حسین رحیم سروش

Considering the lack of food in the world, increasing the production of rice is one of the demands of the global market and one of the important goals of many countries producing this crop plant. The final performance of each organism is affected by the genotypic potential, the environmental effects and the interaction between genotype and environment. The interaction of genotype and environment causes that different genotypes do not have the same reaction under different environmental conditions. Genotypes that can produce higher yields in different regions or under different environmental conditions and maintain their performance stability are considered as successful genotypes. In this study, nine promising rice lines originating from the Hashemi variety, along with two varieties Hashemi and Gilaneh, were evaluated for grain yield in two regions during two years. The objective of this study was to evaluate the stability of the studied lines and introduce the most stable ones in order to introduce the new varieties.

The plant materials of this experiment were nine promising rice lines originating from the Hashemi variety, as a Iranian local variety with good quality, along with two varieties Hashemi and Gilaneh as control varieties. The experiment was conducted in a randomized complete block design with four replications in two regions, Rice Research Institute of Iran (Guilan province, Iran) and Chaparsar Research Station (Mazandaran province, Iran), in two years, 2017 and 2018. The studied traits included grain yield, days to 50% flowering, head rice percentage, milling efficiency, grain length, amylose content and gelatinization temperature. For data statistical analysis, simple analysis of variance was firstly performed for grain yield, and then Bartlett's test was done to check the uniformity of the experimental errors. Combined analysis of variance and comparison of means by Duncan's method was performed with SAS software. To evaluate the stability of the studied lines, Lin and Binns and GGE-biplot methods were used.

The results of combined analysis of variance showed that the effects of genotype and year as well as the interaction of year × place and year × place × genotype on grain yield were significant. Therefore, grain yied stability of the studied genotypes was evaluated using Lin and Binns and GGE-biplot methods. The results of Lin and Binns method indicated that two genotypes Gilaneh and 19603 (Hashemi/IR74720-85-1-2-1), with the lowest intra-location variance, were the most stable genotypes in this experiment. The results of GGE-biplot graphical method also showed that the genotypes 19607, Hashemi and Gilaneh, which formed the vertices of the polygon in the grain yield biplot, were the best or the weakest genotypes in some environments or in all environments. Also, the simultaneous evaluation of stability and grain yield of the studied genotypes identified the promising line 19603 as the best genotype. The graph of ideal genotype also showed that the promising line 19603 had the smallest distance from the hypothetical ideal genotype compared to other genotypes, so it was the best genotype of this experiment.

The results of stability analysis of rice genotypes using Lin and Binns and GGE-biplot methods introduced genotype 19603 as the most stable genotype of this experiment. This promising line along with the promising line 19607 produced the highest average paddy yield in all studied environments. These genotypes with the number of days to 50% flowering less than 95 days, grain length more than seven mm, and medium amylose content and gelatinization temperature, were considered as genotypes with mid-maturing, long-grain (Sadri) and good cooking quality. Therefore, two promising lines 19603 and 19607 are suggested for cultivar introduction programs.

Rice is the staple food of half of the world's population and one of the most important crops in Central and West Asia. To assess variation in some important agronomic traits and grouping of rice genotypes, this study was performed and 49 genotypes from Azerbaijan, Kazakhstan, Afghanistan, Turkey, Kyrgyzstan, Iraq, and Uzbekistan along with 7 genotypes from Iran were evaluated using randomized complete block design with three replications in 2019 and 2020 cropping season in experimental field of Rice Research Institute of Iran, in Rasht, Iran. Analysis of variance showed genotypes were significantly different for all studied traits. Genotype × year interaction effect was not significant for any of the studied traits. The lowest grain yield (2.2 t.ha-1) belonged to BT7 cultivar (Iraq) and the highest grain yield (7.4 t ha-1) belonged to Mishkab2 (Iraq). The shortest plant height (79.3 cm) belonged to QazNIIR-7 (Kazakhstan) and the highest plant height (149.8 cm) recorded for Avanqard (Azerbaijan). Marjan cultivar (Kazakhstan) was the earliest maturity among the studied rice genotypes with 100 days to physiological maturity (after seeding). Correlation studybetween traits indicated negative correlation between grain yield and flag leaf length. Cluster analysis grouped the studied genotypes into seven distinct groups. In general, the existence of high diversity for agronomic traits and grain yield in the studied genotypes showed that this set of germplasm has the potential for to be used in the national rice breeding programs to improve Iranian rice cultivars.

