers BRS-Angela and P2 had positive effects on all yield components, indicating their suitability as potential parents of hybrids in crosses with S3 progenies. The negative genotypic effects were the highest for the testers IAC 125 and UENF 14, indicating that they could be used to adequately identify the progenies with the highest potential among the evaluated genotypes. Overall, at both locations, tester IAC 125 was the best discriminator of the relative merits of S3 progenies, while BRSAngela was the tester with the best hybrid yield.

Drought currently affects several regions worldwide and tends to be more frequent due to climate change. It might compromise food security and the economic structure related to agribusiness. Popcorn has a crucial role in the Brazilian economy, but the cultivars that adapt to water stress, the most prejudicial abiotic stress for crop productivity, are unknown to date. This deficit of popcorn varieties adapted to heat and drought stresses will become more limiting with climate change. Given this scenario, knowing the genetic basis of agronomic traits under stress conditions is essential in promoting crop productivity and plant adaptation to abiotic stresses. Under two contrasting water conditions (WC) and different crop seasons (CS), we aimed to generate information about the combining ability of 10 popcorn progenitors and 15 hybrids through a partial diallel-mating design. The water stress was initiated at the male pre-anthesis stage. Significant genotype*crop seasons (G*CS), genotype*water condition (G*WC), and genotype*crop seasons*water condition (G*CS*WC) interactions were present. Regardless of CS and WC, non-additive effects controlled grain yield (GY), grain number per row (GN), ear length and diameter (ED), and 100-grain weight, while additive effects were present for popping expansion (PE). For each CS, regardless of WC, the cause-effect of GN (2018) and ED (2020) on GY seems to be an opportunity for indirect selection. Utilizing genetically broad-based hybrids is also a good opportunity for obtaining superior genotypes for GY and PE as it is possible to select inbred lines for both of these traits. We recommend the L76 × L61 hybrid for the Brazilian agribusiness context due to its greater productivity and dominance deviations.

The method of regional heritability mapping (RHM) has become an important tool in the identification of quantitative trait loci (QTLs) controlling traits of interest in plants. Here, RHM was first applied in a breeding population of popcorn, to identify the QTLs and candidate genes involved in grain yield, plant height, kernel popping expansion, and first ear height, as well as determining the heritability of each significant genomic region. The study population consisted of 98 S1 families derived from the 9th recurrent selection cycle (C-9) of the open-pollinated variety UENF-14, which were genetically evaluated in two environments (ENV1 and ENV2). Seventeen and five genomic regions were mapped by the RHM method in ENV1 and ENV2, respectively. Subsequent genome-wide analysis based on the reference genome B73 revealed associations with forty-six candidate genes within these genomic regions, some of them are considered to be biologically important due to the proteins that they encode. The results obtained by the RHM method have the potential to contribute to knowledge on the genetic architecture of the growth and yield traits of popcorn, which might be used for marker-assisted selection in breeding programs.

Phosphorus (P) is one of the most limiting factors in low investment agricultural systems. The aim of this study was to evaluate a panel of 29 popcorn maize lines to identify potential genotypes to be developed under P restriction conditions for integration into a breeding program. For this, these lines were phenotyped for complex traits of the shoot, root, and phosphorus use efficiency (PUE) at contrasting and controlled P environments (standard and low P contents of 22 and 4 mg dm−3, respectively) and genotyped with 15 SSR–EST markers. The results indicated that through selection in shoot traits it is possible to obtain indirect gains in traits related to root development that are difficult to measure. In addition, the selection based on traits of shoot and root development at an environment promotes indirect gains in another environment. In the environment supplied with low P, the P uptake were more important for PUE than internal utilization of P. Lines P2, P4, P7, and P9 presented a better development of shoot and root system at the P-low environment, in addition to showing P content above the average in root and shoot. Based on genetic diversity, complementary and inheritance crosses were identified.

