نشریه تحقیقات بیماری های گیاهی
سال دوم شماره 3 (بهار 1393)

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.

In this research combined application of Pseudomonas fluorescens and Silicon against Fusarium oxysporum f. sp. lycopersici and induction of resistance in tomato against pathogen was studied. Effect of different concentrations of silicon (1-7 mM) on growth of F. oxysporum f. sp. lycopersici and P. flourescens was measured. The results showed that all concentrations of silicon had adverse effect on growth of P. fluorescens. Silicon upto 5mM concentration had no effect on the growth of F. oxysporum f. sp. lycopersici، but at concentrations of 6 and 7 mM، growth of the fungus was significantly affected compared with control. Due to the negative effect of silicon on growth of P. fluorescens، 3mM concentration of silicon was selected for greenhouse studies. Greenhouse experiments showed that treatment with P. fluorescens as soil application and silicon as aerial application had the greatest effect on reducing disease indexes and increasing plant growth. Also maximum activity of Phenyl Alanin Amonialyase occurred on the 5th day after combined applications of silicon (as aerial) and P. fluorescens (as soil drench). Use of silicon as an inducer of resistance and P. fluorescens as biocontrol agent and plant growth enhancer can be effective method for control of soil borne plant pathogens such as F. oxysporum f. sp. lycopersici

In order to study the reaction of 23 different advanced wheat cultivars and lines against major foliar diseases in Golestan province، including powdery mildew، brown rust and tan spot، an experiment was conducted in a randomized complete block design with three replications during winter of 2009. Infection was created naturally in the field by planting susceptible rows between the treatments. Evaluation of the treatments was done based on the intensity of different diseases (disease incidence، disease severity، area under disease progress curve (AUDPC) and standardized AUDPC، total seed weight and thousand kernel weight (TKW). Analysis of variance showed that treatments were statistically different (P≤0. 01) based on all recorded data. Results of multiple range test (LSD) showed that the highest and lowest severity of powdery mildew were observed in line 17 (72. 74%) and Gaspard (0%)، respectively. The highest and lowest severity of brown rust was observed in Bolani and Morocco (11. 11%) and Gaspard (0. 12%)، respectively. The highest and lowest severity of tan spot disease was recorded in Morvarid (94. 56%) and Morocco (0%)، respectively. The highest grain yields were recorded in line 11 (4340. 97g) and Morvarid (4013. 19g)، and lowest grain yields recorded in Bolani (184. 03g) and Morocco (250g). The highest and lowest TKW were observed in Cultivars Shiroudi (36. 33g) and Morocco (13. 53g)، respectively

Both the root-knot nematode (Meloidogyne javanica) and charcoal rot (Macrophomina phaseolina) are serious diseases of green bean farms، each of them can cause significant economic loss annually. Since the probability of simultaneous presence of these two disease agents is high، there is a need for assessing the damage of their interaction according to indigenous isolates as well as local environmental conditions. In this research the interaction of M. javanica and M. phaseolina in green beans cv. 418 Jamaran was studied under green house condition. The test was carried out in a completely randomized design with 6 treatments in 5 replicates. The treatments were control، fungus alone، nematode alone، fungus and nematode simultaneous application، first nematode two weeks later the fungus، and first fungus two weeks later nematode. The nematode inoculum was reared on tomato from asingle egg mass. The fungus inoculums were grown on a sterile medium comprised of sand and cornmeal. Seedlings were inoculated at two-leaf stage with 3 eggs and second stage juveniles (J2) of M. javanica per gram soil and/or with 2 g of fungal inoculum per pot. After seven weeks، plant growth parameter as well as its yield; nematode reproduction factor، number of galls، final nematode population; and fungal damage was evaluated in each treatment. The highest damage to green beans as well as the highest growth reduction was observed in simultaneous inoculation treatments. The least gall number and reproduction factor (Rf) was seen in the treatment that was inoculated with M. phaseolina prior to nematode while the highest gall number and Rf was seen in the treatment that was first inoculated with M. javanica. All treatments inoculated with nematodes had greater root weight than other treatments in the absence of nematodes. The least growth reduction was observed in treatments that were inoculated with one of the pathogens only. The results confirmed high susceptibility of green bean to simultaneous infection by these two pathogens.

Sugar beet is among the most important crops in Iran. One of the main causes of the decline in sugar beet production is root rot، damping off and leaf blight caused by R. solani (Kuhn). Unfortunately، chemical control method against soil-borne fungi especially R. solani in sugar beet is not very effective. In this study the control of R. solani by antagonistic aspects of P. oligandrum using six isolates were studied under various laboratory methods including microscopic investigation of the relation of hyphae between antagonist and pathogen، food competition، the effect of volatile compounds، the effects of extracellular fluid secretion in cultured and heat-stable antifungal metabolites. Microscopic observations showed that P. oligandrum hyphae upon contact with R. solani hyphae wrapped around them، caused protoplast shrinkage which resulted in detachment of the protoplast from the cell walls of R. solani، also oospore formed on the hyphae of R. solani. The results of dual culture tests howed that Torbat-e-jam and Mashhad isolates of P. oligandrum had the most food competition with R solani. In volatile compounds tests using 36 hrs-old colony of the antagonist، the isolate of Torbat-e-jam had maximum inhibitory effect (56. 41%) on R. solani in vitro. The extracellular fluids of isolate of Mashhad was %71. 31 percent more effective than the control and concentrations of 30%، 40% and 50% extracellular fluid of isolates from Torbat-e-jam had the most growth inhibition on R. solani mycelium in culture medium، However there was no significant difference among the mentioned concentrations. Evaluation of efficiency of P. oligandrum in inhibition of mycelial growth of R. solani in soil showed that the most inhibition of mycelium growth of R. solani (32%) was occurred when soil was solely inoculated with P. oligandrum. The heat-resistant extracellular fluids of isolate of Torbat-e-jam were %71. 36 percent more effective than the control in inhibiting the growth of R. solani.

In this study، sensitivity of different field crops to isolates of Rhizoctonia solani was studied in order to apply more successful crop rotation program in Kerman Province. Disease severity indices (DSI) were measured by grading scales of 0-5 in vitro and 1-9 in vivo conditions which were regarded as the basis of host susceptibility. The results of disease severity evaluations showed that maize and wheat with DSI of 1. 66 and 0. 58 in laboratory condition and 1. 46 and 2. 63 in greenhouse had the minimum sensitivities respectively. Sugar beet and safflower with severity indices 3/52 and 3/40 in laboratory condition and tomato and melon with 7/22 and 6/37 in greenhouse conditions were the most susceptible species to anastomosis groups 2، 3 and 4. Our results show that anastomosis group 4 had the highest while anastomosis group 3 had the lowest disease severity indices under the two conditions of laboratory and greenhouse. Disease severity indices were different among isolates belonging to same anastomosis groups، and within different anastomosis groups.