The investigation of adaptability and grain yield stability of promising lines is important in dvevelopment and release of new cultivars. Eight rice promising lines developed by crossing local cultivars including; Hashemi, Domsiah, Alikazemi and Deylamani with improved cultivars including; Khazar, Kados and IR60 with optimal yield along with Khazar, Hashemi and Guilaneh as check cultivars were evaluated using randomized complete block design with three replications in six environments (years 2018, 2019 and 2020 and locations Rasht and Chaparsar), Iran. The results of GGE biplot showed that the first component (main effect of genotype) and second component (genotype × environment) explained 61% and 21% (overall 82%) of the total variation in grain yiled, respectively. The results of ranking based on grain yield and yield stability together and in comparison with the ideal genotype indicated that the most superior genotype was G7 (Deylamani/Kados), followed by genotypes G3 (Domsiah/Khazar//Khazar), G8 (Domsiah/Khazar//Domsiah) and G2 (Hashemi/IR60//Hashemi). Therefore, genotypes G7 and G3 were selected as the most adaptable with yield stability for being released as new rice cultivars for target environments. G7 was developed from a cross between Kados, an improved and high-yielding cultivar, and Deylmani, a local and high-quality cultivar, with an average yield of 7.25 ± 0.14 tons per hectare. G3 was dveloped from a cross between Khazar, a high-yielding cultivar, and Domsiah, a local cultivar. G3 was bred with the aim of maintaining the favorable characteristics of cv. Khazar and improving the quality of its cooking through cross with Domsiah, and its average yield was 6.51 ± 0.21 tons per hectare. Both genotypes G7 and G3, with high grain quality (amylose content of 22.02 and 22.09, gel consistency of 42 and 40, gelatinization temperature of 4.71 and 3.96, grain elongation rate of 1.60 and 1.57 for genotypes G7 and G3, respectively) and medium maturity (125.34 and 122.14 from sowing, respectively) can be released as new rice cultivars for target areas.

In order to evaluate the adaptability, yield and some important agronomic and qualitative traits of rice, this study was carried out with 14 rice genotypes, including 12 rice lines and varieties from Rice Research Institute of Iran along with a regional (Khazar) and a local (Hashemi, Esteghlal, Yasmin and Osmancik) check in paddy areas of Iran, Azerbaijan, Turkey and Iraq as the first regional project for Central and West Asian countries under a research program entitled “Establishing a Multi-location Evaluation and Research Network for Genetic Enhancement in Central and West Asia (EMERGE-CWA)”. The experimental design was a randomized complete block design with three replications. Simple and combined analysis of variance, comparison means of traits and stability analysis through GGE Biplot was conducted. Stability analysis results for yield based on compound analysis in three regions of Turkey, Iraq and Iran by GGE Biplot method revealed that the most stable genotypes are Gohar, Dorfak, 184104-34, 184104-11, 18333-12 and 18425-20, respectively. These genotypes had higher yield than average. This research resulted in selecting line 18426-56-3 in Turkey, Shiroodi and Dorfak varieties in Iraq, five promising line including 18425-20, 18436-56-3, 184104-34, 184104-11 and 18433-12 in Iran as the genotypes with high and intermediate yield and desirable agronomic and grain quality characteristics. These genotypes would be utilized in advanced trials of various rice breeding programs to release directly as new varieties.

