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Taste and nutritional value make sweet corn a valued plant and an important component of the human diet worldwide. Kernel nutritive composition of sweet corn has been reported in various papers, but a description of carotenoid and tocopherols profile, especially after cooking is scarce. Therefore, the present study was carried out to compare the carotenoid and tocopherol content in sweet corn before and after cooking. Contents of b-carotene, lutein+zeaxanthin and tocopherols (d-T, b+g-T, a-T) in the kernels of twelve sweet corn hybrids were determined by High-Performance Liquid Chromatography (HPLC) and were expressed as the mean value of three independent measurements. Both genotype and cooking affected the content of the carotenoids and tocopherols in the kernel. The highest content of total carotenoids before and after cooking was found in hybrid ZP486/1su (27.77/45.28 µg/g) whereas the lowest content was in hybrid ZP 355su (10.27 µg/g) before cooking i.e. in hybrid ZP 347su (24.55 µg/g) after cooking. The cooking resulted in a significant increase in the content of total carotenoids and tocopherols, lutein+zeaxanthin, and b-carotene in all hybrids, except the ZP504su in which the b-carotene content decreased. An increase in a-tocopherol after cooking was observed in hybrids ZP485/1su and ZP484/1su, while a decrease was in hybrids ZP481/1su, ZP486/1su and ZP477/2su. The results showed that increasing micronutrient content is genotype-dependent. This study confirmed that cooking increases the nutritional value of sweet corn and gives it additional value in terms of functional food.

Drought is one of the main consequences of climate change that negatively affects plant growth and development, which in turn leads to a reduction in yield. The objective of this study was to investigate the effects of the physiological responses to the drought stress of maize plants (population IP3722), obtained from seeds of different ages (originating from 2012. and 2016) and different previous experience (the seeds formed in 2012. were more exposed to drought than in 2016.). Two populations responded to drought treatment by a significant decrease of shoot fresh and dry weight, this was followed with decrease leaf area and transpiration rate. Drought treatments enabled induction and differentiation of chemical signals of drought (abscisic acid-ABA and xylem pH) and hydraulic signals (leaf water potential), and monitoring of their activity on stomatal conductance. The data showed that hydraulic signals have the same impact on stomatal reactions in the D2012 and D2016 treatments. They also indicated that the chemical signal of ABA works toward stomatal closure, but that the effect depends on whether it originates from the leaf or the root. Leaf-originating ABA had more effect on the closure of D2012 stomata, while root-originating ABA and pH was more active in the D2016.

Twenty-six maize landraces were tested in order to evaluate maize seedling performance as an index for drought tolerance in adult plants. Samples were subjected to polyethylene glycol-induced osmotic stress at the early seedling stage. Grain yield was obtained in field experiments under well-watered (OC) and a combination of drought and high plant density (HD) conditions. Osmotic stress caused a reduction in seedling growth (length, fresh and dry weight), and increase in the shoot and in particular the root proline contents in the majority of landraces, and variations in root peroxidase (POD) activity. Genotypes displaying more pronounced root growth reduction and higher proline contents exhibited decreased POD activity under osmotic stress. Direct positive correlations between the proline content and growth inhibition, and between the proline and soluble protein content were established. Correlations between the changes in POD activity and growth parameters were significant and positive, and significant but negative with the changes in the proline content. In the field, water stress led to a reduction in grain yield in all of the tested landraces. Correlations between grain yield from both experimental sets (OC and HD) and osmotic-induced changes in seedling root growth were negative, which was opposite to the highly significant and positive correlations between the changes in the seedling root proline content and yield. Also, genotypes with the highest seedling root proline content increase under osmotic stress, exhibited the highest stress tolerance index (STI) based on grain yield achieved under both field conditions. Our results indicate that lower changes in POD activity and especially an increased proline content after exposure to osmotic stress during the early seedling stage could be considered as useful indices to facilitate selection efficiency for drought tolerance in adult plants. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR31028: Exploitation of maize diversity to improve grain quality and drought tolerance]

