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Stripe rust cause by Pucciniastriiformis f. sp. tritici is one of the most important diseases of wheat and can cause severe yield loss in many wheat growing regions of the world including Iran. To determine yield loss caused by this disease and evaluate the effect of some chemical components on reduction of yield loss in south of Iran, field experiments were carried out in split plot design with three replications at Ahvaz research station during 2014-2015. Three cultivars; Chamran, Virinak and Boolani, were used and artificial inoculation was performed using an isolate which was collected from south of Iran and designated as Yr27 race variant. Meanwhile the effects of propiconazole and some herbicides on yield loss reduction were studied. In this study, grain yield and area under disease progress curve (AUDPC) were measured. Statistical analysis showed that the level of the yield reduction was significantly different in the three studied cultivars and different treatments. Propiconazole could control the disease significantly. The highest yield loss was observed for cv. Boolani in both with (9%) and without (54%) fungicide treatments. Combined application of propiconazole and herbicides significantly reduced yield loss compared with using them separately. The results of crop loss modeling using integral and multiple point regression models showed that the integral model (L = 0.017AUDPC-17.831) could explain more than 69% of AUDPC variations in relation to crop loss in all cultivars. In multiple point models, disease severity at various dates was considered as independent variable and crop loss percentage as dependent variable. This model with the highest coefficient of determination had the best fitness for crop loss estimation. The results showed that the disease severity at GS39, GS45, GS50 and GS60 stages (Zadok's scale) were more important for crop loss prediction than those in other phenological stages.

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Confocal laser scanning microscopy (CLSM) is a revolutionary advance in the field of light microscopy which, in recent years, has been used on interaction studies between host and pathogen. This study carried out on the flag leaves of the susceptible spring wheat cultivar (Triticum aestivum L.) known as Thatcher and its near isogenic line with the Yr-18 adult-plant resistance gene to stripe rust fungus (Puccinia striiformis f. sp. tritici), by confocal laser scanning microscopy. A suspension of fresh urediniospores of stripe rust, isolate SR99-UA (race, 70E 128) in a light mineral oil ( Soltrol, 170 ) was sprayed on the flag leaves in vitro, then four segments were sampled at 2, 4, 8, 12 and 18 days after inocu-lation. These segments were further divided into 1-2 cm. For detailed observation, two fluorescent dyes Acridin orange and X-Rodamin-1, known to be nucleic acid and calcium binding probes, were used, respectively. CLSM made it possible to visualize host/pathogen interaction in serial without sectioning at a three dimensional level from adaxial to aboxial leaves. According to the results, no difference in pre-penetration behav-ior of the fungus in the two genotypes was observed. During the early stages of penetra-tion, host cell necrosis was occasionally seen only on the resistant genotype. Few dead cells were observed on the susceptible host 12-18 days after inoculation. However, by this time, the resistant host had a markedly high number of dead cells; there were numerous ne-crotic areas or pustules resembling hypersensitive response. In the infected areas and around the pustules of the resistant host a remarkable red color was observed by the presence of a thick fluorescence rich calcium layer. The intensity of calcium fluorescence in the non-infected areas of both genotypes and in the infected areas of the susceptible host were nearly the same, indicating calcium mobilization as part of the defensive re-sponse in resistant near isogenic lines containing the gene Yr-18. This result indicated that calcium mobilization at the point of challenge by the pathogen played an important role in the near isogenic resistance line of Thatcher in the wheat stripe rust pathosystem. This is the first report on calcium mobilization in a cereal rust pathosystem as a part of the re-sistance response.

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In this study, isolate SR99-UA (Race 70E 128) of wheat stripe rust (Puccinia striiformis West. f. sp. tritici Eriks) was used to infect susceptible spring wheat (cultivar Thatcher) and its near isogenic line possessing Yr-18 adult-plant resistance gene. Samples were taken at the flag leaf stage and observed using light, transmission and scanning electron micro-scopes. No major differences in the infection process were detected prior to haustorium formation, but sub-stomatal vesicles appeared to be formed after penetration, slightly ear-lier in susceptible than in the resistant genotypes. Higher numbers of haustoria were formed at any particular time in the susceptible cultivar than in the resistant near isog-enic line 2-3 days after inoculation. In the early stages of infection, host cell necrosis was not observed in the susceptible host, but was occasionally seen in the resistant isogenic line. Fourteen days after inoculation, the number of necrotic cells of hypersensitive re-sponse were higher on the resistant genotype than on the susceptible cultivar at this time when many of the infected mesophyll cells of the resistant host had collapsed. The first clearly developing pustules were usually observed 12 days after inoculation on the suscep-tible cv. Thatcher and 14 days after inoculation on its resistant near isogenic line. Eight-een days after inoculation, the mean number of pustules produced, per unit of infected leaf area, was high on the susceptible cultivar but on the resistant genotype the pustules were much less in number, diminutive and poorly sporulating.