Abstract

Abstract A description is provided for Phytophthora cactorum . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On a very wide range of host plants embracing 54 families (particularly Rosaceae ) and over 150 genera (Nienhaus, 1960; Rangaswami, 1962) including ash, beech, cherry, conifers, apple, pear, apricot, strawberry, cucurbits, eggplant, cacti, gooseberry, rhododendron, lilac, ginseng, rhubarb, avocado, birch, maple and oak. DISEASES: Damping-off of seedlings including ash, beech, cherry and conifers; fruit rot of apple, pear, apricot, strawberry (leather rot), cucurbits and eggplant; leaf and stem rot of cacti, gooseberry, rhododendron, lilac, ginseng and rhubarb; collar rot and crown rot of apple and other fruit trees stem canker of avocado, birch, maple and oak; root rots in general. GEOGRAPHICAL DISTRIBUTION: Widespread in tempetate areas (CMI Map 280). TRANSMISSION: Soil-borne. Widely distributed in soils of apple orchards affected with collar rot (35: 685; 37: 132). Strawberry fruit in unmulched beds and wind-fall apples and pears on the ground frequently become infected by contact with infested soil (4: 101; 35: 685) where the pathogen may occur to a depth of 50 cm and persist for as long as 15 yr. in ploughland previously under apple orchards (42: 75). This has been partially explained by the irregular germination of oospores which require a dormant period (Blackwell, 1943; Legge, 1952). Apple fruit and gooseberry shoot infection are most frequent on lower branches subject to rain-splash which carry zoospores (41: 49). Long periods of rain, heavy dews, fog and high soil moisture favour the spread of the pathogen (39: 250; 45, 2553; 22: 30-31; 42: 391).

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