فهرست مطالب سیامک رحمانپور

Aram is a new oilseed rape cultivar, extracted from the R308 (earlness line) and RGS003 (high-yield cultivar) cross population through pedigree method in three years. To reach high-yielding and compatible lines and cultivars, preliminary and advanced investigations were carried out in Gorgan and Sari (2014-2015) and Zabol, Gorgan, Sari and Borazjan (2016-2017). The line SRL-93-12 (Aram cultivar) with a yield of 2955 kgha-1 and 2774 kgha-1 was the first in the above-mentioned tests, respectively, and the SRL-93-12 line was also recognized as the most stable genotype based on the lowest Lins and Binns superiority index and highest seed yield. Extension research project results on farmers' farms in Behbahan, Moghan, and Gorgan regions showed that the new line with 594 kgha-1 higher yield than the check cultivar was in the first rank. According to the results as well as desirable agronomic traits such as good tolerance to dormancy and uniformity in maturity, this line was released with the name Aram.

The new oilseed rape cultivar Nilofar (R15), is the result of screening and purifying single plants in segregating generations derived from the cross "Symbol×Orient". During five years of consecutive cultivation, screening of single plants was continued to access pure lines using pedigree method and pure lines were selected in F4 generation. During cropping season 2008-2009, 84 pure lines were evaluated in preliminary yield trial. Results showed that Nilofar variety with a mean yield of 3352 kgha-1 had higher grain yield by 45% compared to the Okapi control variety with a mean grain yield of 1833 kgha-1. In the Value for Cultivation and Use (VCU) trial in six research stations of cold and mid cold regions of Iran including Karaj, Isfahan, Hamedan, Islam abad-e- gharb, Khoy and Arak during two cropping seasons 2009-2011, Nilofar variety with an average grain yield of 3783 kgha-1, ranked first and had 16.1% grain yield more than the Okapi. Under delayed sowing date and stopping irrigation from silique development stage in Karaj during two cropping seasons 2012-2014, Nilofar with 1986 kgha-1 and 0.62 kgm-3 in term of grain yield and water use efficiency, respectively, was superior to Okapi with 1626 kgha-1 grain yield and 0.62 kgm-3 water use efficiency. The glucosinolate content of Nilofar variety was less than 10 μmolg-1 of dry matter and the erucic acid content of the oil was less than 2%. The results of the extension research project in Kermanshah province showed that the mean grain yield of the Nilofer variety at two sites of Sarab Nilofer and Mahidasht was 4004 kgha-1, which was 14.8% higher than the Okapi control cultivar. Due to its high grain yield potential and appropriate agronomic characteristics, line R15 was released under the name of Nilofar and is recommended for cultivation in the cold and mild cold regions of Iran.

Saffar (Zabol 10b line) variety was obtained by pedigree method from Goliath×19H cross. Based on preliminary evaluation, this variety showed significant earlier maturity (13 day), in 2010-2011, compared to the other lines of canola. Based on adaptability expieriments in Zabol, Safiabad, Behbahan, Boushehr, Gorgan, Gonbad, Sari and Moghan regions in 2011-2012, its grain yield had not significant difference from control variety RGS, but had a high early maturity. The new variety had a lower rank variance which indicates the Less performance fluctuations and stability in different years and regions compared to control variety RGS. Saffar cultivar with 165 days growth period was 12 days earlier in maturity than control variety RGS in warm south and north regions. The oil content of new variety was 43.15%, which has not significant difference with control variety RGS but in terms of having higher amounts of oleic acid and lower amounts of linolenic acid, it has a better quality. The field response of new variety to stem sclerotinia disease showed good relative tolerance in the north climate, which has significant difference with control variety RGS. Based on outstanding features such as yield stability, early maturity, possibility of escaping from drought and heat in the last season, saving at least one irrigation stage and uniformity in maturity, this line was released with the name of Saffar in 2018 and recommended for late cultivation in warm areas with short growing seasons in warm south and north climate zones of the country such as the south of Kerman, Sistan and Baluchestan, Hormozgan, Khuzestan and Gorgan.

