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 (−7.15%), 100GW (−23.52%), SPAD (−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 >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.

Soil water limitations can cause high losses in agricultural yields. In order to investigate how popcorn varieties are affected by reduced water availability, we evaluated grain yield (GY) and popping expansion (PE) of 20 popcorn lines under water stress (WS) and well-watered conditions (WW), to propose discrimination with regard to the level of water-stress tolerance (T) and agronomic water-use efficiency (WUE), as well as to identify crosses for the breeding of superior hybrid combinations and for inheritance studies. A randomized complete block design with three replications was used. Irrigation was applied at pre-anthesis. The germplasm was discriminated based on the Stress tolerance index (STI), Stress susceptibility index (SSI), Stability index (SIN), Drought resistance index (DRI), and Agronomic water-use efficiency (WUE). Genetic diversity was measured by 15 EST-SSR markers. The reduction in GY under water stress was 55.29% and PE was reduced 29.19%. For the identification of genotypes with higher phenotypic means, STI and WUE were similarly efficient, whereas SSI and SIN identified genotypes with a lower proportional performance loss in the WS compared to the WW environment. For both GY and PE, there was a lack of relationship between WUE (more productive) and T (more ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 17 (4): gmr18184 S.H. Kamphorst et al. 2 stable). To explore the allelic complementarity for WUE, for T and for both, respectively, the combinations L59 x P7, L55 x P1 and L71 x P6 had the best performances. The lines L61, L63 and L65 phenotypically contrasted to those with high WUE and T and could be used for inheritance studies. Genotypes with higher WUE are considered the most appropriate option for breeding programs under WS.

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.

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 S 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 S 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 S progeny 10 combination, was indicated as promising, showing high values for specific combining ability for GY and PE. For the S 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.

In view of the narrow genetic base of popcorn, probably due to its evolution by selection from flint maize types alone, knowledge about genetic divergence is imperative for the formation of heterotic groups. Thus, our objective was to identify heterotic groups of popcorn lines; we did so by exploiting the representative genotype collection of the Active Popcorn Germplasm Bank of the State University of Northern Rio de Janeiro. Thirty-eight popcorn genotypes from different origins were analyzed by two methodologies to identify divergent groups. In the first method, the genotypic data were processed to determine the number of groups, based on Bayesian clustering algorithms, and two clustering methods (UPGMA and Ward), based on three genetic distance algorithms, weighted index, unweighted index, and an index of genetic distance or dissimilarity, proposed by Smouse and Peakall. The second methodology identified groups based on simultaneous use of morphoagronomic and molecular information and extracting the genetic distance matrix by the Gower algorithm, and later applying UPGMA and Ward clustering methods. The consistency of the clustering methods was evaluated by cophenetic correlation coefficients. The significance of these coefficients was examined by the Mantel test. There was significant genetic variability among corn popcorn accesses at morphological and molecular levels. There also ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 17 (3): gmr18083 C. Vittorazzi et al 2 was agreement between multivariate clustering techniques, mainly when using genotypic data provided by microsatellite markers. heterotic groups were identified; these were formed mainly according to the origin of each genotype and/or geographic origin. We found that there is sufficient heterosis to develop new cultivars.

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The objective of this study was to evaluate the effects of additive and non-additive genes on the efficiency of nitrogen (N) use and N responsiveness in inbred popcorn lines. The parents, hybrids and reciprocal crosses were evaluated in a 10x10 triple lattice design at two sites and two levels of N availability. To establish different N levels in the two experiments, fertilization was carried out at sowing, according to soil analysis reports. However, for the experiments with ideal nitrogen availability, N was sidedressed according to the crop requirement, whereas for the N-poor experiments sidedressing consisted of 30% of that applied in the N-rich environment. Two indices were evaluated, the Harmonic Mean of the Relative Performance (HMRP) and Agronomic Efficiency under Low Nitrogen Availability (AELN), both based on grain yield at both N levels. Both additive and non-additive gene effects were important for selection for N-use efficiency. Moreover, there was allelic complementarity between the lines and a reciprocal effect for N-use efficiency, indicating the importance of the choice of the parents used as male or female. The best hybrids were obtained from inbred popcorn lines with contrasting N-use efficiency and N responsiveness.