''Phytophthora citrophthora'', also known as brown rot of citrus, is a soil borne

oomycete The Oomycetes (), or Oomycota, form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms within the Stramenopiles. They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction o ...

that infects several economically important

citrus ''Citrus'' is a genus of flowering trees and shrubs in the family Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, mandarins, lemons, grapefruits, pomelos, and limes. ''Citrus'' is nativ ...

crops. A diagnostic symptom of ''P. citrophthora'' is

gummosis Gummosis is the formation of patches of a gummy substance on the surface of certain plants, particularly fruit trees. This occurs when sap oozes from wounds or cankers as a reaction to outside stimuli such as adverse weather conditions, infect ...

, wherein lesions around the base of the tree exude sap. Other common symptoms include dark longitudinal lesions forming at the soil line, a sour smell, and eventual cracking of the bark. Advanced symptoms include yellowing and necrosis of the

tree canopy In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only p ...

. Girdling action caused by the pathogen around the trunk can often cause the collapse of the tree. Resistant

lemon The lemon (''Citrus'' × ''limon'') is a species of small evergreen tree in the ''Citrus'' genus of the flowering plant family Rutaceae. A true lemon is a hybrid of the citron and the bitter orange. Its origins are uncertain, but some ...

varieties have been developed and their implementation has been effective at controlling the spread of the disease. Fruits that have been infected with ''P. citrophthora'' exhibit symptoms of brown rot characterized by a distinct odor. This disease is most active in the moderate temperatures of spring, fall, and winter months, opposite of most other ''Phytophthora'' species.

Environment

Environment is very important to oomycete life and reproduction. Once thought to be water molds, it is now known that they are in a distinct group called fungal like protists. Oomycetes have the ability to spread via

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion in aqueous or moist environments. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Certain zoospores are ...

s whose multiple

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

require moisture in order to move. For infections to reach field scale, wind and rain conditions must provide adequate moisture for the polycyclic life cycle to occur. ''Phytophthora citrophthora'' is able to survive at lower temperatures with growth occurring at <5 °C but optimum growth occurring between 24 and 28 °C and no growth present past 35 °C. ''Phytophthora citrophthora'' is very commonly found in soils of citrus tree fields, which is where they often overwinter as oospores. This disease can also overwinter on decaying fruit and leaf litter left in the field after harvest as oospores.

Control

Many control methods, including chemical and cultural, exist to combat the effects of infection by ''Phytophthora citrophthora''. Cultural control of this disease mostly includes the use of resistant rootstocks and water management practices. Exposing seeds to water above 48.9 °C for 4–10 minutes can effectively kill

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

s before they can germinate and infect. Keeping grafting lines well above the soil line and adding a

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

based

fungicide Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...

also works to reduce rates of infection. Effective specific chemical controls include foliar applications of Fosetyl-Al and soil applications of metalaxyl.

References

External links

USDA ARS Fungal Database
citrophthora Water mould plant pathogens and diseases Stone fruit tree diseases Cacao diseases Citrus diseases Food plant pathogens and diseases Ornamental plant pathogens and diseases Protists described in 1906 Oomycete species {{plant-disease-stub

Environment

Control

See also

References

External links