نشریه تحقیقات بیماری های گیاهی
سال دوم شماره 4 (تابستان 1393)

Pseudomonas syringae pv. syringae (Pss) is one of the most important pathogens، which infects over than 180 hosts and annually causes significant loss in various plants throughout the world. To investigate the genetic features of the bacterium، 58 isolates from different hosts including pome fruits، grains، stone fruits، some weeds and ornamental plants in Fars، Kohgiluyeh and Boyer Ahmad، Char Mahal-o-Bakhtiari and Isfahan provinces، were selected and evaluated، by ERIC and REP primers. Using these primers، 250-1500 bp DNA fragments were amplified. Analysis of ERIC-PCR fingerprint showed that five clusters exist within Pss strains، but any host preferences، were not visible. This result showed that using ERIC-PCR، we cannot differentiate various isolates of Pss from different hosts. In REP-PCR analysis Pss strains used in this study were divided into the five clusters. Although these isolates were distributed in several clusters، some host specialization could be seen in this heterogenous pathovar. Thus it seems that REP primer is a suitable molecular tool for discrimination of Pss strains which are isolated from different hosts. Cluster analysis of rep-PCR demonstrated that this method is reliable for showing host preference within Pss strains.

Peronospora destructor is casual agent of onion downy mildew disease and is one of the most destructive diseases in humid and cool regions. The different ways to control this disease include fungicide application، change of planting date and use of resistant cultivar. This study was done in improved population of Behbahan onion in order to evaluate the effects of planting date and distance between and in rows on the disease incidence with the aim of nonchemical control of the disease. This study was conducted in factorial experiment as randomized complete block design with 36 treatments and 4 replications in Behbahan Agricultural Research Station. Four planting times (to produce seedling) including 6 Sep، 21 Sep، 6 Oct and 21 Oct were considered as main plots and 3 planting distances; 20، 30 and 40 cm between rows and 5، 7. 5 and 10 cm between plants on rows as sub plots. The results showed that there was significant difference between planting time (P<1%) and between planting spaces (P<5%). The disease severity was reduced to (18. 19%) incase of the planting date test (21 Oct.). The Disease severity was 18. 19% and 72. 71% in 40 cm and 20 cm spacing between rows respectively. Also disease severity was 70. 42% and 64. 48% in 5 cm and 10 cm spacing between plants on rows respectively.

Recently، plant pathogen’s biocontrol is a priority considering hazards and environmental threats of chemical pesticides. Using plant materials as antimicrobes has typically attracted many attentions. The aim of current study was evaluation of plant materials obtained from purple coneflower against Pectobacterium caratovorum subsp. caratovorum the casual agent of potato soft rot. Aqueous، acetone، methanol، ethanol and HCl extracts of coneflower root، stem، leaf and flower were obtained byrotary set while flower essential oils were extracted using Clevenger apparatus. The antimicrobial activity of coneflower extracts and essential oil was evaluated in laboratory with disc diffusion and minimal inhibitory and bactericidal concentration methods. The bacterium was more sensitive to flower essential oil than extracts. Root extracts were more inhibitory compared with other organs’ extracts. Also، aqueous and acetone extracts had very limited antibacterial activities on studied bacterium. Leaf extract possessed more growth inhibitor characteristic rather than bactericide traits. Regarding the results، plant materials obtained from coneflower could be a potent candidate against potato soft rot bacterium and might be considered as a promising biocontrol agent in the future.

Fusarium wilt in common bean by Fusarium oxysporum f. sp. phaseoli occurs worldwide and can result in severe yield loss. Cultural methods are not completely effective to reduce disease loss، therefore are recommended genotypes with genetic resistance. In order to identify resistant genotypes an experiment was carried out by using a randomized completely design with three replicates and 12 treatments (common bean genotypes). Plants were root-dip inoculated with suspension of spores and held in a greenhouse at 25-30° C. Severity of symptoms on plants were measured basis on a scale of 1 to 9 to evaluate of phenotypic resistance four weeks after inoculation. The results showed that Naz، Sayad، WA and Sadri genotypes were resistant، Jegari، Akhtar and E9 moderately susceptible and Khomein، Capsoli، Aej، Shokofa and Talash susceptible. It also indicated that SCAR marker (SU20) was associated with resistance in some of genotypes but not all and among the genotypes evaluated، PCR amplification with primers SU20 produced a single DNA fragment of approximately 750 bp in Naz، Sayad، Sadri، Akhtar، E9 and WA genotypes، while Khomein، Capsoli، Aej، Shokofa، Jegari،and Talash did not.

This research was performed to determine the host range of tomato isolates of Phytophthora capsici، among other common crops in Fars province. Seeds of tomato، squash، cucumber، melon، pepper، watermelon، pea، french bean، onion، carrot، corn، cantaloupe، eggplant، and wheat were sown in sterilized soil and kept in a greenhouse. Seedlings were inoculated by adding 50 ml of a zoospore suspension (1×105 spores per ml) of Ph. capsici onto the soil surface around the stem of each plant in the pot. Plants were kept in a growth chamber. Disease incidence was measured three times at 5، 10، 15 days post inoculation. Twelve of the tested plant species became infected with Ph. capsici and developed symptoms including crown and root rot، and yellowing، which led to plant death after two weeks. Ph. capsici was re-isolated from all symptomatic plants. Tomato، squash، cucumber، melon، pepper، watermelon، cantaloupe and eggplant were the most susceptible، while، pea، french bean، onion، carrot and sugar beet were less susceptible to the pathogen. Wheat and corn did not show any disease symptoms and were considered as non-hosts. The results of this study showed that common Poaceae crops in Fars province are non-host to Ph. capsici and can be used in crop rotation for disease management.

Aflatoxins are very toxic secondary metabolites of some، Aspergilluss sp. that are produced when these fungi grow on different agricultural products under special environmental circumstances. In this study aflatoxinsB1، B2، G1 and G2 in some species of Aspergillus were investigated. These fungi included A. terreus، A. ustus، A. candidus، A. carneus، A. ostianus، A. auricomus، A. niveus، A. niger، A. fumigates، A. parasiticus، A. caespitosus، A. awamori and A. sclerotiorumthat were grown in potato dextrose broth (PDB) and aflatoxins thereof were measured using high performance liquid chromatography (HPLC) methods. Pure cultures of the aspergilli were prepared and identified to species، and then each species was cultured for 22 days in 50 ml flask containing PDB at 26 0C، 80% humidity and in darkness، conditions similar to natural habitat. Fungal exudates in the broth cultures were extracted with 10 ml chloroform، the organic solvent was evaporated and the precipitate was dissolved in 3ml methanol. After filtration through 0. 2 µm milipore filter، the final solute was injected into HPLC instrument. Maximum amount of aflatoxins was secreted by A. parasiticus while aflatoxin G1 was not produced in A. terreus، A. carneus، A. fumigatus، A. niveus، A. parasiticus، A. caespitosus، A. ostianus and A. niger. As well، A. niveus، A. ostianus، A. niger and A. sclerotiorum did not produce aflatoxin G2. No aflatoxin B2 was detected in A. sclerotiorum and A. carneus and no aflatoxin B1 was detected in A. ostianus. Among the four type of aflatoxins (B1، B2، G1 and G2)، B1 and G1 had respectively the maximum and minimum amount of secreted aflatoxins in A. parasiticus.