Olive (Olea europaea L.) is a traditional tree crop in Andalucia, southern Spain. Over the past several years, new plantations have been established in areas where other crops susceptible to Verticillium dahliae, such as cotton, sunflower, and vegetables, usually have been grown. Surveys performed from 1989 to 1996 showed that Verticillium wilt, caused by V. dahliae, has become the most important soilborne fungal disease affecting young olive trees in this area (3). Manure is sometime used as a soil amendment before and after tree planting to increase organic matter content of soil. In 1996, manure was used to establish an olive plantation in Sevilla Province. The dung came from sheep fed on harvested fields of cotton, sunflower, and sugar beet. The remaining manure was left in a pile in the field. In 1998, 2 years after planting, many olive plants in the field showed Verticillium wilt symptoms. Samples were collected from the soil and the surfaces and core of the manure pile for isolation and quantitative assessment of the pathogen. Wet-sieving and sodium pectate agar selective medium were used (1). V. dahliae was isolated from both the manure and soil. Mean inoculum density in the samples taken from the pile and soil were 8.4 and 7.2 microsclerotia per gram, respectively. Although it has been demonstrated that V. albo-atrum survives the digestive process in animals (2), this is the first report on dispersion of V. dahliae by manure from sheep fed on infested stubble. The use of manure infested with V. dahliae may contribute to pathogen dispersion and to the increase in Verticillium wilt incidence in olive orchards in Andalucia. Because animal manure is a potential means for V. dahliae transmission, it is recommended that before manure is applied tests be performed, when feasible, to make sure it is pathogen-free.
References: (1) E. J. Butterfield and J. E DeVay Phytopathology 67:1073, 1977. (2) H. C. Huang et al. Plant Dis. 70:218, 1986. (3) M. E. Sanchez Hernandez et al. Eur. J. Plant Pathol. 104: 347, 1998.