The most important goal in all crop breeding programs is to increase yield, and yield improvement requires the use of efficient statistical methods to identify superior genotypes. In determining the superiority of genotype, in addition to high yield, yield stability in different environments must also be considered.Biplot analyses are good tools for selecting superior genotypes and to increase efficiency in selection.

In the present study GGE biplot method was used for assessment yield and yield stability of 130 genotypes of soybean under two environmental conditions, natural conditions and disease stress (artificial induction of charcoal rot disease), were evaluated in a simple lattice design with two replications at Seed and Plant Improvement Research Institute (SPII), Karaj, Alborz province, Iran, during 2014 and 2015 (four environments).

The results of combined analysis of grain yield/plant revealed that effects of location, genotype and interaction of genotype × location were significant. The results of stability analysis using GGE-biplot method revealed that the first (Genotype) and second (genotype × environment interaction) components explained 70% and 14%, respectively, and the both components 84% of the total variation, which indicates a good validity of the biplot in explaining the variations of genotypes and genotype × environment interaction (G + GE). Polygonal biplot showed that the genotype 66 had the highest grain yield in environment E2 (disease conditions in 2014) and E4 (disease conditions in 2015), however, the genotypes 1, 3, 5, 43, 63, 66, 75, 76, 77 and 89 had a good combination of stability and yield.

Some of these genotypes such as genotype 66 did not show any signs of charcoal rot in both experimental years, they also had a good grain yield.

Downy mildew, caused by Peronospora tabacina, is the most important disease of tobacco in the world which came to Iran in 1963. The northern part of Iran has the highest levels of tobacco cultivation and more than 70 to 80% of the extracted tobacco is obtained from these areas. During the last 30 years, the disease has appeared in 18 years with varying severity in Tirtash region. This research was conducted with the aim of examining the relationship between the amount of disease and climate variables. For this purpose, the amount of disease was recorded as severity percent (EP3) and converted to outbreak occurrence (EP1) and severity levels (EP2) during the 30 years (1984-2014). The growth period of tobacco was considered as a model base and four time windows were defined in this time period and predictor variables were determined among 21 meteorological variables. Correlation of the variables with the disease indicate that the best time window for disease warning was complete length of Farvardin (March 20 to April 20) and average of mean temperature (ATA), total precipitation (SP) and average of wind speed (AWS) had the highest correlation with dependent variables. The highest efficiency of prediction of developed models were 80.7%, 64.5% and 33.8% based on EP1, EP2 and EP3, respectively. The best combination of two predictor variables for disease prediction was obtained by ATA and SP.

Nafis variety (line L72), suitable for cultivation in the cold and moderately cold regions of Iran, is the result of the selection and purification in segregating generations derived from the cross Orient×Modena. Selection of single plants was carried out during five consecutive years using pedigree method until accessing pure lines and then pure lines were screened in F6 generation. Pure lines along with Okapi as check cultivar were evaluated in the preliminary yield trial in experimental farm of Seed and Plant Improvement Institute in 2009. The result showed that mean seed yield of L72 with 3650 kgha-1 was 30.7% higher than Okapi. The study of adaptability of selected lines in Karaj, Hamedan, Zarghan and Kermanshah during 2012-2013 and 2013-2014 showed that line L72 with seed yield of 4137 kgha-1 had the highest grain yield among studies genotypes where its seed yield was 6.7% higher than Okapi and had a good yield stability based on environmental variance statistic. Results of complementary trials for line L72 in Karaj, Hamedan, Zarghan, Isfahan, Khoy and Kermanshah during 2014-2015 and 2015-2016 indicated that this line with grain yield of 4336 kgha-1 had higher yield compared to other genotypes. Field disease assessments indicated high tolerance of L72 to sclerotinia compared to check cultivar Okapi. Results of on-farm trials in farmers' field of Kermanshah province showed that line L72 had 13.7% higher grain yield compared to Ahmadi as check cultivar. Results of on-farm trials in farmers' field of Isfahan province under normal irrigation and irrigation cutting from pod setting stage showed that line L72 had 1.2 and 9.1% higher seed yield than Okapi as check cultivar, respectively. Therefore, due to desirable characteristics of line L72 such as higher seed yield and yield stability and relative tolerance to sclerotinia stem rot compared to Okapi as check cultivar, this line was released as Nafis and is recommended for cultivation in the cold and moderately cold regions of the country.

