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ABSTRACT. Drought tolerance is one of the most important but complex traits of crops. We looked for quantitative trait loci (QTLs) that affect drought tolerance in maize. Two maize inbreds and their advanced lines were evaluated for drought-related traits. A genetic linkage map developed using RFLP markers was used to identify QTLs associated with drought-related traits. Twenty-two QTLs were detected, with a minimum of one and a maximum of nine for drought-related traits. A single-QTL was detected for sugar concentration accounting for about 52.2% of the phenotypic variation on chromosome 6. A single-QTL was also identified for each of the traits root density, root dry weight, total biomass, relative water content, and leaf abscisic acid content, on chromosomes 1 and 7, contributing to 24, 0.2, 0.4, 7, and 19% of the phenotypic variance, respectively. Three QTLs were identified for grain yield on chromosomes 1, 5, and 9, explaining 75% of the observed phenotypic variability, whereas four QTLs were detected for osmotic potential on chromosomes 1, 3, and 9, together accounting for 50% of the phenotypic variance. Nine QTLs were detected for leaf surface area on chromosomes 3 and 9, with various degrees of phenotypic variance, ranging from 25.8 to 42.2%. Four major clusters of QTLs were identified on chromosomes 1, 3, 7, and 9. A QTL for yield on chromosome 1 was found co-locating with the QTLs for root traits, total biomass, and osmotic potential in a region of about 15 cM. A cluster of QTLs for leaf surface area were coincident with a QTL for osmotic potential on chromosome 3. The QTLs for leaf area also clustered on chromosome 9, whereas QTLs for leaf abscisic acid content and relative water content coincided on chromosome 7, 10 cM apart. Co-location of QTLs for different traits indicates potential pleiotropism or tight linkage, which may be useful for indirect selection in maize improvement for drought tolerance.

Quality protein maize (QPM) contains the opaque-2 gene along with numerous modifiers for kernel hardness. Therefore, QPM is maize with high nutritive value of endosperm protein, with substantially higher content of two essential amino acids - lysine and tryptophan, and with good agronomical performances. Although QPM was developed primarily for utilization in the regions where, because of poverty, maize is the main staple food, it has many advantages for production and consumption in other parts of the world, too. QPM can be used for production of conventional and new animal feed, as well as for human nurture. As the rate of animal weight gain is doubled with QPM and portion viability is better, a part of normal maize production could be available for other purposes, such as, for example, ethanol production. Thus, breeding QPM is set as a challenge to produce high quality protein maize with high yield and other important agronomical traits, especially with today's food and feed demands and significance of energy crisis

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As water resources for agronomic use become more limiting development of drought tolerant genotypes become increasingly more important. In maize, under drought stress conditions, an increase in the length of anthesis- silking interval and a decrease of grain yield is observed. Different strategies have been proposed to overcome negative effects of drought on maize. Breeders at Maize Research Institute (MRI) have created and used adapted drought tolerant population - DTP-A (DTP79xDTP12xDwarf), that was shown to be a good source of drought tolerance for locally adapted germplasm. In this research s1 families from DTP-A x B84 were scored for anthesis-silking interval and genotyped with SSR markers using BSA approach, with the aim to create a new gene pool for breeding drought tolerant hybrids. SSR analysis was performed in order to identify putative genomic segments and allele pattern differences responsible for expression of ASI, thus providing an insight into the genetic structure of s1 families. Four SSR loci, different in allelic structure between short and long ASI families, were identified. The main characteristic of these differences was the presence or absence of DTP79/DTP12 alleles. It seems that combination of several different genes and alleles influence ASI expression, with DTP79 alleles being beneficial and DTP12 alleles detrimental. Two chromosome regions identified in this work were congruent with qASI regions reported in Maize Genetics and Genomics Database. Clustering revealed that all sASI families grouped with DTP79, but one of the long ASI grouped with these genotypes too. This could indicate that, although total participation of DTP79 genome was similar in all the analyzed families, only a small portion of its genome influence anthesis-silking interval.

Nutritional value of maize is poor due to deficiency of two essential amino acids - tryptophan and lysine. It was shown than opaque2 (o2) mutations can nearly double the lysine and tryptophan content of the endosperm compared with the normal type. Maize Research Institute Gene bank maintains a collection of opaque2 inbred lines developed in the seventies, primarily based on kernel hardness and analytical methods. In order to describe these lines in more detail they were analyzed for tryptophan content and subjected to SSR analysis with opaque2 markers, a marker for endosperm hardness modifier gene and the most significant amino acid modifier markers. Also, a pathogenicity test for inbred lines tolerance to Fusarium spp., which is one of the most important maize pathogens in our region and a causer of maize stalk, root and ear rot, was performed. Differences in tryptophan content between normal and opaque2 lines were significant. All primers used for distinguishing alleles between normal and opaqu2 inbred lines gave positive results. Each genotype gave a specific allelic pattern with amino acid modifier gene primers, without any obvious correspondence to the tryptophan content. Phythopathogenicity test showed on average higher susceptibility to Fusarium graminearum of opaque2 genotypes. These results gave an insight into the applicability of the methods in describing opaque2 lines to be converted into quality protein maize QPM - genotype in which opaque2 has been incorporated along with associated modifiers