Plant Protection
Year:2018 | Volume:40 | Issue:4 |Papers Count:10

Heavy agricultural use of fertilizers and pesticides has caused tremendous harm to the environment as well as human population. In order to conserve food and environmental safety and avoid pesticide resistant pests, application of alternative methods in integrated pest management (IPM) is needed. IPM is a combination of crop protection practices to keep pests below economic threshold, and one of them is use of resistant host plant. Different factors such as application of fertilizers and pesticides, irrigation and creating optimum conditions for host plant can affect its resistance to pests and diseases. To analyze the effects of foliar spray of phosphorus and potassium on the induction of systemic resistance to the host plant againstTetranychus urticae Koch, three Fosfalim-K concentrations (1=sub-optimal, 10=optimal and 30=supra-optimal ml L-1) and control were sprayed on zucchini and life table parameters of T. urticae were studied in the laboratory conditions. Foliar treatments were applied three times. The raw data were analyzed based on the age-stage, two-sex life table theory. The intrinsic rate of increase (r), the finite rate (l), the net reproduction rate (R 0) and the mean generation time (T) of T. urticae on control were 0.166d-1, 1.18d-1, 10.72 offspring and 14.17d respectively. The systemic induced resistance by Fosfalim-K is expressed in significantly decreased the values of mentioned parameters in the mites fed on plants sprayed with optimal and supra-optimal concentrations (0.111d-1, 1.11d-1, 4.92 offspring, 14.2d and 0.111d-1, 1.11d-1, 3.73 offspring, 11.75d respectively). The age-stage life expectancy and reproductive value were also calculated.

Plant disease can cause quality and quantity reduction of agriculture crops. In some countries, farmers spend considerable time to consult with plant pathologists, as time is an important factor to control disease; so it seems necessary to offer a fast, cheap and accurate method to detect plant diseases. Since the fungal diseasesnamed ‘Powdery Mildew’ and ‘Anthracnose’ cause the greatest amount of damage in cucumber produced in greenhouses, thus in this research the two mentioned fungal diseases detection and classification were studied using image processing and neural networks techniques. Image processing include four main steps: 1) Image acquisition 2) preprocessing 3) extraction of the best color parameters of HSV and L* a* b* color spaces in order to classify and extract defected areas of the leaf and 4) extraction of textural properties of defected areas of cucumber leaf using co-occurrence matrix. Since, two factors of accuracy and time are important in detection and classification of plant disease, thus artificial neural networks (ANN) with back propagation algorithm (BP) and Levenberg-Marquardt (LM) training function were selected as the best model that was able to successfully detect and classify the mentioned plant diseases in 6 seconds with 99.96% accuracy.

Ladybirds as principle predators of aphids, scales, psylles, mites and egg of pests are an important group to study on polymorphism.H. variegata ladybird is known as polymorphic species. In this research, polymorphism of this coccinellid in two different weather conditions of Shahrood and Bastam regions was determined. Sampling was carried out weekly in spring and summer in 2015. The samples were collected from different plants such as fruit trees, ornamental trees, cereal and cucurbit fields by net and white-tray. Having been transferred to the laboratory, the semples were placed in vials with ethanol 75%. Identification was conducted based on general morphological characters as well as of male genitalia. Different morphs were identified based on morphological characteristics including body size, color, pattern and spots numbers on dorsal surface of the elytra and pronotum.26 morphs with great variation in patterns were identified in H. variegata which were didvided into five groups. The morphs No.2 and No.22 had the highest frequency among the other morphs. Results showed that ferquency and diversity of morphs in Bastam were higher than those in Shahrood. Identification of morphs of H. variegata was carried out in the Shahrood and Bastam regions for the first time and could be effective for further research in relation to better use of this coccinellid in biological control programs.

The rice brown spot disease caused byBipolaris spp., is one of the most important diseases in Iran and in the world. In this research, 135 fungal isolates were isolated from 256 collected samples in Guilan province fields. Identification was made based on morphological characteristics of fungi. According to the results, the fungal isolates belonged to: Bipolaris oryzae, Bipolaris victoriae, Alternaria tenuissima, Alternaria infectoria, Alternaria citri, Alternaria alternata, Alternaria franseriae and Alternaria pellucida. The pathogenicity test revealed that all isolates of B. victoriae were pathogenic. In the laboratory, we used various methods such as dual culture, inhibition of B. victoriae growth by culture filtrate, dual culture of the studied antagonistic fungi and B. victoriae by slide culture method and effect of volatile metabolites on inhibition of growth of this fungus. Based on the results, A. pellucida, A. alternata, A. franseriae, A. tenuissima, A. infectoria and A. citri had the highest percentage of mycelial growth inhibition of B. victoriae, respectively. In greenhouse studies, these fungi were inoculated on rice. All of the isolates, except A. tenuissima, effectively reduced disease rating of B. victoriae, and A. pellucida with 38.76% reduction in disease rating was the most effective antagonist in greenhouse studies. The results showed that there are avirulent isolates of Alternaria spp. that can be introduced as potential antagonists to control brown spot disease of rice.