The phenomenon of genotype × environment interaction has important implications for selection of superior genotypes which remains as one of the main goals of crop breeding programs. To investigate the seed yield stability of promising spring rapeseed lines in four field stations in southern warm and dry and northern warm and humid agro-climatic zones of Iran. Sixteen open pollinated spring promising rapeseed lines were sown in randomized complete block design with three replications in two cropping cycles (2015-16 and 2016-17). Combined analysis of variance revealed that the effect of environment on seed yield was significant (P < 0.01). Genotype × environment interaction effect was also significant (P < 0.01) on seed yield. GGE biplot analysis identified four mega-environments; Gorgan (Line G8), Sari (Line G4), Sari-Zabol (Line G13) and Zabol (Line G7). Lines G4 (Asa), G8 (Roshana) and G13 (Aram) with average seed yield of 2714, 3349 and 3817 kg ha-1, respectively, had higher seed yield and yield stability. Line G4 had the highest seed yield stability. Line G11 (RGS003) with 2155 kg ha-1 was identified as low yielding with low seed yield stability. Generally, grouping of spring rapeseed lines based on genotype × environment interaction using GGE biplot analysis is a useful approach for selection and releasing of spring rapeseed cultivars with high seed yield potential and yield stability for target environments.

Sclerotinia sclerotiorum is the causal agent of white rot in aerial parts of a wide range of plants. The aim of this study was to compare the reaction of living tissue of Indian mustard leaves on the growth of this fungus under open and closed leaf stomata conditions.

The pure isolate of the fungus was prepared by the hyphal-tip method on water-agar medium. An experiment was conducted in a fully randomized design with four treatments. The formation of fungal growth inhibiting compounds in the leaf tissue of all treatments was examined using GC-MS.

Analysis of variance of the experimental data showed that the diameter of the fungal colony was significantly smaller in the treatment with open leaf stomata than in the other treatments. Gas chromatography data analysis showed that 1-propene-3-isothiocyanate as a volatile compound inhibits fungal growth in this treatment.

The production of the volatile allyl isothiocyanate compound in Indian mustard leaf inhibits the growth of S. sclerotiorum.

Release of early maturity and tolerant soybean cultivars to phythophtroa disease has a significant effect on development of cultivation and production of this crop in the temperate climate of the country, especially the temperate regions of Lorestan province, that have a good potential for producing soybean in the country. In order to generate and release early mature soybean cultivars, a corporative project conducted by Seed and Plant Improvement Institute (SPII) and Atomic Energy Organization of Iran in 1372 in which seeds of Clark var. were exposed with gama ray. The irradiated seeds were sown in field and were evaluated for the mutated agronomic traits for 4 successive generations and eventually 47 early mature mutants were selected. Finally, after evaluating the selected mutants in the preliminary and adaptability yield trials, M.7 mutant was found as a superior genotype based on its early maturity and desirable grain yield. This mutant with 110 day growth period was 15 day earlier than Clark variety and also with grain yield of 3300 Kgha-1, its yield was 500 Kgha-1 higher than early mature variety TMS. Complementary experiments showed that M.7 mutant is tolerant to water deficit conditions and resistant to root and stem rot disease caused by phythophtora soja. This mutant was released as Kousar by Cultivar Release Committee of Iran in 1394.