To ensure genetic gains in popcorn breeding programs carried out under drought conditions knowledge about the response of morphophysiological traits of plants to water stress for the selection of key traits is required. Therefore, the objective was to evaluate popcorn inbred lines with agronomically efficient (P2 and P3) and inefficient (L61 and L63) water use and two hybrids (P2xL61 and P3xL63) derived from these contrasting parents, cultivated under two water regimes (WW watered—WW, and water-stressed—WS) in a greenhouse, replicated five times, where each experimental unit consisted of one plant in a PVC tube. Irrigation was applied until stage V6 and suspended thereafter. Individual and combined analyses of variance were performed and the genotypic correlations and relative heteroses estimated. The water use efficient inbred lines were superior in root length (RL), root dry weight (RDW), and net CO2 assimilation rate (A), which were the characteristics that differentiated the studied genotypes most clearly. High heterosis estimates were observed for RL, SDW, leaf width (LW), leaf midrib length (LL), and agronomic water use efficiency (AWUE). The existence of a synergistic association between root angle and length for the characteristics A, stomatal conductance (gs), and chlorophyll concentration (SPAD index) proved most important for the identification and phenotyping of superior genotypes. Based on the study of these characteristics, the higher AWUE of the previously selected inbred lines could be explained. The results reinforced the importance of root physiological and morphological traits to explain AWUE and the possibility of advances by exploiting heterosis, given the morphophysiological superiority of hybrids in relation to parents.

The identification of traits associated with drought tolerance in popcorn is a contribution to support selection of superior plants under soil water deficit. The objective of this study was to choose morphological traits and the leaf greenness index, measured on different dates, to estimate grain yield (GY) and popping expansion (PE), evaluated in a set of 20 popcorn lines with different genealogies, estimated by multiple regression models. The variables were divided into three groups: morpho-agronomic traits—100-grain weight (GW), prolificacy (PR), tassel length (TL), number of tassel branches, anthesis-silking interval, leaf angle (FA) and leaf rolling (FB), variables related to the intensity of leaf greenness during the grain-filling period, at the leaf level, measured by a portable chlorophyll meter (SPAD) and at the canopy level, calculated as the normalized difference vegetation index (NDVI). The inbred lines were cultivated under two water conditions: well-watered (WW), maintained at field capacity, and water stress (WS), for which irrigation was stopped before male flowering. The traits GY (55%) and PE (28%) were most affected by water restriction. Among the morpho-agronomic traits, GW and PR were markedly reduced (&gt, 10%). Under dry conditions, the FA in relation to the plant stalk tended to be wider, the FB curvature greater and leaf senescence accelerated (&gt, 15% at 22 days after male flowering). The use of multiple regression for the selection of predictive traits proved to be a useful tool for the identification of groups of adequate traits to efficiently predict the economically most important features of popcorn (GY and PE). The SPAD index measured 17 days after male flowering proved useful to select indirectly for GY, while, among the morphological traits, TL stood out for the same purpose. Of all traits, PR was most strongly related with PE under WS, indicating its use in breeding programs. The exploitation of these traits by indirect selection is expected to induce increments in GY and PE.

Understanding the interaction between genotype performance and the target environment is the key to improving genetic gain, particularly in the context of climate change. Wheat production is seriously compromised in agricultural regions affected by water and heat stress, such as the Mediterranean basin. Moreover, wheat production may be also limited by the nitrogen availability in the soil. We have sought to dissect the agronomic and physiological traits related to the performance of 12 high-yield European bread wheat varieties under Mediterranean rainfed conditions and different levels of N fertilization during two contrasting crop seasons. Grain yield was more than two times higher in the first season than the second season and was associated with much greater rainfall and lower temperatures. However, the nitrogen effect was rather minor. Genotypic effects existed for the two seasons. While several of the varieties from central/northern Europe yielded more than those from southern Europe during the optimal season, the opposite trend occurred in the dry season. The varieties from central/northern Europe were associated with delayed phenology and a longer crop cycle, while the varieties from southern Europe were characterized by a shorter crop cycle but comparatively higher duration of the reproductive period, associated with an earlier beginning of stem elongation and a greater number of ears per area. However, some of the cultivars from northern Europe maintained a relatively high yield capacity in both seasons. Thus, KWS Siskin from the UK exhibited intermediate phenology, resulting in a relatively long reproductive period, together with a high green area throughout the crop cycle. This study was supported in part by the Spanish projects PID2019-106650RB from the Ministerio de Ciencia e Innovación and IRUEC PCIN-2017-063 from the Ministerio de Economía y Competividad, Spain.

