Citrus greening (Huanglongbing disease)
Candidatus Liberibacter asiaticus
Also Known As - Huanglongbing disease (Citrus greening)What is Citrus greening (Candidatus Liberibacter asiaticus)?
Citrus greening, or Huanglongbing (HLB), is caused by Candidatus Liberibacter asiaticus bacteria, transmitted by insects called Asian citrus psyllids (Diaphorina citri). The disease affects various citrus species, including oranges, grapefruits, lemons, limes, and tangerines, among others. Symptoms of citrus greening include yellowing of veins, mottling of leaves, premature defoliation, twig dieback, root decay, stunted growth, off-season flowers, small irregular fruit with a bitter taste, and, in severe cases, plant death.
How does Citrus greening (Candidatus Liberibacter asiaticus) occur?
The bacterium Candidatus Liberibacter asiaticus, causing citrus greening, reproduces within the Asian citrus psyllid vector. Infected psyllids transmit the bacteria while feeding on citrus trees. Within the psyllid's gut and reproductive organs, the bacteria multiply. When the psyllid feeds on healthy trees, it injects the bacteria into the phloem, causing systemic infection. Temperature plays a significant role in the interaction between the bacteria and the insect vector.
Symptoms
1 - Impact on plants
HLB-infected citrus trees exhibit premature defoliation, twig dieback, root decay, stunted growth, off-season flowers, and small irregular fruit. Bitter taste results from disrupted phloem nutrient transport, reducing productivity and risking tree death.
2 - Impact on Soil and Environment
• HLB itself does not directly impact soil health but it can affect nutrient cycling and organic matter decomposition. • Additionally, the removal of infected trees and changes in the landscape can impact regional biodiversity.
Solutions
1 - Cultural Practices
1. Maintain overall plant health through proper fertilization, irrigation, and pruning practices. 2. Use certified disease-free nursery stock for planting. 3. Regularly monitor trees for symptoms and use early detection methods for prompt identification. 4. Remove and destroy infected trees to prevent further spread. 5. Support research and development of HLB-resistant citrus varieties.
2 - Chemical Control
• No antibiotics or specific chemical treatments are available to cure Citrus Greening (HLB). • Integrated pest management (IPM) strategies focus on controlling the insect vectors to manage the disease. • Streptomycin and oxytetracycline antibiotics have been used in the United States on an emergency basis against citrus greening disease. Their use is banned in Brazil and the European Union. • Expansion of antibiotic use is proposed but opposed due to concerns about antibiotic resistance and human health impacts.
