نشریه گیاه پزشکی کاربردی
سال پنجم شماره 1 (پیاپی 17، خرداد 1395)

Cucumber (Cucumis sativus) is one of the important commercial products in Iran and the world rich in fiber and vitamin with high nutritional value. It is continuously attacked by soil-borne pathogens that are not only cause significant economic damage to crop yield, but also reduce quality and marketable of product. One of the most important and destructive soil-borne diseases of cucumber, damping off and root rot and crown caused by Phytophthora drechsleri Tuker. In this study, isolates of three species of biocontrol fungus Trichoderma were evaluated in laboratory and greenhouse conditions. The antagonistic isolates of three species were including Trichoderma harzianum (isolates Th3, Th5, Th6, Th7, Th9), T. longibrachiatum (isolate Tl2) and T. atroviride (isolates Ta1 ,Ta4, Ta8, Ta10) respectively. Dual culture tests were carried out in a completely randomized design with 11 treatments in three replications. Th6 Isolate, with 89.3% in dual culture showed the highest inhibitory effect on the. Hyphae twisting of different isolates of Trichoderma spp. were not observed in contact with Phytophthora but Trichoderma hyphae grown in parallel with Phytophthora hyphae and form Appresorium and Haustarium. Based on the results of this research, the most successful isolates for antagonist activity against P. drechsleri Tuker were Th6, Th5, Th3 and Ta1. These four isolates were selected for greenhouse studies. In greenhouse, tests of soil treatment and seed contaminated with the spore suspension of Trichoderma isolates for evaluating the biocontrol isolates in a completely randomized design with 10 treatments and three replications were conducted. Results showed that the isolates were able to control the disease in different levels. In seed treatment, Th6 and Ta1 isolates with 91.75 and 83.5 percent and afterwards, Th3 and Th5 isolates were more effective in reducing disease in first taking notes after soil treatment respectively. In seed treatment, Th6 and Ta1 isolates were more successful than other isolates and in inoculated treatments with the isolates and Phytophthora, seed germination percentage were recorded as 83.34 and 100 % respectively. In general, the seed treatment was more effective in reducing disease in comparison with soil treatment. Isolates were also effective in increasing plant growth and however, Ta1 and Th6 isolates significantly increased plant weight and height.

Functional response is considered as one of the most important predator-prey interactions which affected by different factors including host plant characteristics. The effect of leaf surface on functional response of Stethorus gilvifrons Mulsant in larval and adult stages to Tetranychus urticae Koch were studied on three hybrids of cucumber leaves. The results demonstrated that leaf surface of host plants, different prey densities and their interactions affect on the numbers of prey killed by a predator. Logistic regression indicated type III functional response for larvae on all hybrids and adult females on Fadia and Sulan hybrids and males on Fadia and Sina leaves. The results of handling time and attack rate emphasize on the importance of physical traits of plant on the performance and searching efficiency of natural enemies that should be considered for optimizing their application in mite biological control.

Bacillus thuringiensis (Bt) is a Gram-positive, sporulate, soil-borne, aerobic and rod-shape bacteria which is the most important microbial control agent for agricultural pests such as Lepidoptera, Coleoptera and Diptera. Effective control of these pests is based on finding and applying the native isolates of each country or region. The first step as the basic for research on Bt, is isolation of native strains and keeping of them as a gene bank of this bacteria. In this research, 24 samples of forest soils in different regions of Golestan province were screened using the method of selective Sodium acetate and 60 numbers isolates of obtained Bt. Initial soil samples were cultured on LBA medium culture and the initial selection of colonies were performed based on morphological shapes of Bt colonies on medium culture and final selection based on microscopical identification of their crystal proteins. In microscopical study, the most of isolates were formed bipyramidal (56/6 %). Then, Bioassay of these native strains on the third age of Helicoverpa armiger larvae was studied. The results of Bioassay evaluation showed that these isolates have significant toxicity effect on these larvae and showed about 55-80 percent mortality. Generally, the results of this research showed that the forest soils are a suitable source for finding effective isolates of Bacillus thuringiensis.

The problems caused by pesticides to human health make necessary to use other control methods of low-risk including pest biological control methods against pests. Deraeocoris lutescens (Schilling) predatory bug has a privileged position in biological control of pests particularly sucking pest. In this research, breeding and feeding rate of predator age in various growth steps and in different temperatures were investigated. Tests were done growth chamber with temperature 25±1°C, 60 ± 5 percent relative humidity, and light conditions (16: 8) (L: D) on bean leaves. In examining the last instars’ nymphs and adult nutrition of nymphs of green peach aphid predator, predators of nymphs 1-2 days were more used than to 3-4 days. In this research, total nutrition average of predator age showed significant increase of green peach aphid with temperature increased from 18 to 30°C. In addition, the maximum and minimum food preference was shown on 3-4 days age of bean aphid and green peach aphid, respectively. Therefore, according to the obtained results, D. lutescens age of a promising predator is in combined pest management plans.

Cucumber is one of the most important crops cultivated in greenhouses and field in Iran. Melon is one of members of Cucurbitaceae family and it has a large sweet fruit. Pseudomonas syringae is a bacterial plant pathogen that causes necrosis in aerial parts of the plants. As isolated P. syringae pv. lachrymans and P. viridiflava have been isolated from cucurbits in Iran and other bacteria not reported as pathogenic bacteria. Whereas agent of blister spot and leaf necrosis of cucumber andnot detected from Iran specially in Mazandaran. In this study, the cause of blisters and necrotic leaf spots cucumbers and melons after isolation from infected plants was identified by using morphological and molecular methods in Mazandaran. Based on the results of molecular tests and sequencing of the rpoB gene sequence, our bacterial agent was similar to about P. straminea, with 99 percent similarity. The results of this study showed the studied bacterium belongs to P. Straminea, and based on rpoB gene sequence closest species to it, was P. mendocina.

Streptomyces are a group of wild-type bacteria and generally saprophytic, more than 400 species have been described and few species are pathogenic. These bacteria exist in many natural environments and antibiotic production is one of the most prominent properties. Few species have parasitic relation with animals and plants, including potato common scab disease. In this research, soil samples were gathered from fields and gardens of Lavasan region at depths of 10-30 cm. After drying and sieving, samples were diluted and cultured in casein-glycerin-agar (CGA). After a week, spored colonies with characteristics of Streptomyces were selected and transferred to the new media. The isolates were classified into three main groups based on phenytoin characteristics including color and form of spore, colony color and melanin production, consumption of hydrocarbons and antibiotic production in culture media. Some strains of each group were identified using 16sRNA sequencing and their phylogeny was investigated. In totally, 38 strains were isolated from 20 soil samples. The results showed that the strains belonged to S. kanamyceticus, S. violascens, S. akiyoshiensis and S. ambofaciens, with a similarity of more than 99%.