Rice grain appearance quality traits (APQ) affect consumer preference and marketing acceptance and long grain rice has many customers on the international markets.In order to identify QTLs controlling grain length, width and length to width ratio (shape) and QTL by environment interactions a study was conducted on two set of recombinant inbred lines (RILs) of two rice populations derived from crosses of Alikazemi / IR67017-180-2-1-2 (ALIR population) and Alikazemi / Saleh (ALSA) cultivars.The treatments of each RIL population with five check varieties were evaluated in augmented based on randomized complete block design with 5 replications in two regions of Rasht and Tonekabon in northern of Iran. Linkage map of the two populations using 87 polymorph microsatellite markers (SSR) covered 1356.0 cM of rice genome with an average distance of 15.58 cM between two markers. In this study, a total of 13 main QTLs (M-QTLs) and 10 pairs of epistatic QTLs (E-QTLs) were identified for three above mentioned traits, including seven M-QTLs and five pairs of E-QTLs for the ALIR population and six M-QTLs and five pairs of E-QTLs for the ALSA population. Two QTLs, qRGL4 (1.1) and qSGL5 (1.01), were increased the grain length with positive additive effect and the highest justified phenotypic variance of 25.2 and 18.4%, respectively. In this study, three QTL clusters were identified for APQ traits. Of these, two clusters were identified on chromosome 3 that was effective in controlling all APQ traits in two populations with alleles from a common Alikazemi parent. The third QTL cluster was determined on chromosome 7 consisting of qGW7 and qGSh7 for grain width and shape in the ALIR population. Therefore it could be stated that the QTLs on each cluster were either tightly linked or had pleiotropic effects with considerable influences in controlling rice APQ traits. A common marker of RM5955 was found in the ALIR population with a genetic distance of about 3.7 centimeters with QTLs of all three traits, and could be considered as a linked marker in breeding program. In this study, ten pairs of E-QTL were identified for three traits including five pairs per population. The epistatic effects in the ALIR population were mostly expressed by significant main QTLs (80%), while they were expressed in the ALSA population more by non-detected main QTLs (60%).The contribution of explained phenotypic variances of M-QTLs in controlling APQ traits were more than epistatic QTLs. QTL by environment interactions revealed that only one main QTL had significant interaction with environment, while no epistatic QTLs with additive × additive effect were found to be interacted with environment. The appropriate QTLs and linked markers in this study can be used in the breeding program to improve the appearance quality of rice grains after fine-mapping and validation.

In future climatic conditions, rice yields depend on environmental conditions of the growing season, such as temperature and available radiation rate, which in unfavorable conditions can lead to yield loss in some rice producing countries (Welch et al., 2010). Achievement to the appropriate plant density per unit area is one of the methods in increasing crop yields through crop management that as a result, all environmental factors fully utilized, while intra- and inter-plant competitions be minimized and on the other hand, suitable plant density can provide sufficient space for agronomical operations and high quality access. In general, suitable rice density is a density that is not detrimental for proper crop development and high grain yield. As the density increased, the number of primary and secondary panicles and spikelet per panicle decreased and the number of panicles per m2 increased linearly and with decreasing density, stem thickness increased (Ebrahimi Rad et al, 2018). Knowing the heat indices, such as the accumulated heat unit, which in most sources are referred to as growing degree days (GDD), can provide basic principles for determining the appropriate phenological stages and planting dates. Evaluation of cumulative GDD for different development stages will allow adjustment of planting date for rice genotype with the aim of adapting the environmental conditions in the growth period. Choosing the appropriate planting date is one of the important factors in effective crop management which has a great role in production control by adapting physiological, morphological and phenological processes of the plant such as germination and emergence, vegetative growth, flowering and maturity with favorable climatic conditions. Management of planting time for optimal production of each cultivar is one of the main factors affecting production that can be easily managed by the farmer based on environmental conditions. Proper planting date will optimize the use of yield factors, while inappropriate planting date will disrupt the balance of yield components in the plant (Esmaeilzadeh et al., 2017). In order to determine proper transplanting date based on GDD and the best plant density in rice (Tisa cultivar), an experiment was conducted at Rice Research Institute of Iran, Tonekabon station during 2015 and 2016. This experiment was carried out as split plot in a randomized complete block design with three replications. The main plot was three transplanting dates with 10 days intervals (May 4, May 14 and May 24) and the sub plot was allocated to plant density at three levels (12×30, 15×30 and 18×30 cm). The results indicated that there was a significant difference between the years of experiment only for the panicle length. The effect of transplanting date was significant in the majority of the measured parameters. The highest grain yield (6573.6 kg/ha) was obtained on May 24 planting date, which did not show any significant difference with the transplanting date of May 14. Although plant density treatments had no significant effect on grain yield, 28 plants per m2 (30×12 cm) had the highest grain yield (6445.2 kg/ha). With delay in transplanting, GDD and number of days from transplanting to tillering stage as well as the time required for panicle emergence and complete maturity increased. The highest and the lowest growth degree-day (GDD) from transplanting to tillering, panicle emergence and full ripening stage were obtained on May 24 and May 4, respectively. According to the results of this research, it can be stated that the farmers of the region can transplant this cultivar between May 14 and May 24 with a plant distance of 12×30 cm (density of 28 plants per square meter).