Maize, wheat and rice are the most important cereals grown in the world. It is predicted that by 2025 maize is likely to become the crop with the greatest production globally. Conservation of maize germplasm provides the main resources for increased food and feed production. Conservation in gene banks (ex-situ) is dominant strategy for maize conservation. More than 130 000 maize accessions, e.g. about 40% of total number, are stored in ten largest gene banks worldwide and Maize Research Institute Zemun Polje (MRIZP) gene bank, with about 6000 accessions, is among them. Organized collecting missions started in 1961. in the former Yugoslavian territory, and up today, more than 2000 local maize landraces were stored. Pre-breeding activities that refer to identification of desirable traits from unadapted germplasm within genebank, result in materials expected to be included in breeding programs. Successful examples are LAMP, GEM and GENRES projects. At the end of XX century, at MRIZP genebank two pre-breeding activities were undertaken: eco-core and elite-core collections were created and landraces fulfilled particular criteria were chosen. In the last decade, MRIZP genebank collection was used for identification of sources for drought tolerance and improved grain quality. According to agronomic traits and general combining ability, two mini-core collections were created and included in commercial breeding programs.

Maize grains contain high level of carotenoids and tocopherols compared with other cereals. Among carotenoids the β-carotene has the highest activity and is considered important in breeding programs of biofortified crops. Changes in carotenoids content in the maize grain could be influence of genotype x environment interaction, or effect of existing relationship between the color of the endosperm and the presence of carotenoids. This research was performed to estimate differences in morphological traits, grain content of tocopherols (α-, β+γ-, δ-), β-carotene, lutein and zeaxantin in local and introduced populations from Maize Research Institute 'Zemun Polje' gene bank. Micronutrient content was detected by using high-performance liquid chromatography (HPLC). Coefficient of variation for morphological traits was less than 10%, except for grain yield per plant which vary about 18,6%. α-tocopherol content was in the range from 1.04-8.42 μgg-1 DW, and β-carotene content varied from 0.26 to 7.95 μgg-1 DW. δ-tocopherol was in significant correlation with number of kernels per row (r=0.700***), and β+γ-tocopherol was in significant negative correlation with plant and ear height (r=-0.601***; r=-0.591**). Correlations between morphological traits and α-tocopherol were weak and without significance. Kernel color was significantly correlated with the content of zeaxantin (r=0,590***) and β-carotene (r=0,398*). For biofortification purposes a pool of 11 landraces with increased content of both, β-carotene and α-tocopherol, will be created based on obtained results.

Predictions of global warming point out that frequency and severity of temperature and rainfall extremes are expected to increase in the following decades. Yield stability could be achieved by improvement in future breeding based on information of cereal reproduction under changed environmental conditions. Landraces are valuable sources of beneficial alleles, e.g. tolerance to drought and improved grain yield, for introgression into adapted germplasm. Twenty-six drought tolerant maize landraces, selected among gene bank accessions and previously tested under controlled drought conditions and in temperate climate, were evaluated, at two sites and two plant densities in Zemun Polje. Since 2014 was with enormous rainfalls and flooding, morphological and agronomical traits were measured. Obtained data, together with the results from dry 2012, were plotted for principal component analysis. One local landrace and two introduced landraces, medium in maturity, were selected according to PC analysis and achieved grain yield that was stable across different climatic conditions.

According to regional reports on climate, more frequent and severe droughts and floods are already apparent. Modern maize breeding for different purposes (e.g. drought tolerance) emphasizes the importance for improved maize ability to withstand adverse environmental conditions. Genotypes with drought tolerance obtain high grain yield under optimal conditions and lower, but stable yield under dry environmental conditions. Field testing was conducted in 2014, on twenty-three maize inbred lines differing in drought tolerance. The inbreds were evaluated in respect to morphological traits (plant and ear height, total number of leaves, number of leaves above uppermost ear, ear leaf length and width), yield components and grain yield per plant. The experiment was set up according to RCB design with two replications. To simulate water stress, two plant densities were applied. According to Principal Component Analysis and cluster analysis, five inbred lines (T1, T2, T4, T8 i T15) performed the highest stability in both experimental conditions. Those inbreds could be used as a source for drought tolerance in breeding programs.

