جستجوی مقالات مرتبط با کلیدواژه « رقم » در نشریات گروه « گیاهپزشکی »

 In this study, ninety- six isolates of Pyrenophora tritici-repentis from Ardabil province were collected and identified. According to the results of molecular data and considering the geographical area, thirty isolates were selected for race identification studies in greenhouse. Genetic diversity was detected between three fungal populations including Parsabad, Germi and Bilesavar in Ardabil province. During the study of gene diversity, the amount of gene flow (Nm) was equal to 1.6890 and the amount of Gst was equal to 0.2284. The rate of genetic diversity for the whole population (Ht) was 0.2993. PhiPT was estimated to be 0.259 (p> = 0.010). According to the results of AMOVA, 74% of total variance was attributed to within populations while only 26% of that was related to between populations. Race1 of the pathogen as the main race was used in Ardabil province to evaluate the resistance of forty wheat cultivars in greenhouses. Inoculation was carried out using fungal conidial suspensions and fungal culture filtrates. The Mean Disease Index in different cultivars was calculated and compared. The results of cultivars' reaction showed that 90% of studied wheat cultivars are in the susceptible group to the pathogen. Four cultivars of Morvarid, Moghan 3, Ehsan and Darya, which together comprise 10% of the studied cultivars, were included in the resistant group. The use of these resistant cultivars is recommended for areas with a high possibility of disease outbreaks. In addition, breeders can use the sources of resistance for future breeding programs.

The major disease of Persian walnut is walnut blight caused by the bacterium Xanthomonas arboricola pv. juglandis. This disease limits walnut production in many regions of the world in particular those with warm and humid springs. All succulent tissues including recent shoots, fruits and catkins may be attacked but their sensitivity decreases over time. Symptoms on leaves begin as small, water-soaked spot that can expand to form angular necrotic lesions surrounded by a yellow hallo. Infection on the hull of the unripe fruits is initiates as a dark spot, which rapidly creates dark sunken lesions. If fruit infection occurs before shell hardening, the kernels are usually destroyed, infection after shell hardening results in dark kernels and poor-quality nuts, while the kernel is until consumable. The main current strategy for walnut blight control is to protect succulent tissues by copper-based sprays from bud-burst. However, multiple copper sprays do not always control the disease and there is the risk of development of copper resistant bacterial strains. Cultivation of resistant cultivars is the most practical, environmental friendly and economical approach for controlling of this disease. So far, there have not been any cultivar completely resistant or immune to this disease. However, variation in susceptibility level has been shown to occur, worldwide. The objective of this study was to determine leaf and unripe fruit resistance of Iranian promising walnut genotypes in response to controlled inoculation with X. arboricola pv. juglandis in orchard and laboratory conditions.

In this research, the relative resistance of leaf and unripe fruits to bacterial blight were studied in a number of promising walnut genotypes replicated during two years of 2015 and 2016. The local genotypes have been selected through massive surveys of native orchards in different provinces of the country. The main selective criterion for walnut selection was late leafing trait. In addition, correlation between leaf blight and unripe fruit blight severities were studied. The material included H1-7, H2-1, SHK2, Vina, Round de montignac (RDM), Lara, G4, G5, B10 and K15 genotypes and cultivars. From this material, KZ3, 88-2, 88-1 and G3 were registered and released in year 2019. Also, Serr, Chandler and Hartley cvs. were used as controls. A mixture of four local bacterial isolates originated from Qazvin, Karaj, Zanjan and Urmie was used as inoculum. The bacterial strains have already been characterized using different phenotypical and molecular tests. They were cultured on Nutrient Agar (NA) plates at 28 ℃. After 72 hours of cultivation, the colonies were suspended in distilled water; the concentration of the suspensions was read by spectrophotometer and after equalization, mixed and used as inoculum. Assessing leaf resistance was performed by spraying one year old grafted seedlings in glasshouse condition and lesion area was recorded 21 days after inoculation. Three leaves (contacting leaflets) of three seedlings were used per genotype. Assessing unripe fruit resistance was achieved by inoculating 45 days old fruits in laboratory condition and lesion diameter data was read 15 days after inoculation. 15 fruits per genotype were used and three lesions were created in each fruit. Statistical analysis of data was performed by Duncan Multiple test range using SAS software.

