نشریه به زراعی نهال و بذر
سال بیست و هفتم شماره 1 (1390)

In most researches that carried out to evaluate the contribution of current photosynthesis in grain yield formation, the role of spike is less considered. Therefore, this study was carried out to compare the role of spike and leaves photosynthesis and soluble stem carbohydrates remobilization under different water stress treatments; at cell division and grain filling stages, on grain yield formation and some related traits in two bread wheat cultivars (Marvdasht and Zagros). Factorial arrangements in randomized complete block design with three replications was used. Inhibiting of spike and leaves photosynthesis treatments at the beginning of grain filling (14 days after anthesis) and water stress treatments at the beginning of grain filling (14 days after anthesis) and grain filling stages were applied. Water stress significantly decreased grain yield in two bread wheat cultivars. Grain yield reduction under water stress in cv. Marvdasht cultivar was greater. Inhibition of whole plant and spike photosynthesis with chemical desiccant (KI) did not simulate drought stress, however, the effect of water stress was intensified by inhibiting current photosynthesis and caused more reduction of grain yield in cv. Zagros. These results showed that under water stress treatments, higher yield stability of cv. Zagros could be related to greater resistance of its photosynthetic system. Inhibition of whole plant and spike photosynthesis at the beginning of grain filling showed that contributions of spike and leaves photosynthesis and soluble stem carbohydrates remobilization in grain yield formation of two bread wheat cultivars were 63%, 43% and 25%, respectively.

To determine the best harvesting time for obtaining maximum quantity and quality tomato seed, a split plot in time arrangement in randomized complete block design with three replications was carried out in Khorasan Razavi Agricultural and Natural Resources Research Center, Mashhad, Iran in 2007 and 2008 growing seasons. Main plots were six tomato cultivars including; Mobil, Peto Early CH, Gina VF, Early Urbana, Kal. J. and Karoon. Sub-plots were harvesting time including; five harvestings from 27th July with a 15 days interval. Fruit yield, seed yield, seed extraction (%), hectoliter weight, purity (%), germination (%) and rate were measured and recorded. Analysis of variance showed that cultivars were significantly different for all traits except seed purity (%). Harvesting time and interaction of harvesting time × cultivar also were significant for all traits. The fourth harvesting time had the highest fruit yield, seed yield, seed purity (%), germination (%), germination rate. These traits increased in fourth harvesting time by 40.4%, 51.8%, 13.2%, 2.8%, 2.9% and 2.1%, respectively, as compared to maximum of these traits in the other harvesting times. The highest hectoliter weight obtained in third harvesting time with 5.7% greater than the other harvesting times. The best time for harvesting for seed production was the fourth harvesting time with Karoon cutlivar.

Drought stress limits crop productivity and salicylic acid (SA) application alleviates stresses in plants. In present research the interactive effects of drought stress and SA was studied on growth, forage and grain yield of maize hybrid (Double Cross 370) in research field of Shahid Bahonar University, Kerman, Iran in 2006 growing season. Irrigation intervals; 7 day as control and 10 day as drought stress was considered as main plots and 0.1 mM SA application; control, seed soaking, spray at 3-4 leaf stage, spray at anthesis, seed soaking + spray at anthesis and spray at 3-4 leaf stage + spray at anthesis as sub plots. Drought stress, reduced chlorophyll, relative water content (RWC), fresh and dry weight of forage and increased electrolyte leakage. On the contrary, SA increased chlorophyll, RWC, forage dry weight and reduced electrolyte leakage. The most effective treatment was seed soaking. Interaction of drought stress and SA was significant for plant height, 1000 kernel weight, grain yield and harvest index. Seed soaking treatment, increased grain yield under stress and non-stress conditions. However, it is concluded that SA significantly alleviated drought stress and increased yield in maize Double Cross 370.

