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

oomycete Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the resul ...

that infects several economically important

citrus ''Citrus'' is a genus of flowering plant, flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as Orange (fruit), oranges, Lemon, lemons, grapefruits, pomelos, and lim ...

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, infection ...

, 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 biology, the canopy is the aboveground portion of a plant cropping or crop, formed by the collection of individual plant crowns. In forest ecology, canopy also refers to the upper layer or habitat zone, formed by mature tree crowns an ...

. 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 trees in the flowering plant family Rutaceae, native to Asia, primarily Northeast India (Assam), Northern Myanmar or China. The tree's ellipsoidal yellow fruit is used for culin ...

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. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mo ...

s whose multiple

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

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 or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

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

copper Copper is a chemical element with the symbol Cu (from la, cuprum) 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 pinkis ...

based

fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...

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

metalaxyl Metalaxyl is an acylalanine fungicide with systemic function. Its chemical name is methyl N-(methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate. It can be used to control ''Pythium'' in a number of vegetable crops, and ''Phytophthora'' in peas. 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 Species described in 1906 {{plant-disease-stub

Environment

Control

See also

References

External links