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IntroductionApomixis is a mechanism of seed formation without fertilization and is observed in more than 300 species in 30 out of 460 angiosperm families, but it is not common in crop species (Bashaw, 1980). It was considered as an obstacle for plant breeding. Indeed, the presence of apomixis in the species Hieracium, in which Mendel was asked to prove the genetic principles he had developed in peas, caused him to withdraw from the scientific world due to his failure to do so (Carneiro et al., 2006). In recent years, however, apomixis is seen as a way to maintain superior genotypes as clones of seeds. As such, apomixis has been a major area of investigation in plant genetics.Unlike in animals where it is a hot topic nowadays, cloning is an ordinary process in plants. Many plant species can be propagated using various plant parts. Clonal propagation has some advantages as well as disadvantages. Apomixis combines the advantages of propagation by seed (higher multiplication rate, easier storage and planting, suitability for machine planting, less seed material use, and less bearing of diseases) with those of propagation by clone (maintaining genetic structure and hence fixing superior genotypes after crossing). However, apomixis manifests itself in different mechanisms that have not yet been fully elucidated. Genetic studies reveal that, though complicated, the trait is controlled by a few genes (Barcaccia and Albertini, 2013). In addition, different phases of apomictic reproduction have been achieved artificially (d'Erfurth et al., 2009). Apomictic reproduction of crop species would lead to revolutionary developments in terms of crop improvement. The benefits of apomixis are estimated to surpass those of the green revolution (Grossniklaus et al., 1998).The aim of this review paper is to discuss the use of apomixis in plant breeding. Our main attention is on its benefits in crop improvement rather than its physiological nature or molecular mechanisms. Methods to achieve apomixis in crop species and its economic advantages are also discussed. Mechanisms of apomixisThere are various mechanisms of apomixis, some of which result in unstable chromosome numbers (Naumova, 1993). Here we only discuss the ones with stable chromosome numbers and those that are important for plant breeding purposes without going into much detail.Development of apomictic seed formation takes place in three stages: a) suppression of meiosis (apomeiosis), b) endosperm formation without fertilization (parthenogenesis), and c) seed formation with (pseudo-Abstract: Apomixis is seed formation without fertilization, commonly observed in wild plant species. It has the advantages of clonal reproduction and propagation by seeds. Although it has a complex inheritance, genes controlling apomictic reproduction are being identified. Transfer of apomixis to crop species through wide crosses has not been successful so far, but transgenic technology offers a more powerful way to introgress apomixis into crop species. When crop species acquire this trait, superi...

Turkey is an important tobacco producing country and leading the world in oriental tobacco production. In the present study, effect of heterosis on yield and quality of oriental tobacco was investigated, and development of oriental tobacco hybrids with high yield and quality properties for Black Sea region of Turkey was targeted. Seven oriental tobacco genotypes with considerable acreages in Turkey (Xanthi-2A, Nail, Gümüşhacıköy, Taşova, Katerini, Canik, Erbaa) and 21 hybrids produced by halfdiallel crosses among them were compared. Field trials were conducted in Erbaa and Bafra locations in 2012 and 2013 growing periods. Cured leaf yields, reducing sugar and nicotine contents of leaves and expertise quality were studied. Xanthi-2A × Katerini (1.70 t ha -1 cured leaf yield and 75% quality grade index) and Nail × Katerini (1.64 t ha -1 cured leaf yield and 75% quality grade index) hybrids showed good yield and quality properties in Erbaa conditions, while Nail × Katerini (1.88 t ha -1 cured leaf yield and 75% quality grade index) and Katerini × Erbaa (1.65 t ha -1 cured leaf yield and 78% quality grade index) had good yield and quality properties in Bafra conditions. It has been concluded that hybrid cultivars that can meet the demands of tobacco sector could be developed from some currently grown oriental tobacco cultivars in Turkey. Based on average of locations, an average of 16.20% and 6.85% heterosis were found as the average of all hybrids for cured leaf yield and expertise quality. Yield effects due to heterosis could be increased in future by adopting growing techniques adjusted for hybrids.