Based on the results, leaf and unripe fruit blight severities were different among different cultivars and genotypes in both years of evaluation. Combined analysis of blight severity data indicated that G3 (Alvand) and 88-2 (Persian) genotypes had the most leaf blight severity and thus, rated as the most susceptible, while Hartley cultivar had the least leaf blight severity and thus, as the most resistant. Based on combined analysis of data, H1-1 and SHK2 genotypes had the most blight diameters of unripe fruits and thus rated as the most susceptible and resistant genotypes, respectively. Leaves of newly released cultivars of Persian, Caspian, Alvand and Chaldoran were rated as susceptible, relatively resistant, susceptible and relatively susceptible, respectively. On the other hand, unripe fruits of Persian, Caspian, Alvand and Chaldoran were classified as resistant, resistant, relatively resistant and susceptible, respectively. Mean leaf blight severities were not different between the two years of study and also there was no difference between unripe fruit severities between two years of the experiment. No significant correlation was found between leaf blight and unripe fruit blight severities.

Charcoal rot Macrophomina phaseolina is one of the most serious soil brone disease of melon with economic importance throughout the world. Due to the failure of crop rotation, clean seeds and chemical control, application of the resistance cultivars and varieties, regarding to their ability in infestation reduction and less tissue destruction would be efficient. This study was to study the reaction of 22 different varieties of melon in Varamin area, as one of the main source of melon production in Iran, under the greenhouse condition. The experiment was taken place with four replications under complete random block design. Feature examined were wet weight, dry weight and pathogenicity index which were monitored in one month. Results of the pathogenicity indices showed than four varities, Honey Dave, Tashkand, Isafahan and Hybrid Ananas T with the lowest infestation index (1-2.1) were recognized as resistant and three varieties of Haj Mashallahi, Samsouri Isfahan, Ananas Mina MN1 with the highest pathogenicity index (>4) were recognized as susceptible. The results of wet weight mean showed that both hajmashallahi and 7065 MA hybrid has the lowest (17.05 gr) and Ananas T Hybrid showed the highest (57.05 gr); for dry weight, Honey Pack hybrid has the highest (7.16 gr) and Daregaz Mashhad showed the lowest (1.99 gr) weight. The results revealed a highly significant difference among the cultuvars which would be a clue to use plant resistance as a key factor in melon charcoal rot management.

Safflower capsule fly, Acanthiophilus helianthi</em> is a serious pest on safflower, could reduce crop yield up to 25 %. To study the reaction of different safflower cultivars to safflower capsule fly in different planting dates, an experiment was conducted during three consecutive years (2006-2009) in split-split plot design with three replications, in Kaboutar-Abad research station (Isfahan, Iran). The main plot was spraying in two levels (sprayed and unsprayed), subplot was sowing date in 8 levels (from early March to late June) and sub-sub plot was cultivar in three levels (Arak, Soffe and Goldasht). Sampling was carried out in 5 times, according to the growth stages of safflower. In each sampling, percentage of infested heads, percentage of damaged seeds and number of larvae per head were counted. The results showed significant difference among planting dates for above three factors. The highest and lowest percentage of infested heads were recorded on late (late May to late June) and early planting dates (early March to early May), respectively. The highest and lowest number of larvae per head and the highest and lowest percentages of damaged seeds were observed on last planting date (late June) and early planting dates (early March to early April), respectively. Significant differences were found for the three factors among the studied cultivars. Goldasht cultivar had the highest percentage of infested head and percentage of damaged seeds. In order to control safflower capsule fly in the region, cultivation of Arak and Soffe cultivars in early planting dates (early March to early April) is recommended.

Common bean is cultivated for feeding in the whole world. The two-spotted spider mite, Tetranychus urticae Koch, and the onion thrips, Thrips tabaci Lindemann, are considered as the two important pests of bean and lots of pesticides are being used for their control. One of the most important strategies in integrated pest management programs is the cultural practice. In the present study the effects of cultivars and bean plant density has been taken into consideration to control these pests in a bean field in Boroujerd district, Lorestan province of Iran. This research was performed as per factorial in a completely randomized block design, with three cultivars (Akhtar, Derakhshan and 285) in five plant densities of 20, 30, 40, 50 and 60 plants per m2. Samplings were carried out weekly and in every sampling date, the number of each pest was recorded. Results showed that bean cultivars had significant impact on the number of eggs in spider mite and in total and 1st instar larval populations of onion thrips. The plant density also significantly affected populations of both the pests. Interactions between cultivar and plant density was not significant for both pests. Overall the highest and lowest population densities of the spider mite observed in the cultivar of Derakhshan with 60 plants density in every m2 and then cultivar of 258 with a density of 20 plants per m2 respectively. The lowest and highest total number of thrips was observed in Akhtar cultivar with 60 plants per m2 and then Akhtar cultivar with a density of 20 per m2, respectively. The results of the present study could be recommended in IPM program for bean fields.

