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Verticillium wilt is considered the most important disease of cotton in the world, including Iran. Cultural practices and the use of resistant varieties are the most common strategies used to control Verticillium wilt of cotton. These strategies are not always available or effective. In recent years, biological control using fungal and bacterial antagonists, has been applied to control some cotton diseases including damping-off. In this study, we investigated the possibility of biological control of Verticillium wilt of cotton using bacterial antagonists. Suspension of eight bacterial strains of Pseudomonas fluorescens and Bacillus spp. isolated from different rhizospheric soils and plant roots in the Iranian cotton fields, were prepared with a concentration of 10 8 cfu/ml. Ten cotton seeds (cv Varamin) were then coated with each bacterial suspension and were planted in soil pre-inoculated with Verticillium dahliae microsclerotia. The efficacy of bacterial antagonists in reducing wilt disease was evaluated by determination of the disease index in different treatments. The results indicated that most isolates were effective in reducing disease (compared to the untreated control) 90 days after sowing. Isolates B5, B6, B2, B7, and B3 were the most effective, respectively, in reducing wilt index. In contrast, isolates B1, B4, and B8 did not significantly reduce the disease. In general, P. fluorescens isolates were more effective than Bacillus isolates. This study suggests that bacterial antagonists might be potential biological control agents of cotton.

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Witches' broom disease of lime (WBDL) is a caused by " Candidatus Phytoplasma aurantifolia". The disease was first observed in the Sultanate of Oman in the 1980s and found to be present in the United Arab Emirates (UAE) in 1989. A putative leafhopper vector, Hishimonus phycitis , reproducing actively on lime trees, was identified in 1991 in Oman and found to be also present in the UAE in 1993. In July 1997, symptoms of the disease were observed in the southeastern region of Iran near Nikshar (Dapas Kur) and Qasr-e-Qand. Joint serological and molecular characterizations confirmed that the symptoms observed in Iran are those of WBDL and that, on the basis of ELISA and PCR, the WBDL phytoplasma in Iran is indistinguishable from that in Oman and the UAE. H. phycitis was easily recovered by D-Vac ® aspiration not only from lime trees in the affected region but also from lime trees in regions free of the disease. From the extent and severity of the symptoms observed and the presence of the vector, some trees must have become infected 10 yr ago. Eradication of the 500 or so affected trees is underway. A few individuals of Diaphorina citri , the psyllid vector of Huanglongbing, were also collected in the survey. This is the first report of D. citri and of H. phycitis in Iran. The origin of WBDL is discussed.

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