Plant Protection
Year:2012 | Volume:34 | Issue:2|Papers Count:16

Rhizoctonia disease of potato is one of the main causes of yield loss in this crop worldwide.In order to survey the importance of causal agent spread by seed tubers, 36 isolates of Rhizoctonia solani were obtained from stored seed tubers and infected subterranean potato plant in the main potato production areas of Hamedan and Kurdistan provinces in the west of Iran. The Examination of anastomosis groups and nuclear conditions showed that all isolates were multinucleate and belonged to AG-3. In pathogenicity tests of 23 selected isolates, over 95 percent were able to cause Rhizoctonia disease symptoms on potato sprouts in greenhouse. In molecular examinations, the genetic similarity of 10 selected isolates was surveyed through RAPD marker using 12 random primers. Results of band patterns revealed that collected isolates from different geographical areas were placed in one clued with 100 percent genetic similarity. Presence of high genetic similarity among isolates obtained from various geographical areas is an indication that the pathogen has distributed in these areas through sclerotia on infested potato seed tubers. Therefore, considering the importance of R. solani AG-3, as the main agent of potato Rhizoctonia disease in Hamedan and Kurdistan provinces and the long survival time of this fungus in soil, the transmission and planting of potato seed tubers covered with Rhizoctonia sclerotia to new fields need to be prevented.

Sugarcane mite, Oligonychus sacchari McGregor, is one of the most important pests of sugarcane plant in Khuzestan province, southwest of Iran. During a two-year study (2007-2008), the biology of the sugarcane mite, O. sacchari, was investigated on three commercial varieties Cp48-103, Cp57-614 and Cp69-1062 under laboratory conditions (temperature 30±1o C, RH% 60±5 and a photoperiod of 16: 8 (L: D) hours).The life table and population growth parameters were calculated by using Jack Knife method. The results showed that the intrinsinc rate of increase (rm), net reproductive rate (Ro), mean generation time (T), finite rate of increase (l) and the doubling time (DT) of sugarcane mite on Cp48-103 variety were 0.253, 22.02, 12.2 day, 1.3 and 2.73 day, respectively. These rates on Cp57-614 and Cp69-1062 varieties were 0.23, 9.7, 9.95 day, 1.3 and 3.03 day, 0.172, 8.25, 12.25 day, 1.2 and 4.02 day, respectively. The longevity of adult female sugarcane mite on three varieties Cp48- 103, Cp57-614 and Cp69-1062 were 14.7, 18 and 18.75 days, respectively. There was a significant difference between the longevity of adult female sugarcane mites. The total mean reproductive eggs of sugarcane mite on three varieties were 41.9, 20.1 and 16.45, respectively. Also, there was a significant difference between the total mean reproductive eggs of sugarcane mite.

Resistance of 16 sugar beet cultivars to Cercospora leaf spot was evaluated in Ghaemshahr region. The experiment was conducted in a complete block design with 6 replications, and, disease severity of cultivars was measured two times. Root yield of cultivars, as well as their disease severity, was compared with each other under natural Cercospora infection in Dezful area (winter crop). In Dezful, the experiment was carried out in complete block design with 4 replications. Reaction of sugar beet cultivars to Cercospora leaf spot was almost similar in Ghaemshahr and Dezful areas. The most resistant and susceptible cultivars to Cercospora leaf spot were Palma and 191, respectively. The cultivars Palma, Canaria, 4K21 and HI0152 produced highest sugar yield in Dezful area and showed highest resistance to the disease in the two regions. The lowest amount of sugar was produced by genotypes 191 and BR1. It seems that for introducing appropriate cultivars to the region, yield of the crop under stress condition should be considered as well as the resistance to the disease.

Two-spotted spider mite, Tetranychus urticae Koch. is one of the most harmful pest of common bean in most areas of Iran, including Lorestan province. The appropriate unit and universe sampling of mite population were investigated in common bean fields in Borujerd, Dorud and Azna in 2008. The results showed that samples should be taken from top, middle and bottom of the plant height. In addition, comparison of three sample units, 3 half leaves per plants (a half leaf from each plant height), 3 leaves per plants (a leaf from each plant height) and 6 leaves per plants (two leaves from each plant height) revealed that there was no significant difference between CV and RV of each female and nymph populations in related to CV, RV and RNP parameters. However, sample unit with 3 half leaves, with the highest amount of RNP, showed a significant difference compared with 3 and 6 leaves. Based on the findings of this research, sample unit with 3 half leaves (three half leaves of alternately left and right from three different plant height) is recommended in the sampling of T. urticae populations in common bean fields.