Rice yield as a complex trait is the main target in most rice breeding programs. To map the main and epistatic QTLs controlling grain yield and yield components, an experiment was carried out using a 129 F6 recombinant inbred lines population (IRA population) originated from a cross between Alikazemi / IR67017-180-2-1-2, in 2015 growing season in two locations, Rasht and Tonekabon, Iran.  The experimental design was augmented design arrangment with five check cultivars in randomized complete block design with five replications. Analysis of variance showed that the linkage map consisted of 87 Single Sequence Repeats (SSRs) covering 1356.0 cM of rice genome in 12 linkage groups with an average distance of 15.58 cM spamming two markers. The results of combined analysis of variance for two locations, using composite interval mapping method, identified a total of 13 main QTLs on rice chromosomes for five measured traits. The qTN3 with 13.9% for tiller number per plant, the qFG4 with 11.6% for filled grain per panicle and the qGY6 with 15.6% for grain yield had significant positive additive effect. Furthermore, the qSG1 with 19.9% phenotypivc variation had a negative additive effect on the number of unfilled grain.panicle-1. These finding suggest that these QTLs can be used in rice breeding programs for improving grain yield. The interaction between additive effect (A) of QTLs and environment (E) was significant on grain yield and number of unfilled grain.panicle-1, but it was not significan on other traits. A total of 18 QTL pairs with significant additive × additive (AA) epistatic effect were identified for all traits. The highest epistasic effects were related to grain yield and number of unfilled grain.panicle-1 with six pairs of QTLs for each of these traits. Only one of the epistatic effects between qSG1-2 and qSG6 had significant AAE effect with a R2aae = of 3.4%. In addition, some QTLs were identified as three gene clusters controlling the grain yield, number of tiller.plant-1 and number of filled grain.panicle-1. Furthermore, five microsatellite markers including RM7551, RM8218-RM3417 and RM5302- RM283 0.2 to 5 cM distance from were identified as linked markers with qGY6, qFG4 and qSG1, respectively. These markers can be considered in the marker-assisted rice breeding program.

To detect main and epistatic QTLs and their environmental interactions for rice important agronomic traits, 242 recombinant inbred lines (RIL) from two F6 rice populations derived from crosses between Alikazemi / IR67017-180-2-1-2 (IRA population) and Ali Kakami / Saleh (SA) cultivars were evaluated in two locations. Results of the present experiment showed that the linkage map of the two populations using 87 polymorph microsatellite markers (SSR) covered 1356.0 cM of rice genome with an average distance of 15.58 cM between two markers. A total of 20 main QTLs (M-QTLs) and 33 epistatic QTLs (E-QTLs) were identified with positive and negative effects. Five M-QTLs and five E-QTLs had a significant interaction with the environment. Eight M-QTLs and ten E-QTLs with significant effect on agronomic traits were stable and did not have any significant interaction with the environment. These QTLs include two M-QTLs and two E-QTLs for reducing plant height, three M-QTLs and three E-QTLs for decreasing heading date, an M-QTL and an E-QTL for increasing panicle length and two M-QTLs and four E-QTLs to increase grain yield. These main QTLs explained 11.12% (qHD6) and 24.5% (qGY1) phenotypic variation, respectively. Therefore, such useful QTLs can be used for gene pyramiding programs to improve rice agronomical traits. Furthermore, six linked SSR markers (RM421, RM178, RM3441, RM5101, RM7551 and RM5302) were identified with less than 5 cM distance from important QTLs, suggesting that such SSR markers can be used in marker-assisted selection to select rice lines with desirable traits in segregation generations.