Dalgan cultivar has obtained from an exotic hybrid cultivar by modified pedigree method. For this purpose, selfing was done on hundreds of F2 population at the time of flowering. F3 seeds along other 17 populations in project with subject Production of canola spring high yielding lines from F2 populations were studied in Karaj, Dezful, Bushehr, Zabol and Hormozgan. Plants selection for reach to pure line by pedigree method was continued and in F7 generation were selected only three pure lines (SAN-12, 2 Behbahan and 3 Varamin). In preliminary yield comparison, SAN-12 was selected in terms of grain yield and earliness compared to control variety RGS003 along with several other lines. In evaluation of adaptation and performance potential of selected lines in four regions of southern warm climate, Dalgan variety (SAN-12) had first rank with yield of 2808 kg/ha. In terms of physiologic maturity, Dalgan variety (SAN-12) was 9 days earlier than the check varieties RGS003. The results of stability analysis by both methods ranking and Lin and Binns superior criteria showed Dalgan variety was high-yielding and stable. Results of on-farm design in two places of Zabol showed that Dalgan variety with mean 2462 kg/ha had highest grain yield. Result of on-farm project in regions of Zabol and Dalgan showed that line SAN-12 compared to RGS003 control had higher grain yield. So with regard to the favorite characteristics such as high yield potential, wide adaptability, earliness, relative tolerance to stem Sclerotinia disease, tolerance to lodging and oil good quality, line SAN-12 introduced to name Dalgan in 2014 year and have been recommended for cultivation in southern warm regions.

Sunflower hybrid cultivars which have been improved and released in Iran are categorized in two early and late maturity groups. Early mature hybrids are low yielding while late matures have problems of limitation in growing season, higher plant height and higher water requirement. So, there is a lack of mid-mature and dwarf hybrids in Iranian sunflower hybrids. New hybrid, Shams was improved by crossing between CMS line AF81-112 and restorer line RF81-82 using simultaneous selection method, self and back-crossing in offseason conditions. In the preliminary evaluation, this hybrid with seed yield equal toexotic hybrid Alstar, moderate maturity and dwarf height was identified as a promising hybrid. In regional experiments in Karaj, Khoy, Zanjan and Eslam Abad seed yield of Shams (4067 kg ha-1)was equal to the exotic hybrid Hysun33 while it was also earlier and shorter than other checks. In adaptability evaluations, its seed yield was equal to Hysun33 and also it was earlier and shorter than Azargol and Hysun33. Under on-farm trials Shams was superior to check varieties in Kermanshah, Mazandaran and west Azarbayjan provinces. This hybrid had a higher seed yield compared to Farrokh and Ghasem hybrids under drought stress condition. Shams and its restorer line were resistant against powdery mildew under greenhouse condition. Shams hybrid considered as a stable and superior hybrid with an average seed yield of 3.5 tons ha-1 had a similar seed yield to those of exotic hybrids, higher yield compared to early mature hybrids of Ghasem and Farrokh and also lower plant height, moderate maturity and suitable capitule shape compared to the late mature hybrid Azergol. This hybrid was released as a new sunflower cultivar for spring cultivation in the temperate and cold regions and for summer cultivation in the temperate regions of Iran in 2017.

