Gas-exchange and photochemical efficiency in seedling and grafted papaya tree grown under field condition.

Rootstock may induce resistance to soil born disease and control tree size in papaya plants. Photosynthetic process of cv. Golden, cv. Sunrise Solo and hybrid Tainung 01 grafted on open pollinated Tainung 01 (F2) seedlings and their respective seedlings were evaluated at Federal University of Goias. Gas-exchange and chlorophyll fluorescence were measured in six-month-old papaya trees using portable photosynthesis system [LI-6200 (Licor, USA)] and Mini-Pam fluorimeter (Walz, Germany), respectively. Photosynthesis (A, μmol m -2 s -1 ), transpiration (E, mmol m -2 s -1 ) leaf-to-air vapor pressure deficit (VPD air-leaf ), stomatal conductance (g s , mol m -2 s -1 ) and chlorophyll fluorescence [F v /F m (maximum quantum efficiency of open photosystem II centers-quantum yield)] were measured using the 13 th and 14 th fully-exposed-leaf from the apex with area of ±6.8 cm 2 and photosynthetically active radiation of ±1400 μmol m -2 s -1 . Grafted papaya did not show significant difference on gas-exchange in all genotypes when compared with seedlings. Average rate of E, A, g s and VPD air-leaf ranged from 14.0 to 14.1 mmol m -2 s -1 , 16.8 to 18.6 μmol m -2 s -1 , 0.368 to 0.421 mol m -2 s -1 and 4.25 to 4.65 kPa, respectively. Chlorophyll fluorescence at 09h00 was the highest (0.83) in Tainung 01 seedlings and the lowest (0.73) in Golden/Tainung 01 combination. Transpiration and stomatal conductance were not affected by rootstock which means that grafting does not jeopardize the water intake in all papaya trees and the new xylem connection seems to maintain stable the root-trunk-atmosphere system.