The fruit flies and cucurbit weevil are the most important pests of melon which can reduce the quantity and quality of the fruits. Several different synthetic insecticides have been used to control melon fruit pests. To reduce the use of chemical insecticides, application of non-chemical methods was tested in melon farms in Semnan region in 2014. Fruit cover with paper and cloth net, kaolin clay (SepidanÒ WP 95%, 50000 ppm), mixture of kaolin (50000 ppm) and sulfur (WDG 80%, 10000 ppm), mixture of kaolin (50000 ppm) and azadirachtin (NimarinÒ EC 15%, 2500 ppm), and dimethoate insecticide (RoxionÒ EC 40%, 1500 ppm) were sprayed over the whole canopy of melon. Based on the field studies, fruit covering and kaolin application deterred oviposition and reduced the fruit pest's damage. The percentages of oviposition deterrence for fruit flies and cucurbit weevil were 93.43, 78.19 for fruit cover with cloth net treatment and 83.49 and 38.19 for mixture of kaolin and sulfur treatment, respectively. The percentages of damage reduction for melon fruit pests were 11, 14, 22, 25 and 86 in cloth net cover, paper cover, mixture of kaolin and sulfur, kaolin and control treatments, respectively. Also, the results showed that fruit weight increased in the kaolin treatments. Therefore, application of fruit covers and mineral compounds such as kaolin and sulfur could be used successfully to reduce fruit pests’ oviposition and their damage on melon.

Bean yellow mosaic virus (BYMV), a member of genusPotyvirus, causes economic losses to several crop species due to its wide host range. During 2012-2014 growing seasons, a BYMV isolate causing mosaic and leaf distortion was detected in sunflower fields of Isfahan province (Iran), tentatively designated as BYSun. Virions of BYSun were purified using two cycles of differential centrifugation on 20% and 30% sucrose cushions. Yields were 15-20 mg per 100g of infected leaves. SDS-PAGE of purified virus preparations revealed a single protein band with MW of about 33.5 kDa for BYSun. Antiserum against BYSun was prepared by five subcutaneous injections of purified viruses into rabbits at weekly intervals. Indirect ELISA indicated that the immunoglobulin obtained had the best results in dilution 1/2500. A 680 bp DNA fragment, corresponding to the partial CI (cylindrical inclusion) region of the viral genome was amplified using potyvirus-specific degenerate primers (CIRev/CIFor) by RT-PCR. BLAST search showed that the most similar sequence in the databases was that of BYMV-S. Phylogenetic analysis of this part of the genome in different BYMV isolates sequences revealed six distinct groups including General, Lupin, Broad bean, W, Pea and S which correlated with original natural isolation hosts. BYSun and BYMV-S were grouped apart from other isolates, so they were placed within a distinct group called “S”.

Yellowing diseases of field and greenhouse-grown cucurbits caused by whitefly-transmitted viruses are increasingly becoming important and cause economic losses in many cucurbits growing areas of the world. Using resistant cultivar is the best approach for plant virus control. To identify potential sources of resistance to an Iranian CYSDV isolate, (Bushehr isolate), fifty one accessions ofCucumis sativus, were evaluated under greenhouse conditions. Cucumber plants were inoculated at first true leaf-stage with viruliferous Bemisia tabaci. Three parameters were used to evaluate the reaction of cucumber accessions to CYSDV, including mean of disease severity index (10 weeks after the inoculation), time of symptoms development and virus accumulation in plant (mean ELISA value 8 weeks after inoculation). Although most accessions showed typical yellowing symptoms induced by CYSDV, the severity of symptoms, virus accumulation (absorption in ELISA) and the time of symptoms development were significantly different between cucumber accessions. Two accessions namely TN-94-229 and TN-94-206 showed delay in symptom development, low disease severity index and low concentration of the virus. They were therefore considered relatively resistant to the CYSDV.