Sugarcane whitefly, Neomaskellia andropogonis Corbett (Homoptera: Aleyrodidae) is one of the important pests of sugarcane fields in Iran. In this study, the efficacy of two new insecticides including Sivanto® and Oberon Speed® was evaluated for controlling different life stages of whitefly on IRC99-02 and CP69-1062 sugarcane varieties under laboratory conditions. The concentrations of 20, 60, 100, 200, and 400 ppm of two insecticides were applied using leaf dipping method. The highest concentration of Sivanto® (400 ppm) caused 67.9% mortality on whitefly eggs in IRC99-02 variety; while Oberon Speed® did not show much ovicidal activity. Sivanto® effectively controlled the adult’s stage and the highest mortality percentage (90%) was observed at 400 ppm in IRC99-02 variety of sugarcane. While at the same concentration, Oberon Speed® caused 60 and 70% mortality in IRC99-02 and CP69-1062 varieties, respectively. Both insecticides were effectively controlled whitefly nymphs and pupae. Our results indicated that both of the insecticides had high toxicity on sugarcane whitefly. Also, parasitoid wasps were compatible with the insecticides and applied insecticides did not negatively affect their parasitism activity.

Weed management is an important agronomic practice. It would be takes 40% of time of small holder farmers, if carried out by hand. Farmers have being interested in more comprehensive programs for weed management that reduce weed populations over time and the use of reduced herbicide doses in order to diminish their production costs. Integrated weed management takes advantages of various methods to suppress weeds in a more common and environmental natural way. Today, it is understood that chemical herbicides are not free of problem. So researchers are working on integrated weed management, which brings all possible methods to control weeds. The use of reduced herbicide doses will cost a fraction of full dose and make them even more affordable to poor farmers who have a limited amount of resources. Researches indicate that there is good potential to reduce the number of herbicide applications and utilize lower herbicide doses within competitive cropping systems. Crop competitiveness advantage is a great potential for weed suppression that provides reducing herbicide dose to avoid its environmental and economic suffers. Therefore, a field experiment was conducted to evaluate the effect of reduced dose of imazethapyr on weed control when two bean cultivars grown in pure stand and intercropping together.
The field experiment was conducted as split plot based on randomized complete block design at the Research Farm of University of Tehran located in Karaj during 2013–2014. Main plots were five doses of imazethapyr (0, 25, 50, 75 and 100 percent of the recommended dose) and sub-plots comprised pure stands and intercropping of two bean cultivars include: Akhtar (the growth habit is upright) and Goli (the growth habit is creeping). Also there is a plot as weed free (control). When the plants were at the third trifoliate stage, determined doses of imazethapyr were sprayed. Weed dry weight and bean yield were analyzed by nonlinear regression. In order to obtain the response curves to the doses of imazethapyr, data were fitted by SigmaPlot software (version 11) according to the standard dose-response equation:Where W is the dependent variable, ED50 is equivalent to a dose of herbicide that reduces weed dry matter by 50 percent and b is the curve slope where the trend is linear. The yield data were fitted using a three-parameter logistic equation:where a is maximum yield, x0 represents a dose of herbicide in which the yield reaches 50 percent and b is the slope of the curve.
The community of weeds in the field mostly consisted of three species; Amaranthus retroflexus, Chenopodium album and Solanum nigrum that all are summer annual weeds. The dose-response model well described the effect of doses of herbicide on weed dry weight. Results indicated that weed species response to herbicide doses differently in bean cultivars and their intercropping. Among dominant weeds, A. retroflexus was determined high sensitive to increasing doses. Bean cultivars were solely different in competition with weeds, as creeping cultivar i.e. Goli with more competitive ability (like: fast early growth and area coverage) was more successful in weed suppression. Herbicide application at reduced dose could also be efficient when we used 75 percent of the recommended dose because led to a yield more than 4000 kg/ha in pure stand of Goli. Pure stand of Akhtar and intercropping showed yields of 3617 and 3641 kg/ha, respectively at 75 percent of the recommended dose. Relative yield total (RYT) for doses of 75 and 100 percent of the recommended dose and weed free control were 0.95, 0.87 and 1.03, respectively.
The results of experiment showed that weed sensitivity to herbicide doses vary differently by species. So that, A. retroflexus dry weight was more affected than C. album and S. nigrum in response to reduced doses of imazethapyr. The application of 25 percent of the recommended dose of this herbicide reduced A. retroflexus dry weight more than 50 percent. It seems that if the dominant weed in a field was the A. retroflexus, the farmer could greatly reduce dose of imazethapyr. However, usually weed community of fields are consisted of several species, therefore, to use reduced herbicide doses, sensitivity of all species should be considered. Also, using bean cultivars that potentially have high competitive ability, it could be a good supplement in combination with reduced doses of herbicide. In this experiment, Goli cultivar presented more potential to combine with reduced doses of imazethapyr.