Charcoal rot is one of important disease of soybeans. In this study, 130 different soybean genotypes were evaluated in a simple lattice design with two replications in 2014 and 2015 in Karaj, Iran. Grain yield and disease-related indices including lesion length, lesion length: plant length ratio, percentage of infected plants and number of microsclerota on stem were measured. The results showed that the lowest (1.11 percent) grain yield reduction was observed for genotype 45 whereas genotype 11 had the highest (60.96 percent) grain yield reduction. The results of this study also showed that genotypes 1, 3,4, 5, 10, 12, 20, 24, 30, 31, 32, 40, 41, 43, 45, 46, 50, 53, 54, 63, 64, 66, 74, 76, 77 and 115 were resistant with low percentage of grain yield reduction and were free of disease symptoms. Genotypes 6, 11, 13, 18, 25, 33, 35, 42, 55, 57, 58, 59, 62, 70, 72, 73, 78, 86, 93, 97, 109, 111, 113, 123, 124, 129 and 130 were identified as susceptible genotypes with high percentage of grain yield reduction and disease symptoms on stem. The correlation between percentage of grain yield reduction and lesion length (r = 0.62**) and percentage of infected plants (r = 0.53*) were positive and significant. The results of stepwise regression analysis showed that lesion length and percentage of infected plants could explain more than 61 percent of the variations observed in the performance of genotypes under disease stress conditions.

Sunflower rust is one of the most important diseases of the host in main cropping areas of Iran and resistance sources among the plant germplasm are accessible. Sunflower rust disease caused by Puccinia helianthi was reported first time at 1822 on collected samples from Eastern south areas of United States. It is considered as an important disease for sunflower cropping areas of South and North America, Argentina, Africa, India, China, and Australia and has been reported on the host worldwide. Incidence and severity of the disease on commercial hybrids had been increased up to early 1990s in Canada. Between 1988-89, the incidence on crop was reported up to 60 percent; whilst highly infected fields were appeared at the end of crop season. Puccinia helianthi has a worldwide distribution on sunflower and all species of Helianthus. There are also four other species which cause rust on cultivated and wild sunflowers. P. enceliae and P. masalis have been reported on wild sunflower and composites from southwest of United States. P. xanthi with a worldwide distribution on Xanthium Spp from Australia and Coleosporium helianthi from eastern areas of U.S. have been reported. Investigations reported some areas of Mazandaran and Golestan provinces showing infection including Behshahr, Kalaleh, Golidagh, Kalpoosh plain and Gonbad. Sunflower rust in Iran is considered as one of the important diseases which cause economic losses every few years. For instance, it caused 10 percent yield loss and 9.8 percent loss for oil yield. Genetic studies revealed that resistance is controlled by two dominant genes R1 and R2. By these identified genes, four physiological races of the pathogen became determinable. The presence of several resistant sunflower lines to rust with different origins reveals genetic variation for resistance to the disease. In this study, the variation of physiological races of sunflower rust was investigated to identify possible new races of the pathogen, Puccinia helianthi, and reaction of the host genotypes was also evaluated to the identified races.
Rust-infected leaf samples were collected from provinces Golestan and West Azarbayjan in 2010, and 8 isolates were inoculated on susceptible cultivar Record for physiological race identification purpose. Employing single pustule technique, the isolates were purified. The isolates after mass-production in separate chambers were inoculated on 9 standard differential lines. Inoculation and incubation methods were the same as for race identification procedure. The reaction of sunflower genotypes was evaluated by measuring pustule coverage percentage (PCP) according to computer-generated leaf diagrams depicting various percentages of leaf area covered with rust pustules. The interpreting resistance method proposed by Gulya and Masirevic (1995) was used in which three reaction patterns are defined as follows: immune (PCP= 0%), highly resistant (0.5%>PCP>0%) and susceptible (PCP.1%).
All collected isolates from the two main areas (i.e. Khoy and Golidagh) infected the non-resistant Perodovic cultivar indicating the pathogenicity of them. In addition, lines HA-335 and 803-1 were susceptible to all isolates. Lines RHA-265 and QHP1 demonstrated resistance to isolates collected from Golidagh, whereas the isolates of Khoy infected both lines. The results showed physiological differences between the main collection areas and presence of two dominant races. On the basis of pathogenicity similarities on common differential lines, races 302 and 300 were determined as dominant for Golidagh (Golestan) and Khoy (West Azarbayjan), respectively. Resistance evaluation of sunflower germplasm against rust disease was done under controlled greenhouse condition. The genotypes were tested by powdering the plants with mixture of the race's spore and Talc powder. The results demonstrated that 10 and 6 sunflower genotypes including hybrids Ghasem and Barzegar, their restorer lines and cultivar Gabor individuals were resistant against races 302 and 300, respectively.
Occurrence and distribution of physiological races of sunflower rust has importance in plant breeding research; as the process of breeding for resistant genotypes would be broken without considering the variation and distribution of the disease physiological races. In addition, genetic resistance to rust is controlled by dominant genes. Thus, access to new resistant sources in sunflower breeding is more likely. Among 23 lines and individuals of sunflower derived at the breeding processes, 16 resistant ones could help breeders to improve and release new hybrids or varieties containing resistance sources to the rust.

