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چکیده
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Alfalfa witches' broom (A WB) is one of the most important alfalfa diseases in Iran. During 2006-2010, reaction of certain tropical alfalfa cultivars to A WB phytoplasma was studied under fi eld conditions in a randomized complete blocks design at three rep li cations in Ashkezar, Yazd province. Alfalfa cultivars were Medicago sativa cvs. yazdi bumi, selection yazdi, barni, mesasersa, bagdadi, nikshahri and sintetik. Samplings were carried out during fifth harvest in each year and di sease incidence ,severity and death rate of infected plants were evaluated. In each culti var sampling were conducted randomly at two points within a 1 m quadrate on a diagonal transect across each of the treatment. Infection of alfalfa plants was based on characte risti c disease symptoms, ELISA test using polyclonal antiserum and direct and nested polymerase chain reaction us in g PI/P7 and Rl6F2n/R16R2 universal primer pairs. Furthermore, population of the pathogen vector, Orosius albicinctus, were assessed in 1-3 years old alfalfa stands. Based on the res ults of this study maximum infection rate were observed in M. sativa cvs. sintetik, nikshahri, bagdadi, selection yazdi, mesasersa, bami and yazdi bumi as 55.88, 54.63, 54.57, 52.83, 48.38, 38 and 34 percent respectively. Disease incidence, severity and dea th rate of infected plants in different cultivars were correl ated and di sease severity was not statisti call y significant difference at 5% level. There was no correlation between vector population and disease incidence in 1 year alfalfa stand but in 2 and 3 year stands there was a direct relationship between disease incidence and vector population. Based on the results of this study planting new fi elds with seeds co llected from healthy plants of yazdi burni and good agronornical practi ce, proper irri gation and fertilization is reco mmended.
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