الفهرس 
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Abstract
The present study aimed to determine the effect of drought stress on rice varieties released as new resistant varieties in Egyptian agriculture for insect infestation. Three new drought tolerant rice varieties (Orabi1, Orab2 and Orabi3) and three Egyptian local varieties (Sakha101, Sakha104 and Giza177) were used in the present study and grown under drought stress conditions (irrigation every 12 days). RAPD-PCR was used for determining molecular markers related to stem borer resistant in rice. The results showed that there was no significant simple correlation co-efficient between infestation percentage (IP) and other characters i.e. plant height (PH), stem diameter (SD), panicle length (PL), the solid and the hollow part of stem diameter (SPsd and HPsd) respectively. The distribution curves were similar to parabola curve. Through solving of functions arrival to estimated factors for each criterion. By using these estimated factors obtained on highly significant positive correlation with infestation as a simple and partial correlation. The results showed that, the behavior of stem borer resistant in rice under drought condition depends on a parabola function through the relationship of IP with stem diameter (SD) and solid part of stem diameter (SPsd). That’s mean there are a standard values and the infestation increased by deviation from it. According to SD and SPsd, the measurements of best plant with highly resistant is SD=4.8 mm and SPsd=2.42 mm. These values represent the standard values, then, the selected plant measurements should be as close as possible to this value. Multiple regression analysis was used for detecting the direct relation between variables (IP as dependant variable and SD with SP.sd as independent variables) in one function. By this equation there was a new factor for infestation percentage dependent on SD and SPsd . This factor correlated with IP by 93%. By this results there was a new term for resistant. It could be named the relative resistance for stem borers which could be used to determined the percentage of resistance for every plant or variety. It estimated from the relative between and for variety. It correlated with IP by 89.57%. Data of analysis of variance common for irrigation conditions in year 2012 showed significant varieties-by-irrigation interaction and highly significant variation among varieties and irrigation conditions. By these results it can be recorded that, the drought condition is a new environment that changes the behavior of infestation and resistance and thus selection of resistant plants. Random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) was performed to detect the genetic diversity among six varieties with different responses to drought tolerance and stem borer resistance and establish DNA markers associated with stem borer resistance. Among ten RAPD primers tested, only five produced bands polymorphic between lines with an average of 9.2 bands per primer (ranging from approximately 143-1570 bp) and 80.95% were polymorphic. Based on band polymorphisms generated by RAPD-PCR after using the primers, the highest similarity value (0.814) was found between Orabi3 and Giza177 and the lowest value (0.533) was found between Orabi2 and Sakha101. The highest genetic distance value (4.69) was found between Orabi3 and Sakha101 and between Sakha104 and Sakha101 and the lowest value (3.32) was found between Orabi3 and Giza177. The dendogram of genetic distances among all tested varieties based on band polymorphisms generated by RAPD-PCR after using the primers separated all varieties into four clusters. First cluster includes Sakha101 and Orabi1, second cluster includes Orabi3, third cluster includes Giza177 and Orabi3 and fourth cluster includes Sakha104.