The contamination of canola seeds to various fungal agents is important like other crops and it is varied annually. Diseases like blackleg and sclerotinia stem rot are considered as the most important diseases in Iran. The possibility of their direct spread through seed contaminations and indirect spread through infected debris in seed masses will have danger of their development. For investigating canola seed contamination to fungal agents, seed samples were collected from seed parties of canola grown in cold areas including Alborz, Kermanshah and Markazi provinces. The surface of seeds were observed to differentiate and separate different abnormal appearances including wrinkle, presence of cracks, oozes, hyphal shape particles, and black spots. The presence of sclerotia of stem rots disease causal agent, and plant debris containing pycnidia of blackleg disease were checked in seed samples using stereo microscope. The identification of fungi on the seeds was done with and without surface disinfection processes. The plant debris in non-sieved seed samples did not have structures similar to pycnidia of blackleg disease. The results obtained demonstrated that the seed samples were contaminated to fungi including  Penicillium sp.,  Alternaria sp.,  Aspergillus sp., and  Rhizopus sp..

The soil samples containing the pathogen، Plasmopara halstedii، were collected، refreshed and mass-produced on susceptible cultivar Record، using whole seedling immersion method. The isolates were inoculated on standard differential lines to investigate the physiological races. Using the dominant race (race 100) of the pathogen in sunflower planting areas، 77 new Iranian sunflower genotypes including hybrids، restorer lines، CMS lines and individuals were evaluated against the disease under controlled conditions. Fifteen days post inoculation، the treated plants were evaluated based on six qualitative disease characteristics including damping-off، sporulation on cotyledons، sporulation on leaves and cotyledons، stunt، leaf mosaic or chlorosis and deformation. They were then converted to quantitative means based on their importance in disease development. Finally the average of the means as disease severity index (DSI) was used for evaluations. Based on the results، 64 genotypes were categorized as resistant and the rest were identified as moderately resistant، moderately susceptible، susceptible، and highly susceptible.

Blackleg disease of oilseed rape، caused by Leptosphaeria maculans، is one of the three most important diseases of the plant in Iran. It is also considered as one of the most important diseases of oilseed rape worldwide which causes serious yield losses. During 2010 the oilseed rape fields were surveyed at province Golestan and plant samples demonstrating suspected symptoms of the disease were collected. Isolation، purification and mass-production of the isolates were done at the Plant Pathology Unit of Oilnseeds Crops Research Department in Karaj. The the isolates were studied based on production of pigments in culture medium PDA. Employing representative isolate from Golestan province، 25 lines and cultivars of oilseed rape were tested against the disease. The well developed and expanded leaves of three- month- old plants were inoculated in central area with the pathogen inoculum، and the diameter of induced lessions was measured. Based on the results lines HW101، HW104، and SW104 demonstrated resistance against the disease.

