Phytophthora - Pathogenicity

Pathogenicity

Phytophthora spp. are mostly pathogens of dicotyledons, and are relatively host-specific parasites. Many species of Phytophthora are plant pathogens of considerable economic importance. Phytophthora infestans was the infective agent of the potato blight that caused the Great Irish Famine (1845-1849), and still remains the most destructive pathogen of solanaceous crop, such as tomato and prevalently potato. The soya bean root and stem rot agent, Phytophthora sojae, has also caused longstanding problems for the agricultural industry. In general, plant diseases caused by this genus are difficult to control chemically, and thus the growth of resistant cultivars is the main management strategy. Other important Phytophthora diseases are:

• Phytophthora alni – causes alder root rot
• Phytophthora cactorum – causes rhododendron root rot affecting rhododendrons, azaleas and causes bleeding canker in hardwood trees
• Phytophthora capsici - infects Cucurbitaceae fruits, such as cucumbers and squash
• Phytophthora cinnamomi - causes cinnamon root rot affecting woody ornamentals including arborvitae, azalea, Chamaecyparis, dogwood, forsythia, Fraser fir, hemlock, Japanese holly, juniper, Pieris, rhododendron, Taxus, white pine, American chestnut and Australian Jarrah.
• Phytophthora fragariae - causes red root rot affecting strawberries
• Phytophthora kernoviae - pathogen of beech and rhododendron, also occurring on other trees and shrubs including oak, and holm oak. First seen in Cornwall, UK, in 2003.
• Phytophthora megakarya - one of the cocoa black pod disease species, is invasive and probably responsible for the greatest cocoa crop loss in Africa
• Phytophthora palmivora - causes fruit rot in coconuts and betel nuts
• Phytophthora ramorum – infects over 60 plant genera and over 100 host species - causes Sudden Oak Death
• Phytophthora quercina – causes oak death
• Phytophthora sojae - causes soybean root rot

Research beginning in the 1990s has placed some of the responsibility for European forest die-back on the activity of imported Asian Phytophthoras.