Journal of Applied Research in Plant Protection
Year:2012 | Volume:1 | Issue:1|Papers Count:6

Macrophomina phaseolina, the causal agent of soybean charcoal rot is an important pathogen in soybean growing regions of the world, including Iran. Survival of M. phaseolina and associated mycobiota on soybean residual was studied every two months over a eight-month period, for two years, under environmental conditions of Golestan province, Iran. In the first year, root segments colonized by M. phaseolina were placed into polypropylene-mesh bags and buried in depths of 0-5, 10-15, and 20-25 cm at M. phaseolina infected and uninfected soil in the field microplots. The percentage of isolation frequencies for M. phaseolina showed a slow decrease linear trend over time, from 93.3% before burial to 73.6 %, eight months later. Trichoderma spp. were isolated at positive slow linear trend and was increased 6% over time. Isolation frequencies of M. phaseolina were similar among the three soil depths over all sampling dates at both soil types. In the second year, mesh bags, included M. phaseolina colonized residual, were buried in the field microplots at infected and sterile soil treated with Trichoderma harzianum MKR 1321 inoculum, in comparison to untreated one. Percentage of isolation frequencies for M. phaseolina decreased 77.5% over time in T. harzianum treated soil compared to 11.2% in untreated soil regardless of soil type. Isolation frequencies of Trichoderma spp. was also increased 93.9% in treated soil. The increase of Trichoderma spp. paralleled with the decreasing in isolation frequencies of M. phaseolina and other fungi. These findings suggest that the combined role of Trichoderma spp. as strong tissue degraders and mycoparasites may lead to reduce the survival of the pathogen M. phaseolina and other associated fungi in burial debris.

Sexual stage of Cercospora beticola has not yet been discovered; however, high levels of phenotypic and genetic diversity as well as resistance against fungicides have been reported in different populations of C. beticola. In present study, mating types of 70 Iranian isolates of C. beticola were determined using specific primer sets and formation of sexual reproduction cycle was evaluated under laboratory and greenhouse conditions. For this purpose, C. beticola isolates were recovered directly from sugar beet plants showing leaf spot disease symptoms in fields of Moghan region, Ardabil province. Pure cultures were established using a single spore technique and subsequently subjected to DNA extraction. Mating types were determined by a modification made in the already designed protocol using a multiplex PCR assay. Analysis of PCR products revealed a 400 bp amplicon specific only for Mat1-2 and an 800 bp amplicon specific for Mat1-1 isolates only. Six different methods were used to induce sexual structures by crossing opposite mating type strians under laboratory and greenhouse conditions. The results for the induction of sexual stage using different crossing protocols were unsuccessful. It seems that some unknown factors are involved in sexual induction or failure in other genes involved in sexual reproduction result in lack of sexual reproduction under field or controlled conditions.

Cucumber mosaic virus (CMV) belongs to the genus Cucumovirus in the family Bromoviridae. Althaea officinalis, commonly known as hollyhocks in the family Malvaceae, is an annual plant whose fruit, flower and root are used as medicinal products. In this study, five samples of hollyhocks leaves with viral symptoms were collected and CMV was detected using DAS-ELISA from the samples. Ta-alth isolate was selected and total RNA extracted. The PCR reaction was performed using CMV-CPF and CMV-CPR primer pair corresponding to the CP region of CMV and as a result, a 675 bp band was amplified. The amplified fragment inserted into pTZ57R/T and transformed into competent cells of E. coli strain DH5α. Extracted recombinant plasmid was analyzed by restriction analysis then sequencing. The GeneDoc was used to compare the generated CP sequence with the counterpart segment of previously reported CMV isolates from Iran and other parts of the world available in GenBank. A phylogenetic tree was generated with Neighbor-Joining (NJ) method in TREECON program which showed that the Ta-alth isolate belonged to subgroup IB of CMV. This is the first report of CMV from Althaea officinalis in Iran.

Trissolcus grandis (Thomson) is the most important egg parasitoid of sunn pest, Eurygaster integriceps Puton in Iran that easily reared on some other pentatomid eggs such as Graphosoma spp. both in laboratory and field conditions. In this study, two factitious hosts, G. lineatum (L.) and G. semipunctatum (F.) were compared in their effect on development and fecundity of T. grandis under three constant temperatures 23, 26 and 29 ± 1 oC, 50 ± 10% RH, and 16L: 8D h photoperiod. Thermal threshold of the wasp was estimated 17.11 and 16.82 ºC for males and females reared on G. semipunctatum, and 18.82 and 18.47 oC for those reared on G. lineatum, respectively. Moreover, thermal constant was obtained as 97.09, 109.89, 76.33 and 91.74 day-degrees for the same treatments, respectively. Titration total protein contents of the eggs in these hosts as well as target host, E. integriceps revealed that more than 99% of variations in thermal requirements of T. grandis among the hosts can be attributed to the protein content of eggs alone. Regression lines of developmental rate of the parasitoid met on temperature around 26.5 ºC that may imply this temperature provides the highest fitness for the parasitoid, as the effect of host disappears and no advantage remains among the hosts. In this temperature, the parasitoid develops by the same rate in all three hosts. The highest value of fecundity was revealed 109.4 ± 12.65 on G. semipunctatum and 91.9 ± 10.36 on G. lineatum that obtained at 26 and 29Co, respectively.

Effect of potassium bicarbonate in management powdery mildew of cucurbits was evaluated to obtain environmentally safe and sound method for prevention and control of the disease. The experiment was carried out in a randomized complete blocks design (RCB) with eight treatments and four replications under greenhouse conditions during 2009-2010. The treatments were different spraying programs of kresoximmethyl (Stroby WG 50%) from strobilorins, tetraconazole (Domark EC 10%) belongs to Triazoles, sulphur (Thiovit WG 80%) plus potassium bicarbonate (Kaliban SP 85%) as well as check treatment (without spraying). The results confirmed the possibility of using potassium bicarbonate at the concentration of 0.5 percent as a part of spraying program in controlling of powdery mildew disease of cucurbits in greenhouse condition. Also, alternate application of kresoximmethyl and tetraconazole and with seven day intervals reduced disease by 94.29 percent compared to the check. Two times spraying of bicarbonate potassium alternatively with tetraconazole and kresoxim methyl as 3rd and 4th or as 2nd and 4th sprayings reduced disease by 87.86 and 86.42 percent, respectively compared to no-spraying check. Three times spraying of bicarbonate potassium following kresoximmethyl or tetraconazole sprayings as 2nd, 3rd and 4th sprayings decreased disease by 75.71 and 74.29 percent, respectively as compared to no-spraying check.

Late blight, caused by Phytophthora infestans, is one of the most important diseases of potato in the world and Iran, especially in Golestan province. With regard to favorable weather conditions in the spring, high prevalence of the disease and hence extensive fungicides application can be observed in potato fields of Gorgan in Ordibehesht (mid April) of nearly every year. For prediction of the probability of the disease occurrence, recorded epidemics data in recent 10 years and weather data of the region were used. In order to modeling, 24 weather variables during six different periods (all the period of Farvardin (March-April), first 10 days, second 10 days, third 10 days, first 20 days and last 20 days of the month) were studied using logistic regression and discriminant analysis methods. After developing and comparing the statistical models, it was revealed that all the periods of Farvardin (March-April) is more suitable than other durations for modeling and four bivariate models were developed using the variables: total percipitation (P), number of rainy days (R), relative maximum temperature (Tax) and relative maximum RH (RHax) which showed total correctness value of 80-100% and coefficient of determination of 99.99%.