In crops improvement، comparison of promising lines with local cultivars can be effective for assessing breeding programs. In order to study the relationships between grain yield and some agronomic traits of rice، a field experiment was conducted on seven promising rice lines Shiroodi cultivar at in Rice Research Institute of Iran (Deputy of Mazandaran-Amol) 2005. The experimental design was randomized complete block with four replications. In this study 11 traits including grain yield and yield component، grain and plant morphological characters were measured. Results of analysis of variance showed significant differences among genotypes in terms of traits under study، which indicates the existence of genetic variations. Mean comparison showed that line 2 are better based on their yields and some other traits. Grain yield showed was positively significant genotypic and phenotypic correlations with plant height (g= 0. 72**، p= 0. 64**)، length panicle (g= 0. 78**، p= 0. 59**)، weight panicle (g= 0. 81**، p= 0. 59**)، number of filled grains (g= 0. 79**، p= 0. 55**) and flag leaf area (g= 0. 64**، p= 0. 5**). Overall results of this study showed that No. 2 line to the superior ratio Shiroodi cultivar for traits، flag leaf area، number of filled grains، weight panicle and length panicle.

Two BC2F4 populations of rice, Hashemi/IR67418-110-3222 (Hashemi/IR-22) and Hashemi/Neda, Hashemi was as recurrent parent, were studied during two years (2009 and 2010) for QTLs detection for plant height, days to 50% heading, growth duration and yield. The role of epistasis and QTL-environment interaction on these traits was also studied. Hashemi/IR-22 and Hashemi/Neda lines were tested with 61 and 65 polymorph SSR primer pairs, respectively, which were distributed on all chromosomes. The total genetic maps lengths of Hashemi/IR- 22 and Hashemi/Neda were 1103.45cM and 1260.53cM, respectively. Four to five QTLs were detected for each trait in Hashmi/IR-22 population with at least two QTLs repeated for each trait during two years. These QTLs explained 5.6% to 37% of the traits phenotypic variation. In Hashemi/Neda population three to four QTLs were detected for each trait, with at least one QTL repeated for each trait during two years. These QTLs explained 5.1% to 43.2% of the traits phenotypic variation. From detected QTLs, only a plant height QTL flanked by RM234 marker on chromosome 7 and a yield QTL flanked by RM3337 and were the same in the two populations. This indicated the important role of genetic background effect on controlling these traits. In each population there were QTLs that simultaneously affected two or more of the studied traits, e. g. plant height, days to 50% heading, growth duration and yield, which suggested pleiotropic or linkage gene effects for these traits. Two QTLs on chromosomes 6 and 8 for growth duration and QTL on chromosome 8 for yield in Hashemi/IR-22 population and one QTL on chromosome 6 for days to 50% heading and growth duration and one QTL on chromosome 3 for yield in Hashemi/Neda showed interaction with environment. Also in each population a pair of QTLs was recognized with significant epistatic effect.

Determining new and higher and stable yielding varieties is one of the most important objectives of rice breeding. To achieve this goal, ten promising lines of rice along with two improved cultivars (Hashemi and Kadous) were compared at National Rice Research Institute in Rasht, Iran, for three years (2006, 2007 and 2008). The experimental design was randomized complete blocks with four replications in these three years. The combined analysis of variance indicated significant difference among genotypes, for the traits studied. This indicates genetic variation among genotypes understudy. The interaction of genotype × year for yield was significant which demonstrate different responses of genotypes during different years. Different stability analysis methods were used to determine the higher and stable yielding variety like: environmental variance, coefficient of variability, coefficient of regression proposed by Finaly and Wilkinson, Deviation from regression by Eberhart and Russel, Shukla's stability variance, Wricke's equivalence, coefficient of determination of Pintus and non-parametric method of rank. By using these analyses it was found that Hashemi was a stable yielding variety. It was also revealed that line No. 9 (IR78530-45-3-1-3), line No. 6 (IR76993-49-1-1) and 8 (IR78533-30-2-1) were found as stable producer lines.

Five improved along with three local rice varieties were crossed in a line× tester method in 2001. Fifteen F1 hybrids and eight parental genotypes were planted in a randomized complete block design with 3 replications at Rice Research Institute of Iran, Rasht, in 2002. The main objective of the research was to estimate the general and specific combining ability and gene action for 10 agrnomic and qualitative traits. Analysis of variance based on line×tester method showed that the mean squares of treatments, parents and crosses for all traits (except grain yield for crosses) were significant at 5% and 1% probability levels. General combining ability (GCA) was positive and significant for grain yield in Gharib and Kadus varieties. There was also positively significant GCA for grain length and shape in Kadus, Hassani, Nemat and in line 830. Therefore, these traits can be positively transferred to progenies. Kadus and Hassani varieties exhibited negative and significant GCA for plant height and 50% of flowering. These genotypes can transfer early maturiy and dwarfism to progenies. The cross Gharib/IR50 had positive and significant specific combining ability (SCA) for grain yield. There were also the same SCA for tiller number in crosses Hashemi/IR28, Gharib/Kadus and Hassani/Line 830. Estimation of genetic variance components indicated that the grain shape was controlled through additive gene effects. It showed that this trait can be transferred into progenies. The other such traits as tiller number, grain length, number of filled grain per panicle and plant height were controlled by dominance gene effects. Therefore, these traits can be effecitively employed to produce hybrid varieties