Brittle rachis is a head shattering mechanism of barley. Two tightly linked complementary genes, btr1 and btr2, were believed to control the non-brittle rachis trait. Position of non-brittle rachis loci btr1btr2 on the short arm of Chromosome 3 was investigated using RFLP markers. Two approaches were employed. First, a Hordeum vulgare subsp. spontaneum fragment that confers brittleness in a cv. Bowman near isogenic line was detected. This fragment is 18-33 cM in length and contains MWG798B, ABG057, MWG014, BCD706 and KFP216 markers of the short arm of Chromosome 3. In the second approach, position of btr1 locus in a H. vulgare subsp. spontaneum (Wadi Qilt 23-38)xH. vulgare subsp. vulgare (cv. Harrington) cross was detected using a selective genotyping approach in BC2F1 generation. F-tests and analysis of genotypic compositions of BC2F1 lines showed that btr1 locus, and supposedly the tightly linked btr2 locus, is in 4.3 cM KFP216-RisP114 interval of short arm of Chromosome 3. Results also yielded clues for the presence of at least two additional loci that affect the non-brittle rachis trait. Allelism tests using genotypes with known non-brittle rachis gene compositions provided additional evidence for presence of such loci.

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ÖzBu çalışmada Tokak yerel arpa çeşidi içinden (PI 470281) moleküler markörlerle seçilen 25 hat Tokat Kazova şartlarında tarla koşullarında incelenmiştir. Araştırmada referans olarak Kanada'nın en önemli maltlık arpa çeşidi Harrington ve Türkiye'de yaygın şekilde tarımı yapılan bir maltlık arpa çeşidi olan Tokak 157/37 kullanılmıştır. Yapılan çalışmada PI 470281 hatları agronomik özellikler yanında (Çiçeklenme süresi, olgunlaşma süresi, bitki boyu, yatma oranı, başakta tane sayısı, başak boyu, 1000 tane ağırlığı, hektolitre ağırlığı, tane verimi, biyolojik verim, hasat indeksi), bazı yem kalite özellikleri (ham kül oranı, ham protein oranı, ADF, NDF) ve çeşitli mineral madde içerikleri (P, K, Ca, Mg, Fe, Cu, Mn, Zn) gibi gıda kalite özellikleri bakımından incelenmiştir. Değerlendirmeye alınan PI 470281 hatları agronomik, yem ve gıda kalite özelikleri yönüyle önemli varyasyonlar göstermiştir. Hatların büyük çoğunluğu Tokak 157/37'den daha yüksek Harrington'dan ise daha düşük tane verimine sahip olmuşlardır. Değerlendirmeye alınan hatlarda 1000 tane ağırlığı yaklaşık 40-51 g, hektolitre ağırlıkları ise 64-69 kg arasında değişmiştir. ADF, NDF oranları referans çeşitlerinden yüksek veya yakın değer göstermişlerdir. %12-14 arasında değişen ham protein oranlarındaki farklılıklar da önemli bulunmuştur. PI 470281 hatları arasında mineral madde oranları bakımından da önemli varyasyonlar tespit edilmiştir. Hatların demir, bakır ve kalsiyum konsantrasyonları referans çeşitlerine yakın veya yüksek değer göstermiştir. Sonuç olarak, Tokak yerel çeşidinin yüksek genetik çeşitliliğe sahip olduğu, bu çeşit içinden geliştirilen safhatlarda, agronomik, yem ve gıda kalite özellikleri açısından ıslahta kullanılabilecekleri varyasyonun bulunduğu sonucuna ulaşılmıştır. AbstractIn this study, twenty-five lines selected from Tokak (PI 470281) barley landrace using molecular markers were investigated in field studies under Tokat Kazova conditions in Turkey. Harrington, a malting barley variety of Canada, and Tokak 157/37, a commonly grown malting barley variety in Turkey, were used as reference. PI 470281 lines were investigated in terms of food and feed quality properties such as crude ash, crude protein, ADF, NDF contents, various mineral contents such as P, K, Ca, Mg, Fe, Cu, Mn, Zn, Cr and some agronomic traits such as days to flowering and maturity and plant height, number of seeds per head, spike length, 1000 seed weight, test weight, grain yield, biological yield and harvest index. PI 470281 lines investigated showed significant variations in terms of their agronomic, feed and food quality properties. Most of the lines had higher grain yields than Tokak 157/37 and lower than Harrington. 1000-seed weights and test weights for the lines investigated varied from 40 to 51g and 64 to 69 kg, respectively. Their ADF and NDF contents were higher than or similar to those of the reference cultivars. The crude protein contents varied from 12% to 14%and were significantly different among purelines. Significant variations were found among PI ...