Drought is a common abiotic stress in tropical and subtropical regions that limits the growth and development of agricultural crops, mainly impacting grain yield. Acting through plant breeding is the most viable alternative for obtaining genotypes more tolerant of environments with stress. This work aims to select popcorn genotypes for environments with drought and to identify discriminating traits for the evaluation of drought tolerance in popcorn germplasm. Fifteen Latin American populations of popcorn were evaluated in water stress (WS) and well-watered (WW) conditions. The evaluated traits were based in morpho-agronomic, physiological and radicular descriptors. Data were submitted to individual and joint ANOVA and GT Biplot analysis. Variability was detected between populations for all traits in both conditions. The drought caused a reduction of 30.61% and 3.5% in grain yield and popping expansion, respectively. Based in GT biplot analysis, 880POP was the most stable in WS and WW, being indicated as a promising population for cultivation in environments with water limitation. This study is going to allow the establishment of a collection of great importance to maize germplasm and to provide information to facilitate the process of selection in breeding programs focused on drought tolerance.

Population growth and the high demand for food production has caused environmental degradation losses in biodiversity. The conservation of genetic resources is the most appropriate strategy for maintaining the variability of species of great importance, such as Capsicum. In this study, we describe the characterization of 69 pepper accessions of four Capsicum species from different regions of Brazil on the basis of qualitative and quantitative descriptors and ISSR markers. The 11 quantitative descriptors grouped the 69 populations into five clades. The fruit traits had the greater discrimination power. A strong correlation was detected between some pairs of quantitative descriptors: petiole and fruit length, fruit diameter and fresh fruit mass, leaf length and leaf width, canopy and plant height, stem diameter and plant height, stem diameter and canopy diameter. A negative correlation was also observed between plant height and pericarp thickness. Moreover, the molecular analysis grouped accessions into five clades. The morpho-agronomic and molecular characterization were efficient to estimate the genetic diversity between accessions, being important tools for the knowledge and use of accessions. This study is of great importance to preserve pepper germplasm and to provide data to facilitate the process of the selection in breeding programs.

The objective of this study was to estimate the direct and indirect effects of agricultural, morphological, physiological, and root traits of popcorn lines, under two conditions of water supply: full irrigation (FI) and drought stress (DS). A complete randomized block design with three replications was used to evaluate the following traits: expanded popcorn volume per hectare (EPV), 100-grain weight (100GW), mean ear length, mean ear diameter, number of grains per row (NGR), prolificacy (PRO), anthesis to silking interval, tassel length, number of tassel branches, plant height, shoot dry matter, green index (SPAD), and canopy temperature depression (CTD), root angle (RA), tap root volume (TRV), and crown root volume (CRV). Analyses of variance and path analysis, and subsequent partitioning of direct and indirect effects were performed. For the traits EPV, PRO, CTD, RA, CRV and TRV, the genotype x environment interaction was significant. Drought stress had significant effects on EPV (&minus, 7.15%), 100GW (&minus, 23.52%), SPAD (&minus, 29.31%), CTD (87.15%), RA (24.54%), and CRV (44.89%). The traits NGR and SPAD were found to be decisive for the expression of EPV. The exploitation of these traits by indirect selection is expected to induce increments in EPV in environments under DS and FI.

To define breeding strategies, the understanding of trait inheritance is critical. The objective of this study was to determine the inheritance of popcorn under different water regimes. To this end, Hayman's diallel methodology was used, with 8 parents and 28 hybrids. The experiment was carried out under well-watered conditions (WW) and water stress (WS). For popping expansion (PE) under both water regimes, the effects of complete dominance and greater importance of the components associated with the dominance effects were observed. In contrast, the number of dominant genes was zero and the determination coefficient in the narrow sense was &gt, 50%, additive effects were also present. For the number of grains per row (GR), ear length (EL), and grain yield (GY) under WS and WW conditions, the dominance effects were the most relevant, and the mean degree of dominance with overdominance effects and greatest relevance of the components associated with this effect were also observed. The same breeding methods can be applied under the studied WS and WW conditions. Exploiting heterosis for GY and related components is a promising way to adapt popcorn to WS. To be able to capitalize on additive and dominance effects, a reciprocal recurrent selection is recommended.

