Disease name: Huanglongbing or Greening Lemon
The scientific name: Candidatus Liberibacter spp. (Candidatus Liberibacter spp.)
The type of disease: Bacterial disease
Species: Rhizobiaceae
Symptoms
Honglongbing (HLB), also known as Greening Lemon, is a devastating bacterial disease that affects citrus trees, including lemons. The main symptom is yellowing or blotching of leaves, which may appear similar to symptoms of nutrient deficiency. However, the yellowing pattern is asymmetrical, with one side of the leaf remaining green while the other side turns yellow. As the disease progresses, leaves may become thick, leathery and twisted, and the veins may become crusty and prominent. Infected trees may also exhibit terminal tips and premature fruit drop. Fruits from infected trees are misshapen, discolored, and have a bitter taste.
The causes of disease
Lemon yellowing is caused by bacteria of the genus Candidatus Liberibacter, which are restricted to plant phloem and transmitted mainly by insect vectors. The main vectors of the disease are the Asian citrus bug (Diaphorina citri) and the African citrus bug (Trioza erytreae). These bacteria invade and multiply in the phloem tissue of the plant, leading to disturbances in the transport of nutrients and water.
Favorable conditions for spread
The spread of the disease depends mainly on the presence and spread of psyllids that transmit the disease. The disease can spread rapidly within orchards if the psyllid population is not controlled. The bacteria can also be transmitted by transporting contaminated seedlings or propagation materials. Environmental factors such as high temperatures and vegetative growth cycles that encourage psyllid reproduction increase the spread of the disease.
Disease course
The disease cycle begins with the psyllid transmitting the bacteria transmitting the bacteria to the healthy tree and injecting the bacteria into the phloem tissue of the plant. The bacteria multiply and spread through the plant's vascular system, causing the characteristic symptoms of yellowing.
Losses
Lemon yellow disease causes significant economic losses in citrus production worldwide, as it can lead to the complete loss of infected citrus trees and orchards. The disease reduces fruit yield and quality, and affected trees usually decline and die within a few years. In areas where the disease is widespread, the entire citrus industry may be threatened, resulting in significant economic impacts.
Control strategies
Strategies to control lemon yellowing include an integrated approach that combines the use of disease-free seedlings, control of insect vectors through spraying of insecticides and biocontrol agents, and removal and destruction of infected trees. Proper use of resistant or tolerant varieties and preventive measures such as biological drainage and monitoring programs are essential to prevent the spread of the disease.
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