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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.

This study was carried out to evaluate the effect of temperature during storage of maize leaves and extracted DNA on its quality and quantity in order to be efficiently amplified using PCR. Leaves were collected from the fourweek-old plants and divided into three groups of 20 samples. The first group of leaves was processed immediately, while the other two were stored at -20°C or - 80°C for 30 days. The DNA extracted from the fresh leaves was divided into three portions with the first being amplified immediately and the other two were stored at -20°C or -80°C for 30 days. The DNA quality and quantity were examined using a biospectrometer, after which the samples were diluted for the PCR assay. The quality of all DNA samples was at an acceptable level with their average OD260/280 ratio in the range from 1.85 to 1.87. The concentration of the DNA extracted immediately from fresh leaf tissue was not statistically different from the stored samples. Both the quality and quantity of DNA in all samples were sufficient for successful PCR amplification with two opaque2-specific molecular markers. Phi057 amplified a ~170bp fragment in QPM and ~160bp in non-QPM, while umc1066 amplified a ~150bp fragment in QPM and ~160-170bp in non-QPM. Our results suggest that appropriate storage conditions do not affect the DNA quality and quantity. This could be useful in marker-assisted selection of target genes, when a large number of samples must be processed prior to pollination, allowing breeders to discard plants lacking the desired alleles and reduce the size of the breeding population.

Quality protein maize (QPM) has high contents of the essential amino acids lysine and tryptophan. The substitution of standard maize (SM) with QPM in feeds can be profitable due to improved livestock performance and decreased use of costly dietary lysine supplementation and protein ingredients. Herein, effects of QPM adapted to temperate climate on broiler performance were tested. A feeding experiment was performed on control (fed with SM) and treatment (fed with QPM) broilers. Each feeding trial of 42 days' duration was carried out in three phases-starter (1-14), grower (15-35) and finisher (36-42). Diets for each growth phase were formulated based on the biochemical analysis of maize kernels. At the end of each growth phase, feed intake (FI), body weight gain (BWG), average daily gain (ADG) and feed conversion ratio (FCR) were calculated. In the first experiment, SM was completely replaced with QPM in treatment group diets. The results indicated better FCR in the treatment group for grower (1.51:1.56) and finisher (1.56:1.61) phases. In the second experiment, QPM content was increased and the soybean component decreased by 3%. This time, FCR improvement was even better but in all three phases-1.16:1.33 for starters, 1.28:1.36 for growers and 1.30:1.46 for finishers. These results indicate a significant financial reduction in the cost of feed as the price of soybean is usually two to four times higher than the price of maize. Overall, it can be concluded that using adapted QPM in broiler diets can be profitable for both feed industry and broiler producers.

Maize Research Institute Zemun Polje has a marker-assisted backcross breeding (MABB) program aimed to incorporate the strong allele of incompatibility gene Ga1 into parental components of the hybrids with specific traits (white kernel). The main objective of this research was marker-assisted development of the white maize hybrid's parental lines with complete cross-incompatibility to foreign pollens. Ga1-S-tightly-linked molecular markers successfully identified heterozygous plants with a percentage of approximately 50% after all three backcrossings. Regarding the background selection, 69% of progenies had recurrent parent's genome (RPG) above the theoretical value for BC3 generation. Also, a few individuals even had 99%, the value theoretically achieved in the BC6 generation, showing that MABB made a genetic gain in RPG recovery. Foreground selection in this generation aimed to identify homozygous dominant individuals. Out of 264 BC3 F2 plants, 70 (26.5%) were dominant homozygotes, which is in accordance with the expected Mendelian ratio. Progenies of the BC3 F2 homozygous dominant plants were planted alternatively with yellow-kernel maize of the same maturity to check cross-incompatibility. Unfortunately, none of the dominant progenies had a 100% white kernel, most likely due to the presence of modifier genes that increase/decrease the effectiveness of pollen exclusion or that, alternatively, modifiers are lost during the backcrossing. It could be expected that successfully employed functional markers (developed from the sequence polymorphisms present within a functional gene(s) associated with phenotypic trait variations) would outbalance the noted impediments and enhance MABB efficiency to transfer the desired gene(s) controlling simple or complex trait(s) into cultivated varieties.

The backcross breeding is one of the most extensively used methods in different crop species. With the development of molecular genetics, molecular markers become widely used as a tool aiding conventional breeding. The main goal of marker assisted backcross breeding (MABB), a form of marker assisted selection (MAS), is to develop backcross progenies carrying the gene of interest with maximum recovery of the recurrent parent's genome (RPG). In this research, twelve inbred lines were chosen for the introgression of favourable alleles for several traits. Thirty SSR markers distributed throughout the whole genome were used to determine genetic similarity among these twelve lines and their BC4 progenies, i.e.to identify the genotypes with the highest proportion of recurrent parent's genome (RPG). Genetic similarity values ranged from 0.79 to 0.99(79-99% RPG).The 48% of progenies had RPG above theoretical value and they were self-pollinated for allele fixation. Also, 41% of them had 99%, what is the value theoretically achieved in BC6 generation. On the other hand, 52% of individuals had lower RPG content than theory predicts. The results of the research confirmed the advantage of using MABB compared to conventional approach, providing faster achievement of the goal, recovering the recurrent parent's genome in fewer generations of backcrossing and thus enabled enhanced selection efficiency and shortened the breeding process.