In this research, the reaction of 138 sugar beet half-sib families and their 11 parental populations to powdery mildew (Erysiphe betae Weltzien Vanha) was studied in a randomized complete block design with three replications at Motahari Research Station, Karaj, Iran in 2013. A linear scale of 0-9 was used for disease rating. On the basis of disease scoring conducted in 10th September, 22 genotypes with a score lower than 2.5 were found to be disease resistant. The families HSF-850, HSF-853, and HSF-848 with the disease score of 1, 1.2, and 1.3, respectively, were the most resistant families. Regression analysis showed that white sugar yield and sugar content were decreased by increasing the disease. Cluster analysis classified the initial populations as well as their half-sib families into 7 groups. Among these, most of the tolerant/resistant genotypes were clustered in the group 5 which could be used for resistance transfer. The cluster 2 included the genotypes HSF-584, HSF-582, HSF-557, HSF-551, HSF-866, HSF-844, HSF-670, HSF-556, HSF-628, HSF–610, HSF-564, HSF-685, HSF–619, HSF–664, and HSF-558 which were considered as families with optimum root yield, white sugar yield, white sugar content and sugar content. Therefore, these families could be used as pollinator parents to develop hybrid varieties or they can be exploited in the next cycle of family selection to develop new half-sib or full-sib families.

Rhizomania disease is one of the world's most important sugar beet diseases. The disease causal agent is Beet necrotic yellow vein virus. This disease is widespread. In this study, impact of rhizomania on sugar beet yield and qualitative characters consisting of root yield, sugar content, sugar yield, sugar extraction coefficient and amount of non-sugar impurities of root (sodium, potassium, and amino nitrogen) were investigated. For this purpose, 12 monogerm sugar beet cultivars including six commercial cultivars resistant to rhizomania, three tolerant cultivars, and three susceptible cultivars to the disease were planted in a randomized complete block design with three replicate in rhizomania non-infested and infested fields. This study was carried out in two years at Fars Agricultural and Natural Resource Research and Education Center (Zarqan). Results showed that rhizomania reduced the sugar yield by imposing a negative effect on root yield and sugar content. The average decrease in sugar yield in infected treatments, for commercial resistant, tolerant, and susceptible cultivars was 25, 54, and 90%, respectively. Under rhizomania infection conditions, sodium content of all cultivars increased, on average by 165%, but their amino nitrogen content showed an average with 43% reduction. The presence of rhizomania symptoms in resistant cultivars and yield reduction under infection conditions showed that Rz1 gene can not cause the full resistance to the disease.

The effect of simultaneous use of entomopathogenic fungus, Beauveria bassiana and different cultivars of wheat was investigated on Russian wheat aphid (RWA), Diuraphis noxia, under laboratory conditions (25 ± 1 °C, 85 % RH and a photoperiod of 16L: 8D). Thirty experimental units of each cultivar were prepared and each replicate was consisted of one first nymphal instar. The nymphs were produced by the adults infected with LC10 of the fungus on each cultivar. The number of nymphs produced by each treated aphid was daily recorded until death. The data were prepared and analyzed according to the two-sex life table using TWOSEX-MSChart software. In the current research, the lowest value of LC10 of the DEBI008 isolate was belonging to the Arg cultivar; however, there was no significant variation among different wheat cultivars on the RWA offspring. Also, the duration of nymphal instar, with exception of the first nymphal instar, had no significant difference between the control and fungal treatments. Only the Alvand cultivar caused to prolong the adult longevity gained from fungus-infected aphids compared to the Arg and Pishtaz cultivars. The results showed that the wheat cultivars influenced direct pathogenicity of the fungus on the RWA.