Climate change is expected to intensify water restriction to crops, impacting on the yield potential of crops such as popcorn. This work aimed to evaluate the performance of 10 field cultivated popcorn inbred lines during two growing seasons, under well-watered (WW) and water stressed (WS) (ψsoil≥ −1.5 MPa) conditions. Water stress was applied by withholding irrigation in the phenological phase of male pre-anthesis. Additionally, two contrasting inbred lines, P7 (superior line) and L75 (low performer) were compared for grain yield (GY) and expanded popcorn volume (EPV), selected from previous studies, were tested under greenhouse conditions. In the field, no genotype x water condition x crop season (G×WC×CS) interaction was observed, whereas GY (−51%), EPV (−55%) and leaf greenness (SPAD index) measured 17 days after anthesis (DAA) (> −10%) were highly affected by water limitation. In general, root traits (angles, number, and density) presented G×WC×CS interaction, which did not support their use as selection parameters. In relation to leaf senescence, for both WS and WW conditions, the superior inbred lines maintained a stay-green condition (higher SPAD index) until physiological maturity, but maximum SPAD index values were observed later in WW (48.7 by 14 DAA) than in WS (43.9 by 7 DAA). Under both water conditions, negative associations were observed between SPAD index values 15 and 8 days before anthesis DBA), and GY and EPV (r ≥ −0.69), as well as between SPAD index 7, 17, and 22 DAA, and angles of brace root (AB), number of crown roots (NC) and crown root density (CD), in WS (r ≥ −0.69), and AB and CD, in WW (r ≥ −0.70). Lower NC and CD values may allow further root deepening in WS conditions. Under WS P7 maintained higher net photosynthesis values, stomatal conductance, and transpiration, than L75. Additionally, L75 exhibited a lower (i.e., more negative) carbon isotope composition value than P7 under WS, confirming a lower stomatal aperture in L75. In summary, besides leaf greenness, traits related to leaf photosynthetic status, and stomatal conductance were shown to be good indicators of the agronomic performance of popcorn under water constraint. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. Funding was also provided by FAPERJ, with the project E26/201.813/2017 to SK and E26/202.761/2017 to AA. Funding to JR by Fundação para a Ciência e a Tecnologia (FCT), Portugal, through the research units UID/UIDB/00239/2020 (CEF), and UIDP/04035/2020 (GeoBioTec) is also greatly acknowledged. JA acknowledges the support of Catalan Institution for Research and Advanced Studies (ICREA, Generalitat de Catalunya, Spain), through the ICREA Academia Program.

To date, no studies on the inheritance of Fusarium spp. ear rot resistance in popcorn are available. The purpose of this paper was to investigate the additive-dominance model to estimate the genetic components of variance, heritability and the inheritance pattern in a diallel for popcorn, by Hayman’s approach. The experiment was carried out in two environments, using eight parent lines. The following traits were measured: grain yield (GY), popping expansion (PE), incidence of ears infected by Fusarium (FusIE), total number of kernels infected by fungi (FunIK) and total number of kernels infected by Fusarium spp. (FusIK). The results indicated that the incidence of FusIK (Fusarium-infected kernels), FunIK (fungus-infected kernels), and FusIE (Fusarium-infected ears) is controlled by dominant genes. Parent L77 had a high number of favorable alleles for all resistance-related traits, as well as for PE. The strategy recommended for reduction of FunIK, FusIK, and FusIE consists of exploiting hetorosis using inbred lines with favorable alleles.

Among the ear rot pathogens, species of Fusarium cause significant economic losses to popcorn production. To generate popcorn genotypes resistant to Fusarium ear rot, the combining ability of popcorn lines in diallel crosses were assessed during two cropping years: the first from Mar to Sep 2015 and the second from Sep 2015 to Jan 2016. The traits analyzed were: average ear weight (AEW, kg ha−1); grain yield (GY, kg ha−1); popping expansion (PE, g mL−1), Fusarium incidence on ears (EIFU, %); Fusarium ear rot severity index (FSI, %), percentage of fungal-infected kernels (KIF), and percentage of Fusarium-infected kernels (KIFU). Non-additive genetic effects prevailed in the expression of resistance to Fusarium ear rot and grain yield, while additive effects were the most prominent in the expression of popping expansion. Among 56 hybrids, seven showed outstanding grain yield, desirable popping expansion, and resistance to Fusarium ear rot. The less susceptible hybrids to ear rot produced high grain yield and popping expansion. Two disease-related traits, KIFu and EIFu, allowed to best differentiate among the genotypes.

