فصلنامه تحقیقات غلات
سال دوم شماره 3 (پاییز 1391)

To evaluate seed yield and some associated characteristics in rice under drought stress conditions, 15 rice genotypes (including seven local and eight foreign varieties) were studied in two environments (normal and drought stress conditions) using randomized complete block design with three replications in research field of Faculty of Agricultural Sciences, Gonbad Kavous University, in 2008. Analysis of variance showed that there were significant effect (p<0.01) of genotypes on all traits in two environments, so that local varieties showed a better response to drought stress than foreign varieties. Mean comparison of genotypes showed that the highest yield belonged to Domsiah and Sorkho cultivars in normal condition and Gardeh in stress condition. Evaluating the reduction percentage of traits mean showed that most damage of drought stress was due to increasing of unfilled grains (23.45%). 100 kernel weight under normal condition (0.89) and the number of filled grains under drought stress condition (0.92) had the highest positive correlation with the grain yield. Results of path analysis showed that the highest positive direct effect on grain yield was related to 100 kernel weight and the number of filled grains in non-stress and stress conditions, respectively, which were considered as the most important agronomic traits for selecting the higher yield cultivars under flooded and drought stresses.

Introducing of new genotypes and cultivars is one of the main reasons for increasing grain yield of crop plants in recent years. This research was carried out to evaluate the yield stability of rice genotypes in Isfahan province. In current study, eleven promising rice genotypes together with Sazandegi as control cultivar were evaluated using randomized complete block design with four replications in two locations of Isfahan province (Fozveh Research Station and Shorefirozan region) during 2008 and 2009. Results of combined analysis of variance for grain yield showed that the simple effects of year and location at 5% and genotype at 1% probability levels were significant. Also, interaction effects of year×location and year×genotype were significant at 5% and year×location×genotype at 1% probability levels. Results of stability analysis of genotypes by different methods showed that the genotypes 11, 2 and 4 were stable and had better responses to experimented environmental conditions than other genotypes. The grain yield of genotypes 2 and 4 was 8061 and 7955 kg.ha-1, respectively, which was 7.1% and 5.7 % higher than the control variety, Sazandegi. Results from current research showed that the genotypes 2 and 4 with desirable stable, high grain yield and suitable grain quality and agronomic characteristics were superior genotypes under Isfahan climate conditions.

The most common irrigation method for Iran's paddy rice fields is continuous flooding that it changes to intermittent irrigation in water shortage. On the other hand, several droughts and also construction and operation of different dams in Sepidroud River watershed cause to decrease the water quality of this river in the recent years. In this study the combined effects of salinity and drought stresses were investigated on horizontal and vertical water flow in cracked soil of a Hashemi cultivar paddy field (most common cultivar in Guilan Province). Treatments were consist of two irrigation strategies, namely continuous and intermittent (6 days intervals) flooding methods by applying 5cm water height and three salinity stress by using irrigation water at three electric conductivity levels of 2, 3 and 4 dsm-1. These treatments applied in two conditions consist of crack width 3 mm and 2 cm. The results indicate that when cracks by average width of 2 cm form in paddy field, daily irrigation of the crop even with inferior quality water can cause to higher yield than intermittent irrigation. In spite of less irrigation water for 6 days interval treatments, continuous irrigation treatments with mm width cracks had the highest water productivity. Also, cracks by average width of 2 cm, increase lateral flow significantly. The effect of irrigation water salinity on lateral flow rate was not significant and cracks became irreversible even after rewetting.

VSM is a simple vegetative simulation model which in spite of needs to a few input data, its accuracy in field scale is acceptable. However due to high uncertainty in input data, its application in regional studies is very limited. In this study, the regional rice estimation was improved by combining VSM model with satellite data of short wave solar radiation and leaf area index. The spatial resolution of remotely sensed leaf area index from MODIS was improved using downscaling technique and high spatial satellite data of Landsat TM. Later its impact was investigated on validation process of regional rice estimation. Comparison of observed and estimated LAI with (or without) downscaling indicated that in case of applying down scaling technique accuracy of LAI maps will increase up to two times (from R2= 0.44 to R2= 0.87). The results indicated also in case of using downscaled LAI data in VSM model, the overall accuracy of regional rice yield estimation will increase dramatically (from R2= 0.64 to R2= 0.91).

