Age-dependent epidemiological insights into Citrus tristeza virus in Assam lemon cultivation

Assam lemon (Citrus limon Burm.), a valuable indigenous horticultural crop from Northeast India, is facing a serious threat from Citrus tristeza virus (CTV), a global pathogen responsible for citrus decline. A study conducted in the Lower Brahmaputra Valley Zone (LBVZ) of Assam aimed to investigate the dynamics of CTV in Assam lemon across six plant age groups (2, 5, 10, 15, 20 and 25 years). Serological [double antibody sandwich- enzyme linked immunosorbent assay (DAS-ELISA)] and molecular [reverse transcriptase-polymerase chain reaction (RT-PCR)] tests confirmed 100 % CTV incidence in the surveyed area. The study examined the influence of plant age and climaticfactors on vector incidence, disease severity and yield. Analysis revealed that minimum temperature, rainfall and evening relative humidity had strong positive correlations with vector presence and disease severity. Regression analysis showed that older plants experienced significantly greater disease severity, with a one-year increase in age leading to a 5.71 % rise in disease severity. Additionally, disease severity negatively impacted fruit yield, with a 1 unit increase in disease severity causing yield reductions ranging from 21.5 % to 42.9 %, depending on the age group. Disease severity increased with plant age, while fruit yield peaked at younger stages and declined in older plants. These findings underscore the critical need for early detection and targeted disease management to mitigate losses and maintain the long-term productivity of Assam lemon orchards. Early intervention strategies are essential to protect this economically important crop from the devastating effects of CTV.