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Introduction Quantitative complex traits in wheat possesses lower heritability compared to qualitative traits or/and molecular markers (Poehlman, 1995). Broadening the genetic base of common wheat by identification and introgression of potentially useful genes from progenitor species is an important germplasm development goal (Ladizinsky, 1985). Phonological characters such the time of spike appearance, days to heading (DH), days to maturity (DM) and even vernalisation requirement indicate quantitative inheritance and low heritability (Kato et al., 2000; Snape, 1987). Differences between developmental stages among wheat genotypes exist worldwide. The characters related to developmental stages affect wheat production and adaptation (Slafer et al., 1999) and major differences in DH among wheat genotypes can contribute to variation for GY and even to variation for physiological characters during the life cycle. Since the screening for natural earliness requires to be conducted under full satisfaction of the photoperiod requirements, they are mostly conducted under controlled conditions such as green houses and growth chambers. Under these controlled conditions, in which for practical and economic reasons, temperatures are substantially higher than those actually experienced in the filed by the crop (Appendino and Slafer, 2003). As the result, screening the genotypes for earliness is difficult due to complexity of the trait and effects of environmental factors such as high temperatures. It is now proved that the complex traits such as GY, HI and earliness are under quantitative control and their effects on genetic variation are relatively small (Yano and Sasaki, 1997). Earliness, however, is less environmentally sensitive and has higher heritabilities than GY (Bezant et al., 1997; Yano and Sasaki 1997). While looking for genetic factors controlling grain yield, genes for yield components should also be determined to provide more information that is useful. One of the traits that affect yield components is vernalisation requirement. Vernalisation genes regulate the requirements of exposure to cold temperatures and it is reported that vernalisation insensitivity promote heading and flowering time (Bullrich et al., 2002). In recent years, considerable emphasis has been placed on the development of molecular or morphological markers for different objectives. Identification of molecular bands or morphological markers associated with earliness or grain weight is the most important step in selecting genotypes having higher yield at the early stages of growth. This is because of the fact that identification of high yielding or early genotypes at the end of growth stage is costly and time-consuming and so scientists have been trying to establish relationships between markers on the molecular or phenotypic levels and quantitative traits such as grain yield. This relationship will help the plant breeders to select for quantitative traits in segregating generation where assessing the genotype is difficult (Diers et al., 1996). Some investigations in maize and oilseed rape have shown that the genetic diversity of parents for restriction fragment length polymorphism (RFLP) markers was significantly correlated with hybrid performance and that yield could be predicted by using molecular markers (Smith et al., 1990). In contrast, some other studies showed that the correlation of hybrid performance with molecular diversity between parents was too low to be of any predictive value (Lee et al., 1989; Godshalk et al., 1990; Dudley et al., 1991). Nonetheless, the automation of (PCR) offers a means to mitigate the time, expense, and safety hazards associated with RFLPs. A single, short DNA primer sequence can direct the amplification of a specific DNA sequence via PCR. These random amplified polymorphic DNA sequences (RAPDs) have shown some promise as molecular markers in wheat (Fritz et al., 1995) so that RAPD markers (He et al., 1992) can effective

GÉNERO
Negócios e finanças pessoais
LANÇADO
2011
1/julho
IDIOMA
EN
Inglês
PÁGINAS
21
EDITORA
Southern Cross Publisher
TAMANHO
310.3
KB

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