Citrus bent leaf viroid (CBLVd) is an emerging and widely distributed viroid along with its variants in
citrus growing areas of world. Activation of defense mechanism is associated with different enzymes
and inhibitors, accumulated in the infected host. Limited studies were found on biochemical characterization
of citrus viroids. Therefore, study was focused on the biochemical activities such as determination
of chlorophyll contents, total soluble phenolics (TSP), phenylalanine ammonia lyase (PAL) and polyphenol
oxidase (PPO) activity in three citrus cultivars kinnow (C. reticulate), feutrell’s early (C. reticulate) and
mosambi (C. sinensis) infected with CBLVd from Sargodha, Pakistan. The results showed that chlorophyll
contents were significantly lower in the diseased leaves samples of all the citrus cultivars as compared to
healthy ones. Whereas, TSP was found in higher concentration in the CBLVd infected samples of citrus
cultivars. Similarly, activities of PPO and PAL was increased significantly in leaves of citrus cultivars
infected with CBLVd as compared to healthy. These findings were in confirmation that chlorophyll contents,
enzymes and inhibitors were associated to response of plants towards pathogen infection. To the
best of our knowledge, these biochemical alterations in host plants against CBLVd were studied for the
first time not only in the Asian region but also in Pakistan. The results will lead to investigate the
biochemical alterations in other citrus viroids infection.