Applied Entomology and Phytopathology
Year:2004 | Volume:72 | Issue:1|Papers Count:14

Random amplified polymorphic DNA (RAPD) markers were used to assess the genetic diversity within and among VCGs of Fusarium oxysporum f. sp. betae in sugar beet fields of Khorasan, Iran. Nine pathogenic isolates from 9 different VCGs along with one pathogenic self-incompatible isolate were selected as representatives. RAPD reactions were performed on genomic DNA, extracted from mycelial mass using University of British Columbia (UBC) primers. Six primers amplified 117 scorable RAPD loci, of which 83 loci (71%) were polymorphic. RAPD profiles could genitically distinguish different VCGs from each other. Cluster analysis placed the self-incompatible isolate GL9 as an outgroup. Estimation of genetic distance or genetic similarity between isolates of each VCGs revealed a higher level of genetic relatedness within a VCG compared to that of among VCGs. The non-pathogenic isolate GL3 was placed with pathogenic isolates KR2 and N36 in the same cluster. However, cluster analysis showed that the isolates KR2 and N36 had by far closer relationship with each other than with isolate GL3. Results of cluster analysis also confirmed the correlation between VCGs and geographic origins of isolates.

Mango inflorescence midge, Erosomyia mangiferae Felt, is another new species of Cecidomyiidae which has been caused heavy damage to mango orchards of Hormozgan province in recent years. The insect biology and distribution, was studied by weekly sampling and use of sleeve cages during 1997-1998. It was collected from all mango orchards in Minab, Roodan and BandarAbbas. The mean percent of infested inflorescence were determined 59.25 and 67.5 in Minab and Roodan respectively. Mango inflorescence midge is only active during flowering season and spends other periods as pupa in soil. when inflorescences appear, the female midges lay their eggs on flower buds and scarcely on tender inflorescence axis. After hatching, the young larvae start theirs feeding, destroy the flower buds and also make small tunnel in branches. Infested flower buds become dark, dry and fall off, also due to secondary infestation by colletotrichum gloeosporioides, in exit route of mature larvae on branches, the damage will be increased and in heavy infestation, fruit setting completely inhibited. After full feeding, mature larvae leave the inflorescences and enter to the soil for pupation. In natural condition of Minab, embryonic, larval and pupal period were determined, 1-2, 6-13 and 6-8 days, respectively. Mango inflorescence midge produce 3-4 overlapping generations in flowering season (January-April) and each generation last about 20 days. The maximum population density was observed at the middle of February in Minab region.

In order to study the effects of weed control treatments on yield and yield components in dry bean under Broujerd region climate, an experiment was conducted in 2002 in randomized complete block design (RCBD) with 12 treatments and 4 replications. Treatments included Two Series: weed free and weed infested up to 14, 28, 42, 56, 70 day after emergence plus weed free check and weed infested check for growing season. This experiment was done using dry bean cultivar Derakhshan (K.R.D-29). Weed competition reduced physiological indices (LAI, TDM, CGR and RGR), morphological indices (pods/plant, seeds and stem height) and yield, but had no effect on 100 seed weight of dry bean. The results of different parameters have been shown and discussed.

Rhizoctonia solani-induced cotton seedling damping off is one of the most important diseases of cotton in Iran. Since the causal agent is a soil born fungus, chemical control is not always effective. In addition, widespread use of chemicals has resulted in pollution of the environment and appearance of resistant races of the pathogen. The need for the search of alternative methods to control this disease is therefore clearly obvious. Biological control could be a promising alternative method. In this study the possibility of biological control of the disease using bacterial antagonists was investigated. Fifty bacterial isolates, isolated from cotton and sugar beet field soil were first screened against R. solani in the laboratory using dual culture method. Seventeen isolates which showed more effectiveness were selected for further evaluation in the green house. In green house experiments the above-mentioned isolates were tested against pre- and post emergence damping off disease using seed coating and soil drench methods. Analysis of the results showed that 7 out of17 isolates reduced cotton seedling damping-off significantly (compared to the control). Of the above isolates 4 belonged to Bacillus spp. and the remaining 3 isolates were identified as Pseudomonas fluorescense based on bacteriological identification tests.

