Psorosis

psorosis, disease of Citrus plant species caused by several related viruses (family Ophioviridae). Given that the psorosis viruses are largely transmitted by bud grafts and not by natural vectors, the disease can have significant economic impacts on citrus crops grown from such grafts, including oranges, grapefruits, and tangerines. Severe infections can stunt growth, and fruit yields may be reduced by one-third or more.

Symptoms vary greatly and include formation in some young leaves of elongated, white to yellow-green flecks, spots, rings, or large translucent areas. Certain symptoms tend to fade as the leaves mature. Rings bordered by sunken grooves may form on the fruit. On trees 6 to 12 or more years old, the outer bark in localized areas commonly becomes scaly, or small irregular pustules and gumlike deposits develop, with the wood being stained underneath. Variously sized cavities or narrow grooves may develop in the large limbs and trunk.

The disease may be controlled by removing seriously affected trees, planting psorosis-free stock, and using only scions and buds from virus-free trees. Quarantine and certification programs exist in many citrus-growing regions to reduce contaminated stock, though many Citrus species can harbour the viruses asymptomatically for more than 10 years.