Conventional breeding methods have been aided by molecular genetic techniques giving the chance for efficient improvement in creation of maize hybrids. Proper choice of statistical methods for data analysis is very important because it ensures greater reliability. The aim of this study was to determine the most suitable statistical approach for molecular marker data analysis. SSR markers were used for the analysis of 10 maize inbreds. Genetic similarity/distance was calculated using three types of data: binary, allele frequency based on densitometry and allele frequency according to band size data applying Simple matching, Jaccard's and Rogers' coefficient. Cluster analysis was performed in NTSYS, 2.11a software. The highest value for Spearman's rank of correlation (0.95) was detected between distance matrices based on binary data. The results showed that binary data Jaccard's coefficient) and allele frequency data based on fragment sizes (Rogers' coefficient) gave identical clusters by visual inspection and according to CIc index.

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.

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.

Protein quality of standard maize kernels is poor, due to the low levels of two essential aminoacids - lysine and tryptophan. The opaque2 mutation which increases lysine and tryptophan content also confers an undesirable phenotype leading to low yields, soft and chalky kernels that renders seeds susceptible to storage pest and ear rots. Quality protein maize (QPM) is the maize with increased levels of these amino acids and good agronomic performances. At the Maize Research Institute, a program on creating QPM germplasm developed for conditions of temperate climatic zone is in progress. The aim of this study was to test quality traits of F2 kernels derived from the crosses between 24 QPM inbred lines with three standard inbred lines and two opaque2 lines. Most of the analyzed 108 genotypes had tryptophan content under the threshold of 0.075 set for QPM (83.5%). However, 50% had elevated tryptophan content in the range from 0.065 to 0.074. High tryptophan content was found in 16.5% of the analyzed genotypes, the highest being 0.088. Only one genotype had quality index over 0.80 (threshold for QPM). Biochemical analysis identified genotypes with good protein quality which will be further tested for agronomic performances in order to potentially be considered as QPM hybrids. .

The combined effect of cytoplasmic male sterility and xenia is referred to as the Plus-Hybrid effect. A mixture of hybrids, in which one is a sterile female component and the other is a fertile pollinator, was sown. The objective of the present study was to determine whether the increase of a hybrid genetic distance would result in the increased gain from Plus-hybrid effects on grain yield. Two ZP hybrids (ZP 1 and ZP 2), i.e. their sterile and fertile counterparts, as well as, five hybrid pollinators (ZP 1, ZP 2, ZP 3, ZP 4 and ZP 5) were selected for the studies. The three-replicate trail was set up according to the randomized split-plot design at Zemun Polje in 2009. SSR markers were used to determine the genetic distance between hybrids. Ten out of total 12 applied primers gave results. Coefficients of similarity were estimated according to Dice and Jaccard. The greatest (0.37), i.e. smallest genetic distance (0.08), according to Dice, was obtained between hybrids ZP 1 and ZP 5, i.e. ZP 1 and ZP 4, respectively. Values of genetic distance according to Jaccard were between 0.14 (ZP 1 and ZP 4) and 0.54 (ZP 1 i ZP 5 ). By using the cluster analysis, four hybrids (ZP 1, ZP 4, ZP 3 and ZP 2) were grouped into one sub-cluster that was loosely linked to ZP 5. The Plus-hybrid effect on grain yield of the hybrid ZP 1 was negative. The greatest gain was detected in the ZP 2st ' ZP 1 combination, between two hybrids that were genetically very similar and belonged to the same sub-cluster, and then in ZP 2st x ZP 3 and ZP 2st x ZP 4 combinations, between hybrids that also belonged to the same sub-cluster. It can be concluded that the Plus-hybrid effect, after all, depends not on the hybrid genetic distance but on the hybrid genotype.

The most significant QTLs for leaf ABA and root characteristics are shown to be on chromosomes 1 (bin 1.06) and 2 (bin 2.04). Assuming that the same QTLs could be present in different genotypes, the objective of this work was to ascertain if the QTLs with major effect detected i n one genotype could be detected in a different genetic background with different molecular markers of that chromosome region. Also, bulk segregant analysis (BSA) of 10 tolerant and 10 susceptible to drought maize populations was performed in order to confirm the potential of this approach in informative marker identification. Probes umc1601, umc1776, bnlg2248, dupSSR27 and bnlg2246 detected allele frequency differences between tolerant and susceptible populations of over 14%. It was also shown that BSA can identify informative molecular markers, although marker analysis of individual plants is necessary for final conclusion about linkage of the marker and the trait of interest.