Agronomic traits of 18 populations comprising a mini core collection for increased grain quality of the Maize Research Institute Zemun Polje were studied, along with two standard kernel type commercial hybrids. For almost all the traits (except root lodging) a considerable genetic variability was found, enabling successful breeding for any of them using this populations. Based on the obtained results, two populations were found to have grain yield at the level of ZP 341 commercial hybrid (one of them is from former Yugoslavia, and another is the introduced one). These two populations will be first to introduce into commercial breeding programs, if it proves they have also favorable biochemical characteristics. On the other hand, three populations had grain yield in the range of 1, 60-1, 91 t/ha, that is even lower than for commercial inbreeds. They will be excluded from the further breeding programs. Most of the populations were earlier than the commercial hybrids, during vegetation and according to the grain moisture at harvest. This is very favorable from a breeding standpoint. The worst characteristic of the population was very high stalk lodging, compared to commercial checks.

The aim of this study was to investigate thirteen maize local landraces from Maize Research Institute (MRIZP) Gene Bank drought tolerant mini-core collection in respect to Fe, Mn and Zn content in grain. In addition, phytate (Phy) and β-carotene contents were determined. According to the results obtained, the highest Fe content was found in grain of LL3, whereas LL1and LL13 were the genotypes with the highest Mn, i.e. Zn content, respectively. However, due to the lowest level of Pphy, along with relatively higher level of Fe, Mn and Zn contents in grain, LL2 could be considered as valuable source in further breeding programs for improved mineral nutrient contents, particularly for Fe. Possible availability of investigated mineral elements was determined according to molar ratio between phytate as inhibiting factor and β-carotene as promoting factor for their absorption. Accordingly, genotype LL2, being with the lowest Pphy content, and genotype LL3, being with the highest β-carotene content (25.63 μg g-1) and the lowest phytate/β-carotene ratio, could be considered as potential sources of favorable genes for further breeding programs for improved nutritional quality, such as enhanced availability of investigated mineral elements.

Drought is a major abiotic stress factor limiting crop growth, development and production worldwide. The objective of this study was to evaluate tolerance to osmotic stress of maize seedlings. More than 6,000 accessions from the Maize Research Institute gene bank were tested under controlled drought (at flowering) in Egypt, and afterwards in temperate climate (Serbia and Macedonia). Out of 41 drought tolerant accessions in the field, five inbred lines were chosen for laboratory testing, as well as one drought sensitive line. These genotypes were exposed to 4% polyethylene glycol-PEG (Mr 10000) for 24 h and 48 h. Nine-day-old seedlings compared to control conditions were analyzed in root and shoot length, fresh and dry weight and proline content. Results showed reduction in all parameters under stress, while only proline content increased in all PEG treated genotypes compared to control.

Drought is one of the most serious a biotic factors limiting crop production worldwide. Prediction of climate change increases the need of better adaptation and breeding for improved drought tolerance in crops. Maize is one of the most sensitive crops to drought, despite of the fact that it is a C4 plant, with high photosynthetic rate and relatively low transpiration rate. In Serbia drought severely decreased maize grain yield, particularly in the last decade. A major task for breeders is to create drought tolerant maize that will successfully cope with negative consequences of global warming are facing scientists today. Enhancing the tolerance of maize has been elusive in terms of conventional plant breeding. Interdisciplinary approaches tried to understand and dissect the mechanism of drought tolerance, but with limited success. Modern genomics and genetics, together with advances in phenotyping and knowledge in physiology and breeding are expected to reveal genes and pathways that confer drought tolerance.

