Rice is an important cereal crop that feeds more than half of the world’s population (Wang and Li 2005). Present production of rice in the world is 496.08 million metric tonnes in and in India the production is 118 million metric tonnes.(USDA 2019/2020). AP production status….???? Demand for rice is steadily increasing, as the number of rice consumers is increasing, especially in developing countries (Khush and Jena 2009). the pAt present the production levels need to be increased by 2 million tonnes every year inorder to meet the food demand of the growing population and to achieve food security in the country.
and it can be possible by increasing heterosis for yield for this systematic evaluation and characterization of germplasm lines to identify superior and genetically divergent germplasm lines is needed. Breeding for high yield would be more effective, if components involved are highly heritable and positively correlated (Kumari et al. 2003). So, determination of phenotypic and genotypic correlation coefficients among various agronomic traits and to analyze their interrelationship, estimation of broad sense heritability and genetic advance for the selected traits is essential as knowledge of correlation that exists between important characters facilitates the planning of a more efficient breeding programme.
However, iIn spite of the efforts in increasing the yield, rice production is severely affected by biotic and abiotic stresses. Among the biotic stresses, rice blast and bacterial leaf blight (BLB) are major devastating diseases that limit rice yield significantly (Ou 1985.,; Mew et al. 1993).
Rice blast disease caused by the fungus Magnaporthae grisea (Ou, 1985) can lead to 20 to 40% loss in yield and reduce grain quality (Le Huu et al., 2007). The pathogen generally infects leaves, leading to leaf blast during the vegetative stage, it also infects the nodes, neck, and panicle during the reproductive stage, leading to node and neck blast. Among all neck blast is the most destructive phase, results in a yield reduction twice that of the leaf blast. Rice blast can be controlled effectively and economically by breeding varieties that harbor blast resistance (R) genes. Although many rice blast resistant varieties have been developed, the property of resistance is unsustainable due to the high pathogen plasticity in the field. Disease resistance conducted by a single R gene is easily broken down during three to five years after the cultivar has been released (Bonman et al. 1986; Hittalmani et al. 2000; Lang et al. 2009). Hence, developing new varieties of rice with broad-spectrum and durable blast resistance has become an important task to be tackled. Collecting a wide variety of rice germplasms and assessing their resistance to blast disease enables to address above issue. Conventional breeding programs are time consuming and less efficient than marker-assisted breeding approaches, DNA markers are more advantageous in precise identification and incorporation of blast resistance genes in a breeding program (Wang et al. 2007; Liu et al. 2013). To date, over 100 blast resistance genes to M. oryzae from japonica (45 %), indica (51 %) and others (4 %) genotypes have been identified and documented (McCouch et al. 1994; Ballini et al. 2008; Huang et al. 2010; Xiao et al. 2010; Sharma et al. 2012).
Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo). Infection at maximum tillering stage results in blighting of leaves, which eventually causes significant yield losses in severely infected fields ranging from 20 to 30%, but this can reach as high as 80% (Mew et al. 1992; Noh et al. 2007; Shin et al. 1992). This disease may appear at any stage of plant growth viz. seedling, vegetative and reproductive stages. The maximum BLB infection is recorded at the tillering stage. Since the bacterial races vary continually influenced by the artificial and natural selection of genes resistance to bacterial blight, it is critical to explore and identify the new resistant resources to control the changeful races (Xia et al., 2012). Since the chemical control is not effective, the utilization of resistant varieties carrying resistance genes have been considered to be the most effective way to control the disease (Nino-Lui et al., 2006). Currently, 42 BLB R-genes have been identified (Vikal et al., 2017). The conventional methods of plant selection for BLB resistance are not easy because of the large effects of the environment and the low narrow sense heritability of BLB resistance. This hinders the development of an accurate, rapid and reliable screening technique. Individual with target gene in a segregating population can be identified with the assistance of DNA markers. Recent progress and technical advances in DNA marker technology permit the rapid and accurate identification of individuals that contain gene(s) for BLB resistance
So, further scope of crop improvement depends on the availability genetic diversity and variability and use of new biotechnological tools. Therefore, the present investigation was undertaken to study the genetic variability for yield and its component characters in various rice germplasm lines and genotyping them using DNA markers linked to disease resistance for the identification of donor with good yield potential as well as disease resistance with the following objectives.