CHANGES in Photosynthetic Activity in Leaves of 'Golden' Mamoeiro Infected with Pmev, Detected by Fluorescence of Chlorophyll a


Publication date: 13/07/2017

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JOSE AIRES VENTURA (M/D) Internal Examiner *

Summary: Papaya (Carica papaya l.) is one of the most consumed fruits in the world due to its nutritional, pharmaceutical and use in the food and cosmetic industry. In Brazil, the second producer of papaya in the world, the production has been severely affected by meleira, disease which is caused by the complex of Papaya meleira virus (PMeV and PMeV2). In order to analyze the changes in photosynthetic activity in 'Golden' papaya leaves infected and not infected by PMeV, the experiment was carried out in which three groups of plants were evaluated: Control, without inoculation; Inoculated with sodium phosphate buffer (Treatment = ↓[𝑃𝑀𝑒𝑉2]) and inoculated with sodium phosphate buffer and latex harvested from plants with meleira symptoms (Treatment = ↑[PMeV2]). The chlorophyll a fluorescence technique was used as a tool. There was a significant increase in quantum photochemical energy conversion in photosystem II (Y (II)) and an increase in the quantum yield of the regulated non-photochemical energy loss (Y (NPQ)) in the inoculated plants. At the same time, transient fluorescence curves showed greater efficiency in the reduction of the primary (Quinone A) and secondary (Quinone B) acceptors of electrons in photosystem II and greater efficiency of reduction of the plastoquinone pool and, consequently, greater efficiency in the reduction of acceptors of the Citb6f complex. The presence of two PMeV viruses and PMeV2 confirmed the presence of two PMeV viruses. A higher photochemical performance index (PItotal) was observed in the plants with the highest viral load from the 35th day after inoculation (DAI), and at 49 DAI, an increase in the reduction activity of photosystem I and PItotal was observed in plants with higher viral load and intermediate values in plants with lower viral load. These results suggest a defensive response of papaya cv. Golden to infection and confirm the presence of the two viruses, PMeV and PMeV2. Therefore, this technique proved to be a tool with great potential as a simple and fast method to study the interaction plant x pathogen and as the mechanisms of virus infection in plants and could also be used to detect the changes in photosynthetic activity in papaya infected with PMeV and PMeV2.

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