It is generally known that a phenotype is formed on the basis of the capacity of its genotype affected by environmental factors. Yield stability is statistically expressed through the GxE interaction. The interaction is a part of the trial variation that includes the factor of the genotype and the factor of the environment. The presence of the qualitative interaction significantly makes difficult the selection of the best genotypes in the process of breeding. As long ago as the early 1960s, many researchers noticed that the application of linear regression could, in many cases, define adaptability and stability of a genotype. However, in cases when data are not well adjusted to the linear model, better results can be gained by the application of the multivariate models (PCA, AMMI, GGE). The estimated maize hybrid stability was compared in this study by linear (Finlay and Wilkinson and Eberhart and Russell models) and multivariate statistical models (AMMI model). Very similar results were obtained by all three models. It was probably due to one dominant factor in the hybrid x environment interaction (different precipitation sums for the environments and the length of the growing season for hybrids). The advantage was given to the AMMI model, as the model with one axis analyses the interaction equally well as linear models, while the model with two axes extracted another part of systemic variation of the interaction effect not adjusted to the linear model.

Standard induction processes of delayed fluorescence (DF) of chlorophyll (induction signals) occur when an intact leaf segment of maize inbreds and hybrids is kept in the phosphoroscope darkroom for more than 15 minutes (t > 15 min), and at the same time the leaf is illuminated with the intermittent white light. Resolved induction processes of DF chlorophyll into transients: A, B, C, D and E occur when the intact leaf segment of maize inbreds and hybrids is kept in the phosphoroscope darkroom for a significantly shorter period (500 s > t > 30 s), with the time rate t of 30 s, prior to its illumination with the intermittent white light. Induction transients: A, B, C, D and E are characterized with the time of their generation: tA = 31±6 ms (A), tB = 5 ± 0,5 s (B), tC = 15±5 s (C), tD = 360±20 s (D) and tE = 670±35 s (E), dynamics of changes in transients intensities (IA, IB, IC, ID and IE) and mechanisms of their generation. The induction processes of chlorophyll DF of the intact leaf of maize inbreds and hybrids resolved into transients: A, B, C, D and E are accompanied by the occurrence and different levels of activation energy (Ea, kJ mol-1) that correspond to critical temperatures ranging from 28 to 33°C. The generation mechanisms of induction transients A, B, C, D and E classify them into two groups. Transients A and B are of a physical character, while the transients: C, D, and E are of a chemical character. It is shown that the generation of the induction transients: B, C, D and E simultaneously follows establishing of the oscillations of induction processes of the DF chlorophyll. Oscillating of induction processes of DF chlorophyll is explained by the ion (K+, Na+, H+, Cl-) transport mechanism across the thylakoid membrane of the intact leaf of maize inbreds and hybrids grown under conditions of air drought, increased temperatures and water deficiency in the medium.

Although the reveal of heterotic groups in maize significantly increased testing efficiency, field trials are still unreplaceable and most time and fund consumable in the process of the hybrid development. The efficiency of breeding programmes could be significantly increased if the hybrid performance could be predicted prior to the field evaluation. Although different marker techniques have been developed and included into current breeding programmes, the satisfactory results have not been obtained yet. The present study is an attempt to inexpensively and rapidly discover indicators that could even partially facilitate the selection of parental pairs in the process of the hybrid development prior to the field evaluation. The phenotypic description of inbred lines according to the UPOV Descriptor was used for the estimation of the phenotypic distances for which it had been assumed that they could, to a certain degree, be an indicator of heterosis. The phenotypic characterization according to the UPOV Descriptor was done for 28 elite inbreds, that are often used in our commercial breeding programmes, and for 24 inbreds originating from the same source, as well as, for an inbred of the unknown origin and their phenotypic distances were estimated. The cluster analysis resulted in the classification that was in high compliance with known information on the origin. It was empirically concluded that great distances of parent inbreds result in good hybrids. Furthermore, high values among certain inbreds belonging to the same heterotic groups are observed on the morphological distance matrix and crosses among them should indeed be tested in the field prior to making any general conclusion on the reliability of the morphological distance in the prediction of heterosis.