Molecular markers associated with high early growth rate of Russian rice (Oryza sativa L.) varieties

The high rate during early growth is expected to be the main basis of next “green revolution”. Many researches take into account that this trait is mainly responsible for physiological advantage of heterotic hybrids in crops. The rapid development of the root system provides an advantage in absorption of mineral substances and the photosynthetic apparatus formation. Heterotic hybrids can quickly overpass the phase sensitive to stresses thereby improving the adaptability to different stress factors. Significant differences between varieties and subspecies in the growth rate of seedlings are widely used for effective breeding. The growth rate is a plant-height-related trait. Heritability of seedling height, weight, and the length of embryo root is very high (87-90 %). This paper is the first report on loci that determine the growth rate during germination period in rice ( Oryza sativa L.) varieties bred in Russia. The aim of our work was to reveal effective SSR markers for chromosome loci and regions which are involved in the control of traits responsible for high rate of early growth in the Russian rice ( Oryza sativa L.) gene pool. Seeds of 32 varieties bred in Russia and hybrids were surface-sterilized for 40 min with a 20 % sodium hypochlorite solution (95.2 % active Cl; ООО Grinfild RUS, Russia). Thirty grains of each sample were germinated (in duplicate) for 7 days at 28-29 °C in a thermostat. Morphophysiological parameters of 20 seedlings of each variety or hybrid, i.e. the weight, the size of coleoptile and the embryonic root formation, were measures. As per the finding of this study, the loci that determine the seedling weight are located on four chromosomes near the markers RM261, RM405, RM463, RM242, RM6314, RM289, and RM126. The embryonic root growth rate is determined by two chromosomal regions on chromosomes 4 and 9, the seedling height - by only one locus located on the chromosome 5 near the marker RM289. One can simplify identification of chromosomal regions that determine target trait values in a set of unknown varieties or hybrids. Bulk breeding methods allows markers with the maximum phenotypic effect to be identified with no need to create a population recombinant inbred lines (RILs) or double haploid lines (DH) for mapping. In particular, exploiting cultivars which are contrast in the traits of interest is much more informative. Such phenotypic analysis reveals the most important loci for the entire group of varieties tested. Next, the markers can be found which are closely linked to the genes that determine the trait in the identified chromosomal region (http://www.gramene.org). Markers that are enough polymorphic to ensure reliable separation of varieties into contrasting groups may be further used in breeding work. Not always genes, differentiating varieties by a certain trait in one region of the world will be effective for another region. Therefore, such preliminary assessment is obligatory. Thus, in this study using original technique to simplifies identification of the loci of interest we have identified 8 chromosomal regions associated with early growth rate in Russian rice varieties.