Grain yield and most of the traits that have economic importance in plants and animals, are inherited quantitatively and using direct selection methods don,t result in larger gains. One of the effective indirect selections methods for improving grain yield and its components is the selection index. In this study, 109 F2 plants that was produced from a cross between Hashemy and Kadous rice varieties were evaluated to determine suitable selection indices. Studied traits were number of days to maturity, plant height, panicle length, flag leaf length, flag leaf width, panicle per plant, grains per panicle, spikelets per panicle, 100-grain weight, grain yield per plant, biomass, harvest index, grain length and grain width. Results revealed that biomass and flag leaf width had highest and lowest, broad sense heritability, respectively. Grain yield had significant positive genetic correlations with grains per panicle, biomass, harvest index, spikelets per panicle, panicle per plant, flag leaf length, panicle length and grain width. Result of path analysis revealed that biomass, harvest index, spikelets per panicle and flag leaf width had positive direct effects on the grain yield while number of days to maturity showed negative direct effect on grain yield. Ten different selection indices based on optimum and base indices were investigated for improving grain yield and yield components. The direct genetic effects (genetic path coefficients) of biomass and harvest index were high. Therefore, an index based on these characters using their genetic path coefficients as economic values, will be useful to select for grain yield. Also for the traits that have higher heritability than grain yield, the use their genetic correlation coefficients with the grain yield as economic values would be a better index for the population improvement. Furthermore, the genetic gain from optimum and base indices were almost similar. However, the base index is recommended due to the easiness of computations and interpretation of results.

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.

Eight rice genotypes with two checks (Dasht and Nemat) were evaluated in three locations of Mazandaran province for two years (1999-2000), in a RCBD with four replications. This study was carried out to determine the qualitative and morphological traits and yield stability to select the best genotypes. The results of combined ANOVA showed significant differences among genotypes. The effects of location, year, genotype×location and genotype×year were not significant. The interactions of year × location, and year×location × genotypes were significant that proved the existence of interaction between genotype and environment. Grain yield stability using ten different methods, showed that Nemat cultivar (genotype 7310) with less variance (S2i) and coefficient of variability (CVi) of environment, less coefficient of regression of mean yield on environmental index (bi) and variance of deviation from regression linear (S2di), was the most stable genotype. Genotype 7304 having bi equal to unity, less S2di and high yield, was the most stable genotype. There were no significant differences between the mean yield of genotype 7304 and genotypes 7302, 7303, 7305 and 7306. Regression line slope of these high yielding genotypes was equal to unity too. Therefore they had high general adaptability. Nemat cultivar and genotype 7305 with less mean and standard deviation of ranking ( , S.D.R) and genotypes 7304 and 7303 based on Wricke, s equivalence (Wi2) and Shukla, s stability variance (σ2i), had the highest stability, respectively. The cooking quality of genotypes 7302, 7304, 7306, 7307 and 7308 was excellent with intermediate amylose content and gelatinization temperature. Consequently the genotypes 7304 and 7302 having higher mean yield compare to Dasht, and desired cooking quality and morphological traits were selected as elite genotypes.