The ability of four bacterial strains include Pseudomonas fluorescens VUPF5, VUPF52 and Bacillus cereus IPRI95, Bacillus subtilis IPRI96 on increase of growth parameters of two cultivars of pistachio in presence and absence of Meloidogyne incognita was evaluated. The experiment was a factorial design in a complete randomized design with the three factors including cultivar (Badami and Sarakhs), disease (presence and absence of nematode) and probiotic bacteria (Pseudomonas fluorescens strains VUPF5, VUPF52, Bacillus cereus strain IPRI95, Bacillus subtilis strain IPRI96 and water) in three replications. All of measured parameters showed considerable increases following treatment with bacterial strains in both cultivars. However, this increase in Sarakhs cultivar was higher than Badami cultivar. The maximum increase in treated pistachio seedlings was recorded for shoot height by 75.1, 12.1, root height by 50.63, 29.6, fresh shoot weight by 115, 34, fresh root weight by 63, 31, dry shoot weight by 34.41, 18.52 and for dry root weight by 1, 17.1 percent in Sarakhs and Badami cultivars respectively as compared with control. The number of galls and number of egg masses four month after inoculation was significantly decreased by 49.7 and 30.5%, for cv. Sarakhs and 64.4 and 71%, for cv. Badami respectively as compared with nontreated seedlings.

The cotton shedder bug, Creontiades pallidus Ramber (Hemi.: Miridae) is one of the most important pests of cotton in Khorasan Razavi province, Iran. In recent years this insect had always been a main pest for cotton in east of Iran especially in Sabzevar region. To evaluate the damage caused by pest on different cultivars (Bakhtegan, Khordad, Sahel, Sepeed, Mehr and Varamin), an experiment was carried out at the Agricultural Research Station of Sabzevar during 2013-2014. Experiment was designed as randomized complete blocks with six treatments and four replications. In this study, ten constant plants in each plot were selected randomly and marked for sampling until the end of the project. On each count, the number of black spots due to feeding of C. pallidus on all bolls of each plant was counted and finally, the mean number of black spots on 10 plants were calculated. Samples were taken on 14 occasions from 14th July to 14th October 2013. Analysis variance showed a significant difference among the cultivars at the level of 1%. The mean comparison of cultivars treatments showed that the highest and lowest damage by C. pallidus were observed on the Varamin, Bakhtegan and Mehr cultivars, respectively.

Greenhouse whitefly, Trialeurodes vaporariorum (Westwood), is an important pest of greenhouse throughout the world that causes serious damage on agricultural products. In this research, some biological parameters of the pest were studied in four cucumber cultivars (Royal Sluis, Soltan, Negin and Vida) at two heights (60 and 90 cm) in a greenhouse at 19-26 °C and 80% ± 5 RH. The developmental time of all immature stages were 27.49 ± 0.34, 28.23 ± 0.3, 26.63 ± 0.24 and 27.44 ± 0.3 days, in all cultivars, respectively, but it was slightly longer at the height of 90 cm compared to 60 cm (28.65 ± 0.24 vs. 26.43 ± 0.14 days, respectively). The preimaginal mortality percent ranged from 4 to 7% in different treatments, although this difference was not significant. Female longevities were 27.9 ± 0.67, 21.35 ± 0.34, 26.71 ± 0.6 and 22 ± 0.46 days in the cultivars, respectively (P < 0.01). It was also averaged as 23.29 ± 0.4 and 26.4 ± 0.66 days at both heights. The number of eggs / female were 203.82 ± 4.89, 132.26 ± 3.57, 210.68 ± 5.31 and 162.79 ± 5.15 in different cultivars with an average of 167.66 ± 5.68 and 187.98 ± 4.75 in 90 and 60 cm (P < 0.01). The sex ratio showed no significance among the cultivars at all heights.

Bean anthracnose caused by Colletotrichum lindemuthianum (Sacc. and Magnus) Briosi and Cav., is one of the major diseases of common bean in relatively cool, wet cultivation areas of tropical and temperature regions. Crop losses can be severe or total, especially when susceptible cultivars are grown in a conductive environment for disease. In this study, first different fungal isolates were obtained from the west and north areas in Iran, purification and pathogenicity done on susceptible cultivar “Talash” with spore suspension with concentrations of 1-2 ×10 6 spores/ml on leaves in the greenhouse. Then the virulence of isolates conducted like pathogencity method on Talash cultivar. Disease severity index, 15 days after the spore spraying was rated using the method described by Van Schoonhoven and Pastor-Corrales. A total of 11 isolates C. lindemuthianum were obtained based on the results of sampling from different regions that had mostly high virulence, with different severity indices of the disease, ranging between 22.2 to 98. In reaction study of 40 bean cultivars or genotypes to causal agent in greenhouse conditions, six cultivars (Naaz, Pachebaghela- ragehghermez, Almas, Shekoofa, Daneshkadeh, Dorsa) and four genotypes (920040, 940040, 21676 and 31167) with infection degree less than 3 showed resistant “R” (25% of all varieties and genotypes) whereas eight genotypes or varieties showed moderately resistant reaction “MR” and the rest were considered as susceptible “S”.

