Phytophthora fungi – primary pathogens of plants

Abstract

Phytophthorais a genus of plant damaging Oomycetesfungi. Phytophthoraspecies are causing economic losses on crops and environmental damage in natural ecosystems worldwide. Phytophthora infestans, causal agent of the Great Irish potato famine in 1845-47 was the first described Phytophthoraspecies in 1876 (Erwin and Ribeiro, 2005). Because of cell walls constructed of cellulose and diploid chromosomes, Phytophthorafungi are resistant to typical fungicides and are highly adaptable to the changing environment. Phytophthorainfection is transferred through the soil and air. Therefore, Phytophthoraspecies are classified into airborne and soilborne. Soilborne Phytophthoraspecies are causal agents of root and collar rots, bleeding bark cankers on stems, and diseases of seedlings of many deciduous and conifer species (Fig. 1). Airborne Phytophthoraspecies are causing aerial bark cankers, twig dieback and leaf necroses (Fig. 2). So far, more than 100 Phytophthoraspecies have been described, and it is likely that worldwide 200-600 species exist being still unknown to science (Brasier, 2009). Phytophthorafungi invade only healthy plant tissue or fresh wounds and the infection in roots of woody plants starts to be visible only after several years, when at least 50% of lateral roots are lost (Erwin and Ribeiro, 2005). Phytophthorainfection is responsible for the big amount of crown diseases, collar rots (up to 90%), and fine root diseases (>66 %) of woody plants (Erwin and Ribeiro, 2005; Jung 2005). Different methods have been used for identification of Phytophthorainfection. They include visual typical symptoms on trees, lateral flow device for in-field testing, morphology of colonies from isolated material, and molecular markers. However, the morphological identification is complicated, because of small morphological differences among species and variable characteristics (Erwin and Ribeiro, 2005). [...]