Bacterial leaf streak of Gramineae in Iran

Bacterial leaf streaks of wheat and barley in Kerman province (Iran) were found to be distinct in etiology. The barley strains were limited in host range and could only infect barley. The wheat strains were pathogenic to barley, wheat, rye, triticale, Bromus spp., Agropyron spp., Elymus junceus, Lolium multiflorum , and Phalaris tuberosa , but not Dactylis glomerata, Cynodon dactylon, Phleum pratense , and oat. Based on host reactions and electrophoretic patterns of cell proteins, the barley and wheat strains were identified as Xanthomonas campestris pv. hordei and pv. cerealis , respectively.     

Paraquat-resistant biotypes of Hordeum glaucum from zero-tillage wheat

There has been a significant increase in the area seeded to minimum- and zero-tilled crops worldwide over the past two decades. These cropping systems rely primarily on the non-selective herbicides glyphosate or paraquat/diquat to control weeds before seeding the crop. Both glyphosate and paraquat/diquat are regarded as low-risk herbicides in the ability of target weeds to develop resistance to them. Following 10–15 years of once annual applications of paraquat and diquat for weed control in zero-tilled cereals, failure of these herbicides to control Hordeum glaucum Steud. in two separate fields occurred. Dose–response experiments demonstrated high-level resistance to paraquat and diquat in both populations; however, the resistant biotypes are susceptible to other herbicides. This is the first report, worldwide, of paraquat resistance following the use of this herbicide in zero-tillage cropping systems and is therefore a harbinger of future problems in minimum-tillage systems when there is exclusive reliance on a contact herbicide for weed control.     

Effects of the sowing depth and temperature on the seedling emergence and early growth of wild barley (Hordeum spontaneum) and wheat

The experiment was conducted under a controlled environment to study the effects of different temperature regimes (15/10°C, 20/15°C, and 25/20°C day/night) and sowing depths (0, 2, 4, and 6 cm) on the seedling emergence and early growth (height gain) of wheat (cv. Marvdasht) and wild barley ( Hordeum spontaneum ). The cumulative emergence and plant height gain over time were modeled with the use of a logistic function. For a particular temperature regime, the maximum percentage emergence (E _max ) of wheat was higher than that of wild barley across all sowing depths. The maximum and minimum E _max values for both species occurred at 20/15°C and 25/20°C, respectively. The time taken to reach 50% of the E _max (i.e. E₅₀) increased with the sowing depth in both species under all temperature regimes. The E₅₀ of wild barley was greater than that of wheat for all temperature regimes, with maximum differences observed at 20/15°C. The greatest maximum plant height (H _max ) was observed at the surface planting for both plants. The H _max was reduced at temperatures either lower or higher than 20/15°C, with a more notable reduction in wild barley. At all temperature regimes, the time taken to reach 50% of the H _max (i.e. H₅₀) increased linearly with the sowing depth but, at higher temperatures, the accelerated growth rate reduced the H₅₀. The wild barley seedling emergence and height gain rate, as expressed relative to those of wheat, revealed the highest superiority of wheat over wild barley at 25/20°C and the sowing depth of 4 cm.     

Genetic analysis of partial resistance to bacterial leaf streak (Xanthomonas campestris pv. cerealis) in wheat

Genetic variability of partial resistance to bacterial leaf streak was investigated in hexaploid winter wheat ( Triticum aestivum. ), using 16 parental genotypes and 48 pure lines (F10) derived from a composite cross programme. Two experiments were undertaken in a controlled growth chamber. Seeds of all genotypes were grown under controlled conditions using a randomized block design with three replications. Each replication consisted of a row of 20 seedlings of each parent and pure line. An Iranian strain of bacterial leaf streak was used for the inoculation of 12-day-old seedlings. In a third experiment, eight genotypes from parents and F10 pure lines representing a large variability for partial resistance were inoculated with four other Iranian strains of bacterial leaf streak. A large genetic variability was observed amongst the 64 genotypes for partial resistance to the disease. Partial resistance heritability estimates were rather high (70%), indicating that the resistance factors may be transmitted by crossing. Amongst all genotypes investigated, 'DC²-30-N2' and 'IBPT-66' displayed the highest partial resistance to the disease. Significant correlations between strains in the third experiment show that a genotype resistant or susceptible to one strain will have similar reactions with other strains. No significant genetic gain was observed for partial resistance in the best pure line of the 48 lines studied, when compared with the best parental line. Increasing the number of pure lines is likely to result in the identification of genotypes that might prove to be more resistant.     

Comparison of three methodologies for efficient seed extraction in studies of soil weed seedbanks

Determination of weed seeds in the soil is tedious and time consuming. To evaluate the different seed extraction methods to improve seedbank estimations, three extraction methods (sieving, cloth bag and flotation) were compared, based on their accuracy and time needed for separation processes and enumeration. Seeds of Datura stramonium,Amaranthus retroflexus,Portulaca oleracea and Plantago major were used to artificially infest soil samples of four textures, namely clay, clay loam, loam and sandy loam containing 19%, 27%, 38% and 65.5% sand respectively. Soil textures had a significant effect on counting time in all extraction methods. In flotation, four submethods involving different solutions and centrifuge rotation speed were examined, but showed no differences, so data were pooled. Counting time in flotation, cloth bag and sieving methods was 9, 16 and 30 min respectively. However, when the time needed for other processes was taken into consideration, flotation and bag methods did not differ significantly. Species‐wise seed recovery was not affected by soil texture in the bag method, suggesting an advantage for this approach as its accuracy is not soil texture‐dependent. Total seed recovery for flotation, sieving and bag methods was 61%, 67% and 75%, respectively, and was not significantly different. Considering the efficiency of methods, the cloth bag technique could be recommended, because it was as time consuming as the flotation method, but required the same minimum equipments and costs as the sieving method.     

Assessment of the allelopathic potential of 17 Iranian barley cultivars in different development stages and their variations over 60 years of selection

Laboratory experiments were conducted to determine the allelopathic potential of 17 Iranian barley cultivars in four development stages and their variations over the last 60 years of collection. Imbibed seeds and water leachates that were extracted from the barley plants at the seedling, tillering, stem elongation, and heading stages were used for the bioassays, including filter paper, neighboring barley seeds in soil, and soil mixed with dried barley residues. The experiments were conducted with the use of wild mustard (Sinapis arvensis) as the test plant. The Germination Rate Index (GRI) and emergence of S. arvensis were inhibited on both the filter paper and soil. The highest inhibitory effect was seen with the tillering stage's water leachate on filter paper. The GRI decreased in response to the increased density of barley imbibed seeds. The germination was less affected by the presence of barley seeds from the soil than those from the filter paper. The GRI of S. arvensis seeds was lower in the older than in the recently developed cultivars. Although there were some fluctuations in the GRI value with time, the germination inhibitory effect has decreased as new, higher‐yielding cultivars have been released.