An experiment was carried out in split plot design with 3 main plot (Planting dates of 11, 21 Nov. and 1 Dec.) and 4 sub plot (cultivars Hyola 401, Hyola 308, PF and Option) and 4 replications in Behbahan Agricultural Research Station during 2005-2007. The experiments were carried out in sprayed and non-sprayed parts. The infected stem length, contamination percentage and index, capsule number, seed number in capsule, 1000 seed weight and seed yield were measured in sprayed and non-sprayed parts and the means were compared with Duncan test. The results showed that the lowest contamination index (0.97 and 1) were observed in Hayol 401 in the first planting date in two years and highest of contamination index (6.26, 7.08, 6.39 and 4.14) were observed in the PF and Option cultivars in the third planting date in 2005 and 2006, respectively. The highest seed yield was observed in Hayol 401 (3726 Kg/hect.) in the first planting date in 2006 and the lowest seed yield was observed in PF and Option cultivars (1738 and 1855 Kg/hect., respectively) in the third planting date. The seed yield reduces evaluated about %12-20 in the first planting date and about %23-33 in the third planting date in all cultivars and non-sprayed parts. Therefore, using suitable planting date of 11 and 21 Nov. and Hyola 401, 308 cultivars, can prevent population pick and damage of aphids in the most sensitive growth stage of canola (flowering stage) and finally yield loss.

The early blight disease caused by Alternaria alternata and A. solani with dominancy of A. alternata is one of the important diseases in the potato growing areas of Iran causing economic losses every year. Experiments were conducted during 2008-2009 to study the interactions of potato varieties، irrigation and planting types on the incidence and the severity of disease in Freidan area، Isfahan province، in a split split plot design on a susceptible potato variety، Agria. The severity of the early blight disease was assessed in 6 classes of infections and/or scoring scales: 0، 10، 25، 50، 75 and 100 at two growth stages; before and after flowering. The infection severity percentages and scoring scale of the disease were determined. The results indicated that، almost all the three factors had a very highly significant effect on the incidence and the severity of the early blight disease. The tested varieties showed significantly different reactions to the disease where disease severity in varieties Marfona and Agria was 12. 99 and 28. 31%، respectively. Also، Sprinkler and tip irrigation with 14. 48 and 16. 59% disease severity were significantly different general irrigation (30. 21%). No significant effect was observed between planting types since disease severity was 20. 61 and 20. 71% in single row and double row planting، respectively. The interactions of variety × irrigation، planting types × irrigation، and year had significant effect in disease severity (25. 74، 5. 62 and 13. 53% respectively). The interactions of the above factors also showed a very highly significant effect. The average yield of Agria and Marfona was 24. 03 and 23. 13 t/ha، respectively. Our results indicated that the severity and development of disease was more in general irrigation than in sprinkler and tip irrigation. The results indicate that resistant varieties can significantly reduce disease development and severity. However، a single-row and double-row planting had no significant effect on disease reduction.

The pink root rot disease، Phoma terrestris (syn. Pyrenochaeta terrestris) causes considerable losses in onion production of Isfahan، Iran. In this study، the effect of a suitable crop rotation system on 441 onion fields in the two main onion growing areas، Baraan and Ghahderijan for the two dominant cultivars، Texas-Early-Grano and Yellow-Sweet-Spanish was evaluated during 2009-1010. The results indicated that، in the fields where onions were grown in rotation with cereals، the disease severity and infection percentage were the least in comparison with other rotation types. Also، the orchards that were recently converted into field crops showed only 2. 83 percent disease severity. Infection rate of onion in rotation with vegetables، alfalfa، and when onion was planted more than one time in the last four years was 17. 66، 27. 00 and 36. 16%، respectively. Between the cultivated varieties، Texas-Early-Grano showed less infection and disease severity (20. 5%) compared with Yellow-Sweet-Spanish (24. 78%).