فهرست مطالب نیلوفر معاون

Russian knapweed (Acroptilon repens) is an invasive weed with high competition ability and one of the most important problematic weeds in the world. In order to evaluate Fusarium oxysporum and Alternaria alternata isolated from Russian knapweed for biological control of this weed and determine the best concentration of spore suspension and the effect of dew periods, two experiments were carried out during 2011-2012, using completely randomized designs with 4 replications. To determine the best concentration of spore suspension, Different concentrations of spore suspension (104, 105, 106, 107 spores ml-1) were considered in the first experiment. In the second experiment, the effect of dew periods (3, 6, 12, 18, 24, 48 hours) was studied. The results indicated that pathogenicity of both fungi was increased through increasing spore density and length of dew period. Plus, the concentration of 107 spores of Fusarium oxysporum and Alternaria alternata with 48 hours dew reduced Russian knapweed dry weight by 72% and 68%, respectively. Also, area under the disease progress curve rose up to 73% and 68% respectively.

Russian knapweed (Acroptilon repens L.) is a noxious perennial weed in the family of Asteraceae which caused various problems in field crops، pastures، grasslands and orchards. For collecting fungal pathogens from this weed، as biocontrol agents، a survey was carried out during 2011-2012 in Mashhad and Chenaran areas (north east of Iran). The isolated fungal agents from infected Russian knapweeds were purified. After primary studies، three isolates of Alternaria alternata، Fusarium oxysporum and Puccinia acroptili as the most effective fungal pathogen on Russian knapweed، were selected for host range tests and further studies. Supplementary studies were conducted to evaluate their effect on the target host at different concentrations consisted of 104، 105، 106، 107 spores ml-1. In a separate experiment، the influence of colorless or black plastic cover and dew periods included of 3، 6، 12، 18، 24، 48 hours on disease expression by P. acroptili was studied. In host range test of P. acroptili no any symptom was detected on wheat، barley، conola، sugar beet، tomato، potato، cucumber، green bean، maize and alfalfa whereas، two other isolates induced disease on some of the tested crops. P. acroptili reduced the dry weight of 4-week old seedlings of A. repens by 61%، compare with control. The most sever disease symptoms on seedlings of the target host was obtained from treating with P. acroptili spores at 107 spores ml-1 and 48 hours dew period under black plastic. This treatment، compared with 3 hours dew period under colorless plastic cover، reduced dry weight of A. repens seedlings by 40%، and disease progress curve on the weed was evaluated 24. 64%. Based on this research، P. acroptili could be considered as a promising biocontrol agent for Russian knapweed.