The extensive use of nitrogen (N) in agriculture has caused negative impacts on the environment and costs. In this context, two pot experiments were performed under different N levels and harvested at different vegetative stages to assess two popcorn inbred lines (P2 and L80) and their hybrid (F1 = P2 &times, L80) for the N use, uptake and utilization efficiency (with the inclusion and exclusion of root N content), to find the contrasting N levels and vegetative stages that effect nitrogen use efficiency (NUE) and to understand the relationship between the traits related to NUE. The hybrid and P2 were confirmed better than L80 for all the studied traits. NUE is mainly affected by the shoot dry weight, uptake and utilization efficiency. Extremely low and high N levels were found to be more discriminating for N use and dry weight, respectively. At the V6 (six fully expanded leaf) stage, root N content (RNC) should be considered, in contrast, at the VT (tasseling stage) stage, RNC should not be considered for the uptake and utilization efficiency. The genetic parameter performance for N use, uptake, shoot dry weight and N content could favor the achievement of the genetic gain in advanced segregating generations.

The identification of the genes responsible for complex traits is highly promising to accelerate crop breeding, but such information is still limited for popcorn. Thus, in the present study, a mixed linear model-based association analysis (MLMA) was applied for six important popcorn traits: plant and ear height, 100-grain weight, popping expansion, grain yield and expanded popcorn volume per hectare. To this end, 196 plants of the open-pollinated popcorn population UENF-14 were sampled, selfed (S1), and then genotyped with a panel of 10,507 single nucleotide polymorphisms (SNPs) markers distributed throughout the genome. The six traits were studied under two environments [Campos dos Goytacazes-RJ (ENV1) and Itaocara-RJ (ENV2)] in an incomplete block design. Based on the phenotypic data of the S1 progenies and on the genetic characteristics of the parents, the MLMA was performed. Thereafter, genes annotated in the MaizeGDB platform were screened for potential linkage disequilibrium with the SNPs associated to the six evaluated traits. Overall, seven and eight genes were identified as associated with the traits in ENV1 and ENV2, respectively, and proteins encoded by these genes were evaluated for their function. The results obtained here contribute to increase knowledge on the genetic architecture of the six evaluated traits and might be used for marker-assisted selection in breeding programs.

The global boom in agricultural production has been associated with the exponential increase of nitrogen (N) fertilizer application. This heavy use of nitrogen in agriculture has caused negative impacts on the environment. Therefore, new alternatives are needed to maintain or increase maize yield but reduce the environmental impact. For this purpose, one possibility is to plant N-use efficient (NUE) cultivars. In this context, the objective of this study was to identify popcorn hybrid cultivars that are highly NUE and N-responsive, bred from crosses between inbred lines with contrasting levels of N-use efficiency. For this purpose, 90 hybrids were evaluated in a 10 &times, 10 triple lattice design at two sites and two levels of N availability (low and ideal availability). The results indicated that for the environment with low nitrogen availability, the lack of nitrogen reduced the chlorophyll content, extended the interval between male and female flowering, and affected the performance of the tested hybrids. However, we observed the existence of hybrids with greater efficiency than the responsiveness to nitrogen and with high productivity. These can even be used on farms where the level of production inputs is low, thus contributing to ensure food security.

Water stress reduces the yield of agricultural crops severely. The objectives of this study were to investigate genotypic differences between 20 popcorn lines in environments under wellirrigated (WW) and water stressed (WS) conditions to determine phenotypic, genetic and environmental relations among agronomic and root traits. The experiment was arranged in a randomized complete block design with three replications per environment. The following traits were evaluated: volume of expanded popcorn per hectare (PV), grain yield (GY), popping expansion (PE), number of rings of adventitious roots (NRAR), number of adventitious roots (NAR), number of tap roots (NTR), number of crown roots (NCR), adventitious root density (ARD), tap root density (TRD), crown root density (CRD), tap root angle (TRA), and crown root angle (CRA). Under WS, the values of the agronomic traits PV, GY and PE were reduced by 74.03, 67.15 and 28.76%, respectively. Water stress had little influence on NRAR, NAR, DR, NTR, and NCR. Due to an adaptive response to WS, increases were observed in TRA and CRA. In general, the estimates of genetic parameters evaluated under WS were higher. Negative genetic associations between agronomic traits and TRD, and CRD were observed in cultivation under WS; selection for trait PV will produce simultaneous gains in GY and PE under this regime. Under well-watered conditions, the development of genotypes with satisfactory GY and PE is difficult. This reinforces the hypothesis that root phenotypes adapted to particular environments should be identified.

