Water relations, photosynthetic capacity, and growth in passion fruit (Passiflora edulis Sims f. flavicarpa Deg.): seedlings and grafted plants 1

Grafting has been used in passion fruit as a promising strategy for the improvement of traditional cultivars, which have roots susceptible to several soil pathogens. However, the effect of grafting on gas exchange, water relations, and photochemical efficiency in passion fruit is still not understood. The objective of this study was to evaluate the photosynthetic capacity, water relations, and the growth of seed-propagated (PPS) and grafted (PPG) passion fruit under drought stress. Ungrafted seedlings of Passiflora edulis f. flavicarpa and seedlings of Passiflora edulis f. flavicarpa (scion) grafted onto Passiflora mucronata (rootstock) were cultivated in a greenhouse in 3.5-dm3 pots. At 37 days after transplanting (DAT), one-half of the seed-propagated plants had the watering suspended (PPSDS, plant propagated by seed under drought stress) as well as one-half of the grafted plants (PPGDS, plant propagated by grafting under drought stress). Another group of plants was kept in soil at field capacity. Gas exchanges, chlorophyll fluorescence emission, chlorophyll content, and leaf and soil water potentials were determined during the experiment. Drought-stressed plants (PPSDS and PPGDS) reduced the stomatal conductance, incident quantum yield (Φi), and root dry mass in relation to the respective watered controls (PPS and PPG). Up to -50 kPa of soil water potential, both PPSDS and PPGDS reduced the photosynthetic rate by 50%, without reducing leaf water potential. The seed-propagated plants showed higher growth characteristics than the grafted plants in both conditions, at the field capacity and in the substrate with water limitation. Grafting showed no effect on water status, fluorescence emission, and gas exchange.