The Spherical mealybug (Nipaecoccus viridis Newsted) is one of the most harmful pest of citrus, oleander and mulberry in green space of Shiraz region. This study was carried out to detect the population dynamics of this pest and the role of biotic and abiotic factors on it in 2007-2008. The spherical mealybug, in both years, started its activity from early May on citrus and oleander trees, but the first sign of its infection on mulberry was detected in early August in most regions. The first population peak of mealybug occurred in the mid-June, though its population decreased in August because of high temperature, and increased under suitable weather condition when the second peak appeared in mid September. The negative effect of ants on natural enemies’ activity, especially during the egg-laying time, was determined. Among the abiotic factors, pruning and pesticide application through the mealybug activity period had the most influence on the pest population dynamics.

Arabis mosaic virus (ArMV) belongs to the plant virus genus Nepovirus in the family Secoviridae. ArMV is transmitted by several species of the nematode vector in genus Xiphinema, and has a very wide natural host range in crop plants and ornamentals. The objective of this study was to determine the distribution of ArMV in the vineyards and rose plantations in Western and Eastern Azarbaijan provinces of Iran. To achieve this aim, a total number of 1043 samples, including 251 rose and 792 grapevine leaves, were collected randomly from the gardens in several districts of Western and Eastern Azarbaijan provinces during the years 2008 to 2009. Using Dot-immunobinding assay and Double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), all samples were tested for the presence of ArMV. Results showed that ArMV was distributed through the rose plantations and vineyards of East Azarbaijan with the relative incidence rate of 30.3% and 46.6%, respectively, and 30.2% and 42% in rose and grapevine of West Azarbaijan province, respectively. Using specific primers for the coat protein gene of ArMV, extracted RNA samples were tested for the presence of ArMV by RT-PCR method. DNA fragments of 440bp and 519bp were amplified from the serological positive ArMV samples. To our knowledge, this appears to be the first precise study on the ArMV distribution through the different rose plantations and vineyards in several districts of West and East Azarbaijan provinces of Iran.

Hippodamia variegate (Goeze) (Coleoptera: Coccinellidae) is one of the most prominent Coccinellid predator of common pistachio psylla, in pistachio orchards. The experiment was performed under laboratory conditions i.e.27±1oC 55±5 rh and 16: 8 L: D. A cohort with about one hundred eggs- less than 24h old- was chosen and put in Petri dishes.Ladybeetle larvae were daily fed with pistachio psylla. Fifteen, 24h old, pairs of adult beetles were selected and their daily fertility and longevity were recorded. Daily fertility, immature developmental time and mortality were analyzed based on Jacknife method using SPSS statistical software. The results indicated that intrinsic rate of increase (rm) and the finite rate of increase were 0.14 (female/female/day) and 1.16 (days), respectively. The doubling time and mean generation time were 4.7and 28.88, respectively. Also, the net fecundity and net fertility rates were 71.19 and 58.9, respectively.

The impairment of the reproductive performance of pesticide resistant individuals in pesticide-free environment is the result of fitness costs associated with pesticide resistance, which is often determined by resource allocation from a basic physiological process to the protection against pesticides, favoring survival at the expense of reproduction. In this study, the fecundity life table parameters of abamectin-resistant and susceptible populations of Tetranychus urticae Koch were studied under laboratory conditions at 24±2oC, 70±10 R.H. and 16: 8 (L: D). In all experiments, reproductive fitness parameters were measured for each population on the Vigna ungiculata (L.) leaves. Standard error of life table parameters was calculated using the Jackknife method.Results showed that susceptible population exhibited significantly higher intrinsic rate of natural increase (rm), finite rate of increase ( l) and net reproductive rate (Ro) than resistant population. No significant difference occurred in mean generation time (T) between the susceptible and resistant populations, but doubling time (DT) of resistant population was higher than that in susceptible one. Results of present study suggest that the resistant population may be less fit than susceptible compartment.