Available online at www.scholarsresearchlibrary.com Scholars Research Library Archives of Applied Science Research, 2010, 2 (6):373-379 (http://scholarsresearchlibrary.com/archive.html) ISSN 0975-508X CODEN (USA) AASRC9 373 Unwanted self-pollination in crossing programs interferes with trait improvement and variety breeding Asadollah Ahmadikhah 1* and Mehdi Mirarab 1 1 Department of Plant Breeding and Biotechnology, Gorgan University of Agricultural Sciences & Natural Resources, Gorgan, Iran; ___________________________________________________________________________________________ ABSTRACT Clear-cut identification of elite crop varieties and hybrids is essential for guarantying purity of hybrid seeds. Unwanted self-pollination in field or during crossing programs is one of the major sources of impurity of hybrid seeds that interferes with trait improvement via conventional breeding programs or variety improvement via backcross scheme. Conventional characterization of hybrid seeds based on specific morphological and agronomic data is time-consuming, restricted to a few characteristics, and is influenced by environment. In contrast, DNA-based markers are highly heritable, available in high numbers, and exhibit enough polymorphism; hence they can be used to trace the alleles came from a given parent. To estimate the interference rate of self-pollination with the variety improvement, hybrid seeds in several backcross generations were studied using SSR markers. Results showed that in the case of hybrid seeds produced under uncontrolled low-stringent conditions frequency of off-types seeds ranged from ~17% (for BC 1 of cross Sadri x Neda) to as high as 50% (for BC 3 of cross Sadri x Neda) and averaged up to 40%, that may be seem an unexpected value. However, in the case of hybrid seeds produced under completely controlled conditions any off-type seeds were not found. Thus, we suggest that make crosses under completely controlled conditions to guarantee the production of true hybrid seeds. Key words: Rice, self-pollination, crossing, improvement. _____________________________________________________________________________ INTRODUCTION Rice is a major staple food crop and serves as a carbohydrate source for more than one third of the world’s population. More than 90% of the world’s rice production is produced and consumed in Asia. With respect to doubling of population of rice eaters in this area by 2025, the demand for rice is expected to outstrip its production. Two technological options for overcoming the problem are (1) exploitation of heterosis and (2) improvement of new high-yielding varieties with desirable traits. For exploitation of heterosis rice breeders utilize three-line hybrid system (CMS line, maintainer line and restorer line) [9]. In the case of former program, it is obvious that any impurities in the hybrids would reduce the expected yield. It has been estimated that every 1% mixture of female line seed in the hybrid seed results in yield reduction of 100 kg per hectare [5].