Agronomic Performance and Biochemical Genetic Markers for Drought Tolerance in Rice (Oryza sativa L.)

Abstract

Rice (Oryza sativa L.) is considered one of the most important food crops not only in Egypt but also world wide. The demands of rice are in continuous increasing. The majority of rice ecotypes are semi-aquatic plants adapted to saturated soil conditions where it is difficult for crop species to survive (Champoux et al., 1995). Agricultural expansion in Egypt depends largely on water which is considered one of the main factors limiting agricultural development, so, one way to save water is increasing water intervals without any sharp effect on the yield. High degree of drought tolerance allows the plant to maintain its growth and development under water stress. The ability of the plant to produce new tillers and resume growth and development after irrigation is an important factor in drought tolerance (Chang et al., 1974). Identifying varieties with high yield potential and drought tolerance is one of the principal objectives of rice breeders.
Several researchers have conducted studies on the effect of water deficit on rice. The effect of water stress on grain yield depends on the duration and timing of water deficit (Lenka and Garnayak, 1991; Castillo et al., 1992; Tsuda et al., 1994). Grain yield and yield components were significantly decreased with increasing irrigation intervals (Nour et al., 1994; Sorour et al., 1998; Adhikary et al., 1999; Sehly et al., 2001; Gaballah, 2009). Drought stress resulted in high spikelet sterility (Nour and Mahrous, 1994; Chauhan et al., 1999). Panicle length was decreased sharply when rice plants were subjected to irrigation intervals every 6 days (El-Wehishy and Ghanem, 1996) or longer than 6 days (Abou El-Hassan,1997).
The conventional methods of plant selection for drought tolerance are not easy because of the large effects of the environment and low narrow sense heritability. Selection for drought tolerance genotypes of rice based on phenotypic performance alone is less reliable and will delay progress in breeding. Recent advent of molecular and biochemical markers, are used to find out drought tolerant rice genotypes.
Molecular marker assisted identification with high power of genetic resolutions has emerged as a robust technique for cultivar fingerprinting, identity profiling, estimating and comparing genetic similarity, and variety protection. Several types of molecular marker i.e., allozymes (Devanand et al., 1999), RAPD (Wang and Lu, 2006; Ichii et al., 2003) and SSR (Nandakumar et al., 2004) have been used in this term. . The application of molecular markers in rice improvement has been reviewed recently (Mackill, 2007). Another indication for a response of the plant against abiotic stress is an increased level of free amino acids. Some of the amino acids are by themselves compatible solutes like proline, others are precursors of compatible solutes, like glycin or alanin (Hanson et al., 1994). But also other amino acids turned out to be enhanced (Rizhsky et al., 2004) which might be necessary for de novo synthesis of induced proteins.
This study aimed to achieve reliable information about the relationships between morphological performance as some growth, yield as well as yield components and drought stress tolerance of 25 rice genotypes and to capture effective molecular and biochemical markers associated with drought tolerance to use in marker-aided selection breeding programs.