Plant Protection
Year:2010 | Volume:32 | Issue:2|Papers Count:8

Biological control of soil borne plant pathogens with antagonistic microorganism has been more attracting interest. Especially, Burkholderia strains have been intensively investigated as biological agents. The objective of this study was finding an effective biologica control agent against the canola damping off caused by Rhizoctonia solani. Rhizoctonia Damping-off is one of the most important diseases of this industrial oilseed. All strains were selected on plates by dual culture using plant pathogenic fungus. Two strains had antagotistic activity in pot test. According to morphological, biochemical and physiological tests, the isolate Bu1 wase indentified as Burkholderia cepacia. Among these Burkholderia strain, Bu1 showed the most antagonistic effect on canola damping off. Seed and soil treatment with the bacteria caused an average reduction in damping off and disease development, 56% and 62% respectively. Results of the biocontrol mechanism tests showed that isolate Bu1 produced antibiotic and volatile metabolite. The isolate was capable of producing sidrophore, protease enzyme and hydrogen cyanide. The strain was a strong colonizer of canola root and so increased plant growth.

The outbreak of sugarcane whitefly, Neomaskellia andropogonis Corbett has been recently recorded in sugarcane fields in Khuzestan province. The seasonal population dynamics of N. andropogonis was investigated in sugarcane fields (cultivar CP69-1062) in Amir kabir agro-industrial in Khuzestan during 2006-2007. One hectar field in the middle of a large field (25 hectar areas) was selected randomly and divided into three equal parts. Each part was a replication. In each part, ten stations were selected randomly and sampled each week. In each station, one sugarcane stalk was selected randomly and the number of eggs, nymphs, pupa, adults and percentage of parasitized pupae were recorded. In both years, the population of all developmental stages rises gradually from early August and continued until late November. The peak of egg population was in mid October (244±9.55 and 168±28.67 eggs per leaf in 2006 and 2007, respectively). Egg population decreased to zero in mid November and late November in 2006 and 2007, respectively. The Peak of nymphal population was observed in mid October (130±2.08 nymphs per leaf and early November (103±60.98 nymphs per leaf) in 2006 and 2007, respectively. Population of nymphal stage disappeared in mid November and late November in 2006 and 2007, respectively. The peak of pupal population was observed in early December (130±21.70 pupa per leaf) and late November (103±24.91 pupa per leaf) in 2006 and 2007, respectively and that of adult population occurred in mid October (35±0.54 adults per leaf) and early November (21±8.54 adults per leaf) in 2006 and 2007, respectively. The adult population decreased to zero in late November in both years. Percentage of pupal parasitism was 85%, 0% in 2006 and 2007 years, respectively.

Mark-Release-Recapture methods are used for delineating foraging territories of termite colonies and estimating their foraging populations. In this research, marking of termites was evaluated by the use of two ingested dyes: Nile Blue (NB) and Neutral Red (NR). In this experiment, filter paper circles were wetted with 1 ml of each dye at concentrations of 0.1%, 0.25% and 0.5% (treatments) and placed into Petri dishes(9.0 cm in diameter), each containing 50 workers (the final stage). In the control treatment, filter papers were moistened with 1 ml of distilled water. Each treatment had four replicates for each dye marker and was kept in a dark incubator (90±5% RH, 28±2oC) for one week. The changes in the weight of workers before and after marking were also compared and analyzed using SAS software and means were compared using LSD test. The mean comparison of NB treatments and NR treatments with control through survival, the percentage of stained workers (after Arcsin  transformation) and the change in the weight of workers showed that concentrations of 0.1% and 0.25% NB and concentrations 0.25% and 0.5% NR did not show significant differences with control. In order to determine the best concentration for fast marking, in the second experiment, marking was studied after 8h thirsty condition. The termites were stained in one day at concentrations of 0.1% NB and 0.5% NR. Therefore, it is recommended to use concentrations of 0.1% NB and 0.5% NR plus 8h thirsty condition for fast marking. Laboratory experiments and preliminary field studies indicated that dye markers can be used for investigation of M. diversus foraging behavior, determining number of colony, distinguishing nestmates in aggressive behavior experiments and examining the transfer of toxicants between test termites.

Fumigant toxicity of various doses of essential oils (185.2, 370.4, 555.5, 740.7, 925.4, 1111.1, and 1296.3 ml/l water) from five officinal plants, including rosemary (Rosmarinus officinalis), lavender (Lavandula vera), fennel (Foeniculum vulgare), tarragon (Artemisia dracunculus) and summer savory (Satureja hortensis) on two stored products pests, cowpea weevil (Callosobruchus maculatus) and red flour beetle (Tribolium castaneum) have been studied. The cowpea weevil was more susceptible than red flower beetle for all essential oils have been tested. The essential oil of rosemary showed the most fumigant toxicity among the tested plants so that mortality of cowpea weevil in treatment with the least dose of related essential oil reached 100% after 12 h. The mortality of red flower beetle was 5% at the same time; however, after 24 h it reached 30%. The essential oil of tarragon that showed the least fumigant toxicity caused 100% mortality in cowpea weevil after 18 h and 95% mortality in red flower beetle after 24 h. The mortality of cowpea weevil in treatments with high doses of essential oils from lavender, fennel and summer savory after 5, 18 and 18 h reached 100%, respectively. This time was 24 h for the red flower beetle, treated with mentioned treatments. The LT50 calculated for cowpea weevil and red flower beetle in treatment with lavender essential oil were 24.96 and 4.78, that of rosemary 30.14 and 11.73, of fennel 15.64 and 8.71, of tarragon 11.74 and 6.10 and essential oil of summer savor were 12.28 and 3.60 h, respectively.