  Dorfak (Line No.424) is a single cross derivative between Sepidrood, a high yielding improved rice cultivar used as male parent and Salari, a traditional landrace with premium cooking quality and poor in yield as female parent. The cross was attempted in 1988 and the F2 generation onwards of the cross was raised in the pedigree breeding approach. The F2 single plant selections were based on early, synchronous flowering habit, increased number of tillers, high yielding potentials with reduced plant height and resistance to blast disease. However, the selections based on grain quality were initiated from F5 generation (1994) onwards. Amongst the different selected pedigree families of the selections made earlier, the line 424 was identified as high–yielding, semi-dwarf, resistant to blast and possessing good cooking quality characteristics in 1995. This selected line was entered into preliminary yield trials and advance yield trials in comparison to improved cultivars like Khazar and Sepidrood. Multi-environmental trials were conducted at three sites over 3 years (1996-98) and the pooled analysis of these trials averaged over sites and years, revealed highly significant differences (P 1) for yield. The line 424 performed consistently, yielding in the range of 5.5 to 6.3 tha-1 with an yield advantage of 17.4% over improved cultivars like Khazar while 34.5% over traditional check cultivar Binam in three on-farm trial sites. The selected line 424 was named as Dorfak and was released for cultivation in Guilan province in 2002. Dorfak is a semidwarf (plant height 110 cm), aromatic, short duration cultivar (120 days) with 17 productive tillers, 115 grains per panicle, good grain and cooking quality features. Rice kernel characteristics clearly showed that line 424 was a highly transgressive in nature especially for kernel length and length/width ratio. However, for all other grain quality traits, Dorfak was much closer to the traditional landrace parent i.e. Salari. Dorfak, was released in 2002 for cultivation, to a large extent combined the premium cooking quality features of the traditional landraces and the yield of improved cultivars, hence becoming popular with the farmers and consumers alike.   Â

Rice is the principal agricaltural crop in most Asian contries,often accounting for more than half of total cropped area. In recent years,rice production in Iran has been increased from 2.4 million ton in 2000 to 3.1 million ton in 2003. This increase in rice production is highly attributed to the wide-scale adoption of improved rice cultivars. Kadous (IR64669-152-2-3) is a new high yielding rice cultivar with good grain quality that was selected during 1994-2000 after receiving 185 germplasm accessions from IRRI. It was evaluated in observational nurseries and preliminary yield trials in1994-1995.In these experiments,Kadous yielded 5.8 tha-1, higher than the yields of improved check cultivars Khazar (5.0 tha-1) and Bejar (5.2 tha-1). It was evaluated in regional yield trials at six sites in Guilan and Mazandaran provinces in 1996 and 1997, and performed consequently, yielding an average of 5.6 tha-1, which was 0.7 and 2-2.5 tha-1 more than Khazar and local cultivars, respectivly. The Eberhart and Russell method was adopted to verify the yield stability of Kadous.The agronomic package involved a hill spacing of 25 cm x 25 cm and 90 kg Nha-1. Its maturity duration (125 days) was 1 and 2 weeks earlier than Khazar and Neamat cultivars, respectivly. It is an aromatic,semidwarf (110 cm), lodging and blast- resistant, medium-duration cultivar (125 days), with good grain quality characteristics. Its milling recovery rate is 67% with 52% head rice. In addition, the intermediate amylose content,gelatinization temperature and gel consistency of Kadous indicates a good cooking quality that preferred by Iranian consumers. Kadous was released by the Ministry of Jihad-e-Agriculture and the Agicultural Research and Education Organization in 2004.

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 order to determine the adaptation and stability of grain yield in 8 rice promising genotypes as well as two commercial cultivars (Khazar and Neamat), as control, a field experiment was carried out in three locations in Gilan province during 1997 and 1998 cropping seasons. The experimental design was randomized complete block with 4 replications and planting distance was 25 cm × 25 cm. Analysis of variance showed significant differences for grain yield among genotypes. Combined ANOVA was also performed following Bartlett test (for uniformity of error variances). Year and location effects were considered random while genotypic effect fixed. The F test was calculated based on expected mean squares. Results showed significant differences among the genotypes. The effects of location and year and genotype location and genotype year interactions were not significant. It means that the genotypes had similar response over different locations and years. However, the interaction effects of year location, and year location genotype were significant. Stability of genotypes were evaluated using six different methods including: variance (S2i) and coefficient of variability (CVi)of environment (parameter no.1), coefficient of regression of mean yield on environmental index (bi) (parameter no.2), variance of deviation from regression (S2di) (Parameter no.3) and within location variance (MSy/p) and C.V. (parameter no.4). Results of these methods were different more or less; however, genotypes no.7604 and 7606 as well as Khazar and Neamat were determined as stable genotypes, because low S2i, CVi and MSy/p and bi equal to unity and low and non- significant S2di. Consequently, due to higher mean yield compared to Khazar and the desired cooking and milling qualities, these two genotypes were selected to be released.

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).