Plant Protection
Year:2013 | Volume:36 | Issue:1|Papers Count:7

The cyst nematode Globodera rostochiensis is one of the most important causal agents of disease on potato in Hamadan province which reduces crop yield every year. In this study, the biological control of the nematode by the fluorescent pseudomonads isolated from potato rhizosphere was investigated. Infested soils were collected from potato fields and the cysts were isolated. The nematode second juvenile stage was obtained by cyst exposure to potato root extract (variety Marfona) collected from excess water following plant watering. From potato healthy soil, 108 Pseudomonas strains were isolated by serial dilution method on King's B medium. In a randomized design by three replicates, the effects of bacterial strain filtrate culture on nematode larva mortality were evaluated. Results indicated significant differences among the strains antagonistic activity. The upper score was obtained for Pseudomonas strain SN20 by 69.96% nematode mortality and the lowest score for Pseudomonas strain SN22 by 54.28% mortality. A total of five pseudomonas strains were selected for further investigation under green-house conditions in a complete block design by three replicates based on the results of the laboratory experiment. Significant differences among the strains 1 % level were observed and Pseudomonas strains SN17 and SN20 showed the highest effect with 42.47% disease severity reduction. Plant length was increased 55.10% by the Pseudomonas strain SN20. Characterization of the phenotypic features of the strains revealed their belonging to Pseudomonas fluorescens and P. putida.

Danaus chrysippus L. (Lep.: Nymphalidae) is the most important pest on Calotropis procera Aiton in Bushehr-Iran. The larvae make the main damage by feeding on leaves and shrubs. The purpose of this project was the study of bioecology and larval population fluctuation of D.chrysippus, carried out between 2006 and 2007 in Saadabad area in Bushehr-Iran. The sampling was carried out weekly by a two stage cluster sampling method in nature. For the biology studies, the eggs were collected from the nature and were developed in petri dishes and 10×12 plastic dishes from egg to adult under laboratory conditions at 25±2oC and 22±2oC, %60±10 RH and 16/8 LD. The results showed that the first adults emerged and gradually laid eggs in February 2006. The peak of larval population was observed in 2nd and 3rd weeks in March then reduced gradually. The egg laying was observed in the first week of April. The larval population peaks were in the middle of April, the 2nd and 3rd weeks of May, the last week of June and in July. During the summer and the winter of 2007, no forms of this butterfly was observed in Saadabad. The total period from egg to adult was 37.08±0.5 and 26.07±0.8 days at 22°C and 25°C respectively, in laboratory conditions. This butterfly had 5 generations a year. The generations overlap was observed. In the summer, the butterfly migrated to Bushehr mountains near the Fars province. In the winter, D.chrysippus migrated to coastal lines near the Hormozgan province.

Induction of systemic resistance to cucumber against marginal leaf blight disease caused by Pseudomonas marginalis using silicon application (as 1 & 2 mM of sodium silicate) was studied under greenhouse conditions. Results indicated that application of 2 mM of sodium silicate remarkably increased resistance in cucumber against the pathogen. According to the results, disease severity in plants treated with 2mM sodium silicate was reduced to 62% comparied to the control plants. One of the systemic resistance induction mechanisms by sodium silicate is stimulating the production of pathogenesis related proteins in plants which are indicator of systemic acquired resistance (SAR). We assayed the activity of chitinase and b- 1, 4 glucanase enzymes for induced resistance in plants treated with 1 and 2 Mm sodium silicate in 0, 24, 48 and 96h after inoculation by P. marginalis. Results showed that the highest activity of chitinase and b- 1, 4 glucanase enzymes were scored 96 h after treating plants with sodium silicate. b- 1, 4 glucanase activity was 0.025 U/mg proteinand chitinase activity was 0.0085 U/mg protein. These results suggested the importance of the chemical elicitor role for induction of systemic resistance to cucumber against P. marginalis.