A two year study was carried out at Rice Research Institute of Iran in 2010 and 2012 in order to study the response of rice and paddy weeds to a new dual purpose herbicide penoxsulam in comparison with current used herbicides. First year treatments included penoxsulam doses in 24, 30, 36, 42 & 48 (gr.ai.ha-1), butachlor+bensulforunmethyl (BSM), butachlor+cinosulfuron and anilofos+Cinosulfuron and the second year treatments were penoxsulam at two levels (3 & 40 gr.ai.ha-1), oxadiargyl+BSM, thiobencarb (TB) and TB+BSM. All common herbicides were studied in recommended doses. Results showed penoxsulam phytotoxicity on rice 2 & 4 WAT was similar and more than current used herbicides respectively. Penoxsulam efficacy on barnyardgrass control in first and second year of trial was similar and less than current used herbicides. Also penoxsulam efficacy on sedges and broadleaf control was less than current used herbicides in both years. Decreased efficacy of penoxsulam in barnyardgrass control in the second year of study was probably because of water shortages and lack of permanent flooding. In first year of study average efficacy of butachlor+BSM or cinosulfuron to control “sedges and broadleaf” was 99, 89, and 85 % in 2, 4 and 10 WAT and penoxsulam in max recommended dose and similar rating times 61, 40 and 57 respectively. In second year of experiment penoxsulam max efficacy on ricefield bulrush (Schoenoplectus maritimus) and pondweed (Potamogeton nodusus) control was 31% and BSM in mixture with graminicides decreased their biomass more than 90% in 4-WAT. The highest grain yield 3650 kg/ha recorded in butachlor+cinosulfuron in first year. Butachlor + BSM yielded 291 kg/ha, statistically similar to hand weeded and recommended dose of penoxsulam. Dual purpose herbicide anilofos+ethoxysulfuron lacked enough efficacy on all weeds control and yielded similar to infested treatment statistically. Also the second year results confirmed the first year’s one, and showed mixture of graminicides (thiobencarb or oxadiargyl) with BSM had the highest grain yield (
3666 kg.ha-1) and penoxsulam in two investigated doses showed 25 and 48% less yield in comparison respectively. Based on results of this study penoxsulam in comparison with current used herbicides had more durable toxicity on rice, less consistency on barnyardgrass control and also lacked enough efficacy on two important perennial weed pondweed and ricefield bulrush.

In this study, 24 SSR markers associated with QTL controlling cold tolerance and four markers associated with cold genes were used to determine the genetic affinity of nine parental lines (including four Iranian susceptible lines and five tolerant IRRI lines) and their 20 hybrid combinations to cold stress. The Evaluation of relationship between SSR markers associated with QTLs controlling cold tolerance with susceptible and tolerant genotypes indicated that RM292, RM261, RM270, RM263, RM283, RM7200, RM7003, RM239 RM6770, RM101 and RM335 were able to separate four Iranian susceptible genotypes from five IRRI tolerant genotypes. Hassani and Binam genotypes had the most and the least similarity with IRRI genotypes, respectively. Markers associated with cold genes didn’t show any polymorphism between parents. Among the 24 used SSR markers, 18 markers were polymorph that amplified 51 polymorphic bands. The maximum band number (six and five) was produced by RM84 and RM202, respectively. The minimum band number (two) was produced by RM335, RM292, RM420, RM341, RM261, RM270 and RM283. PIC value for SSR primers varied from 0.25 to 0.40. Cluster analysis using UPGMA based on SSR markers and simple matching coefficient separated 9 parental lines and their 20 hybrid combinations into four groups, including 6, 5, 15 and 3 genotypes, respectively. Totally, hybrids were more similar to the IRRI genotypes. Results of canonical discriminant function Analysis using the Fisher’s linear method showed that the UPGMA method separated the genotypes with the 93.1  accuracy.