Morphological and biochemical changes in asymptomatic and moderately symptomatic plants infected with sugarcane white leaf (SCWL) phytoplasma

Abstract
Sugarcane white leaf disease associated with sugarcane white leaf (SCWL) phytoplasma is an important disease in sugarcane resulting in significant losses in production in Asian countries including the major regional producing countries of India and Thailand. In this study the morphological and biochemical traits in SCWL phytoplasma infected sugarcane plants, both asymptomatic (AS) and symptomatic (S1-S3) and their corresponding to phytoplasma loads, were investigated. This study found that as symptom development progressed, cane statues including plant height, leaf length, and leaf width, were reduced and corresponded with declines in both chlorophyll and dietary fiber content. Total soluble solids (TSS) were less in AS cane plants, being 16.83 ± 1.0 °brix compared to 20.58 ± 1.6 °brix in healthy plants, declining further with the progression of symptoms. This feature could be potentially used in the identification of AS sugarcanes. Phytoplasma titres increased from 2.36E + 05 copies/µg plant DNA in AS infected leaves, peaking at 1.20E + 08 copies/µg plant DNA in S3 infected leaves, before declining in severely (S4) infected leaves. AS infected plants also exhibited a peak in total phenolic compounds. By tracking the development of symptoms in sugarcane white leaf disease and the corresponding increases in titres of SCWL phytoplasma, decline in chlorophyll and dietary fiber, decrease in TSS, and a peak in total phenolic compounds at the asymptomatic stage, this study confirmed that SCWL phytoplasma significantly impacts the sugarcane host plants as early as the AS stage, this stage is potentially the focus point for early detection and interventions for controlling proliferation SCWL disease.