Environmental friendly pesticides with a natural origin can be used as an alternative to chemicals in plant pests control programs. From this perspective, the extract of Ginkgo biloba L. plant is important. In this study which was conducted in 2010, the ethereal extract of exocarp and kernel of G. biloba seed was analyzed using a Gas Chromatograph Mass Spectroscope. The components included ginkgolide A, Band C, bilobalide, catechin, compferol, bilobtine, quercetin and isoginkgotine. Ginkgolide A, with an abundance of 28.7 and 18.7 percent in the kernel and exocarp, respectively, was the prevalent metabolitye among the components. Catechin was only observed in the exocarp extract while quercetin was only found in the kernel extract. The repellent effects of extracts on Tetranychus urticae Koch was tested using a Y-tube olfactometer, which is an enclosed bioassay to resolve responses to test and control volatiles. Both extracts showed significant repellency for the pest, and there were no statistical differences between the extracts. The significance of this similarity is the possible utilization of waste products from drug facilities to produce compounds with repellent effects.

Ustilago hordei (Pres) Lagerh is a fungus that causes covered smut of barley. This disease reduces yield and is a limiting factor in barley fields of Iran. One hundred forty four isolates of U. hordei were collected from 36 regions of Khuzestan province during 2009 and the genetic diversity of 100 isolates was evaluated by molecular markers. Four out of 14 primers were selected on the basis of successful amplification, reproducibility and production of DNA polymorphic bands. Four RAPD primers amplified 71 loci of which 63 were polymorphic. The maximum and minimum polymorphisms were obtained by OPA04 (19 Loci) and OPA10 (11 Loci), respectively. The highest PIC value was 0.33 (OPAI8) but OPA03 and OPA10 primers had the lowest amount (0.29). Two primers, OPA04 and OPAI8, showed highest MI and can be used for studying genetic diversity of U. hordei throughout the country. Cluster analysis of banding patterns from all four primers placed isolates into 46 fingerprint groups using UPGMA and Jaccard's coefficient. This is the first study on genetic diversity of U. hordei using molecular marker.

The species of Larinus spp. feed on developing achiness of flowerhead of plants in the family Asteraceae and cause decrease in seed production of these plants. In this study, the life cycle parameters of the weevil Larinus affinis Fremuth on Echinops aucheri Boiss were studied in Kerman under natural conditions during 2010 and 2011. This weevil overwintered as adults under ground litter. The females inserted their eggs into the flowerhead of weed, usually one egg laid per flowerhead. The larvae feed on developing achiness of flowerhead and caused an average 95.6% decrease in seeds production in infested flowerheads. Overwintered females lived up 45.9±3.8 to 48.6±0.7 days. The mean of fecundity was 40.3±4.9 to 60.6±10.8 eggs per female. The eggs were hatched 6±0.3 to 8.3±0.3 days after being laid. Development of larvae and pupa required 51.4±0.4 to 53.6±0.5 days and 6.7±0.3 to 7.6±0.2 days, respectively. This weevil had one generation per year on the flowerhead of E. aucheri. The L. affinis larvae feed on developing achiness of flowerhead of E. aucheri and can be useful in prevention of reproduction of this weed in Kerman.

In order to identify antagonistic fungi of citrus nematode (Tylenchulus semipenetrans) in the east of Guilan and west of Mazandaran, soil and root samples were collected from infested orchards. Juveniles, eggs and females were extracted from soil and roots. To isolate the antagonistic fungi, suspensions of eggs and juveniles were cultured separately on water agar media containing streptomycin. Hyphale growing from nematodes and eggs or female fragments were purified on W.A. and were transfered to PDA plates for identification. The fungi identified were Paecilomyces lilacinus, Fusarium oxysporum, Acremonium strictum, Fusarium solani and Cladosporium cladosporioides. These fungi were evaluated in vitro for their parasitism of eggs and their effects on egg hatch and juvenile mortality. Results showed that all isolates of fungi parasitized Tylenchulus semipenetrans eggs, inhibited egg hatch and killed juveniles. Among them, Paecilomyces lilacinus and Acremonium strictum were the most efficient and parasitized 79.11 and 70.66 % of eggs 5 days after inoculation, respectively. The highest percentage of second- stage juvenile (j2) morality (48.33%) was observed in samples treated with Acremonium strictum .