The root-knot nematode, Meloidogyne javanica., is one of the most serious pests of agricultural crops and causes considerable losses in tomato fields. Various management strategies are adopted to control this pathogen in infested fields. Application of nematicides being the most commonly used practice. Since nematicides causes pollution of under ground water, attention of scientists have been converted towards other safe and efficient alternatives. Among plants with nematicidal effect, neem has been found to have good control effects on root knot nematode. In this investigation, efficacy of neem oil at different concentrations viz., 0,5, 12.5, 25, 50,75 and 100 percent, and whole fruit, seed kernel and coat powder and cake at different ratios viz., 0, 10, 20 and 30 g/kg of soil against M. javanica was studied on artificial inoculation with 2000 J2 under controlled conditions. The results showed that root dip treatment for two hours resulted in reduction of galls and egg masses and the maximum reduction was observed at 100% concentration. Addition of 10 ml. of oil directly to artificially infested soil also resulted in reduction of population, egg masses and galls. Similar results were obtained by addition of neem powders and cake to the soil and maximum reduction was observed at 30 g of the powders per kg of soil. Kernel powder had the highest effect among the neem products studied in this investigation on the tested nematode.

In order to study of competitive ability of winter wheat genotypes against weeds, a three year trail was conducted as preliminary (1999) and complementary (2000-2001) experiments at weed research station of Plant Pests and Diseases Research Institute in Karaj. The preliminary experiment was carried out in randomized completed block design (RCBD) with four replications in a factorial arrangement of treatments. Treatments included twelve genotypes of wheat at two levels (weedy or weed free). The results of preliminary experiment showed that wheat genotypes 6618, M-75-13, M-75-15 were more competitive (MC) and Alamoot, Ghafghaz and M-75-5 were less competitive (LC) genotypes. Avena ludoviciana and Goldbachia laviegata were showed to be the dominant broad- and narrow-leaf weeds in the complementary experiment. The complementary experiment was conducted as a RCBD with four replications. Treatments included six wheat genotypes at three weedy levels (Goldbachia laviegata, Avena ludoviciana and weed free control). The results of complementary experiment indicated that using competitive index (CI), weed biomass and grain yield in pure and mixed stand. lines 6618 and M-75-5 were as MC and LC, respectively Results indicated that CI was a suitable index for determination of MC from LC wheat genotypes. The comparison of morphological and physiological characteristics of lines 6618 and M-75-15 can be used as an important criterion for determination of competitive ability of wheat against weeds in breeding programs.

In order to determine economic threshold of wild mustard competition in winter wheat, and to evaluate economic threshold response to wheat seed rate and nitrogen fertilizer, an additive series experiment was conducted during 2001-2002 at agricultural research station of mashhad university. The experiment included 3 factors: wheat seed rate (175, 215, and 255 kg/ha), nitrogen rate (150, and 225 kg N/ha), and wide range of wild mustard densities. Rectangular hyperbola equation was used to describe wheat yield losses. With increasing wheat seed rate from low to medium, and high level, the maximum yield loss due to high density of wild mustard, was reduced from 57.17 to 50.88, and 41.66, respectively. Increasing nitrogen rate over optimum rate of wheat, resulted in increased of percentage yield loss per unit wild mustard density as density approach zero and also maximum yield loss due to high density of wild mustard. Results showed that economic threshold was increased 116 % due to increase of wheat seed rate, and decreased 53 % follow by increasing of nitrogen over optimum rate of wheat.

Study on population of pod borers (Helicoverpa spp.) on expectation and spring planted chickpeas carried out for two years in Maragheh (region) and Kermanshah (region). Eight promising varieties of Kabuli and Desi types planted in RCBD (split plot) with three replications. Planting dates attvibutedt main-plots and varieties to sub-plots. The results showed that in Maragheh region because of the unconformity of pest biology and plant phenology, expectation planting scaped from the pest damage. Mean number of larvae and infestation of pod borers on spring planted plots was higher than expectation planted plots. Analysis of variance results for population of pod borers and infestation rate indicated that there is a significant difference between expectation and spring plantings. On the contrary in Kermanshah, population of density pod borers in expectation planting was more than spring planting but the yield of expectation planting was than spring planting. Therefore the utilization of resistant varieties in winter planting will be affective in sumage reduction.