The multivariate analyses are useful tools to estimate the genetic variability between accessions. In the breeding programs, the Ward-Modified Location Model (MLM) multivariate method has been a powerful strategy to quantify variability using quantitative and qualitative variables simultaneously. The present study was proposed in view of the dearth of information about popcorn breeding programs under a multivariate approach using the Ward-MLM methodology. The objective of this study was thus to estimate the genetic diversity among 37 genotypes of popcorn aiming to identify divergent groups associated with morpho-agronomic traits and traits related to resistance to Fusarium spp. To this end, 7 qualitative and 17 quantitative variables were analyzed. The experiment was conducted in 2014, at Universidade Estadual do Norte Fluminense, located in Campos dos Goytacazes, RJ, Brazil. The Ward-MLM strategy allowed the identification of four groups as follows: Group I with 10 genotypes, Group II with 11 genotypes, Group III with 9 genotypes, and Group IV with 7 genotypes. Group IV was distant in relation to the other groups, while groups I, II, and III were near. The crosses between genotypes from the other groups with those of group IV allow an exploitation of heterosis. The Ward-MLM strategy provided an appropriate grouping of genotypes; ear weight, ear diameter, and grain yield were the traits that most contributed to the analysis of genetic diversity.

The expansion of agriculture, coupled with the need for sustainable cropping, is one of the greatest challenges of the scientific community working on the generation of new cultivars adapted to abiotic stress conditions. The aim of this study was to evaluate the variability of popcorn lines as to responsiveness and efficiency in phosphorus use, as a first step towards the implementation of a breeding program interested in the practice of sustainable agriculture. Twenty-five popcorn lines were evaluated in two locations with different phosphorus levels in the soil, using a randomized block design. The following traits were measured: plant height, ear height, female flowering date, male flowering date, male-female flowering interval, ear diameter, ear length, 100-grain weight, grain yield, popping expansion, and expanded popcorn volume per hectare. A combined analysis of variance and test of means were performed, and the lines were classified as to their phosphorus use efficiency, according to their production performance in the different environments. The genetic diversity between the lines was estimated by Tocher’s and UPGMA clustering methods, using generalized Mahalanobis distance. Lines L59, P7, P2, P3, P4, P8, P10, P9, L66, L70, L69, and P5 were efficient and responsive, whereas lines L75, L80, L61, L77, L63, L65, P1, L54, L53, L88, and L71 were inefficient and nonresponsive. Genetic variability was greater in the environments with low phosphorus in the soil, suggesting that the selection pressure exerted in the stressing environment is a decisive factor to obtain a higher expression of variability.

Molecular markers are a useful tool for identification of complementary heterotic groups in breeding programs aimed at the production of superior hybrids, particularly for crops such as popcorn in which heterotic groups are not well-defined. The objective of the present study was to analyze the genetic diversity of 47 genotypes of tropical popcorn to identify possible heterotic groups for the development of superior hybrids. Four genotypes of high genetic value were studied: hybrid IAC 125, strain P2, and varieties UENF 14 and BRS Angela. In addition, 43 endogamous S3 progenies obtained from variety UENF 14 were used. Twenty-five polymorphic SSR-EST markers were analyzed. A genetic distance matrix was obtained and the following molecular diversity parameters were estimated: number of alleles, number of effective alleles, polymorphism information content (PIC), observed and expected heterozygosities, Shannon diversity index, and coefficient of inbreeding. We found a moderate PIC and high diversity index, indicating that the studied population presents both good discriminatory ability and high informativeness for the utilized markers. The dendrogram built based on the dissimilarity matrix indicated six distinct groups. Our findings demonstrate the genetic diversity among the evaluated genotypes and provide evidence for heterotic groups in popcorn. Furthermore, the functional genetic diversity indicates that there are informative genetic markers for popcorn.

The successful development of hybrid cultivars depends on the reliability of estimated combining ability of the parent lines. The objectives of this study were to assess the combining ability of partially inbred S3 families of popcorn derived from the open-pollinated variety UENF 14, via top-crosses with four testers, and to compare the testers for their ability to discriminate the S3 progenies. The experiment was conducted in the 2015/2016 crop season, in an incomplete-block (Lattice) design with three replications. The following agronomic traits were evaluated: average plant height, grain yield (GY), popping expansion (PE), and expanded popcorn volume per hectare. The top-cross hybrid, originating from the BRS-Angela vs S3 progeny 10 combination, was indicated as promising, showing high values for specific combining ability for GY and PE. For the S3 progenies that showed high and positive GCA values for GY and PE, the continuity of the breeding program is recommended, with the advance of self-pollination generations. Fasoulas' differentiation index discriminated the BRS-Angela tester as the most suitable for identifying the superior progenies.