CHANGES IN THE WATER STATUS OF PAPAYA LEAVES INFECTED WITH PAPAYA MOSAIC-VIRUS

Papaya mosaic virus causes systemic infection of papaya affecting leaves that are yet to enter the steady-state at the time of inoculation and all the subsequent leaves produced afterwards. Advancement in disease syndrome is marked by progressive reduction in leaf area. Relative water content (RWC) increases marginally under the disease. Leaf water content per unit area or per unit dry weight increases with time and symptom severity. Laminar dry matter content remains low under infection although some dry matter accumulation occurs later. An increase in stomatal density accompanies laminar reduction but large fluctuations in density occur with symptom severity. Frequency of normal stomata and rate of transpiration decrease progressively under disease syndrome. More than 20% stomata remain permanently closed during advanced stage of infection at 90 days after inoculation. The diurnal variation in RWC and transpiration rate almost vanishes at this stage. These findings indicate failure of stomatal apparatus due to disease favouring their closure.