Diseases of canola including stem white rot caused by Sclerotinia sclerotiorum and blackleg caused by Phoma lingam are considered as the most important diseases in Iran. Seed infections have their own importance and vary annually under different conditions. For this investigation، 26 canola fields located in three areas of Eastern (Kalaleh)، Central (Ali Abad)، and Western (Kord-Kouy) regions of Golestan Province were selected to study both diseases. At the cropping season، seed samples of every 10 plants demonstrating the diseases were collected separately and transferred to plant pathology laboratory. Seed weight and seed germination factors were measured for each samples even on non-infected samples. The colonies grown were studied employing fungal identification keys. The seed weight of samples infected to blackleg did not show considerable difference with the control samples whereas sclerotinia had decreased this factor totally. There were not sensible differences between treatments for seed germination. Fungi including Alternaria، Penicillium، Aspergillus، Rhizopus، and Sclerotinia were identified on seed samples in this experiments. The seeds of blackleg infected plants did not result in seed contamination and only one sample of Sclerotinia affected plants demonstrated the fungal colonies of the pathogen.

Sclerotinia stem rot (white stem rot), an important fungal disease, which is caused by Sclerotinia sclerotiorum, is one of the serious diseases of various plants such as canola. Use of resistant cultivars is an effective method to control the disease. A greenhouse experiment based on cotyledon inoculation using mycelial suspension of two different isolates of S. sclerotiorum was conducted to evaluate 12 canola cultivars (including seven spring type and five winter type) against the pathogen. The results demonstrated that response to S. sclerotiorum was significantly different among cultivars (P = 0.05). Interaction between isolates and cultivars was also significant (P = 0.05). Hyola 401 with the highest and Zarfam with the lowest infections, were the most susceptible and the most resistant cultivars, respectively. The results of this experiment showed that cotyledon test is a reliable and rapid method for screening canola cultivars against white stem rot fungus.

Sunflower downy mildew is one of the most important and destructive diseases of this crop in West-Azarbaijan. The disease causes epidemic damages and yield losses at favorite environmental conditions for the pathogen activity. Application of disease resistant cultivars is considered as one of the effective control methods. During the growing season of 2009 in West-Azarbaijan, infected sunflower plants were collected and used as a source of Plasmopara halstedii for inoculation of standard differential lines to identify the variation of pathogenicity. The resistance of seven open-pollinating cultivars and two hybrids of sunflower to the dominant race (race 100) of P. halstedii, was evaluated employing the whole seedling immersion (WSI) method in the greenhouse. In this investigation, nine macroscopic disease symptoms including damping-off, sporulation on cotyledons and leaves, sporulation on leaves, stunting, sporulation on cotyledons, mosaic on leaves, deformation of leaves, lesion on hypocotyls and root reduction on the inoculated plants were considered for disease rating and calculating the disease severity index (D.S.I). The experiment was conducted in three replications for each cultivar. The analysis of variance (ANOVA) was performed and the means were compared using Duncan multiple range test (P = 0.05) in SAS ver. 9.1 (SAS institute Inc., Cary, NC.). According to the analysis of variance (ANOVA) for disease severity index, cultivars and hybrids were classified into five significantly different groups (P< 0.05): resistant, moderately resistant, moderately susceptible, susceptible, and highly susceptible. Cultivars Lakumka and Master were in the same group as resistant cultivars, whereas Record was highly susceptible.

In the present study eight symptoms of Plasmopara halstedii (Farl) Berl and de Toni including damping-off, sporulation on cotyledons and true leaves, sporulation on cotyledons, stunting, leaf mosaic or chlorosis, deformation, hypocotyls lesions and root reduction on the inoculated plants were compared as disease infection characteristics for assessment of resistance and suceptibility of sunflower cultivars and hybrids. Three days-old seedlings were inoculated with spore suspension of P. halstedii using whole seedling immersion method (WSI). Reactions of cultivars were recorded 15 days later. A strong correlation between the above symptoms, and sporulation on cotyledons and true leaves (SCL) as the main infection characteristic of the disease was determined. The most suitable regressional model for resistance determination was calculated based on mosaic (M), stunting (S), hypocotyle lesjons (HL) and root reduction (RR) symptoms. Among other regressional models tested for resistance determination, another model with high R2 value was also determined using only mosaic symptom.