Phytophthora OR Die Back disease: Some facts

Phytophthora OR Die Back disease: Some facts

Phytophthora: contains many species

that are pathogenic on a wide range of host plant species, causing diseases of all plant parts including roots, crown, stems, branches, leaves and fruits. Some species are
restricted to belowground infections, some to aboveground infections, some to both.

Spreads through Sporangia; it release motile zoospores  into soil water, and these swim to small roots (a chemotactic response to root exudates), encyst and germinate on the root surface. Penetration occurs within 24 h of germination .The fungus then spreads in the young feeder roots causing a rot which may extend into the baseof the stem. P. cinnamomi survives in dead plant material & also survive in the soil as mycelium, sporangia, zoospore cysts, chlamydospores and oospores and survival can be extended in the presence of an organic substrate. Mycelium of P. cinnamomi can survive for at least 6 years in moist soil.The pathogen can be moved naturally by soil-splash, by wind-blown soil or debris, or by water movement and run-off in drainage/irrigation ditches. The most likely means of more distant movement is in contaminated soil or plant debris.

CONTROL:Cultural control measures include alleviation of high soil moisture levels and improving aeration by increasing drainage, and attention to mineral nutrition. Soil solarization also controls P. cinnamomi.

Chemical control is possible with systemic fungicides, particularly fosetyl-aluminium (and phosphonic acid) and metalaxyl by soil drenching or stem injection. Bordeaux mixture has been used to successfully control many diseases caused by different species of Phytophthora. Ectomycorrhizal fungi like Paxillus involutus effectively controlled root rot caused by Fusarium oxysporum and Fusarium moniliforme in red pine. Inoculation of sand pine with Pisolithus tinctorius, another ectomycorrhizal fungus, controle disease caused by Phytophthora cinnamomi (Ross and Marx 1972).