فصلنامه گیاه پزشکی
سال چهلم شماره 4 (زمستان 1396)

Heavy agricultural use of fertilizers and pesticides has caused tremendous harm to the environment as well affects human population. For concerning about food and environmental safety and avoiding 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, one of them is resistant host plant. Different factors such as application of fertilizers and pesticides, irrigation and creating optimum conditions for host plant can affect its resistance. Data from previous studies have indicated that foliar sprays of phosphate and potassium salts can induce systemic protection against foliar pathogens. To analyze the effect of foliar spray of phosphorus and potassium on induction of systemic resistance to the host plant against two-spotted spider mite its development and reproductive rate was studied on zucchini sprayed with three Fosfalim-K concentrations (1=sub-optimal, 10=optimal and 30=supra-optimal ml L-1) and control 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 of Chi and Liu. The intrinsic rate of increase (r), the finite rate (λ), the net reproduction rate (R0) 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 r, λ, R0 and T values in mites fed on plants sprayed with optimal and supra-optimal concentrations. The age-stage life expectancy and reproductive value also were calculated.

Plant disease can cause quality and quantity reduction of agriculture crops. In some countries farmers spend considerable time to consult with plant pathologists, whereas time is an important factor to control disease, so it seems to offer a fast, cheap and accurate method to detect plant diseases. Since the fungal disease named ‘Powdery Mildew’ and ‘Anthracnose’ cause the greatest amount of damage in cucumber produced in greenhouses, thus in this research the mentioned two fungal disease detection and classification were studied using image processing and neural networks technique. Image processing steps includes 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 area of the leaf and 4) extraction of textural properties of defected area 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 was selected as the best model that was able to successfully detect and classify 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. vareigata ladybird was introduced as polymorphic species. In this research, polymorphism of this coccinellid in two differents weather conditions of Shahrood and Bastam regions was determined. Samplying was carried weekly in spring and summer in 1394 year. Samples were collected from different plants such as fruit ornamental and forest trees, farms, brushwood and patch. Samples were collected by net-trap and white-tray. After transferring to the laboratory, they were placed in glass with alcohol 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 of pattern. was identified of H. vareigata in which. placed in 5 groups. 2 and 22 morphs had the highest abundance among the other morphs. result showed that abundance and diversity of morphs was higher in Bastam than those in ShahroodIdentification of morphs of H. variegata is carried in the Shahrood and Bastam regions for the first time and could be effect for next researches in relation to better usage of this coccinellid in biologic control programs.

The rice brown spot disease caused by Bipolaris spp., is one of the most important diseases in Iran and world. In this research, 135 fungal isolates were isolated from 256 collected samples in Guilan province fields. The base of identification was 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 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 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 reduce the quantity and quality of the product. Several different synthetic insecticides have been used to control melon fruit pests by farmers. To reduce the use of chemical insecticides, application of non-chemical methods were tested in the melon farms in Semnan region in 2014. Fruit cover with paper and cloth net, kaolin clay (Sepidan® WP 95%, 50000 ppm), mixture of kaolin (50000 ppm) and sulfur (WDG 80%, 10000 ppm), mixture of kaolin (50000 ppm) and azadirachtin (Nimarin® EC 15%, 2500 ppm), and dimethoate insecticide (Roxion® 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 percentage of oviposition deterrence for fruit flies and cucurbit weevil, were 93.4, 78.2 for fruit cover with cloth net treatment and 83.5 and 38.2 for mixture of kaolin and sulfur treatment, respectively. The percentage 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 show that the fruit weight was 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 pest oviposition and its damage on melon.

Bean yellow mosaic virus (BYMV) is a member of genus Potyvirus within the large and economically important family Potyviridae. During 2010-2012 growing seasons, a BYMV isolate 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. SDS-PAGE of purified virus preparations revealed a single protein band with MW of about 33.5 kDa for BYSun. The prepared antiserum against BYSun reacted specifically with infected but not with healthy broad bean sap in serological tests. A 680 bp DNA fragment, corresponding to the partial CI (cylindrical inclusion) region of the viral genome of four selected isolates, was amplified using CIRev/CIFor primers able to detect members of the family Potyviridae. BLAST search showed that the most similar sequence in the databases was that of BYMV-S. Nucleotide sequence identities of BYSun whole genome to those of other BYMV isolates ranged from 75 to 98%. The deduced amino acid sequence of BYSun polyprotein was 85-99% identical to other isolates of BYMV. Phylogenetic analysis of most parts of the genome (especially CP) of different BYMV isolates sequences revealed eight distinct groups including General, Lupin, Monocot, Broad bean, W, Pea, Canna and S. These groups correlated with original natural isolation hosts. BYSun and BYMV-S grouped apart from other isolates, so it was placed within a distinct group called “S”. BYSun is the first isolate of BYMV with fully sequenced genome in Iran.

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 of Cucumis 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, However, 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 relative resistant to the CYSDV.