Effects of three threshing methods (T30 thresher, Tractor powered thresher and cereal combine) on kernel fissuring, seed germination and seedling growth of rice (Oryza sativa L. cv. Hashemi) were evaluated in an experiment conducted in 2008. At the first stage, number of fissured kernels and number of fissures on kernel were measured. Germination and seedling growth of intact and fissured seeds were measured at the second and third stages. Results showed that the cereal combine produced the maximum (13%) and Tractor powered thresher and T30 thresher had less negative effects on kernel fissuring (9.7% and 4.7%, respectively). Germination test showed that the intact seed of three threshing methods had the maximum germinability (98%), germination index (2.5), and germination energy (0.90). Seedling vigor test also showed that the intact seeds obtained from the three threshing methods had the maximum shoot height (24.8 cm), leaf area (5.2 cm2), shoot dry matter (11.8 mg), total root length (125.5 cm) and root area (2.7 cm2) that were significantly different as compared with fissured kernels. In conclusion, evaluation of threshing methods effect on kernel fissuring, germinability and seedling growth revealed that the unsuitable threshing method (cereal combine) may negatively affect germination and seedling vigor of the paddy that are going to be used as seed in the next cropping season.

To evaluate the effects of different levels of sprinkler irrigation and plant density on yield, yield components and water use efficiency of grain maize KSC 302, an experiments was carried out in field station of Seed and Plant Improvement Institute, Karaj, Iran in 2006 and 2007 growing seasons. Split-plot arrangements in randomized complete blocks design with three replications was used. Main plots were three irrigation levels: 75%, 100% and 125% ET and sub-plots were three plants densities: 80000, 90000 and 100000 plant per hectare. Results showed that increasing irrigation levels from 75% to 125% had significant effect on grain yield and yield components, however, its effect on water use efficiency was not significant. 100% ET level had the highest WUE (1.03 Kg/m3). Effect of different plant densities on grain yield, yield components, and water use efficiency was not significant. Results revealed that 125% ET level and 90000 plant density had the highest yield and yield components, and 100% ET level and 100000 plant density had the greatest WUE. Therefore, under non-limited irrigation water resources the best option is application of 12000 m3.ha-1 of irrigation water and 90000 plant density, and under limited irrigation water conditions the best option is application of 10000 m3.ha-1 of irrigation water and 100000 plant density are suitable for areas similar to Karaj conditions.

To produce alfalfa (Medicago sativa L.) seed, application of appropriate harvesting time and appropriate agronomic techniques are useful. These factors were studied in a field experiment using of stripe split plot arrangements with four replications. Seed yield and its components and forage of alfalfa cv. Hamedani were evaluated. Row spacing in three levels including; 40, 50 and 60 cm and stage of the first cutting of forage (ht1) including four phenological stages were studied. Analysis of variance showed that ht1 had a significant effect on seed yield per unit area,1000-seed weight, duration of seed ripening and plant height. Row spacing also had significant effect on the forage yield of the 1st cut at the 5% probability levle. The interaction between two factors was significant on the forage yield of 1st cut and 1000-seed weight at the 5% probability level. Seed yield after ht1 at the onset of flowering time was three times greater than the end of reproductive stage. Seed yield from the 60 cm row spacing was 2.5 times more than the 40 cm row spacing. Seed yield of 130 kg ha-1 was produced from one year old alfalfa stand with 60 cm row spacing.

A field experiment was conducted in 2006- 2007 cropping season to evaluate the effect of seed priming on growth trend and grain yield of barley cv. Abidar using randomized complete block design with three replications at Dryland Agricultural Research Institute (DARI), Maragheh, Iran. Treatments included: hydropriming, osmopriming (in %10PEG-6000 and 5 mM CaCl2), nutrient priming (in 10 mM Zn, 50 mM P, 100 mM P, 10 mM Zn + 50 mM P, 10 mMZn + 100mM P) and control (without priming). Superior treatments were selected from primary laboratory test which was conducted with 21 treatments in a completely randomized design with four replications. These treatments were superior in regard to %viable seeds, percentage and rate of germination, electrical conductivity, root, shoot and seedling dry weight. Results of field experiment showed that seed priming improved growth indices such as dry matter accumulation (DMA), crop growth rate (CGR) and relative growth rate (RGR). The highest grain yield (2072.3 kg/ha) belonged to hydropriming. Nevertheless, seed priming improved grain yield of barley cv. Abidar by about 32% as compared to control. The benificary effect of seed priming on growth and grain yield of barley cv. Abidar were attributed to rapid seedling emergence and establishment, and consequently the optimum use of light, soil moisture and nutrients by the plants developed from the primed seeds.