h. rahim soroush

Application of selection index for screening desired plants based on complex quantitative traits can be more effective than direct selection. This study was conducted using an F2 rice population consisting of 87 plants derived from a cross between two cultivars Gharib and IR28. The purpose was to establish suitable selection indices for increasing yield and its related traits in research farm of Rice Research Institute of Iran (RRII), Rasht, in 2005. Studied traits included the days from sowing, germinated grain to maturity (MD), plant height (PH), panicle length (PL), flag leaf length (FL), flag leaf width (FW), number of panicles per plant (PP), number of grains per panicle (GP), number of spikelets per panicle (SP), 100-grain weight (GW), grain yield per plant (GY), biomass (BM), harvest index (HI), grain length (GL) and grain breadth (GB). Among the studied traits, 100-grain weight (GW), biomass (BM) and harvest index (HI) (0.99) and flag leaf width (FW) (0.35) showed the highest and lowest broad-sense heritability, respectively. Path coefficient analysis revealed that BM, HI, GP had positive direct effects on GY. Calculation of five different selection indices based on optimum and base indices indicated that selection for BM, HI and GP using genotypic path coefficients and their heritability as economic values would be a suitable selection criterion for improving population. Moreover, this study showed that both optimum and base indices show the same genetic progress for the studied traits. Since evaluation of base index, is much easier than the optimum index, it is highly recommended.

To determine the genetic structure, general and specific combining ability of some important agronomic characters, eight rice cultivars including 5 lines and 3 testers were crossed in Rice Research Institute of Iran (RRII), at Rasht, in 2000. Parental lines and F1 were planted in a Randomized Complete Block Design with three replications in the year 2001. Eleven important agronomic traits including yield and its components were recorded. Analysis of variances based on line×tester method showed that the mean squares for all traits were significant at 1% level. General combining ability (GCA) was positive and significant for grain yield in Khazar and Salary. Kanto and Salari have showed a negative and significant GCA for fertile tillers, as one of the most important yield components. Lines 213, 229 and Domsiah had negative and significant GCA for days to 50% of flowering. The lines with positive GCA can inherit those characters to progenies positively. While the lines with negative GCA can negatively transfer those characters to progenies. Estimation of components of genetic variance indicated that the number of fill grain per panicle and days to 50% of flowering were controlled by additive gene effects. It indicated that these traits can be transferred into progenies. For traits such as grain yield, fertile tillers and length of flag dominant gene effects was predominant.

In recent years most activities of Rice Research Institute, has been focused on introduction of high yielding as well as high quality rice cultivars. In 1994, 185 lines introduced from International Rice Research Institute (IRRI) to Rice Research Institute of Iran (RRII), were evaluated in observational and statistical experiments in RRII for two years, and eight lines were selected. These lines had better performance, morphological characteristics, early maturity and higher yield than other lines. Results of different experiments carried out during next five years, showed that line IR67015- 94-2-3, introduced later as Shafagh cultivar was more high yielding and stable in different environments of Mazandaran province compared to the other lines. This cultivar is medium in maturity with average yield of 7.7 tha-1. The best planting space for Shafagh cultivar is 20 x20 and 18 x 30 cm for traditional and machine transplanting, respectively. Based on different experiments on soil analysis and crop requirements, 115 kg N ha-1, 50 kg P2O5ha-1 and 50 kg K2O ha-1 are recommended. Results revealed that this cultivar has similar responses as Nemat and Dasht cvs to all major diseases and pests, but more tolerant to lodging. Its plant height and thousand-grain weight are around 110 cm and 25g, respectively. (Also see Tables 1 and 2 in Farsi Text).

In order to study the genetic diversity of quantitative and qualitative traits of 36 lines and cultivars of rice, an experiment was conducted using a simple lattice design in 2000. In this study, 17traits including grain yield, number of panicle per plant, number of filled grains per panicle, 100 grain weight, leaf length, leaf width, leaf area, plant height, culm length, amylose content of the grain, gel consistency, panicle weight, grain length, grain width, grain shape, days to 50% flowering and maturity were measured on 10 randomly selected plants for each plot. Analysis of variance showed significant differences among genotypes for all traits and revealed the existance of genetic variation among genotypes. The phenotypic coefficients of variability were greater than the genotypic ones for all the traits although differences for most of them were small. The highest phenotypic and genotypic coefficients of variation were obtained respectively for gel consistency, leaf area, leaf width and number of panicle per plant. The highest general heritability was estimated for plant height and the lowest for panicle weight. Results of genotypic and phenotypic correlations indicated that number of panicle per plant, number of filled grains per panicle, panicle weight, days to 50% flowering and maturity had positive correlation with yield, wbile the rest of the traits had a negative correlation. Cluster analysis with Ward's method, classified all of the genotypes into five clusters. Genotypes of the third cluster including four pure lines Nos.4,21,22 and 24 had high yield, high number of panicle and filled grains per panicle, intermediate amylose and lower plant height, therefore, these suitable traits can be transfered through hybridization programs. Genotypes of the. first and fifth clusters can also be used to improve yield and grain cooking quality respectively.