Iranian Journal of Crop Sciences
Year:2002 | Volume:4 | Issue:3|Papers Count:8

A field experiment was conducted to determaine the critical period for weed control in sunflower in Borugerd in southwestern Iran in 1999 cropping season. Treatments included weed free and weed interference periods up to 10, 20, 30, 40 days after emergence and weed free during growing season. Treatmensts were replicated four times in a complete randomized block design. Gampertz and Logestic equations were fitted to weed free and weed interference data. Results showed a critical period of weed control based on 5% and 10% of acceptable yield loss from 10-43 and 18-33 days after emergence (DAE) equal to 250-1250 and 300-950 GDD or V2 to R1 and V2 to V9 stages, respectively. Weed interference reduced the height, oil and kernel yield. Oil percent was not affected by weed interference or control.

The theory and analysis of diallel crosses have been defined and developed by many scientists. Griffing in 1965 described the diallel analysis in four methods with four models. In this study estimation of genetic parameters through different methods of Griffing approach was compared. Seven lines of Brassica napus L. were crossed in all possible combinations including reciprocal crosses. Forty two F1s together with seven parents were planted using randomized complete block design with 2 replications. Combining ability analysis was carried out for 12 agronomic characters on the basis of four methods of Griffings approach. Estimation of additive (σA2) and dominance (σD2) genetic variances and calculation of dominance ratio (σD2/σA2) was carried out for these methods. The estimation of additive and dominance genetic variances in the method 3 were negative for all characters and in method 2 and 4 they were negative only for some characters. However, in method 1 additive genetic variance was positive for all characters. Considering the estimation formula for additive and dominance genetic variances it was concluded that, when mean square specific combining ability (SCA) is greater than mean square of general combining ability (GCA), estimation of additive genetic variance is negative. This situation was observed in methods 2, 3, and 4 but not in method 1. It was indicated that components of genetic variances was better estimated in method 1 than the other methods in this study. Results indicated that the method 1 provided consistent estimation of additive and dominance genetic variance and was superior in comparison with the other Griffing methods.

Drought stress is one of the limiting factors in crop production. In order to estimate drought stress effects on ABA accumulation and stomatal conductivity of sugar beet (Beta vulgaris L.) leaves, an experiment was conducted in Karaj and Mashhad, in 1999. Research was carried out in factorial experiment based on RCBD with 3 replications. In this experiment 9 genotypes of sugar beet were tested. Treatments were water stress (50 days non irrigation in early growth period) and non stress. Results showed that drought stress significantly affected the ABA accumulation in leaves, and genotype x stress interaction was also significant. White sugar yield genotypes decreased as ABA increased in drought stress treatment. The correlation coefficient between root yield and ABA accumulation was low and non-significant. It is concluded that genotypes had enough time after drought stress to compensate for their yields. Stomatal conductivity decreased when ABA increased. It was due to stomatal closure and decreasing the transpiration.

Plants are exposed to environmental stresses. Water and nitrogen availability are two major factors for crop production under different conditions. In order to determine the effects of water deficit and different nitrogen rates on growth and developmental stages, yield and yield components of corn, two field experiments were conducted using a randomized complete block design in 200I growing seasons. Two corn hybrids (KSC 108 and KSC 301) were used under water and nitrogen stresses at vegetative and reproductive growth stages in two locations (Hamedan and Karaj). The result indicated that phenological stages delayed under water and nitrogen stresses in different treatments. Leaf area index decreased as availability of water and nitrogen decreased. Significant differences were observed between two hybrids for biological yield, grain yield and yield components. The lowest biomass and grain yield were produced in water stressed plants at both vegetative and reproductive stages. The different rates of nitrogen utilization shown significant effect on grain yield. Water deficit at vegetative and reproductive growth stages decreased the grain yield by 15% and 20%, respectively in comparison with controls. Relative water content reduced by 15-18% under water and nitrogen stresses. There were no significant differences in harvest index, but stress index (SI) was different between stressed treatments. The maximum stress index (SI) belonged to KSC 301 under water stress at the vegetative and reproductive growth stages.

In order to evaluate and determine the most effective traits for improvement of grain yield in bread wheat genotypes, an experiment was conducted with 567 genotypes. The experiment was conducted using augmented with two replications in which cv. KaradjI and cv. Sardari were used as control. Analysis of variance indicated non-significant difference between blocks for all the traits. Results of correlation analysis showed that majority of the traits had positive and significant correlation with single plant kernel yield. Step-wise regression analysis indicated that seven traits (spike grain yield, biological yield, harvest index, 1000 kernel weight, grain no./plant, grain no./spike and spike length) entered to the model and estimated 99% of grain yield variation in plant. Path analysis determined that grain no./plant, biological yield and 1000 kernel weight had the most positive direct effect on plant grain yield. Therefore, results indicated that indirect selection for these traits under irrigation condition will lead to improvement in plant grain yield.

Chamomile is an annual plant that belongs to Asteraceae (Composite) family. The flowers have an active substance which is called "essential oil". The most important constituent in essential oil is "chamazulene" that is used widely in pharmaceutical, food, perfumery and flavouring industries. The main aim of this study was determine the effects of sowing date and plant density on flower yield and active substance of Chamomile. The experiment was carried out at Khojir Research Station, in 1998. The treatments were three sowing dates (25 March, 4 April and 14 April) and three plant densities (50x20, 50x30 and 50x40 cm). The experimental design was in randomized complete blocks with three replications (treatments were arranged in factorial combinations). Characteristics such as fresh and dried flower yield, essential oil content of flower, chamazulene percentage and essential oil and chamazulene yield. Mean comparison was carried out using Duncan Multiple Range Test (at 5% level). Results showed that the highest fresh and dried flower yield, essential oil yield, chamazulene percentage and chamazulene yield were obtained from the first sowing date (25 March). Plant density also showed significant effects on these characters (except essential oil in flower and chamazulene percentage). The highest fresh and dried flower yield, essential oil yield and chamazulene yield were obtained from the plant density (50x20 cm). According to the results of this study, the best sowing date was 25 March and the most suitable plant density was 50x20 cm.

In order to study the effect of tillage methods on soil bulk density, soil porosity, soil moisture and yield of wheat an experiment as a complete block design with 4 replications was conducted in ICARDA from 1985-86 to I997-98 growing season. Tillage methods were: no tillage, sweep, moldboard and chisel plough. Results showed that in depth of 0-10 cm of soil, moldboard had lower bulk density than other tillage methods but in 10-20 cm of soil depth, no tillage treatments had the highest bulk density. In 20-30 and 30-40 cm of soil depth. sweep had the highest bulk density compared with other tillage methods. However, in 0-10 cm of soil surface. moldboard had higher porosity than other tillage methods. In 10-20 cm of soil depth, no tillage had the lowest porosity and in 20-30 and 30-40 cm of soil depth, sweep had the lowest porosity. Soil moisture content in 1987-88 growing season, that was a wet season, in all tillage methods in all dates of sampling was not significant, but in 1989-90 growing season which was a dry season the differences in soil moisture content between tillage methods were significant. In this growing season in all dates of samplings, soil in mold× board treatment compared with the other treatments had the lowest moisture and no tillage had the highest. In 1992-93 growing season, a moderate season, also soil moisture content in moldboard treatment the lowest. Biological, straw and grain yield in all years in no tillage treatment was significantly lower than the other tillage methods, however, there were no significant differences between sweep, chisel and moldboard.