Melampsora

Melampsora is a genus of fungal plant pathogens in the family Melampsoraceae, order Pucciniales. The group comprises numerous species that cause rust diseases on woody plants, especially willows (Salix) and poplars (Populus). Melampsora spp. have a wide distribution in temperate regions and are of interest for forestry and horticulture due to their potential to affect tree growth and vitality.

Life cycle and hosts: Many Melampsora species are heteroecious, requiring two distinct hosts to complete their life cycle. The typical cycle involves a dicot host such as Salix or Populus and a conifer host, commonly a species of Larix (larch) or sometimes Pinus. On the deciduous host, rust pustules produce spores that cause leaf symptoms, while on the conifer host another set of structures forms and releases spores that continue the cycle when conditions are favorable. Some Melampsora species can also occur on a single host, but the classic life history of the genus involves alternating hosts.

Symptoms and impact: Infected leaves develop yellow to orange rust pustules, leading to discoloration, premature leaf drop, and reduced photosynthesis. In forestry and ornamental settings, heavy infections can slow growth and reduce yield or aesthetic value. Management often involves monitoring, fungicide applications in high-value plantings, and, where possible, using resistant cultivars or removing alternate hosts to disrupt the life cycle.

Notable species: The genus includes several well-studied species, such as Melampsora larici-populina, a major rust of poplars in many regions, and Melampsora allii-populina, associated with poplar hosts. Other Melampsora species infect willows or other woody hosts, contributing to the diversity of rust diseases across temperate ecosystems.