In this research, population fluctuation of canola aphids and their natural enemies were investigated during 2007-2008. Random samples of 50 plants were taken twice a week. Mustard aphid (Lipaphis erysimi Kalt.), green peach aphid (Myzus persicae Sulzer) and cabbage aphid (Brevicoryne brassicae L.) were recorded on canola. However, the mustard aphid with relative frequency of 79% was dominant. The cabbage aphid and green peach aphid ranked second and third with relative frequencies of 12% and 9% respectively. The mustard aphid appeared in mid December, the green peach aphid in late December-early January and the cabbage aphid in mid February. The mustard aphid and green peach aphid peaked in middle of March and cabbage aphid peaked in late of March, then after their number decreased in late April. Predatory species Coccinella septempunctata L., Episyrphus balteatus De Geer and Chrysoperla carnea Stephens with the relative frequencies of 69%, 24% and 7% were collected on canola respectively. Coccinellids, syrphids and chrysopids peaked in middle of March, late of March and in middle of April, respectively. Prasitoid Diaeretiella rapae Mclntosh and two hyperparasitoids Pachyneuron aphidis Bouche and Aphidencyrtus aphidovorus Mayr were obtained from mummies. The highest percent of the parasitism was 32% in late March, early April and the average precent of parasitism was 13%.

The amount of nitrogen fertilizer is an effective factor on the growth, development as well as reproduction of phytophagous insects. To investigate the effect of nitrogen fertilization on green aphid, Schizaphis graminum, wheat considering as a significant host for aphid was treated with four nitrogen levels. Nitrogen fertilization treatments included zero (check) 50, 100, and 150% of recommended levels. Rearing containers were placed into environmental chamber (25±1oC, 70±10% RH, and 16:8 L:D photoperiod). The results showed that increase in nitrogen fertilization resulted in increase in the percentage of soluble nitrogen concentration in plants (%). The aphids feeding on plants receiving higher nitrogen fertilizer (150%) had longer reproduction period, maturity period as well as greater fecundity and longer longevity, although nitrogen fertilization had no effect pre-reproduction period and post-reprodution period. Intrinsic rate of increase of aphid was calculated on various treatments using Wyatt and White method. The intrinsic rate of increase in treatments of 0, 50, 100, 150% were determined as 0.246, 0.266, 0.263, and 0.267 (female/female/day), respectively. The results demonstrated that green aphids feeding on fertilized plants showed to have greater reproduction abilities of aphids comparing check treatment (%).

“Molecular farming” is the use of plants, and potentially animals, as the means to produce therapeutic and industrial valuable proteins using genetic engineering techniques. Firefly luciferase is one of the most important industrial enzymes which has various applications in biotechnology and molecular biology such as microbial contamination detection by ATP amount, preparation of cancer diagnosis kits, drug screening, biosensors, protein folding and protein-protein interaction examinations, pyrosequencing, etc. luc is also used as an ideal reporter gene in order to optimize gene transformation systems in genetic engineering. In this study, Iranian firefly Lampyris turkestanicus luciferase gene (luc) was cloned and introduced into tobacco plants. The gene was isolated by PCR and appropriate primers, designated according to luc termini, restriction sites and a plant highly expression sequence (Kozak sequence), and then cloned in pCAMBIA1304 vector, under the control of CaMV35S promoter and NOS terminator. The construct was confirmed by several methods: colony PCR, PCR, digestion, sequencing and BLAST analysis. The Agrobacterium–mediated transformation method was used to introduce luc into tobacco genome and putative transgenic plants were selected on the selective medium containing hygromycin and cefotaxim. Finally, transgenic plants were confirmed by PCR analysis on transgenic and control plants’ genomic DNA.

The seasonal abundance patterns of the wheat spike aphids were studied by weekly sampling of five winter wheat fields in Gorgan region in northern Iran during two growing seasons, 2006 and 2007. Spatial distribution of different developmental stages and morphs of the aphids were described by fitting data to Poisson (random) and negative binomial (clumped) distributions, as well as by calculating dispersion indices. A sequential sampling plan was also developed using the fixed-precision method of Green for estimating the density of adults, nymphs and total population. Sitobion avenae (F.) and Schizaphis graminum (Rondani) were two main species infesting wheat spikes in this region. The first aphid colonies appeared on spikes during early April and peaked (16.01±2.86 aphid per spike) during early May. Based on R2 and F of regression analysis, Taylor’s power law provided a more adequate description of variance/mean relationships than did Iwao’s patchiness regression model, and the b values ranged from 1.034 (alate adults) to 1.545 (apterus adults). Aphid population, especially nymphs and apterous females, was aggregated during most of the growing season and negative binomial models fitted data sets better than the Poisson series. However, alate morphs showed a noticeable tendency to the random distribution and 63.7 percent of their data sets fitted the Poisson distribution. Regarding sampling cost or required sample size, the developed fixed-precision sequential sampling plans showed an acceptable performance for estimating aphid density at the precision level of 0.25. Optimum sample size was flexible and depended upon the aphid density and desired level of precision, and ranged from 25 spikes in density of 16.01 aphids/spike to 268 spikes in 0.168 aphids/spike at the precision level of 0.25. The information presented in this study may be used in population management of aphids in wheat fields.